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The Peach

Botany, Production and Uses

This page intentionally left blank

The Peach Botany, Production and Uses

Edited by

Desmond R. Layne Department of Horticulture, Clemson University, Clemson, South Carolina, USA and

Daniele Bassi Dipartimento di Produzione Vegetale, University of Milan, Milan, Italy

CABI is a trading name of CAB International CABI Head Ofﬁce Nosworthy Way Wallingford Oxfordshire OX10 8DE UK

CABI North American Ofﬁce 875 Massachusetts Avenue 7th Floor Cambridge, MA 02139 USA

Tel: +44 (0)1491 832111 Fax: +44 (0)1491 833508 E-mail: [email protected] Website: www.cabi.org

Tel: +1 617 395 4056 Fax: +1 617 354 6875 E-mail: [email protected]

© CAB International 2008. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners. A catalogue record for this book is available from the British Library, London, UK. Library of Congress Cataloging-in-Publication Data The peach : botany, production and uses /edited by Desmond R. Layne and Daniele Bassi. p. cm. Includes index. ISBN 978-1-84593-386-9 1. Peach--Breeding. 2. Peach--Diseases and pests. 3. Peach-Harvesting. I. Layne, Desmond R. II. Bassi, Daniele. SB371.P42 2008 634’.25--dc22 ISBN:

978 1 84593 386 9

Typeset by AMA Dataset Ltd, UK. Printed and bound in the UK by Biddles, King’s Lynn.

2007045093

Contents

Dedication Contributors

vii x

Preface

xiii

Acknowledgements

xvi

1. Botany and Taxonomy D. Bassi and R. Monet

1

2. History of Cultivation and Trends in China H. Huang, Z. Cheng, Z. Zhang and Y. Wang

37

3. Classical Genetics and Breeding R. Monet and D. Bassi

61

4. Genetic Engineering and Genomics A.G. Abbott, P. Arús and R. Scorza

85

5. Low-chill Cultivar Development B.L. Topp, W.B. Sherman and M.C.B. Raseira

106

6. Fresh Market Cultivar Development W.R. Okie, T. Bacon and D. Bassi

139

7. Processing Peach Cultivar Development T.M. Gradziel and J.P. McCaa

175

8. Rootstock Development G.L. Reighard and F. Loreti

193

v

vi

9. Propagation Techniques F. Loreti and S. Morini

221

10. Carbon Assimilation, Partitioning and Budget Modelling T.M. DeJong and A. Moing

244

11.

264

Orchard Planting Systems L. Corelli-Grappadelli and R.P. Marini

12. Crop Load Management R.P. Marini and G.L. Reighard

289

13. Nutrient and Water Requirements of Peach Trees R.S. Johnson

303

14. Orchard Floor Management Systems T.J. Tworkoski and D.M. Glenn

332

15. Diseases of Peach Caused by Fungi and Fungal-like Organisms: Biology, Epidemiology and Management J.E. Adaskaveg, G. Schnabel and H. Förster

352

16. Diseases Caused by Prokaryotes – Bacteria and Phytoplasmas D.F. Ritchie, M. Barba and M.C. Pagani

407

17. Viruses and Viroids of Peach Trees M. Cambra, R. Flores, V. Pallás, P. Gentit and T. Candresse

435

18. Insects and Mites D.L. Horton, J. Fuest and P. Cravedi

467

19. Nematodes A.P. Nyczepir and D. Esmenjaud

505

20. Preharvest Factors Affecting Peach Quality C.H. Crisosto and G. Costa

536

21. Ripening, Nutrition and Postharvest Physiology A. Ramina, P. Tonutti and B. McGlasson

550

22. Harvesting and Postharvest Handling of Peaches for the Fresh Market C.H. Crisosto and D. Valero

575

Index

597

Colour plates 1–73 can be found following p. 144. Colour plates 74–163 can be found following p. 336. Colour plates 164–245 can be found following p. 496.

Dedication

Richard E.C. Layne Richard E.C. Layne served as Research Scientist (1963–1996) and directed the fruit breeding programme (1969–1996) at the Agriculture and Agri-Food Canada Research Centre at Harrow, Ontario. While at Harrow, his scientiﬁc research, new cultivar development and outreach efforts signiﬁcantly impacted the Canadian tree fruit industry and many other temperate, fruit-growing regions around the world. After growing up on the tropical island of St Vincent, West Indies, he attended McGill University, where he earned his BSc degree in Agronomy. Next, he earned MS and PhD degrees in Agronomy from the University, of Wisconsin. His ﬁrst research experience with fruit crops occurred when he began his new job with Agriculture Canada at Harrow in 1963. During his tenure at Harrow he was responsible for the introduction of 36 new fruit cultivars, ornamentals and rootstocks. Speciﬁcally, these included 15 peaches (ten cultivars, three ornamentals and two rootstocks), 13 apricots (12 cultivars and one rootstock), four nectarines and four pear cultivars. In addition to Ontario, these cultivars play signiﬁcant roles in the fruit crop industries of Michigan, New York, Pennsylvania, New Jersey and various European countries. This vii

viii

is due, in part, to their improved bud and wood cold hardiness, superior disease resistance, attractive colour, good eating quality and consistency of production. In Ontario, his peach cultivars span the entire ripening season. Those that are currently most widely planted include ‘Harrow Diamond’, ‘Harrow Beauty’, ‘Harson’, ‘Harrow Dawn’, ‘Harrow Fair’ and ‘Harblaze’ (nectarine). His apricots also span the ripening season in Ontario, with ‘Harcot’ and ‘Harogem’ being those cultivars most widely planted. ‘Haroblush’, ‘Harojoy’, ‘Harostar’, ‘Hargrand’ and ‘Harval’ are becoming more widely planted now. His ‘Harlayne’ apricot with natural resistance to Plum pox virus has become a donor of this resistance trait in conventional breeding programmes around the world. ‘Harrow Delight’, ‘Harrow Sweet’ and ‘AC Harrow Delicious’ pears all offer improved tolerance to ﬁreblight. In addition to his cultivar development work, his pioneering work on cold hardiness physiology and applied work on scion/rootstock relationships, peach orchard management and integrated production systems including irrigation have added signiﬁcantly to the pomological scientiﬁc literature. This includes more than 130 publications and six book chapters. He has received numerous research awards and served in important leadership roles during his career. These include the Wilder Silver Medal (1996) awarded by the American Pomological Society (APS) and Outstanding Researcher (1993) by the American Society for Horticultural Science (ASHS). In 1992 he was elected a Fellow of ASHS. He received the Carroll R. Miller award from ASHS in 1977, 1978, 1982 and 1985 for ‘excellence in research dealing with the improved production and utilization of peaches’. He received the Paul Howard Shepard Award for the best paper published by the APS in 1967 and 1982. He was President (1991/2) of the APS and he was also President of the Canadian Society for Horticultural Science (1976/7). He has been an international consultant to the USA, Brazil and China, and participated in an exchange fellowship with INRA, France. As a young boy, I fondly remember going with my dad to his research orchards and seeing and tasting the results of his labours. I had the privilege of learning much about other cultures and the importance of scientiﬁc collaboration and exchange while sitting at the dinner table at our home as we hosted scientists visiting my dad from around the world. While in college assisting him in his breeding and orchard management programmes at Harrow, I developed a passion for pomological research and extension that has been the focus of my career. My dad has been and continues to be a great friend, mentor and inspiration; and I fondly dedicate this book to him. Desmond R. Layne

Silviero Sansavini Silviero Sansavini has been Professor of Pomology at the University of Bologna, Italy, since 1974. After growing up on a small fruit farm in the heart of one of the major fruit-growing areas in northern Italy (the Romagna part of the Po Valley), he attended the University of Bologna, where he earned a degree in Agricultural Science. His early career involved a stint as an extension phytopathologist, before being hired at the same university, where he went through the ranks to Full Professor, and served as Chairman of the Department of Fruit and Woody Plant Sciences almost continuously from 1977 to the end of 2007. A ‘man with a mission’, he has promoted the art and science of fruit growing throughout his career by leading many nationally funded research projects and participating in many collaborative international ones, including several funded by the EU. As a natural consequence of this commitment and activity, he has been convener and/or organizer of well over 100 scientiﬁc meetings or extension events at the international and national levels. He was elected Chairman of the International Society for Horticultural Science in 1994 and in his 4-year tenure he organized a signal event for horticulture: The World Congress on Horticultural Research (Rome, 1998), the ﬁrst joint venture carried out by the International Society for Horticultural Science and the American Society for Horticultural Science (ASHS), which marked the ﬁrst

ix

time that horticulturists from all over the globe had convened to discuss political and economic aspects related to worldwide horticultural research. He has received many awards recognizing his dedication to horticulture: from the National Canners Association Award (assigned by the ASHS for his work on ‘ripening of nectarines and canning peaches’) to the Wilder Medal 2000 awarded by the American Pomological Society, the Gold Veitch Memorial Medal from the Royal Horticultural Society (London, UK) and an Honorary Degree in Horticultural Sciences from the University of Budapest, Hungary. At the national level, he has been recognized by the Italian Ministry of Higher Education. He was named ASHS Fellow in 1995. His editorial activity is tireless. He has been Editor since 1986 of the monthly Italian journal Rivista di Frutticoltura, and is an editorial board member of the following journals: Tree Fruit Production (Binghamton, New York, USA), Fruits (CIRAD, Montpellier, France), L’Arboriculture Fruitière and the International Journal of Agronomy, Agricultural Ecosystem and Plant Genetics (INRA, Montfavet, France). Throughout his career he has edited the proceedings of innumerable symposia and meetings at the international and national levels. He is also Member of several academies: the Italian National Academy of Agriculture, the Italian Academy of Science, a Corresponding Member of the Academie d’Agriculture of France, the Italian Academy of Grape and Wine and the prestigious Academy of ‘Georgoﬁli’ (Florence, Italy). He is author, co-author or editor of more than 500 papers, proceedings and books on biological, physiological and genetic aspects of pome and stone fruits. His in-depth command of very diverse facets of horticultural research is witness to his passionate commitment to horticulture as a whole, his scientiﬁc curiosity and his hard-working and demanding attitude, which are the unique traits that have attracted hundreds of students from Italy and abroad to work with him. His students, many of whom have followed his path in research, value the privilege of working with one of the most dedicated, open-minded and challenging personalities of the international fruit science community. Daniele Bassi Luca Corelli-Grappadelli

Contributors

Abbott, Albert G., Department of Genetics and Biochemistry, 116 Jordan Hall, Clemson University, Clemson, SC 29634, USA. Adaskaveg, James E., Department of Plant Pathology and Microbiology, University of California – Riverside, 242 Fawcett Laboratory, Riverside, CA 92521, USA. Arús, Pere, Institut de Recerca i Tecnologia Agroalimentàries (IRTA), E-08348 Cabrils (Barcelona), Spain. Bacon, Terry, Sun World International, Inc., 16350 Driver Road, Bakersfield, CA 93308, USA. Barba, Marina, Instituto per la Patologia Vegetale, Via Bertero 22, I-00156 Rome, Italy. Bassi, Daniele, Dipartimento di Produzione Vegetale, University of Milan, Via Celoria 2, I-20133 Milan, Italy. Cambra, Mariano, Departamento Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Carretera Moncada – Náquera Km 4.5, Apartado Oficial, E-46113 Moncada (Valencia), Spain. Candresse, Thierry, Plant–Virus Interactions, UMR–GDPP–IBVM, INRA Bordeaux-Aquitaine, BP 81, F-33883 Villenave d’Ornon Cedex, France. Cheng, Zhongping, Wuhan Institute of Botany, The Chinese Academy of Sciences, Hubei 430074, People’s Republic of China. Corelli-Grappadelli, Luca, Dipartimento di Colture Arboree, University of Bologna, Via Fanin 46, I-40127 Bologna, Italy. Costa, Guglielmo, Dipartimento di Colture Arboree, University of Bologna, Via Fanin 46, I-40127 Bologna, Italy. Cravedi, Piero, Instituto di Entomologia e Patologia Vegetale, Piacenza Campus, Università Cattolica del Sacro Cuore, Via Emilia Parmense 84, I-29100 Piacenza, Italy. Crisosto, Carlos H., Department of Plant Sciences, University of California, Kearney Agricultural Center, 9240 South Riverbend, Parlier, CA 93648, USA. DeJong, Theodore M., Department of Plant Sciences, 3037 Wickson Hall, One Shields Avenue, University of California, Davis, CA 95616-8683, USA. Esmenjaud, Daniel, INRA, UMR ‘Interactions Biotiques et Santé Végétale’ (IBSV), 400 Route des Chappes, F-06560 Sophia-Antipolis Cedex, France. Flores, Ricardo, Instituto de Biología Molecular y Celular de Plantas, CSIC/Universidad Politécnica de Valencia, Avenida de los Naranjos s/n, E-46022 Valencia, Spain.

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xi

Förster, Helga, Department of Plant Pathology, University of California, One Shields Avenue, Davis, CA 95616, USA. Fuest, Jaime, Department of Entomology, University of Georgia, 463 Biological Sciences Building, 120 Cedar Street, Athens, GA 30602-2603, USA. Gentit, Pascal, Virology Laboratory, CTIFL, BP21 Lanxade, F-24130 La Force, France. Glenn, D. Michael, USDA–ARS Appalachian Fruit Research Station, 2217 Wiltshire Road, Kearneysville, WV 25430, USA. Gradziel, Tom M., Department of Plant Sciences, 2055 Wickson Hall, One Shields Avenue, University of California, Davis, CA 95616-8683, USA. Horton, Dan L., Department of Entomology, University of Georgia, 463 Biological Sciences Building, 120 Cedar Street, Athens, GA 30602-2603, USA. Huang, Hongwen, Wuhan Institute of Botany/Wuhan Botanical Garden, The Chinese Academy of Sciences, Hubei 430074, People’s Republic of China and South China Institute of Botany/South China Botanical Garden, Guangzhou 510650, People’s Republic of China. Johnson, R. Scott, Department of Plant Sciences, University of California, Kearney Agricultural Center, 9240 South Riverbend, Parlier, CA 93648, USA. Layne, Desmond R., Department of Horticulture, Clemson University, 50 Cherry Road, Clemson, SC 29634-0319, USA. Loreti, Filiberto, Dipartimento di Coltivazione e Difesa delle Specie Legnose ‘G. Scaramuzzi’, Sezione di Coltivazioni Arboree, Facoltà di Agraria, University of Pisa, Via del Borghetto 80, I-56124 Pisa, Italy. McCaa, James P. (‘Pat’), Del Monte Foods, PO Box 30190, 2716 East Miner Avenue, Stockton, CA 95213, USA. McGlasson, William (‘Barry’), Center for Plant and Food Science (PAFS), University of Western Sydney, Hawkesbury Campus, Locked Bag 1797, South Penrith Distribution Centre, NSW 1797, Australia. Marini, Richard P., Department of Horticulture, The Pennsylvania State University, 119 Tyson Building, University Park, PA 16802, USA. Moing, Annick, Unite de Physiologia Vegetable, INRA Domaine de la Grande Ferrade, 71 avenue Edouard Bourlauz, BP 81, F-33883 Villenave d’Ornon Cedex, France. Monet, René (retired), National Institute for Agronomical Research (INRA), Bordeaux Research Centre, Bordeaux, France. Morini, Stefano, Dipartimento di Coltivazione e Difesa delle Specie Legnose ‘G. Scaramuzzi’, Sezione di Coltivazioni Arboree, Facoltà di Agraria, University of Pisa, Via del Borghetto 80, I-56124 Pisa, Italy. Nyczepir, Andy, USDA–ARS Southeastern Fruit and Tree Nut Research Laboratory, 21 Dunbar Road, Byron, GA 31008, USA. Okie, William R. (‘Dick’), USDA-ARS Southeastern Fruit and Tree Nut Research Laboratory, 21 Dunbar Road, Byron, GA 31008, USA. Pagani, Maria Cristina, BASF Corporation, 26 Davis Drive, Research Triangle Park, NC 27709, USA. Pallás, Vincente, Instituto de Biología Molecular y Celular de Plantas, CSIC/Universidad Politécnica de Valencia, Avenida de los Naranjos s/n, E-46022 Valencia, Spain. Ramina, Angelo, Dipartimento di Agronomia Ambientale e Produzioni Vegetali, University of Padova – Agripolis, Viale dell’Università 16, I-35020 Legnaro (PD), Italy. Raseira, Maria do Carmo Bassols, Empressa Brasileira de Pesquisa Agropecuaria/Embrapa Clima Temperado, Caixa Postal 403, 96001-970 Pelotas, Rio Grande do Sul, Brazil. Reighard, Gregory L., Department of Horticulture, Clemson University, 50 Cherry Road, Clemson, SC 29634-0319, USA. Ritchie, David F., Department of Plant Pathology, North Carolina State University, 2406 Gardner Hall, Campus Box 7616, Raleigh, NC 27695-7616, USA.

xii

Schnabel, Guido, Department of Entomology, Soils and Plant Sciences, Clemson University, Clemson, SC 29634-0315, USA. Scorza, Ralph, USDA–ARS Appalachian Fruit Research Station, 2217 Wiltshire Road, Kearneysville, WV 25430, USA. Sherman, Wayne B., Department of Horticultural Sciences, 717 Hull Road, 2133 Fifield Hall, PO Box 110690, University of Florida, Gainesville, FL 32611-0690, USA. Tonutti, Pietro, Scuola Superiore Sant’Anna, Piazza Martiri della Libertà 33, I-56127 Pisa, Italy. Topp, Bruce L., Department of Primary Industries and Fisheries, Agency for Food and Fibre Services, Queensland Horticulture Institute, Maroochy Research Station, PO Box 5083 SCMC, Nambour, QLD 4560, Australia. Tworkoski, Thomas J., USDA-ARS Appalachian Fruit Research Station, 2217 Wiltshire Road, Kearneysville, WV 25430, USA. Valero, Daniel, Department of Food Technology, Head of Post-Harvest and Quality, University Miguel Hernández, Ctra. Beniel – km. 3,2, E-03312 Orihuela, Alicante, Spain. Wang, Ying, Wuhan Institute of Botany, The Chinese Academy of Sciences, Hubei 430074, People’s Republic of China. Zhang, Zhonghui, Wuhan Institute of Botany, The Chinese Academy of Sciences, Hubei 430074, People’s Republic of China.

Preface

Before the 19th century, many non-Asians believed that the peach originated from Persia (modern-day Iran). Peach probably came to Persia from China along the silk trading routes in the 2nd or 3rd century BC. The Persian origin hypothesis was due, in part, to the fact that peaches were brought from Persia to Europe by the Roman army in the 1st century BC. Alphonse De Candolle in his ‘Origin of Cultivated Plants’ (1885, Appleton and Co., New York, pp. 221–229) contended that peach originated in China. In his tome, ‘The Peaches of New York’ (1917, J.B. Lyon Co., Albany), U.P. Hedrick made the same assertion. In fact, Chinese literature refers to peach more than 1000 years before it ﬁrst appeared in any European writings. There is documented evidence of peach cultivation in China for more than 3000 years ago. The peach is a symbol of immortality in Taoist mythology. The Queen Mother (goddess) of the West (Xi Wang Mu) had a jade palace that was surrounded by a beautiful garden containing the peach trees of immortality. In the classic Chinese novel, ‘The Journey to the West’ (Wu, Ch’eng-en ~1590 AD, translated by Anthony C. Yu), Sun Wukong, or the Monkey King (picture inset), attained immortality as a result of a memorable visit to this garden: ‘I have been authorized by the Jade Emperor,’ said the Monkey King, ‘to look after the Garden of Immortal Peaches.’ The local spirit hurriedly saluted him and led him inside. The Monkey King then asked the local spirit, ‘How many trees are there?’ ‘There are three thousand six hundred,’ said the local spirit. ‘In the front are one thousand two hundred trees with little ﬂowers and small fruits. These ripen once every three thousand years, and after one taste of them a man will become immortal with healthy limbs and a lightweight body. In the middle are one thousand two hundred trees of layered ﬂowers and sweet fruits. They ripen once every six thousand years. If a man eats them, he will ascend to Heaven with the mist and never grow old.

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At the back are one thousand two hundred trees with fruits of purple veins and pale yellow pits. These ripen once every nine thousand years and, if eaten, will make a man’s age equal to that of Heaven and Earth, the sun and the moon.’ Highly pleased by these words, the Monkey King made thorough inspection of the trees and a list of the arbors and pavilions before returning to his residence. One day he saw that more than half of the peaches on the branches of the older trees had ripened, and he wanted very much to eat one and sample its novel taste. Closely followed, however, by the local spirit of the garden, the stewards, and the divine attendants, he found it inconvenient to do so. He therefore devised a plan on the spur of the moment and said to them, ‘Why don’t you all wait for me outside and let me rest a while in this arbor?’ The various immortals withdrew accordingly. The Monkey King then took off his cap and robe and climbed up onto a big tree. He selected the large peaches that were thoroughly ripened and plucking many of them, ate to his heart’s content right on the branches.

Peach is revered as a delicious and healthy summer fruit in most temperate regions of the world. It is highly perishable but, depending on market demands and fruit availability, it can be a very proﬁtable fruit crop for the careful farmer. Today it is a major fruit crop of commerce in China, Italy, Spain, the USA, and Greece, the top ﬁve producing countries, respectively. Currently, there are nearly 1.5 million ha of peaches in production worldwide with the vast majority planted in China (approx. 46%). Tremendous diversity exists within the cultivated peach germplasm for tree size, growth habit, ﬂower size and colour, chill hour requirement, fruit size, shape, ﬂesh texture, ﬂesh colour, ﬂesh acidity, stone adherence to ﬂesh, etc. As a result, many hundreds of cultivars of peaches are grown successfully from climatic and geographic regions as diverse as southern Canada to the highlands of Thailand. Because of the small genome size (about twice that of Arabidopsis), peach has been selected as a model species for studying genomics in the Rosaceae. An extensive physical map/genetic map has been developed and vast genetic information is available through an online database. Marker-assisted selection in conjunction with conventional breeding techniques will undoubtedly lead to new cultivars with enhanced pest resistance, nutritional value and other novel traits. Until a reliable transformation and regeneration protocol can be developed, however, some of the novel genetic advances that have occurred in other fruits and crop plants remain to be fully realized. Management of light interception, careful pruning and training, orchard ﬂoor, soil fertility, water availability and crop load are just a few of the many complexities of producing peaches proﬁtably. Combining these factors with the reality that peach is subject to many difﬁcult to manage pests makes it even more of a challenge. Breeding for pest resistance has resulted in some improvements in tolerance to a few diseases and insects, but if trees are left unattended in most locations, they will die prematurely. Thus, careful rootstock and cultivar selection, combined with proper site selection and pest management (monitoring, forecasting, thresholds, cultural and physical controls, biological and chemical control), are vital for success. This comprehensive treatise by 49 research scientists from eight countries summarizes the current state of knowledge in topics ranging from botany and taxonomy to breeding and genetics of cultivars and rootstocks, propagation, physiology and planting systems, crop and pest management and postharvest physiology. The goal was to provide research scientists, extension personnel, students, professional fruit growers and others with a vital resource on peach and its culture. Desmond R. Layne Daniele Bassi

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Daniele Bassi

Acknowledgements

The Editors would like to acknowledge the chapter authors and the following individuals for critical external peer review of chapter manuscripts in this text: T. Beckman, W. Bentley, D. Byrne, J. Clark, J. Cline, K.R. Day, R. Ebel, L. Georgi, J. Girona, R. Gucci, F. Hale, A. Iezzoni, R.E.C. Layne, S. Lewis, A. Liverani, N.W. Miles, A. Naor, M.L. Parker, J.C. Pech, J. Rushing, M. Rieger, E. Sanchez, S. Scott, W. Shane, H. Sherm, C. Xiloyannis and J. Walgenbach. The Editors would also like to acknowledge the following individuals and organizations that helped underwrite the expenses for the colour plate section of the book. In the USA, these included Dr Norman F. Childers, National Peach Council (USA), Al Pearson, Adams County Nursery, the Burchell Nursery, Inc., South Carolina Agricultural Experiment Station, South Carolina Peach Council, Titan Peach Farms and Jerrold A. Watson & Sons. In Italy, these included Apofruit, Apoconerpo, Orogel Fresco, Pempacorer, the Growers Consortium for Crop Development (Newplant), the Crop Research Center (CRPV), the Apulian Nursery Consortium (COVIP) and the Italian Society for Horticultural Science (SOI).

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1

Botany and Taxonomy Daniele Bassi1 and René Monet2 1University

2National

of Milan, Milan, Italy Institute for Agronomical Research (INRA), Bordeaux Research Centre, France (retired)

1.1 Introduction: Origin and Dissemination of Peach 1.2 Species Systematics: Cultivated Peach and Wild Relatives 1.3 Peach Morphology: Description and Variability of the Main Organs Tree Leaf Flower and fruit development Fruit appearance and composition Endocarp (stone, pit) and seed 1.4 Peach Biology and Phenology Floral biology and fruit set Chilling and heat requirements Phenological phases Time of ﬂowering Time of ripening (fruit development period) 1.5 Cultivar Classiﬁcation Peach description sheet Morphological and commercial classiﬁcations Phenological classiﬁcation

1.1 Introduction: Origin and Dissemination of Peach The botanical name of peach (Prunus persica (L.) Batsch) refers to the putative country of origin, Persia (actual Iran), and Linné (1758) ﬁrst named the species based on this opinion (Amygdalus persica). Only in the 19th century was the Far East geographical origin (western China) ﬁnally acknowledged (De Candolle, 1883; Hedrick, 1917; Vavilov, 1951); written

1 2 3 3 6 11 16 25 25 25 26 27 27 27 29 29 30 30

records and archaeological evidence date peach domestication at least as far back as 3000 BC (Li, 1984). Faust and Timon (1995) gave a detailed account of the possible genetic and geographic origin and dissemination of the peach and related species. Taking into consideration the long history of cultivation of this species and its growing role in several countries over the centuries, many scholars have attempted the classiﬁcation of the species

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

1

2

D. Bassi and R. Monet

and its related forms. Early writings classiﬁed almond and peach under the same species, but later they were classiﬁed as separate entities (De Candolle, 1883) although possibly sharing the same putative ancestor. The close geographic origin may account for this hypothesis: while peach is native to the Tarim basin north of the Kun Lun mountains, almond is native to the south of the same mountains (beside the northern borders of Afghanistan and Pakistan). The westward movement of peach could have brought it into Persia (actual Iran) in the 2nd to 1st century BC, shortly before the arrival of the Roman army. Early Latin scholars mentioned peaches in Italy in the 1st century BC. The ‘Gallic’ peaches, described of French origin, may account for a possible second, independent arrival of the tree to Europe. Thus, peach could have reached France through the Balkan route almost simultaneously to its arrival in Italy, along the Danube river and the Black Sea region (Werneck, 1956). Additionally, in the Middle Ages, France became probably the second major point of origin after China, according to many records. Peach was brought to the American continent in two different waves. The ﬁrst was led by the Spaniards, starting in Central America from the ﬁrst half of the 16th century. In northern America, peaches were later cultivated by the native peoples and propagated by seeds. This early introduction in the Americas has given rise to many landraces, most featuring the non-melting ﬂesh. Some are still cultivated for local fresh markets or even exploited as valuable sources for interesting traits such as ‘evergreen’ (Diaz, 1974) and disease resistance, e.g. powdery mildew or rust (Rodriguez and Sherman, 1990; Pérez et al., 1993). Interestingly, even today, non-melting local cultivars for the fresh market are very popular in southern Europe (Greece, southern Italy and Spain). The second wave of peach introduction in the USA was a direct import from China in the mid-1850s, when the well-known ‘Chinese Cling’ was grown at the Delaware Experimental Station. This tree originated ‘Elberta’, one of the main ancestors of the modern cultivars grown in the USA and elsewhere in the most important peach-growing countries (Okie et al., 1985; Scorza et al., 1985).

1.2 Species Systematics: Cultivated Peach and Wild Relatives The argument about the scientiﬁc name of peach was ﬁnally set by the classiﬁcation of Bailey (1927) that grouped all stone fruits under the Prunus genus. Hedrick (1917) stated as not rational a classiﬁcation of peach species based almost exclusively on the morphological traits of the fruits. Consequently, the species classiﬁcation based on fruit traits (shape, glabrous skin) or tree growth habit is to be regarded as an early attempt, before Mendel’s laws enlightened the mere intraspeciﬁc nature of those singly inherited traits. The following classiﬁcation is summarized after Knight (1969), Watkins (1976) and Rehder (1990). Peach is included in the Euamygdalus Schneid. section of the Amygdalus subgenus, and can be distinguished from almond (Prunus dulcis (Mill.) D.A. Webb) because the mesocarp of the latter becomes dry and splits at maturity, while the leaves are serrulate. P. persica (L.) Batsch is a diploid species (2n = 16) with a medium tree height (up to 8 m); the leaves are lanceolate, glabrous and serrate, broadest near the middle, with a glandular petiole; the ﬂowers are generally pink, but also white or red; the fruit is pubescent or glabrous, ﬂeshy and the mesocarp does not split; the stony endocarp is very deeply pitted, furrowed and very hard. The main species related to peach are listed below; all of them show fruits with very poor eating quality, although some could be interesting for disease resistance traits or as rootstocks. Prunus davidiana (Carr.) Franch. is a wild species native to north-eastern China, where it is used as a seedling rootstock, given its tolerance to drought, although it is very sensitive to nematodes; the tree is tall (up to 10 m), with a reddish-brown bark; the leaves are long and glabrous, ovate-lanceolate, broadest near the base; the ﬂower is white or light pink; the pit is small and pitted; the ﬂesh is freestone. Accessions of this species have been hybridized with peach to improve disease resistance on scion cultivars to plum pox, powdery mildew, leaf curl, etc. (Moing et al., 2003) or to

Botany and Taxonomy

breed interspeciﬁc rootstocks adaptable to marginal soils or to replant problems (Pisani and Roselli, 1983; Roselli et al., 1985; Edin and Garcin, 1994). Prunus ferganensis (Kost. and Rjab) Kov. and Kost. is a wild form found in western China classiﬁed as a subspecies of P. persica; a wide variability in terms of fruit types can be found (yellow- and white-ﬂeshed peaches, nectarines, etc.); the leaves have parallel veins and there are parallel grooves in the stone, both single Mendelian traits (Okie and Rieger, 2003). The seed can be cyanogenic glycoside-free (not bitter). It has resistance to powdery mildew. Prunus kansuensis Rehd. is a wild species found in north-east China, also used as a seedling rootstock in China; it is a bushy tree with glabrous winter buds, early-blooming, even so the ﬂowers are considered to be rather resistant to frost (Meader and Blake, 1939); the leaves are villous along the midrib near the base, broadest below the middle; the style is longer than the stamens. The fruit quality is very poor (astringent); the stone is furrowed (with parallel grooves) but not pitted. Prunus mira Koehne is a wild species found in far-west China (eastern Tibet); the tree is tall (up to 20 m) and long-living, up to 1000 years (Wang, 1985); the leaves are lanceolate, villous along the midrib beneath, rounded at base; the ﬂowers are white. The fruit is very variable in shape, colour and size; the stone is smooth, although in some types it resembles P. persica. Some forms are cultivated in Tibet and it is also used as a seedling rootstock in some regions of India. It is reputed as an ancestor of P. persica, having been spread south and east from the Himalayan mountains (Yoshida, 1987).

1.3 Peach Morphology: Description and Variability of the Main Organs

orange-white while young, turning dark orange when older with large lenticels. The tree can live for 20–30 years, but in commercial plantings the average duration is limited to 12–15 years at most, because of either the cultivar becoming obsolete or the loss of productivity. Fruit production begins from the second or third year. Fruiting wood and buds One-year-old shoots are reddish-green, turning dark grey-silver when older. Buds are found at the base of the leaves. Each node normally displays three buds: two lateral ﬂower buds and one vegetative bud in the middle, but up to four or ﬁve ﬂower buds can be found and sometimes even more, particularly in the ornamental types. Sometimes only one ﬂower bud is present beside the vegetative, or even only three vegetative buds. There is variability in setting ﬂower buds, where the genotypes with high bud set transmit the character to the progeny with high heritability (Weinberger, 1944); the resulting seedlings tend to be precocious (Rodriguez and Sherman, 1986). Different types of shoots can be found, with different contribution to yield and fruit quality. ●

●

Tree The trunk is straight and smooth, with a reddish-greenish bark in the ﬁrst year, later becoming dark grey-silver. The root system develops within 50–60 cm in depth, depending on soil type; roots are

3

●

One-year-old shoot: wood of good vigour (50–100 cm) with ﬂower buds along its axis, which ends with a vegetative bud (Fig. 1.1/Plate 1). It is the most important wood in commercial cultivars, since in peach fruit size is positively related to shoot vigour and total current-season wood available (Manaresi and Draghetti, 1915; Marini and Sowers, 1994). Flower bud set may be uneven along the shoot and cultivars may be classiﬁed according to basal, middle or apical distribution (Bellini and Scaramuzzi, 1976). Brindle: a 1-year-old fruiting shoot of weak vigour (about 10–25 cm) with ﬂower buds along its axis, which ends with a vegetative bud. This is the most important wood (‘hangers’) for canning peaches, where medium to small-sized fruits are most prized. Feather: side shoot arising from a bud in the same year as that when the bud was formed.

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Fig. 1.1.

●

●

●

One-year-old fruiting shoots at bloom.

Spur (or dard): a very short (about 1–3 cm), 1-year-old shoot that terminates in a vegetative bud (vegetative spur), eventually surrounded by one or more ﬂower buds (fruiting spur). Water sprout: wood of high (excessive) vigour, with no ﬂower buds. Branch: a limb older than 4–5 years.

Okie (1998) describes a ‘collar’ trait as a swollen collar growing where the shoot attaches to the trunk, resulting in knobs when the shoot is eventually eliminated. The trait seems monogenic and recessive. INTERNODE LENGTH AND DWARFISM. Internode length is inﬂuenced by both quantitative and qualitative Mendelian traits. Tree size, however, is predominantly inﬂuenced by qualitative traits, independently of the growth habit (see section on ‘Tree growth habit’ below), particularly in the case of the dwarf phenotypes, where internodes are less than 10 mm in length (Fig. 1.2/Plate 2). The regular dwarf tree also features a dense canopy due to larger and thicker leaves. The ﬁrst dwarf phenotype was described by Lammerts (1945) from the ‘Chinese Dwarf’ peach as recessive and monogenic (Dw/dw). He

also described bushy trees obtained in a ratio of 15:1 by self-pollinating the ‘Babcock’ peach as recessive and controlled by two genes (Bu1/bu1, Bu2/bu2). Hansche (1988) described a more sizereducing dwarf trait than Dw/dw in a progeny from ‘Redcal’ peach (heterozygous for that trait) and reported it as monogenic and recessive (Dw2/dw2). Chaparro et al. (1994) described an even smaller dwarf (Dw3/dw3), with a very thin stem and willow-like leaves. Monet and Salesses (1975) described one more dwarf mutant, smaller than Dw/dw. Heterozygous individuals are semi-dwarf; by self-pollination, these individuals give three phenotypes: normal, semi-dwarf (like the F1 parent) and dwarf with Mendelian proportions 1:2:1. It is a monogenic trait with incomplete dominance (N/n). Gradziel and Beres (1993) reported a similar semi-dwarf as above, featuring internode length half of the standard size, with thicker shoots and greener leaves. The tree is upright but open and with 1-year-old shoots from 30 to 50% shorter than standards. When crossed to standard growth habit genotypes it shows an intermediate heritability (1:1).

Botany and Taxonomy

Fig. 1.2.

5

Dwarf peaches in a commercial orchard.

Okie (1998) described ‘mini-pillar’, a tree form growing upright with wavy twigs where the internode is about half the normal length. TREE GROWTH HABIT. The tree growth habit (or tree form) can be deﬁned as the overall appearance of a tree’s canopy, i.e. the whole set of a tree’s vigour, which could be expressed as the total amount of dry matter or by the rates of shoot growth (quantitative traits) and structural (type of fruiting shoots and their distribution through the canopy, their angle and internode length) traits that determine its natural architecture (Bassi, 2003). For a better understanding of the canopy architecture, two types of branch angle should be taken in consideration: (i) the ‘crotch’ angle, formed by the 1-year-old fruiting shoot (basal part) and the limb from which it grows; and (ii) the ‘extension’ angle, formed by the reference axis (trunk or branch from which the 1-yearold fruiting shoot grows) and the juncture line between the shoot’s point of origin and its apex at full growth (Fig. 1.3/Plate 3). This latter parameter makes it possible to account for the direction of the shoot’s distal part, which, regardless of the crotch angle, can be vertical, upright, outwards (deviating more or less from the vertical), weeping or procumbent

(Scorza, 1984, 2002; Scorza et al., 1989, 2002; Bassi et al., 1994; Bassi, 2003). Several growth habits are known in peach (see a comprehensive list in Chapter 3, Table 3.1). ●

●

●

Arching: similar to the upright (see below), but with a distinct curvature in the 1-year-old shoots (Werner and Chaparro, 2005). Columnar: marked by branches and shoots growing vertically at a notably narrow crotch angle (no more than 35–40°) that makes the tree look like a column (or ‘pillar’). Compact: marked by a large number of lateral shoots and relatively short internodes that produces a dense canopy. The overall shape is semi-spherical for a bush-like appearance. A genetic curiosity, ‘corky triangle’, has been observed in a progeny resulting from a self-pollination of ‘Redhaven’ peach (Monet and Bastard, 1982). A triangular ‘corky’ (necrotic) zone develops close to most buds on the epidermis of the shoot. This character is associated with a lower size of the tree due to a short internode. The ‘Compact Redhaven’ peach studied by Van Well (1974),

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●

●

●

●

●

●

●

Fig. 1.3. Relationship between crotch (α) and extension angles (β). (From Bassi, 2003.)

Fideghelli et al. (1979) and Mehlenbacher and Scorza (1986) shows this character. It is possible that the ‘corky triangle’ recessive and monogenic (T/t) trait and ‘compact’ tree characters are under pleiotrophic control of the same mutation.

Open: overall tree shape varying from goblet to slightly ﬂat (transversal diameter more developed than the vertical). The 1-year-old fruiting shoots are marked by a wide crotch angle (about 60–70°). Spreading: intermediate between open and weeping. Spur: marked by the prevalence of spurs; the internodes can be shorter than normal, in which case the canopy size could be semi-dwarf or dwarf. Standard: the prevailing growth habit in commercial cultivars; it is marked by medium crotch angle (40–60°) and internode length; canopy shape is generally semispherical or slightly upright (the canopy’s vertical diameter is more developed than the cross-section’s). Twister: a unique branching pattern where after 15–30 cm of growth of the shoot, the phyllotaxy increases from normal 135° to about 180°, with buds and leaves aligned at the opposite sides of the stem, on the same plane; after 15–20 nodes the shoot stops growing and normal shoots break from buds below, repeating the same pattern, i.e. normal ﬁrst, then twisted; the trait seems monogenic and recessive (Okie, 1998). Upright: the canopy is more developed in height than in width and is larger (in diameter) than the columnar. One-yearold shoots and branches are marked by a relatively narrow crotch angle (about 50°) and vertical growth. Weeping: marked by shoots of medium or wide crotch (larger than 70°) and extended (more than 90°) angles, bending downward (positive geotropic growth), the result being a proﬁle that is gobletlike or more developed in width (Monet et al., 1988).

The main growth habits are sketched in Fig. 1.4 and summarized in Table 1.1. Leaf For peach, new shoots and leaves form following anthesis. Two temporary lateral stipules are found at the petiole base; they abscise when the leaf is fully developed (Fig. 1.5/Plate 4).

Botany and Taxonomy

7

Fig. 1.4. Main growth habit in peach: (a) standard; (b) columnar; (c) upright; (d) compact; (e) weeping; (f) open (from Bassi, 2003).

The leaf blade may be ﬂat or wavy. The wavy blade results from a differential growth of the leaf margins and this is recessive and monogenic (Wa/wa; Scott and Cullinan, 1942); it also has very sharply serrated margins. This leaf character was reported as often associated to a dwarf tree growth habit, with poor set. A narrow-width leaf (willow-like shape) with very serrated margins was reported by Chaparro et al. (1994). This phenotype, designated as Wa2/wa2 and genetically linked to the dwarf gene Dw3, does not have the wavy leaf edges as the original homozygous wa/wa trait, other than showing a narrow width. One more narrow-leaf trait was reported by Okie and Scorza (2002), partially dominant over standard shape (probably several genes are involved), the tree size being sometimes smaller and weaker than standard (Fig. 1.6/Plate 5). Progenies segregate for variable width:length ratio from 10 (narrow) to 0.25% (standard

shape). Narrow leaves show higher water use efﬁciency than standard (Glenn et al., 2000). There are glands at the margin of the leaf, located at the blade base and at the petiole; three phenotypes are known that show Mendelian inheritance with incomplete dominance, the absence being recessive (E/e; Connors, 1921): (i) reniform (homozygous dominant); (ii) globose (heterozygous); and (iii) eglandular (homozygous recessive) (Fig. 1.7/Plate 6). The leaves with reniform (kidney-shaped) glands have crenate margins, varying in number from two to eight or more, those located on the margin being smaller than those on the petiole. The leaves with globose glands have serrate-crenate margins, but glandless leaves with serrate margins are frequently found on the same tree; the glands are round, smaller than reniform, varying in number from none to over eight, those on the petiole being stalked.

8

Table 1.1.

Characteristics of main growth habits in peach. (Data from a comparative trial in Italy, trees not pruned; from Bassi, 2003.) Tree size (height)

Columnar Upright Standard

Very tall Very tall Medium (regular) Semi-dwarf Dwarf Small Small Small

Open Weeping Compact

Canopy

Angle (degrees from vertical)

Trunk cross-sectional area (cm2)

Height (m)

Width (m)

Crotch (°)

154 ± 16 183 ± 12 180 ± 3.9 76 ± 3.2 59 ± 2.9 230 ± 18 205 ± 25 170 ± 16

5.0 ± 0.5 5.0 ± 0.4 3.6 ± 0.3 2.8 ± 0.1 1.8 ± 0.4 2.7 ± 0.2 2.5 ± 0.2 2.5 ± 0.3

1.5 ± 0.33 2.5 ± 0.3 2.8 ± 0.2 2.3 ± 0.4 2.7 ± 0.3 3.0 ± 0.25 4.2 ± 0.3 3.8 ± 0.33

36.8 ± 7.9 49.6 ± 6.7 59.4 ± 9.3 58.9 ± 8.9 58.2 ± 13.8 65.7 ± 12.0 73.0 ± 12.0 66.7 ± 9.3

Extended (°) 30.8 ± 11.5 41.6 ± 6.5 53.9 ± 13.8 55.2 ± 14.1 60.5 ± 10.2 70.0 ± 19.0 120.0 ± 13.0 71.6 ± 15.5

Internode length (mm) 19.1 ± 2.9 25.1 ± 2.9 28.0 ± 3.0 19.0 ± 3.0 7.5 ± 0.9 23.0 ± 3.0 26.0 ± 0.3 20.0 ± 3.0

D. Bassi and R. Monet

Tree form (by crotch angle)

Botany and Taxonomy

Fig. 1.5.

Leaf stipules at petiole base.

Fig. 1.6.

Narrow leaves (left) compared with normal sized. Scale in centimetres.

Marginal reniform glands are pale green, while marginal globose glands are yellow. The eglandular phenotype is associated with a strong susceptibility to powdery mildew (Podosphaera pannosa (Wallr.:Fr.) Braun &

9

Takamatsu), and it is systematically eliminated in breeding operations, although this phenotype could show a good degree of resistance to leaf curl, Taphrina deformans (Berk.) Tul. (Wickson, 1889; Monet, 1983). Cultivars

10

Fig. 1.7.

D. Bassi and R. Monet

Leaf glands: (a) reniform; (b) globose; (c) eglandular (note close-up, below).

with globose glands are generally more susceptible to powdery mildew than those with reniform glands (Saunier, 1973). The leaf blade is darker on the adaxial side and the colour of the main veins is related to the ﬂesh colour: yellowish (in yellowﬂeshed fruits) or greenish-white (in whiteﬂeshed fruits). The ‘redleaf’ trait, ﬁrst described in a US feral population named ‘Tennessee Natural’, a seedling rootstock (Hedrick, 1917), shows purple-red epidermis, particularly on the young leaves and fruits, while ﬂowers are dark pink (Fig. 1.8/Plate 7). The lamina tends to recover the regular green colour late in the season, but the leaf veins remain purple. Blake (1937) showed that the character is incompletely dominant and monogenic: Gr/gr. At the heterozygous level, the leaves appear copper-red or copper-red green even at the young stage, while when homozygous they are darker red. From observations on ‘Flordaguard’ (homozygous ‘redleaf’) seedlings, two additional ‘redleaf’ phenotypes have been described, suggesting the presence of at least one additional gene (Okie, 1998). In one phenotype the red fades slowly to a bronze colour. In a second phenotype the red fades quickly and

completely (‘quick fade’) to green before leaves attain full size, except the main vein and petiole for some time. In a third phenotype the leaves fade at an intermediate rate, with a red-green mosaic on fading full-size leaves, as in the dominant homozygous. At the end of the season all types fade to completely green. The ‘quick fade’ is reputed as monogenic and recessive.

REDLEAF.

ANTHOCYANIN DEFICIENCY.

The character was ﬁrst observed on the old US peach cultivar ‘Summer Heath’. The shoots remain green after ligniﬁcation. Flowers have light pink petals, sepals are green and the fruit skin is feebly pink. The overall anthocyanin content is very low. The character is recessive and monogenic: An/an (Monet, 1967).

ANTHOCYANINLESS. These trees bear white ﬂowers; the receptacle and the sepals are green while the stamens are yellow (instead of reddish). The young shoots remain green even after ligniﬁcation. The fruits are yellow at maturity without any trace of red pigments (Fig. 1.9/Plate 8). The character was described as recessive and monogenic: W/w (Lammerts, 1945). ‘Anthocyaninless’ is reported epistatic to ‘redleaf’ (Chaparro et al., 1995).

Botany and Taxonomy

Fig. 1.8.

11

Redleaf (left) and greenleaf (right) peach trees.

GREEN APHID RESISTANCE. Resistance to green peach aphid (Myzus persicae Sulzer) was found on a weeping tree (‘Weeping Flower Peach’) and on a seedling rootstock (‘Rubira’) by Massonié et al. (1982). It is a resistance based on a hypersensitivity reaction and the aphid makes only a testing probe on young shoots or leaves. Around the testing site, within a few days, a typical necrotic zone develops (Fig. 1.10/ Plate 9). The trait is monogenic and the resistance is dominant over the sensitivity (Rm1/ rm1; Monet and Massonié, 1994).

Flower and fruit development Peach has hermaphroditic, perigynous ﬂowers. The reddish-green calyx is gamosepalous and falls (‘split-jacket’ or ‘shuck-split’ stage) after the initial swelling of the fruitlet. The inner surface of the calyx, where the nectaries are located, is white-greenish in white-ﬂeshed and yellow to deep orange in yellow-ﬂeshed fruits. The petals are separated and two shapes of corolla are known: (i) showy (rose-shaped) with large petals (Fig. 1.11/Plate 10); and (ii) non-showy (bell-shaped) with small petals, where the anthers emerge from the corolla before full anthesis (Fig. 1.12/Plate

11). Connors (1920) and Bailey and French (1949) studied the inheritance of the ﬂower shape and the non-showy was found to be dominant (Sh/sh), the large-sized showy being dominant over the small-sized showy (L/l). Normally there are ﬁve petals, from pure white to dark red, although most cultivars display a pale to dark pink. In ornamental forms pure white and red colours are commonly found, and chrysanthemum-like petals have also been reported (Yoshida et al., 2000) (Fig. 1.13/Plate 12). The number of petals changes according to the semi-double and the double ﬂower traits. In the former phenotype the petal number varies from 12 to 24, the number of stamens transformed in petals being very low. In the latter trait the majority of stamens are transformed in petals arranged in two concentric circles of petals, the inner being darker than the outer, thus conferring the impression of a double ﬂower. The inheritance of double ﬂower is not known but Lammerts (1945) observed that three genes are involved in the semi-double trait: a recessive conditional (d1) and two that modify the number of petals in excess (dm1 and dm2). Examination of the phenotypic

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Fig. 1.9. Fruit skin colour variability. From top centre going clockwise to the right: a yellow nectarine (anthocyaninless); a white peach (anthocyaninless); a yellow peach (100% blush); a white peach; a non-melting peach; a yellow flat nectarine; a white flat peach; a white nectarine; a yellow nectarine.

Fig. 1.10.

Hypersensitivity reaction on a resistant peach after a proof bite by a green aphid.

Botany and Taxonomy

Fig. 1.11.

13

Flower type: showy.

Fig. 1.12. Flower type: non-showy.

frequencies observed by Lammerts (1945) suggests a simpler explanation with one recessive gene responsible for the presence of supernumerary petals (D1/d1). The genes that regulate the organs’ morphogenesis are

homeotic: their mutation transforms one organ to another. As many as 20 to 30 stamens are attached to the calyx. The anthers are reddish unless male sterility (anthers without pollen) is

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D. Bassi and R. Monet

White, simple

Red, simple

White, semi-double

Red, semi-double

Variegated, white and red

Chrysanthemum-like, red, semidouble

Pink, semi-double Fig. 1.13.

Flower diversity in ornamental peach cultivars. (Courtesy of M. Yoshida, Japan.)

present: sterile anthers look pale yellow instead of reddish before dehiscence. Following self-pollination, some progenies may be male sterile but individuals bearing this trait are typically eliminated from selection. Nevertheless, some male sterile cultivars were largely cultivated, the most famous being ‘J.H. Hale’ because of the outstanding quality of its fruits. Scott and Weinberger (1944) listed a series of cultivars heterozygous for the trait. Male sterility was ﬁnally described as monogenic and recessive (Ps/ps; Bailey and French,

1949). A new nuclear male sterility trait was found in ‘White Glory’ (a weeping, ornamental cultivar) which is different from the gene of ‘J.H. Hale’: Ps2/ps2 (Chaparro et al., 1994; Werner and Creller, 1997). Microsporogenesis begins in winter (Knowlton, 1924; Draczynski, 1958) and is followed by meiosis close to bud swell. The gynoecium is superior and it is obviously glabrous in nectarines (see section on ‘Skin adherence and pubescence’ below). Abnormally high temperatures during ﬂower bud

Botany and Taxonomy

initiation may lead to double or triple gynoecium (and pistils), which in turn may eventually give rise to double or triple fruits (discarded during thinning because they are of no commercial value; Fig. 1.14/Plate 13). The eight-nucleate stage of the megagametophyte happens a few days before full anthesis, when the two polar nuclei migrate into the middle of the embryo sac, which elongates after union of the polar nuclei and doubles its length at the time of fertilization. The ovary contains two ovules, but normally only one is fertilized. Time from pollination to fertilization depends on temperature, varying from 24–48 h (Toyama, 1980; Baipo et al., 1989) to 12 days (Herrero and Arbeloa, 1989). The endosperm becomes multinucleate about 10 days after fertilization and cellular after 5–6 weeks (Harrold, 1935; Lilien-Kipnis and Lavee, 1971). Around 8 weeks after full bloom the integuments reach the maximum size (about 20 mm). The ﬁrst division of the zygote occurs about 2 weeks after ovule fertilization (Harrold, 1935). The embryo ﬁlls the testa, absorbing the nucellus and the endosperm in about 100–110 days from full bloom. Thereafter it completes its growth by dry matter accumulation: starch, protein and lipids (about 50%). The ovary (fruit) undergoes four main stages

Fig. 1.14.

Flat fruit, from a double ovary.

15

of growth. The ﬁrst, rather rapid stage (stage I) is marked by cell division (the length of this phase is nearly the same no matter the fruit development period, FDP). This is followed by a slower stage (stage II) where most of the dry matter is employed in pit hardening and seed and embryo growth (this period is very short in very early-ripening genotypes, where at fruit maturity the stone is incompletely ligniﬁed and the embryo does not reach full maturity, in vitro rescue being necessary to recover germination and plant development). The third stage (stage III) is more rapid because cell enlargement and elongation is according to FDP. The last stage (stage IV) is the ripening phase (Lilleland, 1933; Tukey, 1933; Harrold, 1935; Gage and Stutte, 1991). The fruit peduncle remains attached to the shoot after fruit senescence and natural abscission.

Fruit appearance and composition Shape and size (weight) The peach fruit is a drupe. Almost all commercial cultivars share round (globose) or elongated (either oval or more or less oblong)

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D. Bassi and R. Monet

fruits (Fig. 1.15, left and right, respectively/ Plate 14), elongated shapes being dominant over round (Blake, 1932). The ﬂat (or ‘saucer’ or ‘pan-tao’, from the Chinese words ‘ﬂat peach’) fruit, introduced from China, has long been a botanic curiosity in Western countries (Fig. 1.15, centre/Plate 14). The fruit is ﬂattened at opposite poles and the shape affects not only the fruit but also the pit, which is ﬂattened too and rather small. The seed is spherical and has poor germination. The trait is monogenic and dominant over round/elongated: S/s (Lesley, 1940). The homozygous genotype is lethal. Fruit weight varies from less than 50 g in wild forms to 80–110 g for the very, very early-ripening genotypes to over 680 g (Li, 1984), although commercial standards require from 180 to 230 g, depending on FDP and ﬁnal use. Fruit weight follows a quantitative inheritance. Connors (1922) reported that prepotency in fruit size inheritance depended on parent (Fig. 1.16/Plate 15). Lesley (1957), working on self-pollination up to the seventh generation on several lines, observed an inbreeding effect on fruit size for only one line. Similar ﬁndings are reported by Monet et al. (1996), who had no inbreeding effect after three selﬁng cycles and

Fig. 1.15.

reported a bias towards large size in assessing progenies from parents differing in fruit size. Skin adherence and pubescence Skin adherence to the mesocarp was reported as recessive to non-adherence, even if inﬂuence from ﬂesh texture may occur (Lesley, 1957). Two major phenotypes are known about epidermis surface: (i) the standard, fuzzy peach; and (ii) the nectarine, with a glabrous skin. The nature of the nectarine skin character was described as recessive (Rivers, 1906; Blake, 1932; Blake and Connors, 1936) and monogenic: G/g (Bailey and French, 1949). Faust and Timon (1995) indicated that the nectarine mutation probably ﬁrst appeared in the most north-western part of China, in the Tarin basin (part of the Turkistan region). As early as the 14th century, nectarines were noted in Europe (Gallesio, 2003). From studies of the fuzzless skin trait, three different types of heritable skin surface (at a microscopic level) were described (Fogle and Faust, 1975). One more phenotype, intermediate between nectarine and peach, with a rough surface, was also described. It has a pleiotrophic effect on lack of pubescence (or trichomes) on

Main fruit shapes in commercial cultivars: globose (left), flat (centre), oblong (right).

Botany and Taxonomy

Fig. 1.16.

17

Fruit size gain in F1 progeny from distant-size parents.

dormant buds, which look shiny and smooth (Okie and Prince, 1982). The trait was described as monogenic and recessive: Rs/rs (Okie, 1998). The locus controlling the nectarine trait is probably closely linked to or has a pleiotrophic effect on several other traits. Several nectarine sports, compared with their peach progenitors, often show smaller and rounder fruits (reduced cell number), greater speciﬁc gravity, higher soluble solids and organic acids. Other traits may also be involved in the mutation, e.g. the FDP and the chill unit requirement (Wen et al., 1995). The smooth skin of nectarines makes them more susceptible to russeting, mechanical bruising and pest damage (e.g. thrips) than peaches but exploitation of the nectarine trait has led to tremendous advances in peach breeding. During the period from the 1970s to the 1990s, nectarine cultivars became so popular that their proﬁts overtook that of standard peaches. Presently, in some countries such as Italy, their prices have reached a steady level, comparable to the standard peaches. Nectarine features are so distinct that sometimes they are regarded by marketers as an independent species. Indeed, the bright

and glossy over-colour and sometimes distinct ﬂavour play signiﬁcant roles in driving consumer demand in most markets. Skin and flesh colour Skin (ground) and ﬂesh colour, white or yellow, are among the most popular and commercial criteria for peach cultivar classiﬁcation, due to the peculiar features of these phenotypes (Figs 1.9 and 1.17/Plates 8 and 16). ‘White’ peaches are revered for their distinct ﬂavour and/or aroma (Robertson et al., 1990), although most of them are either too soft or too susceptible to skin bruising and ﬂesh browning and thus not competitive with the ‘yellow’ types, where carotenoids (the orange pigments) could mask oxidation from bruising or other blemishes. Xanthophylls, the yellow pigments, are synthesized via hydroxylation from carotenoids: lutein from b-carotene, zeaxanthin, antheraxanthin and violaxanthin from bcarotene (Demmig-Adams and Adams, 2002). Carotenoids are photosynthetically active pigments, while xanthophylls dissipate the light excess that can disrupt photosynthesis. Carotenoids and xanthophylls are localized

18

D. Bassi and R. Monet

in chloroplasts (chromoplasts) and are found in very small amounts in white peaches. Among carotenoids, b-carotene and b-cryptoxanthin are the primary provitamin A factors, their concentrations reaching around 2000 mg/kg of fresh weight (FW) for the former and up to 3400 mg/kg FW for the latter (Tourjie et al., 1998). Connors (1920) showed that white ﬂesh is dominant to yellow ﬂesh. Bailey and French (1949) suggested the symbols Y/y for the two alleles. Anthocyanins, the glycoside derivatives of the anthocyanidins, are responsible for all colours from blue to red and are localized within the cell vacuoles, in either the epidermis or the ﬂesh. They are synthesized from ﬂavonoids via phenylalanine. The presence of anthocyanins is independent of the skin ground colour, either yellow or white, and can be of quantitative or qualitative origin. The quantitative trait is positively inﬂuenced by light exposure and the pigments reach the maximum concentration at full ripening, while the qualitative trait, expressed only in the epidermis, is not related to light nor to ripening and the localization is limited to the skin. There are two indepen-

dent genes regulating the phenotype of qualitative origin. One is the dominant ‘redleaf’ trait (see section on ‘Redleaf’ above); the second is recessive and is expressed in the fruits’ epidermis only, which looks much brighter than in ‘redleaf’, and was designated as Fr/fr (Beckman and Sherman, 2003). A qualitative suppressive trait for fruit red skin, dubbed ‘highlighter’ (H/h; Beckman et al., 2005), was recently reported. When homozygous recessive it completely suppresses the red pigments, but only in the fruit, whereas the w/w trait is characterized by the absence of anthocyanins in any plant tissue. While carotenoids are rather heat-stable, anthocyanins are very labile and subject to browning in canning operations; this has led to the selection for ﬂesh of canning peaches that is anthocyanin-free. Since localization of anthocyanins in skin is independent from that in ﬂesh, commercial canning peaches may or may not develop a red over-colour, given the fruit is peeled before canning. When anthocyanins are present in the ﬂesh, their localization is mainly under the skin and/or close to the pit, the latter reported as dominant over no red (Lesley, 1957). The

Fig. 1.17. Flesh colour variability. From left, top row: non-melting flesh, two yellows (greenish and bright yellow), white; bottom row: red flesh (‘blood’), a yellow melting (anthocyaninless), a yellow and a white melting (flat shape), a white stony-hard (anthocyaninless).

Botany and Taxonomy

amount and distribution of anthocyanins throughout the mesocarp depends on the cultivar (quantitative trait) and may be variably expressed among the fruits on a given tree. Red (‘blood’) flesh peaches One exception to the erratic distribution of the red pigments within the ﬂesh are the ‘red ﬂesh’ (or ‘blood’ ﬂesh) peaches (Fig. 1.18/ Plate 17) and nectarines (Fig. 1.19/Plate 18), where almost all of the ﬂesh is heavily stained by anthocyanins (Gallesio, 1817–1839) independently of the basic ﬂesh colour, either white or yellow (Fig. 1.20/Plate 19). In both types, when the ‘red ﬂesh’ trait is present, the skin has a distinct purple, dull ﬁnish. The trait was ﬁrst described as dominant by Blake (1932), and conﬁrmed by Werner et al. (1998). Flesh compounds influencing flavour and aroma Several compounds contribute to the overall ﬂavour of the ﬂesh: aromatics (volatiles), organic acids, phenolics and sugars are among the most known.

Fig. 1.18.

19

Among the aromatics or volatiles (alcohols, aldehydes, esters, etc.) that contribute signiﬁcantly to the typical peach aroma, peculiar distribution patterns of hexanal (up to about 740 ppm), trans-2-hexanal (up to about 120 ppm), linalool (up to about 250 ppm), g- and d-decalactone (up to about 130 and 25 ppm, respectively) between white- and yellow-ﬂeshed cultivars were found, with the former showing higher total amounts (Robertson et al., 1990). The main organic acid is malic (over 50% of the total), followed by citric, quinic and succinic acids. When individually analysed, total acids, expressed as malic acid, may range from 0.9 up to about 1.6% FW. Ascorbic acid (vitamin C) content in peach fruits is generally low (below 10 mg/100 g FW), but in some cases it may be threefold higher (Liverani and D’Alessandro, 1999). Sugar content is generally based on assessing the soluble solids content (SSC) by refractometer. This value may reach up to 20% or more, although the average values found in commercial cultivars range from 9 to 15% (Byrne et al., 1991; Crisosto et al., 1998). When individually analysed, total sugars

Red ‘blood’ flesh in peach. (Courtesy of A. Liverani, Forli, Italy.)

20

Fig. 1.19.

D. Bassi and R. Monet

Red ‘blood’ flesh in nectarine. (Courtesy of A. Liverani, Forli, Italy.)

Fig. 1.20. Genetic variation for red ‘blood’ flesh trait in peach. (Courtesy of W.R. Okie, Byron, Georgia, USA.)

may reach up to 16% FW; the main sugar being sucrose, ranging from 45 to above 80% of total sugars, followed by either glucose or fructose (Bassi and Selli, 1990; Byrne et al., 1991) and sorbitol; other alcohol-soluble

sugars are in low or barely detectable amounts: inositol, mannose, xylitol and xylose. Low-quality peaches may exhibit a fourfold lower amount of fructose (the sweetest sugar in peaches) and a threefold higher

Botany and Taxonomy

amount of sorbitol but similar SSC compared with high-quality peaches (Robertson et al., 1988). Some genotypes show a distinct low acidity level, resulting in the so-called ‘lowacid’ (LA) trait. In early times, this character was described as an attribute of the ‘honey peaches’ group (Reimer, 1906), easily distinguishable from the ‘acidic’ peaches by a remarkably sweet taste. The trait is well known and regarded in the Far East countries (e.g. China, Japan, Korea), where very sweet fruits are particularly appreciated. From progenies obtained by self-pollination of ‘Redwing’ and ‘Robin’ white peaches heterozygous for the trait, Monet (1979) described the low or sub-acid as a dominant and monogenic character (D/d). The LA phenotype shows mainly citric and malic (about 50%), but also quinic (about 20%) acids in lower concentrations than standard phenotypes, while total acidity is from two- to fourfold lower (0.4 versus 1.4: average values from pooled LA and standard cultivars, respectively). The pH of the LA ranges above 4.0, while in standard phenotypes the pH is below 3.9. The ratio between SSC and titratable acidity (TA) is almost four times higher in the LA phenotypes (Yoshida, 1970; Monet, 1979; Ventura et al., 1995; Moing et al., 1998; Liverani et al., 2003). SSC is comparable to that in the standard phenotype, although LA types show more sucrose and less glucose (Liverani et al., 2003). For a better taste of the LA peaches, SSC above 12% is suggested, in order to overcome the bland feeling of a low acidity coupled with too low sugar content (Delgado, 1998). Nevertheless, the TA of the best-tasting LA cultivars is at least twice that in most of the other LA cultivars (Liverani et al., 2003). Phenolic compounds may play a signiﬁcant role in ﬂavour because they are responsible for the ‘astringent’ taste. When comparing low- and high-quality white-ﬂeshed cultivars, Robertson et al. (1988) noted that for those rated as unacceptable, there were comparable amounts of sugars and acids but seven times more phenolics than in the high-quality cultivars (120–140 mg/100 g FW). Oddly, even higher phenolic contents (up to 150 mg) found in commercial white peaches of local origin in Italy were rated as acceptable (Bassi and Selli,

21

1990). The discrepancy between these reports may be due to the differences in the aromatic proﬁles of the cultivars evaluated. It is possible that the very strong aroma of the Italian white peaches partially masked the taste of the phenolics present. Polyphenolic compounds are also responsible for the browning resulting from their oxidation by the enzyme polyphenyloxidase (PPO). Mechanical damage of the cells (skin, ﬂesh) results in the rupture of the vacuoles where the polyphenolic compounds are stored, thus exposing them to enzymatic oxidation by PPO. As a result, quinones are formed that polymerize to brown-coloured pigments. Since these traits are of a quantitative nature, their heritability can be estimated (Hansche and Boynton, 1986) so that cultivars with low susceptibility can be selected. Flesh becomes more astringent in many cultivars under cool summer temperatures (D. Bassi, personal observation). Flesh texture The composition of the cell wall strongly affects ﬂesh texture. So far at least three main distinct phenotypes are known, even if not all is understood in terms of genetic determination and biochemical pathways during the ﬁnal ripening stages. The ﬁrst two phenotypes, described by Bailey and French (1932), are the melting (M) and the non-melting (NM). The M texture shows a prominent softening in the last stage (stage IV) of ripening, until a complete melting. Variability in ﬁrmness (or rate of softening) is found within this phenotype and Yoshida (1976) distinguished between soft, medium and ﬁrm. The ‘ﬁrm’ type (FM) softens rather slowly and is less susceptible to bruising during handling, thus allowing an easier management of harvest timing and other grading and shipping operations, and displays a longer shelf life. In addition, it shows a rather high amount of water-insoluble pectins and of Ca bound to the cell wall (Mignani et al., 2006). The NM phenotype (the so-called ‘canning peach’) shows a ﬁrm texture when fully mature, softens slowly when overripe but never melts. Rather, it becomes rubbery (because the loss of water) during the

22

D. Bassi and R. Monet

senescence stage, when most cultivars could display a peculiar off-ﬂavour (Sherman et al., 1990). However, Beckman and Sherman (1996) noted that it is possible to select for the absence of off-ﬂavours within breeding progenies. The lack of softening in the NM phenotype is related to the loss of endopolygalacturonase (endoPGase) activity, the enzyme responsible for cleaving pectins (polygalacturonic acid chains) from the cell wall in the M fruits (Lester et al., 1996). Morgutti et al. (2006) detected a mutation in the endoPG gene, exploitable for early marker-assisted selection of the trait, even when heterozygous. The melting trait was described to be dominant over the non-melting (M/m; Bailey and French, 1932). See the section on ‘Flesh adherence to endocarp (stone, pit)’ for more details about the inheritance of this trait. M and NM phenotypes develop a rather high amount of ethylene between stage III and stage IV, often more abundantly in NM types (Mignani et al., 2006). The NM ﬂesh is also much less susceptible to mealiness, a rather common storage chilling injury disorder (Brovelli et al., 1998). Recently, a large QTL (quantitative trait locus: a DNA zone containing several genes responsible for a given quantitative trait) for mealiness was detected for the

Fig. 1.21.

endoPG locus, conﬁrming the previous observation that this disorder occurs particularly in M freestone phenotypes (Peace et al., 2005b). The third ﬂesh texture phenotype was ﬁrst described by Yoshida (1976). He classiﬁed a very ﬁrm and crispy, ‘stony-hard’ (SH) ﬂesh type as belonging to the M family. However, this type never melts, as in ‘Yumyeong’, a white-ﬂeshed peach from Korea. Its fruit resembles an NM phenotype, becoming rubbery when senescent, and can be either whiteor yellow-ﬂeshed (Fig. 1.21/Plate 20, Fig. 1.22/Plate 21), the only remarkable difference from NM being the almost complete lack of ethylene production (Goffreda, 1992; Haji et al., 2001, 2003; Tatsuki et al., 2006), although it can be stress-induced, as from storage below 10°C (Tatsuki et al., 2006; Gamberini, 2007; Begheldo et al., 2008). The recessive gene was named Hd (Scorza and Sherman, 1996). Water-insoluble pectins in cell walls are rather high, as Ca is bound to them, although its content is variable (Bassi et al., 1998). Stonyhard ﬂesh is often LA, but when progenies are obtained for breeding purposes, and this ﬁrm texture segregates with the acidic (nonlow acid) character, a prominent sour taste prevails (J.C. Goffreda, New Jersey, 1997, personal communication).

Stony-hard fruit: white (anthocyaninless) flesh.

Botany and Taxonomy

From the biochemical point of view, the lack of ethylene evolution is due to the transcription suppression (and not to its mutation) of the 1-aminocyclopropane-1-carboxylic acid synthase isogene (Pp-ACS1), a key gene of the ethylene enzymatic pathway (Tatsuki et al., 2006, 2007). From the genetic point of view, the independent inheritance of the SH ﬂesh from M and NM has been demonstrated, also suggesting an epistatic effect of SH, since when exogenous ethylene is applied the SH/M (hdhd/f–) phenotype is induced to melt, while the SH/NM (hdhd/f1f1) keeps ﬁrmer, as a standard NM ﬂesh (Haji et al., 2005; see also Table 3.1). From the practical point of view, SH fruits are often very difﬁcult to distinguish from NM or very ﬁrm, unripe, M phenotypes. Therefore, evaluation of progenies from controlled crosses segregating for SH is puzzling. SH ﬂesh identiﬁcation on the tree is very timeconsuming to determine (several passes are required in order to check ﬁrmness evolution) and sensory evaluation (by tasting) is not always reliable. So far, the only sound method for SH texture phenotyping is to measure ethylene production (Goffreda, 1992).

Fig. 1.22.

Stony-hard fruit: yellow flesh.

23

Furthermore, there is a possible fourth flesh texture trait (‘very, very firm’), whose phenotype resembles very much the SH flesh in firmness and crispiness, but when fully ripe becomes melting and develops ethylene, although in an unpredictable fashion from year to year (I. Mignani, Italy, 2007, personal communication). This flesh texture, firmer than the ‘firm’ M types, is found in many recently developed new cultivars (both nectarines, e.g. ‘Big Top’, and standard peaches, e.g. ‘Rich Lady’ and ‘Diamond Princess’). It was first commercially introduced from private breeders from California, and is sometimes (e.g. ‘Big Top’ and others) associated with the lowacid trait. Its remarkable keeping quality, particularly on the tree, is a rewarding character for both growers and consumers. However, this ﬂesh type is very difﬁcult to assess, and the same problems as described above for SH ﬂesh phenotyping are experienced. Work is in progress to fully understand this trait, from both the biochemical (physiological) and genetic points of view, since it seems to be a dominant Mendelian trait over the standard M type.

24

D. Bassi and R. Monet

A tentative classiﬁcation of peach fruit ﬂesh phenotypes is presented in Table 1.2. Flesh adherence to endocarp (stone, pit) The ﬂesh may or may not adhere to the endocarp. According to Bailey and French (1932) this trait is controlled by the ‘freestone’ locus, where the freestone (F_) allele is dominant over the clingstone (ff). Intermediate behaviour (semi-freestone or semi-clingstone) with varying degrees of adhesion is observed, particularly in early-ripening genotypes (FDP less than 100 days) (Weinberger, 1950). Rapid ﬂesh maturation, due to early ripening, delays the appearance of the freestone phenotype, thus the semi-freestone phenotypes should be regarded as ‘physiologically clingstone’ but ‘genetically freestone’ (Beckman and Sherman, 1996). Since the intensity of these characters changes during fruit ripening, ﬂesh adherence to the endocarp in early genotypes should be assessed at full ripening or even at the early stage of senescence. Bailey and French (1932) suggested that the ﬂesh adherence to the pit gene and the ﬂesh texture gene were linked on the same chromosome. This was the ﬁrst published linkage in peach genetics.

However, since in the studied families one phenotype was missing (freestone-NM, as expected by recombination), the Bailey and French interpretation was reconsidered, although semi-freestone peaches with NM ﬂesh have been observed where a thin layer of ﬂesh adheres to the stone (Beckman and Sherman, 1996). The genetic nature of this latter phenotype is not clariﬁed yet, and the semi-freestone trait in NM ﬂesh genotypes should be regarded as of different nature than in M peaches (T.G. Beckman, Georgia, 2005, personal communication). Using the data of Bailey and French (1932), Monet (1989) suggested the three-alleles-one-locus theory. The three following phenotypes resulted: freestone-M (FF, Ff or Ff1), clingstone-M (ff or ff1) and clingstone-NM (f1f1), with dominance from left to right. From recent studies on progenies segregating for endocarp adherence and ﬂesh texture (M and NM), four alleles for the endoPGase enzyme were found responsible for the same three ﬂesh phenotypes as above at a single locus (F): freestoneand clingstone-M and clingstone-NM; the fourth allele is a null-allele (absence) that has the same phenotypic effect as the f1 allele, a mutation that nulliﬁes the enzyme function (Peace et al., 2005a). A diagnostic PCR test was made available to detect all four alleles.

Table 1.2. Tentative classification of peach fruit flesh phenotypes from chemical analysis and sensory evaluation at physiological maturity. (From Yoshida, 1976; Bassi et al., 1998; Haji et al., 2005; Mignani et al., 2006.) Pectinsa Flesh texture

Firmness

Soluble

Insoluble

Calciuma

Ethyleneb

Melting Soft Firm Very, very firmc Stony-hard Non-melting

Low High Very high Very high Very high

+++ +++ ++ + +++

+ ++ ++ +++ +++

++ +++ ++ ++ +++

++ ++ + –/(+) +++

aFlesh

content; no clear-cut threshold between different phenotypes. produced by whole fruits. cSimilar to the ‘stony-hard’, but produces ethylene and becomes melting in the very last stages of ripening (e.g. ‘Big Top’ nectarine). Number of + represents relative content within columns, respectively; – means absence; (+) means traces. bAmount

Botany and Taxonomy

Thus, the Monet (1989) hypothesis of three alleles at the same locus controlling both ﬂesh texture and endocarp adherence was conﬁrmed and the previous theory of Bailey and French (1932), suggesting a linkage between ﬂesh texture and its adherence to the pit, should be rejected. SH cultivars known so far are all clingstone (A. Liverani, Italy, 2005, personal communication).

Fruit ‘keeping’ quality and resistance to manipulation (bruising) ‘Keeping’ quality is related to resistance of the fruit to blemishes caused by excessive softening and refers mainly to ﬁrmness of the ﬂesh. Bruising depends mainly on skin resistance to browning; thus a rather ﬁrm fruit (ﬂesh) could also be prone to bruises if the skin is too delicate.

25

elliptic (in ovate or elliptic fruit) to roundoblate (in ﬂat fruits). It contains one (exceptionally two) seed(s), whose cyanidic glucoside content makes them taste very bitter. This latter trait is monogenic and dominant over the non-bitter phenotype (Sk/sk; Werner and Creller, 1997) that can be found in some nectarines, e.g. ‘Fantasia’, Early Sungrand’, etc. Although the locus for the nonbitter seed is very close to the nectarine trait (12 cM), it could be recombined with pubescent skin via cross-breeding. Seeds are highly germinable after stratiﬁcation, their chilling requirement being related to the chilling requirement of the mother tree (Pérez, 1990; Pérez et al., 1993). Viability is hampered in early-ripening genotypes (FDP less than 100–120 days). For these, aseptic embryo culture is needed to ensure germination, allowing rescue of immature embryos as early as 50 days after full bloom (Fig. 1.23/Plate 22) (Tukey, 1935; Ramming, 1985).

Endocarp (stone, pit) and seed The endocarp is ligniﬁed, the outer surface being deeply furrowed and pitted. In very, very early-ripening genotypes (FDP less than 55–60 days) ligniﬁcation is limited and the endocarp may be rather soft, thus allowing consumption of the entire fruit, when the seed is not bitter. Two examples in Italy are ‘Borgia’ and ‘Lucrezia’ (Bassi and Rizzo, 1995). A more or less pronounced ridge is present in the ventral suture, and a needle (very acute tip) could be present at the apex. The latter trait is undesirable in canned peaches because its fragments are difﬁcult to eliminate from processed fruits. Endocarp splitting (at the carpel suture) or shattering (radial fractures) may affect either early- or late-ripening cultivars. Both are commercially undesirable and the former a consumer hazard in eating the stone fragments. While it is possible to select against these undesirable traits, it is reported that cultural practices to improve fruit size (supplemental irrigation, girdling, etc.) may also increase the incidence of endocarp splitting or shattering. The stone shape changes according to the fruit shape, from globose (in round fruit),

1.4 Peach Biology and Phenology Floral biology and fruit set Peach is an insect-pollinated species and it is self-fertile. Even if some genotypes show a low fruit set, no evidence has ever been reported of self-incompatibility as happens in most other Prunus species. Flower fertilization from self-pollination is generally high (ranging from 10 to 90% of fruit set), resulting in a high number of fruitlets (Szabò and Nyéki, 1999); thus crop reduction by fruit removal, i.e. thinning, is required in order to gain commercial fruit size. Even if cross-contamination in closely planted trees may reach around 14–25% (Fogle and Dermen, 1969; Fogle, 1977), cross-pollination under normal conditions is lower than 5% (Hesse, 1975; Fogle, 1977). The only character affecting yield is male sterility, but this trait has been eliminated in presentday commercial cultivars. Some genotypes, mainly nectarines, could be affected by a continuous fruit drop, well after the ‘June drop’, even leading to substantial crop losses.

26

D. Bassi and R. Monet

Fig. 1.23. Comparison between mature (left) and immature (right) embryos taken from ‘Spring Crest’ peach at two different stages: the immature embryos fail to germinate under standard stratification procedures and need to be rescued in vitro as the very early-ripening genotypes.

Chilling and heat requirements Chilling requirement is the amount of cold (temperature below a given threshold) required by ﬂower and leaf buds in order to complete morphological development (particularly for reproductive organs) and rest. Several methods have been proposed so far to measure this physiological requirement. The simplest method is that of Weinberger (1950), where the number of hours below 7°C is taken in account. This method is popular worldwide, but it does have some limitations. Richardson et al. (1974), with their ‘Utah model’, deﬁned chilling units (CU), giving speciﬁc weight to different temperatures, understanding the role of negation of rest above a given threshold (16°C) before rest completion. A better evaluation of the effect

of ﬂuctuating temperatures and their role in negation of rest in the low-chill areas was given by the ‘dynamic model’ of Erez et al. (1990). While CU can be measured by artiﬁcial methods (Dennis, 2003), a simple and cheaper method is to utilize standard cultivar bloom times as an indication of the chilling requirement of unknown genotypes (Scorza and Sherman, 1996). See Chapter 5 for further details. Ranking known genotypes for CU, the lowest level may be around 50 CU (‘FlordaGrande’), up to more than 1500 CU. Analogous to chilling, heat requirements refer to the amount of heat (temperature above a given threshold) after endo-dormancy is fulﬁlled to achieve organ development, from bloom (Richardson et al., 1974; Citadin et al., 2001) and foliation to fruit maturation.

Botany and Taxonomy

The ‘evergreen’ trait has been described, where the terminal growth never stops (no terminal bud formation) unless killed by frost (Lammerts, 1945; Diaz, 1974), while lateral buds show about 450 CU. The trait, probably due to lack of phytochrome response and resulting from a deletion of the wild type (Bielenberg et al., 2004), was found to be monogenic and recessive: Evg/evg (Rodriguez et al., 1994). In subtropical regions, it allows the yielding of two crops per year. The trait is a candidate model system to study winter dormancy in woody plants (Wang et al., 2003). Phenological phases The peculiar stages of morphological development of the main organs (bud, ﬂower, leaf and fruit) from bud break to leaf fall are termed phenological phases (Fig. 1.24/Plate 23). The occurrence of the single stages (e.g. bud break, full bloom, split-jacket, etc.) plays a key a role in determining speciﬁc orchard operations (e.g. the spray schedule against pests and diseases) or in cultivar assessment for the evaluation of their environment adaptability. Time of flowering Time of ﬂowering depends on the CUs necessary to fulﬁl rest and on the growing degree hour (GDH) accumulation in order to reach full bloom. Even if the two traits are genetically distinct, it is not simple to separate the two components in selection breeding, particularly because the threshold temperatures needed for their fulﬁlment have not been determined (Scorza and Okie, 1991). Since bloom date is quantitatively inherited and heritability is rather high, breeding could be addressed based on the parents’ behaviour in a given environment, where up to 40 days from the earliest- to the latest-blooming cultivar has been recorded. For further details see Chapter 5. Time of ripening (fruit development period) There is no relationship between ﬂowering and ripening time.

27

While wild peaches exhibit from medium to late ripening, i.e. an FDP from 120 to 210 days from full bloom to the onset of ripening, the FDP of commercial cultivars may range from as early as 55 (Ramming and Tanner, 1987) and 60 days (Bassi and Rizzo, 1995) to as late as 270 days, e.g. some local cultivars from Sicily, Italy (Caruso et al., 1992; Caruso and Sottile, 1999). An interesting ripening mutation (‘slow ripening’) described in progenies of ‘Fantasia’ nectarine hinders completion of ripening (Fig. 1.25/Plate 24). Fruit development is apparently halted before the end of the cell expansion phase (stage III) and the ﬂesh either never softens or softens very slowly, while it keeps a crispy texture (but not of the nonmelting type). The skin ground colour and ﬂesh are greenish and the ﬂavour is very poor, despite lower acidity and higher pH and soluble solids (but similar total sugars) than ‘Fantasia’ (Brecht and Kader, 1984; Brecht et al., 1984). Ethylene and carbon dioxide production are very low, no aroma is developed and the fruits remain ﬁrm on the tree even after leaves abscise in autumn. The fruit of this mutant is susceptible to internal breakdown. After ripening-inducing treatments using propylene gas, the fruit eventually becomes soft and advances the onset but not the level of ethylene, without improving the poor texture and ﬂavour. The ripening behaviour seems intermediate between climateric and non-climateric classes of fruits, suggesting a basic similarity between those two categories. The trait was classiﬁed as monogenic and recessive (Sr/sr), ‘Fantasia’, ‘Flamekist’ and ‘Fairlane’ nectarines being heterozygous for this trait (Ramming, 1991). Although the trait regulating FDP is clearly quantitative, the presence of major genes can be clearly presumed by two pieces of evidence. First, when measuring the time of ripening in large progenies from distant (in terms of FDP) parents, grouping of offspring in bimodal or trimodal distribution is often observed. Almost all of the offspring ripen within the parental dates, with some seedlings ripening earlier or later (Yamaguchi et al., 1984; Bassi et al., 1988). Second, bud sports, known mutants from commercial cultivars, show FDP that are roughly separated

28

D. Bassi and R. Monet

(a)

(c)

-

(b)

Dormant bud

Bud swell (d)

Split-jacket

Small fruitlets (cell division)

(i)

Fruit set (k)

(j)

Pit hardening

(l)

Final swell (n)

(m)

Fig. 1.24.

Late bloom (h)

(g)

Petal fall

(f)

(e)

Full bloom

Early bloom

Fruit veraison

Pink stage

Commercial ripening

(o)

Physiological ripening

Main phenological stages in peach. (Courtesy of E. Bellini, Florence University, Italy.)

Botany and Taxonomy

Fig. 1.25.

Slow-ripening nectarine trees after leaf fall (dormant season).

by weekly intervals, as in ‘Red Gold’ nectarine (Bassi et al., 2004): this opens an interesting insight for genomics in search of QTLs.

●

1.5 Cultivar Classification

●

Several cultivars, local types and landraces have been described in peach. Due to the rather high number of morphological Mendelian traits, the cultivar classiﬁcation could be addressed under several keys. For the comprehensive list of these traits please refer to Chapter 3. In addition, physiological and quantitative traits of economic importance also play a signiﬁcant role in horticultural peach taxonomy (phenology). Peach description sheet After Zielinski (1955), Bellini and Scaramuzzi (1976) and Bellini et al. (2007), for a comprehensive characterization of a given cultivar the following organs should be described. ●

29

Tree: see section on ‘Tree growth habit’ above.

●

●

Shoot (on at least 30 one-year-old fruiting shoots, after leaf abscission): length, internode length, number of ﬂower buds/ nodes, ﬂower bud distribution along the stem, bark colour. Flowers (on at least 30 items, at full bloom): type, colour, petal size (length and width), length of the pistil towards the stamens; colour of calyx (inner and outer). Leaf (on at least 30 items collected from the middle section of fruiting shoots, excluding the petiole): colour of the blade (green, purple) and main veins (greenish or yellowish); size (blade length and width), shape (length:width ratio and position of the broadest width referred to the middle); surface (ﬂat, wavy); apical and basal angle of the blade; margin shape (crenate or serrated); glands (eglandular, globose, reniform). Fruit (on at least 30 items): weight; size (length, diameters: suture and cheeks); shape (two sections: along the suture and equatorial); base cavity depth and width; apex shape and tip (or beak, if present); suture (line (no cavity), deep, medium or shallow). Skin: pubescense (absent, light, coarse); red blush (per cent coverage and pattern at physiological ripe stage:

30

D. Bassi and R. Monet

uniform, dotted, striped, etc.). Flesh: ﬁrmness (by penetrometer); colour (yellow, white); red ﬂesh (‘blood’ trait: present, absent); anthocyanins distribution (under skin, close to the pit, in the middle); ﬂavour (by taste assessment); browning potential; texture (melting, non-melting, stony-hard: for better evaluation of the latter, ethylene production measurement is suggested); ﬁbrousness (ﬁne, coarse, medium); measurement of: sugars (total soluble solids); titrable acidity; pH. Stone: adherence to ﬂesh (air-free, free, semi-cling, cling); size (length, width and breadth); shape; colour; surface (rough, smooth); ridge; grooves and pits; propensity to split or shatter.

FLESH COLOUR

1. 2.

White Yellow

FLESH TEXTURE

1. 2. 3.

Melting Non-melting Stony-hard

FLESH ACIDITY

1. 2.

Acidic Low-acid

Phenological classification CHILLING REQUIREMENT

Cultivars could be classiﬁed under several criteria, depending on scope of evaluation.

1. Evergreen (no dormancy under tropical or subtropical climates). 2. From very low (less than 100 CU) to very high (over 1000–1200 CU); most commercial cultivars ranging from 650 to 900 CU.

TREE USE

BLOOM DATE

Morphological and commercial classifications

1. 2.

Fruit production Ornamental (ﬂowers, leaves, growth habit)

FRUIT TYPE (COMMERCIAL)

1. 2. 3.

Peach (pubescent skin) Nectarine (glabrous skin) Canning peach (non-melting ﬂesh)

FRUIT SHAPE

1. 2.

Round/elongated Flat

Could be reported either as the calendar date referred as to that particular place, or as the amount of CU and GDH to accomplish rest and to start blooming. RIPE DATE

As above, it could be recorded as a calendar date, when the very ﬁrst fruits (5–10%) accomplish physiological ripening (i.e. they become palatable), or as the number of days from full bloom to the onset of ripening (FDP).

References Bailey, L.H. (1927) The Standard Cyclopedia of Horticulture. Macmillan, New York. Bailey, J.S. and French, A.P. (1932) The inheritance of certain characters in the peach. Proceedings of the American Society for Horticultural Science 29, 127–130. Bailey, J.S. and French, A.P. (1949) The inheritance of certain fruit and foliage characters in the peach. Massachusetts Agricultural Experiment Station Bulletin No. 452. Baipo, W., Yincai, Q., Yongfa, Z. and Hua, C. (1989) The effect of meteorological factors on the pollination, fertilization and fruit setting of the peach. Acta Horticulturae Sinica 16, 11–15. Bassi, D. (ed.) (2003) Growth Habits in Stone Fruit Trees. Il Divulgatore, Bologna, Italy. Bassi, D. and Rizzo, M. (1995) ‘Borgia’ e ‘Lucrezia’, nuove pesche extraprecoci ottenute all’Università di Bologna. Rivista di Frutticoltura e di Ortofloricoltura 2, 73.

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Monet, R., Guye, A. and Roy, M. (1996) Effect of inbreeding and crossing inbred lines on the weight of peach fruit. Acta Horticulturae 374, 77–82. Morgutti, N., Negrini, F.F., Nocito, A., Ghiani, D., Bassi, D. and Cocucci, M. (2006) Changes in endopolygalacturonase levels and characterization of a putative endo-PG gene during fruit softening in peach genotypes with nonmelting flesh and melting flesh fruit phenotypes. New Phytologist 171, 315– 328. Okie, W.R. (1998) Preliminary descriptions of five new peach genes. Acta Horticulturae 465, 107–110. Okie, W.R. and Prince, V.E. (1982) Surface features of a novel peach × nectarine hybrid. HortScience 17, 66–67. Okie, W.R. and Rieger, M. (2003) Inheritance of venation pattern in Prunus ferganensis × persica hybrids. Acta Horticulturae 622, 261–264. Okie, W.R. and Scorza, R. (2002) Breeding peach for narrow leaf width. Acta Horticulturae 592, 137–141. Okie, W.R., Ramming, D.W. and Scorza, R. (1985) Peach, nectarine, and other stone fruit breeding by the USDA in the last two decades. HortScience 20, 633–641. Peace, C.P., Crisosto, C.H. and Gradziel, T.M. (2005a) Endopolygalacturonase: a candidate gene for freestone and melting flesh in peach. Molecular Breeding 16, 21–31. Peace, C.P., Ahmad, R., Gradziel, T.M., Dundekar, A.M and Crisosto, C.H. (2005b) The use of molecular genetics to improve peach and nectarine post-storage quality. Acta Horticulturae 682, 403–409. Pérez, G.S. (1990) Relationship between parental blossom season and speed of seed germination. HortScience 25, 958–960. Pérez, S., Montes, S. and Mejìa C. (1993) Analysis of peach germplasm in Mexico. Journal of the American Society for Horticultural Science 118, 519–524. Pisani, P.L. and Roselli, G. (1983) Interspecific hybridization of Prunus persica × P. davidiana to obtain new peach rootstocks. Genetica Agraria 1/2, 197–198. Ramming, D.W. (1985) In ovulo embryo culture of early maturing Prunus. HortScience 20, 419–420. Ramming, D.W. (1991) Genetic control of a slow-ripening fruit trait in nectarine. Canadian Journal of Plant Science 71, 601–603. Ramming, D.W. and Tanner, O. (1987) Goldcrest peach. Fruit Varieties Journal 41, 52–53. Rehder, A. (1990) Manual of Cultivated Trees and Shrubs Hardy in North America. Dioscorides Press, Portland, Oregon. Reimer, F.S. (1906) The honey peach group. Florida Agricultural Experiment Station Bulletin No. 73. Richardson, E.A., Seeley, S.D. and Walker, D.R. (1974) A model for estimating the completion of rest for Redhaven and Elberta peach trees. HortScience 9, 331–332. Rivers, S. (1906) The cross-breeding of peaches and nectarines. Report on Third International Conference on Genetics. Royal Horticultural Society, London, pp. 463–467. Robertson, J.A., Meredith, F.I. and Scorza, R. (1988) Characteristics of fruit from high and low-quality peach cultivars. HortScience 23, 1032–1034. Robertson, J.A., Horvat, R.J., Lyon, B.G., Meredith, F.I., Senter, S.D. and Okie, W.R. (1990) Comparison of quality characteristics of selected yellow and white-fleshed peach cultivars. Journal of Food Science 55, 1308–1311. Rodriguez, A.J., Sherman, W.B., Scorza, R. and Wisniewski, M. (1994) ‘Evergreen’ peach, its inheritance and dormant behavior. Journal of the American Society for Horticultural Science 119, 789–792. Rodriguez, G.A. and Sherman, W.B. (1990) ‘Oro A’ peach germplasm. HortScience 25, 128. Rodriguez, J. and Sherman, W.B. (1986) Relationship between parental flower bud set and seedling precociousness in peach and nectarine, Prunus persica (L.) Batsch. Fruit Varieties Journal 40, 8–12. Roselli, G., Pisani, P.L. and Cerulli, M. (1985) Observations on the performance of various Prunus davidiana × Prunus persica hybrids as rootstocks for peach. L’Informatore Agrario 12, 75–81. Saunier, R. (1973) Contribution a l’étude des relations existant entre certains caractères a déterminisme génétique simple chez le pêcher et la sensibilité a l’oidium, Sphaeroteca pannosa (Wallr) Lev. des cultivars de cette espéce. Annales des Amélioration des Plantes 23, 235–243. Scorza, R. (1984) Characterization of four distinct peach tree growth types. Journal of the American Society for Horticultural Science 109, 455–457. Scorza, R. and Okie, W.R. (1991) Peaches (Prunus). In: Moore, J.N. and Ballington, J.R. Jr (eds) Genetic resources of temperate fruit and nut crops. Acta Horticulturae 290, 177–231. Scorza, R. and Sherman, W.B. (1996) Peaches. In: Janick, J. and Moore, J.N. (eds) Fruit Breeding. Vol. I. Tree and Tropical Fruits. Wiley, New York, pp. 325–440.

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Scorza, R., Mehlenbacher, S.A. and Lightner, G.W. (1985) Inbreeding and coancestry of freestone peach cultivars of the eastern United States and implications for peach germplasm improvement. Journal of the American Society for Horticultural Science 110, 547–552. Scorza, R., Lightner, G.W. and Liverani, A. (1989) The Pillar peach tree and growth habit analysis of compact × Pillar progeny. Journal of the American Society for Horticultural Science 114, 991–995. Scorza, R., Bassi, D. and Liverani, A. (2002) Genetic interaction of pillar (columnar), compact and dwarf peach tree genotypes. Journal of the American Society for Horticultural Science 127, 254–261. Scott, D. and Cullinan, F. (1942) The inheritance of wavy leaf character in the peach. Journal of Heredity 33, 293–295. Scott, D.H. and Weinberger, J.H. (1944) Inheritance of pollen sterility in some peach varieties. Proceedings of the American Society for Horticultural Science 45, 229–232. Sherman, W.B., Topp, B.L. and Lyrene, P.M. (1990) Non melting flesh for fresh market peaches. Proceedings of the Florida State Horticultural Society 103, 293–294. Szabò, Z. and Nyéki, J. (1999) Self-pollination in peach. International Journal of Horticultural Science 5, 76–78. Tatsuki, M., Haji, T. and Yamaguchi, M. (2006) The involvement of 1-aminocyclopropane-1-carboxylic acid synthase isogene, Pp-ACS1, in peach fruit softening. Journal of Experimental Botany 57, 1281–1289. Tatsuki, M., Haji, T. and Yamaguchi, M. (2007) The peach 1-aminocyclopropane-1-carboxylic acid synthase isogene, Pp-ACS1, is required for fruit softening. In: Ramina, A., Chang, C., Giovannoni, J., Klee, H., Perata, P. and Woltering, E. (eds) Advances in Plant Ethylene Research. Proceedings of the 7th International Symposium on the Plant Hormone Ethylene. Springer, Wageningen, The Netherlands, pp. 175–180. Tourjie, K.R., Barret, D.M., Romero, M.V. and Gradziel, T.M. (1998) Measuring flesh colour variability among processing clingstone peach genotypes differing in carotenoid composition. Journal of the American Society for Horticultural Science 123, 433–437. Toyama, T.K. (1980) The pollen receptivity period and its relation to fruit setting in the stone fruits. Fruit Varieties Journal 34, 2–4. Tukey, H.B. (1933) Artificial culture of sweet cherry embryos. Journal of Heredity 24, 7–12. Tukey, H.B. (1935) Artificial culture methods for isolated embryos of deciduous fruits. Proceedings of the American Society for Horticultural Science 32, 313–322. Van Well, R.G. (1974) Com-Pact Redhaven. Fruit Varieties Journal 28, 37. Vavilov, N.I. (1951) The Origin, Variation, Immunity and Breeding of Cultivated Plants. Selected Writings of N.I. Vavilov. Chronica Botanica Company, Waltham, Massachusetts. Ventura, M., Courvoisier, V. and Sansavini, S. (1995) Relazione tra scambi gassosi e qualità di pesche e nettarine durante la maturazione. In: Proceedings of ‘XXII Convegno Peschicolo’. Chambers of Commerce of Forlì-Cesena and Ravenna, Cesena, Italy, pp. 71–80. Wang, Y.L. (1985) Peach growing and germplasm in China. Acta Horticulturae 173, 51–55. Wang, Y., Reighard, G.L., Scorza, R., Jenkins, T.C. and Line, M.J. (2003) Characterizing the evergrowing phenotype in peach. Acta Horticulturae 618, 455–462. Watkins, R. (1976) Cherry, plum, peach, apricot and almond. In: Simmonds, N.W. (ed.) Evolution of Crop Plants. Longman, London, pp. 242–247. Weinberger, J.H. (1944) Characteristics of the progeny of certain peach varieties. Proceedings of the American Society for Horticultural Science 45, 233–238. Weinberger, J.H. (1950) Chilling requirement of peach varieties. Proceedings of the American Society for Horticultural Science 56, 122–128. Wen, I.C., Koch, K.E. and Sherman, W.B. (1995) Comparing fruit and tree characteristics of two peaches and their nectarine mutants. Journal of the American Society for Horticultural Science 120, 101–106. Werneck, H.L. (1956) Romischer und vorromischer Wein- und Obstbau in Ostereichischer Donauraum. Verhandlungen der Zoologisch-Botanischen-Gesellschaft, Wien. Werner, D.J. and Chaparro, J.X. (2005) Genetic interaction of pillar and weeping peach genotypes. HortScience 40, 18–20. Werner, D.J. and Creller, M.A. (1997) Inheritance of sweet kernel and male sterility. Journal of American Society for Horticultural Science 122, 215–217. Werner, D.J., Creller, M.A. and Chaparro, J.X. (1998) Inheritance of the blood-flesh trait in peach. HortScience 33, 1243–1246. Wickson, E.J. (1889) California Fruits 308. Yamaguchi, M., Yoshida, M. and Kyotani, H. (1984) Studies on the distribution of ripening time of certain progenies in peach breeding. Bulletin of the Fruit Tree Research Station, Series A 11, 15–33.

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2

History of Cultivation and Trends in China Hongwen Huang,1,2 Zhongping Cheng,1 Zhonghui Zhang1 and Ying Wang1

1Wuhan

Botanical Garden/Wuhan Institute of Botany, Chinese Academy of Sciences, People’s Republic of China 2South China Botanical Garden, Guangzhou, Chinese Academy of Sciences, People’s Republic of China

2.1 Origin of the Peach 2.2 History of Peach Cultivation in China Pre-Qin Dynasty (1100–221 BC) Eastern and Western Han Dynasty (222 BC–220 AD) From Wei–Jin Dynasty to Sui–Tang Dynasty and Five Dynasties period (221–960 AD) Song, Yuan, Ming, Qing Dynasties and Republican period (961–1948 AD) 2.3 Current Status of Chinese Peach Production and Trends in China Peach germplasm collection, repositories, evaluation and utilization in China Main peach cultivars, peach production and growing regions in China Rapid development of greenhouse production Peach postharvesting, processing and marketing in China Problems faced by the Chinese peach industry Current trends of Chinese peach production 2.4 Summary/Conclusion

2.1 Origin of the Peach The peach originated in China (Wang and Zhuang, 2001), where it is a symbol of long life (Fig. 2.1/Plate 25). Numerous pieces of evidence have revealed that China has the longest history of peach cultivation in the world. One discovery demonstrated that peach growing in China dates back to Neolithic times. When a Neolithic village site was discovered in Hemudu village, Yujao city, Zhejiang province in 1973, ﬁnds included wild peach stones dating back to 6000–7000 BC

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(Chen, 1994). A similar archaeological ﬁnding in Taixi village of Gaochen city, Hebei province, at the site of ruins from the Shang Dynasty (1600–1100 BC), revealed two peach stones measuring 1.6 cm × 1.0 cm and 2.0 cm × 1.2 cm. Their shape, size and surface groove patterns were almost the same as those of current peach cultivars in China. An expedition conducted by the Chinese Academy of Sciences during 1973–1976 discovered tremendously diverse genetic resources of wild peach that are still widely grown in large areas of China, including Tibet, Gansu, eastern Shaanxi,

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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south-eastern Tibet. Some trees having trunk circumferences of about 6 m appeared to be more than 300 years old. A fruit tree survey team of the Tibet crop resource expedition during 1981–1982 also found an ancient Tibetan peach tree with a height of 21 m and a trunk circumference of 10 m, which was believed to be more than 1000 years old. This tree was located in Changdu region of Tibet, where the Hengduan Mountains–Sanjiang (Three Rivers) area was being geo-botanically investigated (Duan et al., 1983). Obviously, Tibet and Gansu province, where P. mira and Prunus kansuensis Rehd. are native, should be regarded as one of the original native centres for peach. The peach has a remarkably extensive distribution throughout China: from Taiwan and southern Guangdong provinces in the subtropics, to cold temperate regions as far north as in Yanbian, Jilin province (Wang and Zhuang, 2001); from the west and southwest regions as far as Xinjiang and Tibet autonomous districts, to east regions as far as all coastal provinces in China. However, commercial peach cultivation is limited within the latitude range of 23–50°N (Fig. 2.2/Plate 26).

2.2 History of Peach Cultivation in China The peach is one of the most ancient domesticated fruits in China. As early as 4000 years ago, the value of peach had been recognized and exploited by the Chinese with extensive efforts on natural selection and domestication. Several unique historical phases of Chinese peach domestication and cultivation are summarized in the following. Pre-Qin Dynasty (1100–221 BC) Fig. 2.1. A Chinese painting by Ma Tai (1885– 1935), telling a story that an old man with white hair but a young, boyish face always steals peaches. People make fun of this long-lived man, but he explains ‘Peach is good for my health’.

southern Henan, south-western Sichuan and western Yunnan provinces (Qu and Sun, 1990). Tibetan peaches (Prunus mira Koehnes) were found in Jiacha and Lang counties of

There may be even earlier descriptions of peach in ancient Chinese texts. ‘桃 pronounced Tao’ (Chinese name for the outdated genus Amygdalus) refers to peach and is described in the ShiJing (The Book of Odes or The Book of Songs), written between 1100 and 600 BC (Anon., 11th–6th century BC). The tao is described in the ShiJing – Weifeng chapter as ‘Peach growing in garden, its fruit for eating’, indicating that peach was cultivated in China

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Fig. 2.2. Chinese peach production regions: (I) north-west drought region; (II) northern China plain region; (III) Changjiang River humid region; (IV) Yunnan–Guizhou high plateau cold region; (V) Qinghai–Tibet plateau cold peach region; (VI) north-eastern China cold region; (VII) southern China subtropical region.

3000 years ago. In the ShiJing – ZhouNan chapter, the biological characteristics of peach are concisely described as ‘桃之夭夭，灼灼其华。桃之夭夭，其叶蓁蓁。桃之夭夭，有贲其实’, illustrating beautiful ﬁre-like ﬂowers when blooming, ﬂourishing foliage and dense fruiting, symbolizing a family’s prosperity, happiness and luck. The ShiJing –DaYa chapter describes peach as ‘投我以桃，报之以李。园中有桃，有贲其实’, clearly evidencing that peach was widely cultivated and fruit were produced plentifully during that time. Later,

a historiography book LüShiChunQiu (300 BC) depicts peach blooming in spring as ‘仲春之月桃始华’ (Lü, 300 BC). The earliest illustration of peach cultivation and ecological requirements in Chinese ancient literature probably occurs during the Zhanguo period (Warring States, 500–300 BC). In the encyclopaedia GuanZi – DiYuan volume (Guan, 5th century BC), it is written ‘五沃之土，宜彼群木，其桃其李’, explaining that peach cultivation requires good soils and peach responds to high fertilization. It concisely illustrates a

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relationship between peach growth and soil conditions. In addition, HanFeiZhi – WaiChu volume 33 (Han, 280–233 BC) describes ‘子产治郑，桃李之荫于街者莫援也’, which explains that besides use as edible fruits, the peach was also used for landscaping as a shade tree in the current Xinzheng area, Henan province. During this pre-Qin Dynasty period, peach was widely grown in southern China. According to the Chinese Agricultural Archaeological Plate Collection, peach stones have been discovered at many archaeological locations in southern China, from the Eastern Zhou Dynasty (770 BC) at Jiangling, Hubei province and from the Zhanguo period (Warring States, 475–221 BC) at Pujiang, Sichuan province and at Hezhang, Guizhou province. Eastern and Western Han Dynasty (222 BC–220 AD) During this historical period, cultivar selection and cultural techniques were developed, resulting in a new era of peach domestication in China. Fifteen records related to peach are identiﬁed in ShiJi (a history annals, 100 Bc) (Sima, 1st century BC), 19 records in HanShu (history annals of the Han Dynasty, 1st century AD) (Ban, 39–92 AD) and 14 in Post-HanShu (history annals of the late Han Dynasty, 3rd century AD). These records encompass a variety of peach-related delineations from town and street names, mountain and river names and even ofﬁcial titles. In ErYa (ancient dictionary for terms and names) – Shimu chapter (notes in trees) (Anon., 2nd century BC), there are records of species, varieties and cultivars for peaches described as ‘旄，冬桃’ and ‘榹，山桃’, indicating the two most important species of Prunus persica and Prunus davidiana of modern peach production. In XiJingZaJi (a miscellanea) edited by Ge Hong (Ge, 1st century AD), the fruit trees in the emperor’s garden (current Xian, Shaanxi province) are described, including many peach varieties: ‘Qin Tao’ (Shaanxi peach), ‘Si Tao’ (peach), ‘Xiang He Tao’ (locally named peach), ‘Shuang Tao’ (frost peach), ‘Jin Cheng Tao’ (locally named peach), ‘Qi Di Tao’ (fancy petiole peach) and ‘Zi Wen Tao’ (purple paper peach).

Thus, many locally selected peach varieties existed in China more than 2000 years ago. The relationship of peach blooming to local climate is written in Pre-HanShu (dynasty annals) – GouXu Records as ‘桃方华时，即有雨水，. . . . . ，谓之桃花水耳’, . indicating a very similar rainy season during P. persica blooming as normally occurs at the present time in south and south-central China. Peach culture techniques were also developed during this period. SiMinYueLing (farming calendar) written by Cui Shi during the Eastern Han Dynasty (Cui, 2nd century AD) provides ‘正月…自朔及晦可移诸树，. . . 唯有果实者及望而止’, indicating that peach trees should be planted or transplanted in January in the Lunar calendar, but fruiting trees should not be transplanted. It clearly suggests that peach planting should be done in February and good peach production requires fertile soils. Wang Bao even records a high-density planting of peach in TongYue from the Western Han Dynasty (Wang, 1st century AD), stating ‘种植桃、李. . . . . ，三丈一树，八尺为行，果类相似 . ，纵横相当’ that suggests a 6.93 m × 1.85 m spacing.

From Wei–Jin Dynasty to Sui–Tang Dynasty and Five Dynasties period (221–960 AD) The traditional Chinese peach culture was established during these centuries. New production techniques were advanced and new uses for peaches were further exploited. First, peach cultivar development by seedling selection and domestication of wild trees resulted in a large number of new cultivar releases. For example, GuangZhi written by Guo Yigong in the Eastern Jin period (Guo, 4th century AD) records ‘there are winter peach, summer white peach, autumn white peach and many local peaches cultivated in low reach region of HuangHe (Yellow River), among many beautiful peaches having an outstanding autumn dark-red peach’. YeZhongJi written by Lu Hui in the Western Jin period (Lu, 3rd century AD) describes ‘a hook-nose peach weighting one kilo growing at ShiHu garden’ (currently LinZhang region, Hebei province). During the Northern Wei period (386–534 AD), a very famous book QiMinYaoShu (encyclopaedia

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for living) written by Jia Sixie (Jia, 533–544 AD) lists more than ten cultivars previously described and also adds a new variety, ‘Nai Tao’. In addition, from the Wei–Jin period, records of high-quality peach cultivars are found in TaoFu (peach poetry) by Fu Xuan (Fu, 2nd century AD) in Western Jin, such as ‘early summer ripening’, suggesting an existence of early cultivars, and ‘sweet and crispy’ for nonmelting peaches. Furthermore, selection and cultivation for ornamental and yellow-ﬂeshed peaches are recorded during the Tang Dynasty (618–907 AD); for example, KuaiYuanTianBaoYiShi (a historiography book) describes a ‘new ornamental peach with thousand-leaf like ﬂowers was introduced into the Emperor’s garden’. TangShu (history annals of the Tang Dynasty) records: ‘In ZhenGuan 21 [Tang Dynasty calendar, 647 AD], western KangJu country [now the north-west Xinjiang autonomous region] pays tribute to a goose-egg sized and gold coloured peach, called “golden peach”’. Second, knowledge about tree biology and propagation was extensively improved, setting the foundation for the traditional system of Chinese peach cultivation. QiMinYaoShu (encyclopaedia for living; Jia, 533–544 AD) summarizes a cultivated peach tree life cycle that is very similar to modern peach production. ‘桃性早实，三岁结子，七八年便老，老则子细，十年则死’ illustrates that peach is precocious, fruiting at age 3 years, production declines at age 7–8 years when fruits are getting smaller, and trees die in 10 years. For seed germination and seedling propagation, seed stratiﬁcation was well understood and traditional methods were well developed at this time. These are illustrated in QiMinYaoShu: ‘桃熟时，于墙南阳中暖处，深宽为坑。选取好桃数十枚，劈其核，即内牛粪中，头向上，取好烂粪和土厚覆之，令厚尺余。至春桃始幼时，徐徐拨去粪土，皆应生芽，合取核种之，万不一失。其余以熟粪粪之，则益桃味’, indicating that seed stratiﬁcation was crucial to embryo development for seed germination and that fermented manures are good both for seed stratiﬁcation and for improvement of peach fruit ﬂavour and overall quality. In addition, a layering propagation method is also developed and summarized in the book, detailing shoot types and soils that should be used.

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Third, planting and transplanting are precisely summarized in QiMinYaoShu as ‘以锹合土掘移之’, encouraging planting and transplanting seedlings with soil balls holding the roots. Various peach pruning methods had also been developed and are documented in the book, such as the application of girdling or mechanical injury to the tree trunk to suppress vegetative growth, increase fruiting and raise production. Some of these methods are concisely illustrated in QiMinYaoShu as ‘桃性皮急，四年以上，宜以刀竖其皮’, explaining that the ring bark method should not be used until trees are 4 years old and cutting should be careful on the bark. This demonstrates that ancient Chinese peach growers had a good understanding of tree reproduction biology and management practices in peach production. Finally, frost protection and pest control techniques were developed along with practices in peach orchard management. This overall frost protection method for all fruit trees including peach is well documented in QiMinYaoShu (Jia, 533–544 AD) as ‘凡五果（包括桃树）花盛时遇霜，则无子。常预于园中，往往贮恶草生粪，天雨新晴，北风寒切，是夜必霜。此时放火作熅，少得烟气，则免于霜矣。’, illustrating that all ﬁve kinds of species (including peach) are vulnerable to frost damage during blooming. Frost damage to ﬂowers will cause production failure. To prevent frost damage, orchards need to be stored with straws and manures. Whenever a halt in rain occurs with a clean sky and cold wind from the north, it signals an overnight frost. Burning straw mixed with manures and releasing smog will prevent frost damage. This smoking method for preventing ﬂower frost is still one of the major applications widely used in peach orchards in northern China. Application of pest control measures also began during these centuries. As documented in QiMinYaoShu: ‘凡五果及桑正月一日鸡鸣时，把火遍照其下，则无虫灾’, saying that in cultivation of the ﬁve kinds of species and mulberry, lighting up the overall orchard using torches in the Chinese New Year will prevent insect damage. In fact, this idea and method underline the principle that the current application of ultraviolet light for insect control is based on. The above ancient Chinese literature during the time of the Wei–Jin to Sui–Tang

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dynasties and the Five Dynasties period probably sheds light only on the tip of the iceberg of a rich Chinese peach cultivation history, abundant natural resources and welldeveloped understanding of cultural technology. Some historical knowledge about germplasm resources, tree biology, propagation and orchard management is still worthy of further study. Song, Yuan, Ming, Qing Dynasties and Republican period (961–1948 AD) During these 1000 years, domestic and international exchanges in agriculture played an important role in Chinese peach production and development. Peach production regions were continuously expanding and many new production regions were developed. As information and technology was spread domestically, and to some extent abroad, peach culture developed further during this time. Over many years, Chinese peach growers systematically domesticated and continuously selected improved germplasm. This resulted in substantial improvements of peach culture and production in China. For example, LuoYangHuaMuJi (LuoYang ﬂower and tree collections) written by Zhou ShiHou (1081 AD) records 30 peach varieties: ‘Xiao Tao’ (small peach), ‘Shiyue Tao’ (October peach), ‘Dong Tao’ (winter peach), ‘Pan Tao’ (ﬂat peach), ‘Qianye Tao’ (thousand-leaf peach), ‘Chan Tao’ (twisted peach), ‘Erse Tao’ (doublecoloured peach), ‘Hehuan Erse Tao’ (dualcolour happiness peach), ‘Qiangyefei Tao’ (thousand-leaf pink peach), ‘Dayu Tao’ (big royal peach), ‘Baiyu Tao’ (white royal peach), ‘Jin Tao’ (golden peach), ‘Yin Tao’ (silver peach), ‘Bai Tao’ (white peach), ‘Kunlun Tao’ (Kunlun Mt. peach), ‘Hanli Tao’ (big peach), ‘Yanzhi Tao’ (crimson peach), ‘Zao Tao’ (early peach), ‘You Tao’ (smooth and waxy skin peach), ‘Renmian Tao’ (people face peach), ‘Mi Tao’ (honey peach), ‘Pingding Tao’ (nontip peach), ‘Pang Tao’ (fat peach), ‘Ziye DaTao’ (purple-leaved big peach), ‘Li Tao’ (gift peach), ‘Fang Tao’ (square peach), ‘Fenzhou Tao’ (local township named), ‘Putian Tao’ (local township named), ‘Hongrang Tao’ (red-ﬂeshed peach) and ‘Guang Tao’ (non-pubescence peach).

The honey peach (typical southern, melting, low-acid type) and the non-tip peach are probably the progenitor varieties that all southern Chinese peaches are derived from. The Yuan Dynasty’s WangZhen’s Farming Book written by Wang Zhen in the 14th century (Wang, 1313 AD) lists two additional early peach varieties, ‘Luosi white’ (ﬁne white) and a late variety ‘Guoyan red’ (passing wild goose red). The most famous Chinese pharmacopoeia is the BenCao GangMu written by Li Shizhen during the Ming Dynasty (Li, 1578 AD), which classiﬁes peach varieties by colours, fruit shapes and maturity date into different categories, saying ‘桃品种甚多，其花有红、紫、白、千叶二色，其实有红桃、绯桃、碧桃、缃桃、白桃、乌桃、金桃、银桃、胭脂桃，皆以色名者也；有锦桃、油桃、御桃、方桃、匾桃、偏核桃，皆以形名者也；有五月桃、十月冬桃、秋桃、霜桃，皆以时名者也’, meaning that there are many varieties of peaches. The ﬂower colours vary from red, purple, white to double colours. The fruit colour variations range from red to pure white. Varieties are named after their colours (including pink peach, light-pink peach, crimson peach, red peach, dark-red peach, purple peach, golden peach, silver peach and white peach); also, they are named after their shapes and appearance (including tip peach, smooth peach, royal-type peach, square peach and ﬂat peach); in addition, some are named after their maturity (including May peach, October peach, autumn peach, winter peach, etc.). Slightly later at the end of the Ming Dynasty, QunFangPu (Florilegium) written by Wang Xiangji (Wang, 1621 AD) gives detailed descriptions for some known cultivars, besides listing previous cultivars; for example, ﬂat peach is described as ‘shape like a cake, taste sweet’. It also records details about Shanghai honey (melting) peach as ‘it is native to Shanghai, but best peaches are produced from the GuShangBaoXi garden with sweet taste little less than lychee’. ShuiMiTaoPu (melting honey peach register) by Chu Hua in the Qing Dynasty (Chu, 1813 AD) records: ‘Melting peach was from the Gu’s fragrance garden in Ming Dynasty, it is juicy and tastes sweet, so called melting peach’. The origin of this type of peach was unknown, but probably derived from peaches from Beijing or Kaifeng.

Cultivation and Trends in China

Peach production in the Qing Dynasty was further expanded and some major production regions included Taiyuan, Shanxi province; Kaifeng, Luoyang, Shangqiu, Henan province; Chengdu, Sichuan province; Hangzhou, Zhejiang province; Hejian, Shenxian, Suning, Hebei province; Feicheng, Shandong province; and Nanhui, Baoshan, Shanghai city. Until the Republican period (1920s), new peach production regions were developing very rapidly, extending into many new areas including Wuxian, Wuxi, Yangzhou, Zhenjiang, Jiangsu province (eastern China); Suzhou, Dangshan, Anhui province (central eastern China); Ningling, Yanshi, Henan province (central northern China); Fenghua, Zhejiang province (eastern China); Zibo, Shandong province (northern China); Taigu, Shanxi province (north-western China); and central Shaanxi and eastern Gansu province (western China). During these ten centuries, peach culture technology had also developed to a new level. The documentations recorded in the Chinese literature are also more detailed. For example, NongSangYiShiZuoYao (farming, clothing, dieting abstracts) written by Lu Mingshan in the Yuan Dynasty (Lu, 1314 AD) describes how peach trees should be planted as ‘桃树栽时提根与地平，使侧根舒畅易活’, explaining that when planting a tree, holding the tree and making its lateral roots spread will improve the survivability. In ZhiBenTiGang written in the Qing Dynasty, Yang Shen (Yang, 1774 AD) illustrates more precisely that successful planting of peaches depends on a good understanding of root–shoot balance: ‘Planting: if a tree has more shoots and less roots, shoots need to be thinned; or if a tree has less shoots and more roots, then roots need to be thinned’. This documented how to maintain a balance between shoots and roots. ‘The peach seedlings should be planted in spring time when they are still in dormancy, otherwise, trees should be planted in autumn when their leaves fall off. Planting pits need to be deep and wide for root spreading and development, watering planted trees sufﬁciently and returning the surface soil on to the roots slowly will ensure soil to be settled on roots well’. This is not surprising because largescale peach planting and production growth occurred during this time. Evidently, ancient

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Chinese peach growers gained rich experiences from these 1000 years of cultivation and they greatly improved their understanding of peach tree physiology. They summarized the relationship between successful planting of peach trees and the growth balance of root and shoots. During the same time, propagation and orchard management techniques had been greatly developed, noted in ShuiMiTaoPu (juicy peach register) as ‘桃树生二，三年可接，多在春分前，秋分后，高树根二，三尺许锯去，以快刀修光，使不沁水，又向靠皮带膜处（韧皮部与形成层接合部），以上切下一寸余，却以水蜜桃东南北枝两边削成马耳状者，在口中含热插下，用纸封固，外涂以泥，在加匿叶护之’, saying that the peach can be grafted on 1- or 2-year-old seedlings, usually before vernal equinox or after autumnal equinox. The seedling top is cut off at 60–90 cm from the ground using a sharp knife and a cut between bark and wood about 3–5 cm is made. The scion-wood should be collected from the east or south side of the canopy of the mature ‘juicy peach’. A mouse-ear shaped piece is cut from buds of the scionwood and inserted into the cut of the seedling (the scion piece can put in the mouth for warmth and moisture), and then wrapped with paper and soil slurry. The grafting techniques for peach propagation were well developed during this time. Also, orchard management in southern China was well understood during this period as described in this book: ‘the peach growing in the south usually suffers waterlogging that resulted in root rot and orchard failures during rainy season. Deep ditches are needed for good drainage and fruit quality. The peach is drought tolerant but sensitive to waterlogging, welldrained orchards produce large and high quality fruits’. The characteristics of peach loving full sun and good drainage and drought tolerance are well documented. Good orchard practice for high yields and high quality had been developed in almost all major peach production regions in China during this time. Throughout the 4000-year history of peach cultivation, Chinese peach growers have made signiﬁcant contributions to peach domestication and peach industry development through exploring wild germplasm,

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selection and cultivar development, development of thorough understanding of tree physiology and development of many important cultural practices. China’s rich heritage of peach cultivation is worthy of great appreciation worldwide and of study by modern pomologists.

2.3 Current Status of Chinese Peach Production and Trends in China Peach is one of the top ﬁve most important fruit tree crops in China. Since China became the largest peach producer in the world in 1994, peach planting and production have increased steadily up to 1.4 million ha and 4.38 million t in 2003. Of this production approximately 80% was in white-ﬂeshed melting peach cultivars and 20% in other cultivars. The total area planted in China has remained static at around half the world total of 2.2 million ha in recent years. The massive production of Chinese apples and pears is having a marked effect on world supplies and trade in pip fruit and fruit juices. The increase in peach production could likewise have a similar impact on the international market. Peach germplasm collection, repositories, evaluation and utilization in China The national peach germplasm survey conducted during the 1950s has played an important role in current germplasm collections and repositories. Five species and 16 varieties and forms were identiﬁed within subgenus Amygdalus of genus Prunus. In addition, 800 traditional landraces and cultivars were documented (Wang et al., 1989; Guan and Wang, 1993). These efforts have resulted in the establishment of three national peach germplasm repositories in Beijing, Zhengzhou and Nanjing. Local efforts in peach germplasm collection also occurred simultaneously in Shanghai, Dalian and Shanxi. Altogether, more than 1000 germplasm accessions have been collected and maintained to safeguard against genetic erosion or complete loss due to recent rapid changes in the Chinese economy and society (Wang et al., 1989). The efforts, together

with active programmes in screening and evaluation, continued throughout the 1990s. In addition, a number of foreign cultivars were introduced to China, such as ‘Kanto 5’ and ‘Myoujou’ from Japan, and ‘NJN’ and ‘Babygold’ from the USA. In China, the peach national repositories also serve as breeding centres. Many new varieties have been developed from these three national and other local repositories. The repositories also conduct joint efforts in evaluation of the existing germplasm, particularly some unique genotypes. For example, the Fruit Germplasm Checklist (edited by the Fruit Research Institute of the Chinese Academy of Agricultural Science, 1993, 1998) lists 648 good peach genotypes (landraces) with detailed information on place of origin, fruit maturity, fruit size, ﬂesh characteristics, free- or clingstone, soluble solids, soluble sugars and acid, vitamin C, pollen viability, and other unique characteristics and uses. Screening and evaluation efforts at the repositories have resulted in a marked increase in the understanding of special genotypes and the effective use of germplasm. First, some commercial cultivars have been selected directly from those superior genotypes and used in peach production, such as the northern variety ‘Feicheng Tao’ with big fruit size and good transportability and storage quality, as well as ‘Shenzhoushuimi’ (Shengzhou melting honey), ‘Hanlumi’ (Cold dew honey), ‘Huayumi’ (Flower pure honey) and ‘Baihua’ (White ﬂower). These traditional varieties are widely used in Chinese peach production and have generated tremendous beneﬁt to both peach growers and the local agricultural economy. Second, the germplasm resources have been used as breeding materials in conventional breeding programmes for cultivar improvement. For example, ‘Shanghaishuimi’ (Shanghai melting honey) has played an essential role in newly released cultivars both domestically and in foreign countries. In fact, many new cultivars are derived from ‘Shanghaishuimi’, such as ‘Okubo’, ‘Hakuho’, ‘Yuhualu’ and ‘Zhaohui’. Meanwhile, new introduced nectarines and their pollens have been used for hybridization with traditional Chinese varieties, resulting in a number of new Chinese nectarine varieties. This has greatly improved the nectarine varieties

Cultivation and Trends in China

available and expanded nectarine production in China. Third, progress has been made for selection of pest-resistant genotypes that have proved very useful in breeding programmes. The results of germplasm evaluation have provided valuable resistance genetic materials that have been directly or indirectly used in both conventional breeding and new genetic engineering programmes. This includes ‘Gansu Tao-1’ (P. kansuensis Rehd.) and ‘Shouxing Tao-1’ (dwarf peach, P. persica var. densa Makino) with proven root-knot nematode resistance.

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Main peach cultivars, peach production and growing regions in China

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Common (white ﬂesh, melting) peach (P. persica Sieb et Zucc.): ‘Chunlei’ (Spring

Common peach: ‘Baixianglu’ (White fragment dew), ‘Yuhualu’ (Rain ﬂower dew), ‘Yulu’ (Pure dew), ‘Yinhualu’ (Silver ﬂower dew), ‘Beinong-2’ (Beijing Agricultural University – 2), ‘Zhaoxiang’ (Morning glow), ‘Xianghui-1’ (Glow ray-1), ‘Beinong Zaoyan’ (Beijing Agricultural University – Early beauty), ‘Sunagawase’ (Japanese cultivar), ‘Kurakato’ (Japanese cultivar). Yellow-ﬂeshed peach: ‘Flavorlate’, ‘Fertilia Morettini’. Flat peach: ‘Zaokuimitao’ (Early chief ﬂat peach), ‘Zaohuangpantao’ (Early yellow ﬂat peach), ‘Wuyuexuanbiangang’ (May fresh ﬂat peach), ‘Zaolupantao’ (Early dew ﬂat peach). Nectarine: ‘Armking’, ‘Ruiguang-2’ (Lucky ray-2), ‘Ruiguang-3’ (Lucky ray-3), ‘Yanguang’ (Beauty ray).

Mid-season cultivars (91–120 days from full bloom to harvest) ●

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Very early cultivars (less than 65 days from full bloom to harvest) ●

bud), ‘Chunhua’ (Spring ﬂower), ‘Zaoxialu’ (Early morning glow dew), ‘Huiyulu’ (Sunshine rain dew). Flat peach (P. persica f. compressa (Loud.) Rehd.): ‘Zaoshoumi’ (Early big honey), ‘Zaolupantao’ (Early dew ﬂat peach). Nectarine: ‘Shuguang’ (Dawn), ‘Huaguang’ (China glory). Early cultivars (66–90 days from full bloom to harvest)

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A great number of peach cultivars have been developed in China with many different fruit characteristics, adaptability and market values (Wang, 1990; Wang and Zhuang, 2001). Consequently, the cultivars in Chinese peach production vary in different geographic regions and even in different provinces. The China Fruit Plant Monograph – Peach Flora (Wang and Zhuang, 2001) registers 495 cultivars with detailed information about cultivar characteristics and production. This resulted from an extensive evaluation of more than 1000 germplasm accessions conducted by the two main national peach germplasm repositories at Beijing and Zhengzhou. Below, we brieﬂy list the main high-performance cultivars widely used in current Chinese peach production by their ripening date (Wang, 1990; Liu et al., 1999; Guo et al., 2000; Zhu et al., 2000; Wang and Zhuang, 2001). Although many varieties have been selected and developed in China and are used in current peach production, including melting peach, nectarines, ﬂat peach and ornamental peach, the majority of the Chinese cultivars are whiteﬂeshed and melting type, accounting for more than 80% of the total cultivars in current Chinese peach production (Zhu et al., 2003).

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Common peach: ‘Zhaohui’ (Morning sunshine), ‘Baifeng-2’ (White phoenix-2), ‘Zaoxiangyu’ (Early fragment jade), ‘Datuanmilu’ (Big honey dew), ‘Japan-89’. Yellow-ﬂeshed peach: ‘NJC88’, ‘Cullinan’, ‘Lianhuang’ (Even yellow), ‘Chengxiang’ (Orange fragment), ‘Myoujou’, ‘Redhaven’ (USA), ‘Babygold-5’, ‘Babygold-6’. Flat peach: ‘Sahuahongpantao’ (Splash ﬂower red ﬂat), ‘Baimangpantao’ (White awn ﬂat), ‘Changshengpantao’ (Longevity ﬂat), ‘Fenghuapantao’ (Fenghua ﬂat), ‘Chenpupantao’ (Chenpu ﬂat), ‘Yulupantao’ (Pure dew ﬂat). Nectarine: ‘Zhongyoupantao’ (Mid nectarine ﬂat), ‘Zaohongzhu’ (Early red bead).

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Late-season cultivars (121–150 days from full bloom to harvest) ●

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Common peach: ‘Baihua’ (White ﬂower), ‘Xinbaihua’ (New white ﬂower), ‘Shenzhou’ (Shenzhou white honey), ‘Shenzhouhongmi’ (Shenzhou red honey), ‘Wanshuomi’ (Late big honey), ‘Feichengtao’ (Feicheng peach), ‘Jingmi’ (Beijing honey), ‘Jingyu’ (Beijing jade), ‘Longhuashuimi’ (Longhua melting honey), ‘Early red-2’. Yellow-ﬂeshed peach: ‘Elberta’ (USA), ‘Fillips’, ‘Jincheng’ (Golden orange), ‘Jinxiu’ (Splendid), ‘Long 1-2-4’ (Dragon 1-2-4), ‘Xizhuang-1’ (West village – 1). Flat peach: ‘Huangroupantao’ (Yellow ﬂesh ﬂat), ‘Jiaqingpantao’ (Jiaqing ﬂat), ‘Lihepantao’ (freestone ﬂat). Very late season (more than 150 days from full bloom to harvest)

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Common peach: ‘Dunhuadongtao’ (Dunhuang winter peach), ‘Qingzhoubaipimitao’ (Qingzhou white skin honey peach), ‘Yexiandongtao’ (Yexian winter peach), ‘Zhonghuashoutao’ (China longevity peach).

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Yellow-ﬂeshed peach: ‘Bositao’ (Persian peach). Nectarine: ‘Hongliguang’ (Red plum shine). Peach production

The total land area devoted to peaches and nectarines in China has seen a more than fourfold expansion during the period 1984– 2006 (141,351 to 652,700 ha, respectively) (Fig. 2.3). More than 45% of the total land area devoted to peaches in the world is in China. Moreover, the total production (tonnes) has followed a similar increase. By 1993, China produced more peaches than any other country in the world (Fig. 2.4). Each year since then China’s production has increased, so that, by 2006, China produced 7.5 million t. This represented 44% of the total supply. The top ﬁve producing countries in 2006 were China, Italy, Spain, the USA and Greece, producing 44%, 10%, 7%, 5% and 5% of the world total, respectively. For the last 30 years, average yield (kg/ha) has been less in China than in the other top producing countries (Fig. 2.5). However, since 1990, Chinese average yield has increased each year such that in 2006 it

700,000 650,000 600,000 550,000

Total area (ha)

500,000 450,000 China Greece Italy Spain USA

400,000 350,000 300,000 250,000 200,000 150,000 100,000 50,000

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6 19 1 6 19 3 65 19 6 19 7 6 19 9 71 19 7 19 3 75 19 7 19 7 7 19 9 8 19 1 8 19 3 8 19 5 8 19 7 89 19 9 19 1 9 19 3 9 19 5 9 19 7 99 20 0 20 1 0 20 3 05

0 Year Fig. 2.3. Total peach and nectarine area (hectares) in the top five producing countries during the period 1961–2006. (Source: http://faostat.fao.org, accessed August 2007.)

Cultivation and Trends in China

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8,000,000 7,000,000

Total production (t)

6,000,000 5,000,000 China Greece Italy Spain USA

4,000,000 3,000,000 2,000,000 1,000,000

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6 19 1 6 19 3 6 19 5 6 19 7 69 19 7 19 1 73 19 7 19 5 7 19 7 7 19 9 8 19 1 8 19 3 8 19 5 8 19 7 8 19 9 9 19 1 9 19 3 9 19 5 9 19 7 9 20 9 0 20 1 0 20 3 05

0 Year Fig. 2.4. Total peach and nectarine production (tonnes) of the top five producing countries during the period 1961–2006. (Source: http://faostat.fao.org, accessed August 2007.)

24,000 22,000 20,000 Average yield (kg/ha)

18,000 16,000 14,000

China Greece Italy Spain USA

12,000 10,000 8,000 6,000 4,000 2,000 19 6 19 1 63 19 6 19 5 67 19 6 19 9 7 19 1 73 19 7 19 5 77 19 7 19 9 8 19 1 8 19 3 8 19 5 8 19 7 8 19 9 91 19 9 19 3 9 19 5 97 19 9 20 9 0 20 1 03 20 05

0

Year Fig. 2.5. Average peach and nectarine yield (kilograms per hectare) in the top five producing countries during the period 1961–2006. (Source: http://faostat.fao.org, accessed August 2007.)

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was just slightly less than the USA (11,506 versus 12,731 kg/ha, respectively). The ﬁve top peach-producing provinces are Shangdong, Hebei, Henan, Hubei and Jiangsu (Wang, 2003). With current changes in the agricultural industry in China, peach acreage seems to be increasing in Sichuan and Hunan provinces where citrus was overproduced. The same trend is also occurring in Yunnan, Guizhou, Fujian, Jiangxi and Guangxi provinces where peach production is developing in higher elevation areas. In addition, peach greenhouse production and highdensity cultivation have recently emerged in limited areas of northern China. Peach-growing regions The natural range of wild peach is spread widely over much of China. However, commercial peach production is limited within the latitude range 25–45°N (Fig. 2.2/Plate 26). It is largely concentrated in northern, central to eastern and north-western China. In general, peach production in China can be divided into seven regions based on regional climate and ecological differences (Wang and Zhuang, 2001). Peach cultivars in these main production regions are divided into regional groups that are signiﬁcantly different from one another. 1. North-west drought peach region includes Xinjiang and Ningxia autonomous region, Shaanxi and Gansu provinces. 2. Northern China plain region, the most important traditional and current peach production area in China. The northernmost boundary region corresponds to the Qinling Mountains and the Huai He River, including Beijing, Tianjing, Hebei province, and southern Liaoning, Shangdong, Shanxi, most of Henan, Jiangsu and northern Anhui provinces. 3. Changjiang River humid region, having a large area in central and eastern China, including southern Jiangsu, Zhejiang, Shanghai, southern Anhui, Jiangxi and Hubei and both Chengdu and Hanzhong plain areas. 4. Yunnan–Guizhou high plateau cold region, a small-restricted area including Yunnan, Guizhou and south-west Sichuan provinces. 5. Qinghai–Tibet plateau cold region, a limited area in the Tibet autonomous region, most of Qinghai and western Sichuan provinces.

6. North-eastern China cold region, this is the northernmost region of Chinese peach production, further than 41°N latitude, including Jilin and part of Heilongjiang provinces. 7. Southern China subtropical region, with south limit at 23°N latitude, including a large area to the south side of the Changjiang River of Fujian, Jiangxi, southern Hunan, north Guangdong, north Guangxi and Taiwan provinces. The ﬁrst ﬁve regions are suitable peach production regions, while the last two are marginal regions, as shown in Fig. 2.2/Plate 26.

Rapid development of greenhouse production Protected cultivation of peach was successful as early as 1995 in Shandong Agricultural University (Gao et al., 2004) (Fig. 2.6/Plate 27). Greenhouse cultivation of peach has greatly extended the peach marketing season in China. Very early peach cultivars with low chilling requirement and late- or very lateseason cultivars have been promoted for the extreme early and late seasons, respectively, with ﬁvefold higher market price than regular orchard-produced peaches. A systematic greenhouse cultivation technique has been developed, including applying plant growth regulation chemicals, reducing the size of foliage, summer pruning, girdling in the autumn, artiﬁcial application of drought stress, root pruning, and use of dwarﬁng rootstocks and dwarﬁng or semi-dwarﬁng cultivars. The microclimate in the greenhouse is adjusted to maximize peach production by controlling light, water, temperature, humidity and CO2:O2 ratio. In addition to applying extra artiﬁcial illumination, ﬁlms with better transparency have been used for covering materials, and reﬂective ﬁlms have been used on the ground and in the air for regulating light. Ripening stimulation is usually regulated by controlling temperature during bloom time between 5°C (night) and 22°C (day) and during fruit ripening at 25–30°C, which accelerates the ripening by 10 to 50 days. Large differences between night temperature and day temperature can improve the fruit quality. Delaying ripening is more

Cultivation and Trends in China

Fig. 2.6.

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Modern greenhouse peach production.

often practised in the northern areas. Improved insulation in greenhouses plus the frozen ground of the semi-ground greenhouses in northern China can be effective to hold a low temperature (< 7°C) in the greenhouse for 50 days during spring, when temperature is rising in March to May. This can effectively delay bud break in the spring and prolong fruit ripening for 10–30 days. The humidity and water content in the soil are usually regulated according to the growing season by irrigation. Other techniques are also used in the greenhouse, which include breaking dormancy with chemicals (hydrogen cyanamide) and applying different types of fertilizers based on the cultivars and growth season. Typical spacing in the greenhouse is 1 m × 2 m. This high planting density usually requires a special summer pruning method called PCR pruning (postharvest canopy removal) for controlling tree size. Trees before PCR are shown in Fig. 2.7/Plate 28. The method includes pruning off all current shoots as soon as fruits are harvested, followed by several summer tippings of new growing shoots for enhancing ﬂower bud formation. Trees after

PCR are shown in Fig. 2.8/Plate 29. Foliar disease control could be a problem due to high humidity in the greenhouse production system, but greenhouse management such as ventilation and irrigation controls usually regulates humidity. The greenhouse peach production system usually remains productive for about 10 years. Intercropping systems for greenhouse peach cultivation are also being developed for maximizing the output of greenhouse productivity, such as strawberry intercropped between rows in a peach greenhouse. Currently, greenhouse peach production has reached about 14,000 ha (Li et al., 1995; Wang et al., 1995; Zhu and Wang 1997; Wang and Niu, 1998; Zhang and Yu, 2002). Peach postharvesting, processing and marketing in China Nearly all fresh peaches produced in China are marketed within the country. Marketing is as for all other fresh fruits and vegetables: farms or farming cooperatives send peaches to distribution centres (large trading centres organized

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Fig. 2.7.

Modern greenhouse peach production before postharvest canopy removal.

Fig. 2.8.

Modern greenhouse peach production after postharvest canopy removal.

Cultivation and Trends in China

by local governments), and from there the fruit are sent to fruit stores or wholesale centres in cities. Most peach production for local fresh markets requires little packing. For distant provincial markets, packing and transportation are necessary. Fruits are usually harvested before completely ripe (70–80% ripe) and packed in cardboard boxes (50 cm × 40 cm × 20 cm; about 10 kg of fruit per box) for storage and shipping. For prolonged supplies to the markets several storage techniques are usually used, mostly by cold storage, although controlled-atmosphere storage and low-pressure storage are used to a certain extent (Du et al., 2000). Cold storage usually applies 0–1°C temperature and 85–90% relative humidity, while controlled-atmosphere storage is created with 0–1°C temperature, 5% CO2 and 1–3% O2. The processed peach products in China are mostly canned, dry fruit and sliced dry products. Recently a new series of processed products has been developed with advances of modern industrial technology, including peach juice, peach tea drinks, beer, fruit jelly and peach candies (Zheng, 1995; Zheng et al., 2001). Approximately 80% of Chinese peach production is for the domestic fresh market. Small quantities of fresh peach, mostly whiteﬂeshed melting peach, have been exported to South-east Asian countries since the mid1950s. There is a trend for increased fresh peach exports to neighbouring countries in recent years. Substantial amounts of processed products are also exported to European and American markets (Wang and Zhuang, 2001). Problems faced by the Chinese peach industry Although peach production has become an important rapidly developing industry, the lack of overall industry organization and long-term strategic planning presents barriers for future proﬁtability (Jiang, 2000; Zhu et al., 2003). Some of the problems that need to be overcome include the following. Cultivars in production For a healthy industry, China needs a balanced proportion of different ripening peaches for a

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prolonged market supply. Particularly, the overproduced early-season peaches have greatly hampered industry development for market supply. Also, an unbalanced ratio of the white-ﬂeshed melting peach does not meet consumer demand for a diversity of peach fruit types (Chen and Liu, 1999; Wang, 2000). Orchard management Poor orchard management is responsible for low yields per hectare, and poor fruit quality. A large percentage of peach orchards might be currently operated in extensive (low-care) cultivation. For example, high-density orchards without appropriate canopy management have caused production to decline rapidly and shortened peach tree life. Driven by short-term proﬁt return, large-dose application of chemical fertilizers without or with less organic manures has overridden recommended management practices of balanced fertilization based on orchard age, yields, soil types and climate difference. Under these orchard practices most good cultivars cannot reach their highest yields and quality for marketing (Chen, 2002; Wang, 2000). Postharvest issues Lack of postharvesting facilities and expenses associated with handling fruit have hampered quality control (Du et al., 2000; Zhao and Chen, 2004). Protocols for peach cleaning, sorting and packing have not been well developed and are necessary for a well-regulated marketing system. Also, a lack of storage facilities and poor coordination between storage and transportation systems have caused tremendous losses during storage and transportation in some high-yielding years and reduced proﬁt returns to peach farmers (Zhao and Chen, 2004). A well-organized provincial or regional marketing system is urgently needed. Small family farms Most Chinese peach production is on familybased small farms. This small-scale and locally operated production and marketing is probably responsible for the poor coordination of

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orchard production, postharvest handling and storage and shipping (Zhu et al., 2003). Consequently, it is difﬁcult to standardize the production protocols and regulate quality controls. The current system must change, or the Chinese peach industry will remain less competitive within the world markets.

purposes to enhance the applications of unique Chinese peach resources (Wang and Zhuang, 2001). These new strategic goals will contribute greatly to new peach cultivar improvement and beneﬁt the world peach industry.

Applied research and extension education

Chinese peach production will be readjusted according to market needs and new cultivar releases will be accelerated in the future. Based on peach production zones in China, the peach cultivars used in the different peach-growing regions will be more marketoriented and readjusted to market changes. For a prolonged market supply, the peach cultivars in different ripening dates may be structured as the ratio of 5:35:30:25:5 for very early cultivars (<65 days after full bloom, this category includes protected cultivation of peaches and nectarines), early-season cultivars (66–90 days after full bloom), mid-season cultivars (91–120 days after full bloom), lateseason cultivars (121–150 days after full bloom) and very late-season cultivars (>151 days after full bloom), respectively (Zhu et al., 2003). The peach market tends to have greater demand for early cultivars with larger fruit size and good ﬂavour; for mid–late cultivars with larger size, good appearance and storage quality; and for very late cultivars with medium size, no fruit cracking, good appearance and stress tolerance (Jiang, 2000). New peach cultivar development will focus on more novel characteristics, such as high content of carotene and ﬂesh browning tolerance for yellow-ﬂeshed cultivars; new nectarines with wide adaptability, larger size, high fruit quality and light red or goldencoloured skin; and new ﬂat peach cultivars with larger size, good appearance and rich ﬂavour and aroma, and less fruit cracking. New novel cultivars will be promoted to develop niche markets. New breeding programmes for ﬂat peach cultivars will have a greater emphasis on dwarf or semi-dwarf and compact tree forms for high-density plantings and ornamental ﬂower types. Low-chilling genetic resources of both Chinese and foreign origin will be used to develop <500 chill-hour peach cultivars for growing in southern China (Wang et al., 2000). With targeted exploration

Variety trials and an extension education system are not well established. Consequently, new cultivar propagation increases and sales are not regulated and some cultivars are overplanted before they are adequately tested (Wang, 2000).

Current trends of Chinese peach production Germplasm collection and evaluation Germplasm collection and evaluation needs to be a more scientiﬁcally based, long-term commitment for further industry development. It has been recognized among Chinese botanists and peach researchers that the lack of investigations in peach native centres and the lack of genetic diversity assessment across China’s diverse geographic and climatic regions are hampering a more scientiﬁcally based coverage of the existing gene pool of native peach germplasm in China (Zhao et al., 2000). More research efforts will need to be devoted towards documentation and inventory assessment of wild germplasm and genetic differentiation across native centres in different Chinese geographic regions. New molecular ﬁngerprinting techniques will need to be widely used to establish the authenticity of Chinese traditional cultivars and landraces and to enhance management in Chinese peach repositories. Furthermore, molecular investigations into the taxonomic uncertainties of subspecies, varieties and forms within the genus should be considered. Evaluating and discovering new genes regulating novel and important traits, such as compact tree forms, weeping habits, double petals and different ﬂower colours, sweet kernels and pest resistance, etc., will be incorporated into peach breeding programmes for a variety of

Cultivars/market

Cultivation and Trends in China

of wild peach genetic germplasm and new biotech applications in peach breeding, cultivars with stress tolerance and pest resistance may be developed and used in the Chinese peach industry. Cultivar replacement time will be reduced from the current 20–30 years to a 10–15-year period with 80% newly released cultivars in the production. The ratio of melting peach versus non-melting peach will be changed from the current 9:1 to 7:3 or 6:4 in the future (Jiang, 2000). Production systems Production systems are moving towards large-scale, intensive and industrialized organizations or cooperatives. Current production systems based on family operations should be gradually reformed to a more industrialized system of professional farm cooperatives comprising farms with large centralized packing and shipping or processing facilities (Yi, 2003). This will help the Chinese peach production and industrialization system to be upgraded to a more competitive, world standard, highly commercialized and efﬁcient system. The new development of intensive

Fig. 2.9.

Conventional peach orchard.

53

production and marketing organizations will enhance China’s efforts to fully participate in the world market as a new member of the World Trade Organization. Orchard system management The peach orchard system will probably be changed from currently intensive tillage to less tillage or free tillage or even biodegrading ﬁlms for weed control and for improving fruit quality and yield. Fertilization in peach orchards should reconsidered using traditional organic fertilizers for high-quality fruit. Irrigation systems will need to be more waterefﬁcient with wide application of dripping or microsprinkler irrigations (Shi et al., 1990). The traditional low-density orchards with large tree size (Fig. 2.9/Plate 30) have been changing to current higher-density orchard systems (Figs 2.10 and 2.11/Plates 31 and 32). New rootstocks for compact or semi-dwarf tree forms have played an important role in high-density orchard development. Recently, in addition to using semi-dwarf peach cultivars, dense-pubescent cherry (Prunus polytricha Koehne) and Chinese dwarf cherry (Prunus

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H. Huang et al.

Fig. 2.10.

Modern high-density peach orchard.

Fig. 2.11.

Modern high-density peach orchard (dormant).

humilis Bunge) are being widely used as rootstocks to reduce tree size (Wang and Zhuang, 2001). Rootstock breeding for high-density orchards has resulted in speciﬁc selections such as ‘Ailihong’ (Dwarf bright red, P. persica var. densa) that has short internodes and is

suitable for high-density plantings (Gao et al., 1992). In application of available dwarf rootstocks and other dwarﬁng resources from different Prunus species, further exploitation and development of rootstocks will be more focused on new rootstocks with dwarf characteristics

Cultivation and Trends in China

combined with the potential of improving fruit quality and yields in high-density orchards. Planting space will be more optimized towards the speciﬁc requirements of different cultivars and rootstock types to improve sunlight penetration and fruit quality (Zhu et al., 2003). Peach pruning systems tend to be more simpliﬁed and less labour-intensive. A variety of different pruning methods are used in Chinese peach orchards, such as vase ﬁgurative, modiﬁed vase, multi-scaffold, natural open centre and modiﬁed central leader forms (Wang et al., 1989). Recent development of simpliﬁed training and management systems has been aimed towards the demand of high-density orchards or less labour-intensive management systems (Wang et al., 1999). A single leader form has been developed for high-density orchards, while the ‘V’ shape and two-scaffold ‘Y’ forms are widely used in newly planted orchards (Liu, 1997; Wu et al., 1998; Xu et al., 1998). The tree training process has also been simpliﬁed to increase earlier fruit production with the aid of summer pruning applications. Greenhouse cultivation Greenhouse cultivation has been showing great market potential in recent years. Further efforts are needed towards the selection and evaluation of suitable candidates of either early cultivars with low chilling requirement or very late cultivars with high quality. This development should signiﬁcantly prolong the market window of fresh fruit supplies (Wang et al., 2002). Greenhouse cultivation technology will be improved into a central computerized system for managing fertilizers, water, light, temperature and gas (CO2) in the greenhouse (Wang and Zong, 1996). Biotechnology applications In vitro propagation has been successfully developed for peach, which could be used in the production of virus-free rootstock and increase propagation efﬁciency (Wu et al., 2003). Marker-assisted selection can dramatically reduce the time, labour and space cost during the selection processes for peach breeding programmes. High-throughput genotyping using microsatellite markers can even be easily

55

used in regular biological laboratories. With more research efforts devoted to the genetic transformation of Prunus species, genetically modiﬁed peach and nectarines might be available for peach production in the future. This may include environmentally friendly, genetically engineered cultivars with a wide spectrum of pest resistance, frost tolerance, compact tree forms, semidwarf or dwarf varieties, as well as new cultivars with novel genes regulating ripening and postharvest storage and shipping characteristics (Liu et al., 1991; Jiang et al., 1993; Wei and Timon, 1994; Ma and Li, 1999; Zhang et al., 2001). New pest control approaches Many common peach diseases and insects occur in China, including brown rot (Monilinia fructicola (Wint.) Rehm), leaf curl (Taphrina deformans (Berk) Tul.), anthracnose (Gloeosporium laeticolor Berk), bacterial leaf spot (Xanthomonas pruni (Smith) Dowson), canker (Valsa leucostoma (Pers.) Fr.) and gummosis, as well as insects including the pyralid moth (Dichocrocis punctiferalis Guen.), aphids (Myzus persicae Sulzer), leaf moth (Thosea sinensis Walker), trunk borer (Aromia bungii Fald.) and rootknot nematodes (Meloidogyne spp.) (Wang et al., 1989). Different pest control approaches such as chemical, agricultural, physical and bio-controls are being utilized for Chinese peach production. Future improvement in peach pest controls should be geared towards the bio-control approaches to meet the growing market demand for organic fruits. Other more sophisticated integrated pest management systems will also be developed for achieving fruits free of pesticide residues (Chen, 2002; Ma et al., 2002; Ma and Jia, 2003). Ornamental peach Peach has become one of the most important ornamental trees for early spring bloom in China. Due to the rich culture and history of peach cultivation, more exotic and ornamental peach varieties have been used for recreation tourism, shade trees and cut ﬂowers (note ornamental ‘chrysanthemum’ peach, Fig. 2.12/

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Fig. 2.12.

Ornamental ‘chrysanthemum’ peach.

Fig. 2.13.

Ornamental ‘longevity’ peach. (From Wang and Zhuang, 2001.)

Cultivation and Trends in China

Plate 33; and ‘longevity’ peach, Fig. 2.13/ Plate 34). Many peach ﬂower gardens have been established all over China, including Peach Origins in Hunan, Broken Bridge near West Lake, Peach Peak in the Yellow Mountains, Dragon Spring Recreation Site in Chengdu, Sichun, Xiangshan in Beijing, Leting in Hebei, etc. In Hong Kong, Macau, Guangzhou and the Zhujiang triangle region, the peach ﬂower is called ‘the Christmas tree in China’, since the peach ﬂower is one of the most important cut ﬂowers for the Chinese Spring Festival in south-eastern provinces. Chinese people in southern Asia, especially Singapore, are very fond of peach ﬂowers. Recently, peach ﬂowers have become more popular in big cities, including Beijing, Shanghai and Dalian, for cut ﬂowers during the Chinese Spring Festival holiday (Jiang, 2000).

57

germplasm, selection and cultivar development, development of a thorough understanding of tree physiology and development of many important cultural practices. Tremendously diverse genetic resources of wild peaches are still widely grown in large areas of China and will provide valuable breeding materials for cultivar improvement and for supporting the sustainable peach industry. China is now the largest peach producer in the world, with a total planted area of 2.2 million ha and an annual production of about 6 million t, which accounts for half of the total world acreage and nearly half of the total world production. Although many problems remain, China’s peach industry will continue to improve and facilitate many new developments for the future.

Acknowledgements 2.4 Summary/Conclusion China has played a crucial role in peach domestication for world peach cultivation. Throughout the 4000-year history of peach cultivation, Chinese peach growers have made a rich heritage for the world of peach cultivation through exploring wild

We would like to thank Chen Xuzhong, research associate of Wuhan Botanical Garden, for translating the Chinese references and Qing Lin, Professor of Beijing Agricultural College, for providing photographs. This work was supported by CAS key project KSCX2-SW-104.

References Anon. (11th–6th century BC) ShiJing (The Book of Songs). This book compiles the works from the 11th century BC to the 6th century BC, 305 volumes in total; the poems being divided into three categories: Feng (Ballads), Ya (Festal Odes) and Song (Sacrificial Songs). Anon. (2nd century BC) ErYa. This is one of the earliest reference books serving as a dictionary for names and terms, and was probably written (author unknown) between the Qin Dynasty and the Han Dynasty; 20 chapters in total, but only 19 chapters remain. The descriptions about plant classification in the ErYa were reprinted in 1962 in the Collected Papers of Science History, issue 4. Ban, G. (39–92 AD) HanShu. Ban Gu was a historian of the Western Han Dynasty, HanShu is the historical annals; it describes the development of philosophy, economy and literature for a period of 200 years in the Western Han Dynasty. Chen, P. and Liu, J.-X. (1999) Present situation of Chinese peach new variety selection. Hebei Fruits 3, 8–9. Chen, W.-H. (1994) Illustrated Handbook of Ancient Relics of Chinese Agriculture. Jiangxi Technology Press, Nanchang, China, pp. 99–100. Chen, W.-Y. (2002) Technical standards for organic cultivation of ‘Feicheng’ peach. Hebei Fruits 4, 20–21. Chu, H. (1813 AD) ShuiMiTaoPu (melting honey peach register). ShuiMiTaoPu is a monograph on the cultivation of honey peach in Shanghai region, including history, cultivar description, propagation method, culture technique and orchard management. Reprinted in Guangxu 26 (1900 AD) in the Journal of Agronomy October, No. 124, 1–4.

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Cui, S. (2nd century AD) SiMingYueLing – Vol. 69. Cui Shi was an agronomist of the Eastern Han Dynasty and SiMingYueLing is the earliest farming calendar in China; it describes and records all activities of army, farming, industry, business and the way of living. Du, J.-C., Ma, K. and Wang, X.-N. (2000) Research advances in storage and handling technology for peach. Northern Fruits 6, 1–3. Duan, S.-L., Zong, X.-P., Liu, X.-Y., Zuo, Y.-Z. and Duan, Y.-C. (1983) Preliminary report on germplasm resources of fruit trees in Xizang. Acta Horticulturea Sinica 4, 217–223. Fruit Research Institute, China Academy of Agricultural Science (ed.) (1993) Fruit Germplasm Checklist. China Agricultural Press, Beijing. Fruit Research Institute, China Academy of Agricultural Science (ed.) (1998) Fruit Germplasm Checklist. China Agricultural Press, Beijing. Fu, X. (2nd century AD) Peach Ode. Gao, H., Wang, S. and Wang, J. (2004) Fruit protected cultivation in China. Acta Horticulturae 633, 59–66. Gao, M.-X., Liu, P.-Z. and Ren, J.-X. (1992) Relationship between sunlight distribution and yield and fruit quality of different tree training systems. China Fruits 4, 10–13. Ge, H. (1st century AD) XiJingZaJi. Ge Hong was a Taoistic theorist and doctor; the book XiJingZaJi is an adversaria about Taoism and agricultural activities in XiJin region (now Xi’an city, Shanxi province). Guan, H.-R. and Wang, X.-S. (1993) Present situation of peach resource and development trends in China. Land and Natural Resources Research 2, 62–65. Guan, Z. (5th century BC) GuanZi-DiYuan. Translated and interpreted by Xia, W.-Y. (1958), Zhonghua Press, Beijing, pp. 59–60. Guo, H., Zhou, J.-T., Zhao, M.-Z., Yu, M.-L. and Ma, J.-J. (2000) Brief description of good peach cultivars. Journal of Fruit Science 17(Suppl.), 72–74. Guo, Y.-G. (4th century AD) GuangZhi. This is a chorography about geography, climate, local culture and agriculture. Han, F.-Z. (280–233 BC) HanFeiZi. Han was a philosopher in the late Warring States Period; the book after his name compiles his works, 33 volumes in total. Jia, S.-X. (533–544 AD) QiMingYaoShu. QiMingYaoShu is an encyclopaedia for living; 92 chapters in total, divided into ten volumes. The book records crops, fruit tree cultivation and breeding techniques, etc. Reprinted in 1963 by Agricultural Press, Beijing, pp. 49–52. Jiang, H.-J., Pan, J.-S. and Meng, X.-F. (1993) The study of meristem-tip culture in vitro for peach. Acta Agriculturae Universitatis Pekinensis 19, 49–52. Jiang, Q. (2000) The status and development trend of China’s peach production. Beijing Agricultural Science 18, 35–38. Li, S.-Z. (1578 AD) BenCaoGangMu. Li Shizhen was a traditional Chinese medicine doctor in the Ming Dynasty; BenCaoGangMu is one of the most important Chinese pharmacopoeias. Reprinted in 1957 by People’s Medicine Publishing House, Beijing, 1256 pp. Li, Y.-W., Wang, X.-H. and Zuo, Q.-Y. (1995) Greenhouse peach cultivation. Shanxi Fruits 2, 14–15. Liu, H.-C. (1997) Two pruning methods for Y form peach tree training in greenhouse. Beijing Agriculturea 8, 18. Liu, M., Wu, Z., Ding, G.-Q., Wang, F.-T. and Liu, Y.-H. (1999) A new very late mature peach variety – Zhonghuashoutao. China Fruits 3, 7–8. Liu, Y.-S., Hu, N.-Y. and Lu, G.-M. (1991) Research on ovule culture in vitro for early-mature peach. Acta Botanica Boreali-Occidentalia Sinica 19, 37–43. Lü, B.-W. (300 BC) LüShiChunQiu (Lü’s spring and autumn annals). Lu, H. (3rd century AD) YeZhongJi. YeZhongJi is an adversaria at an ancient place, Yezhong in the Western Jin Dynasty (currently Lin-Zhang region, Hebei province). Lu, M.-S. (1314 AD) NongSangYiShiZuoYao (farming, clothing, dieting abstracts). Reprinted in 1962 by China Agricultural Press, Beijing, pp. 26–27. Ma, F.-W. and Li, J.-R. (1999) Callus formation from cultured protoplasts of Prunus davidiana. Acta Agriculturae Boreali-Occidentalis Sinica 8, 73–76. Ma, Z.-J., Huang, X.-H., Yong, W., Du, Y.-Q. and Wei, W.-D. (2002) Field trial of Kurarinone natural pesticide efficiency against red mite and Carposina niponensis Walsingham. Journal of Ningxia Agricultural College 23, 75–76. Ma, Z.-S. and Jia, Y.-Y. (2003) New techniques for disease and pest control in organic peach production. Hebei Fruits 4, 24–25.

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Qu, Z.-Z and Sun, Y.-W. (1990) Systematic Pomology. China Agriculture Press, Beijing, p. 69. Shi, Y.-Z., Liu, Y.-R. and Liang, Y.-W. (1990) Study on drip-irrigation in peach orchard. Journal of Fruit Science 7, 105–108. Sima, Q. (1st century BC) ShiJi (a history annals, 100 BC). Sima was a historian, literateur and thinker in the Western Han Dynasty; ShiJi is the first general history in China. Wang, B. (1st century AD) TongYue. Wang, J.-Y. (2003) China’s fruit production and development suggestions. China Fruits 6, 42–44. Wang, L.-R. (2000) Reviewing present situation of US peach and nectarine production and development of Chinese peach industry. China Fruits 3, 44–46. Wang, L.-R., Zhu, G.-R. and Zuo, Q.-Y. (1995) Choosing peach variety for protected cultivation. China Fruits 4, 34–35. Wang, L.-R., Zhu, G.-R. and Zuo, Q.-Y. (2000) Advance in breeding of low chilling peaches and nectarines. Journal of Fruit Science 17, 57–62. Wang, X.-J. (1621 AD) QunFangPu (Florilegium). QunFangPu is a farming book with literary quotations, art and culture; it illustrates each plant’s morphological traits and cultivation method (including fruit trees). Reprinted in 1957 by Zhonghua Press, Beijing. Wang, Y.-P., Yang, F.-K., Luo, C.-X., Hu, X. and Mu, C.-G. (2002) Technique of delaying maturity for greenhouse peach cultivation in cold zone. Shanxi Fruits 2, 16–18. Wang, Z. (1313 AD) WangZhen’s Farming Book. This is a monograph about crop cultivations (including fruit and vegetable). Reprinted in 1981 by China Agricultural Press, Beijing, pp. 127–128. Wang, Z.-H. (1990) Peach Cultivars. China Agricultural Press, Beijing. Wang, Z.-H. and Zhuang, E.-J. (2001) China Fruit Monograph – Peach Flora. China Forestry Press, Beijing, pp. 42–51. Wang, Z.-H., Lu, Z.-Y., Hu, Z.-L. and Zhang, K.-B. (1989) Peach. In: China Agricultural Science and Technology Achievements in Forty Years. China Agricultural Press, Beijing, pp. 179–184. Wang, Z.-Q. and Niu, L. (1998) Present situation and research priorities for China’s protected fruit production. Economical Forest Research 16, 62–65. Wang, Z.-Q. and Zong, X.-P. (1996) Research and development in Chinese peach breeding and cultivation technology for 21 century. Economical Forest Research 14(Suppl.), 20–23. Wang, Z.-Q., Liu, S.-W., Niu, L., Fan, W. and Liu, H.-C. (1999) Study on the training and pruning system for nectarines in protected cultivation. Journal of Fruit Science 16, 185–191. Wei, S. and Timon, B. (1994) Improvement in propagating virus-free peach (P. persica) plants in vitro. Jiangsu Journal of Agricultural Science 10, 1–4. Wu, Y.-J., Zhang, S.-L., Zhang, L.-L., Shen, J.-Q. and Wu, D.-J. (2003) Shoot regeneration from immature cotyledons of peach. Journal of Zhejiang University (Series – Agricultural & Life Sciences) 29(1), 93–96. Wu, Y.-L., Xu, Z.-N. and Zhuang, E.-J. (1998) Technique for central leader pruning system in high density peach cultivation. China Fruits 3, 22–23. Xu, Z.-N., Wu, Y.-L. and Zhuang, E.-J. (1998) Field experiments with central leader training and pruning system for the high-density peach orchard. Journal of Fruit Science 15, 317–321. Yang, S. (1774 AD) ZhiBenTiGang. ZhiBenTiGang is an agricultural textbook for field crop, fruit tree and mulberry. Reprinted in 1957 by Zhonghua Press, Beijing, pp. 67–69. Yi, F.-H. (2003) Present situation, prospects and strategies for Chinese fruit industry development. Abstracts of Chinese Horticulture 6, 4–5. Zhang, Y.-Q. and Yu, D.-Q. (2002) Present situation of development and countermeasure for protected horticulture. World Agriculture 11, 41–43. Zhang, Y.-Q., Chen, D.-M., Jin, Y.-F. and Zhang, S.-L. (2001) Regeneration of peach plantlets from callus derived from explant. Acta Horticulturae Sinica 28, 342–344. Zhao, G.-X. and Chen, X. (2004) Fruit storage technology. Northern Fruits 1, 69–71. Zhao, M.-J., Guo, H., Yu, M.-L., Zhou, J.-T. and Ma, R.-J. (2000) Research advance in peach genetic resource. Journal of Fruit Science 17(Suppl.), 46–49. Zheng, F.-G. (1995) A series of processed products from ‘honey’ peach. Food Science 16, 66–67. Zheng, H.-Y., Yin, Y.-N., Yu, C.-G. and Xu, J.-H. (2001) Processing technique for series of nectarine products. Jiangsu Food and Fermentation 4, 35–37. Zhou, S.-H. (1018 AD) LuoYangHuaMuJi; hand-written copy in the Qing Dynasty. This is a monograph describing flower and fruit tree cultivation in present-day Luoyang region, Henan province.

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Zhu, G.-R. and Wang, L.-R. (1997) Protected peach cultivation and key techniques. Deciduous Fruits 3, 42–43. Zhu, G.-R., Wang, L.-R., Zuo, Q.-Y. and Fang, W.-C. (2000) Good peach cultivar resources. China Seed Industry 2, 16–19. Zhu, G.-R., Wang, L.-R. and Fang, W.-C. (2003) The status of peach production in China and development strategies. Deciduous Fruits 4, 14–16.

3

Classical Genetics and Breeding Rene Monet1 and Daniele Bassi2

1National

Institute for Agronomical Research (INRA), Bordeaux Research Centre, France (retired) 2University of Milan, Milan, Italy

3.1 Classical Peach Genetics Qualitative (single) characters and their inheritance Quantitative characters Ploidy 3.2 Peach Breeding First steps Objectives Floral biology and selection cycles Methodology Technique

3.1 Classical Peach Genetics With the rediscovery of Mendel’s laws at the beginning of the 20th century, breeders, who had worked empirically before, became interested in character inheritance and tried to verify if these laws had general application. First results came from the observation of progenies obtained for species improvement rather than from speciﬁc genetic studies. For fruit trees, where mutated individuals are scarce and reproductive cycles slow, genetic studies were neglected for a long time. Nevertheless, peach was an exception. Breeders and researchers have collected many data on character inheritance, so this species can be regarded as a model for genetic knowledge advancement. Here, we review results that

61 61 66 66 68 68 69 72 72 74

are useful for a breeder as well as those in relation to single (Mendelian) or quantitative characters.

Qualitative (single) characters and their inheritance The most important single traits found in peach are described and discussed in Chapter 1. They are grouped in Table 3.1 with their mode of inheritance and citation of the ﬁrst author(s) who studied them. The small number of available mutants, the long time needed to create F2 generations and the land occupied by trees did not permit the location of the genes which determine the characters described above on the eight linkage groups expected in peach. Only molecular

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

61

62

Table 3.1.

Qualitative, Mendelian traits in peach and association to specific genomic linkage groups. (Updated from Sansavini et al., 2006.)

Phenotype and symbol

Genotype

Tree Broomy (columnar or pillar) (Br)

br/br

Arching (Ar)

Bushy (Bu) Compact (Ct) Dwarf (Dw)

Semi-dwarf (N) Weeping (Pl)

Standard

2

Br/br br/pl br/dw br/Ct Brbr/plpl

bu1/bu1 bu2/bu2 Ct/– dw/dw dw2/dw2 dw3/dw3 n/n pl/pl

Dw/– Br/Br Pl/Pl ct/ct

Incomplete dominance; phenotype is upright when Br is heterozygous with the alleles for the standard, dwarf, compact or weeping growth habits See: Columnar

Upright weeping; similar to the Up, but with a distinct curvature of the 1-year-old shoots; from F2 or backcross progenies of columnar (Br) × weeping (Pl) crosses; Br is epistatic to Pl Bu1 and Bu2 are independent

6

Short internode (<10 mm) Very dwarf Extremely dwarf, thin stem Incomplete dominance Incomplete dominance, featuring open, intermediate canopy when heterozygous (Pl/pl) (Bassi and Rizzo, 2000). Pl from pleureur (to weep, in French) This growth habit results from the allelic status of any of these known genotypes

Reference

Scorza et al. (1989, 2002); Yamazaki et al. (1987); Chaparro et al. (1994)

Scorza et al. (1989)

Werner and Chaparro (2005)

Lammerts (1945) Mehlenbacher and Scorza (1986) Lammerts (1945) Hansche (1988) Chaparro et al. (1994) Monet and Salesses (1975) Monet et al. (1988)

R. Monet and D. Bassi

Upright (Up)

Linkage groupa Note

I1/– I2/– t/t

Evergreen (Evg)

evg/evg

Anthocyanin deficiency (An) Anthocyaninless (W)

an/an w/w wv/wv

Resistance to root-knot nematode, Meloidogyne javanica (Mj)

Mj1/–

2

Mj2/– Mi/–

22

Resistance to root-knot nematode, Meloidogyne incognita (Mi) Resistant to both species Green aphid resistance (Rm)

1

Two dominant genes; incompatibility found only in some nectarines Epidermic suberification at bud base in 1-yearold shoot Also called evergrowing (Bielenberg et al., 2004): terminal buds do not go dormant Pale pink flowers White flowers; no red anywhere Wv is unstable and produces variegated flowers (peppermint) Mj1 and Mj2 are independent

E/E E/e e/e

Redleaf (Gr)

Gr/–

Albinism (C) Wavy-leaf (Wa) Crinkle leaf (CL)

c/c wa/wa cl/cl

Willow-leaf (Wa2)

wa2/wa2

Monet and Bastard (1982) Lammerts (1945); Rodriguez et al. (1994) Monet (1967) Lammerts (1945) Lammerts (1945); Chaparro et al. (1995)

Lownsberry and Thomson (1959); Sharpe et al. (1970); Lu et al. (2000)

Weinberger et al. (1943); Lu et al. (2000)

Mij/ Rm1/–

Leaf Foliar glands (E) Reniform Globose Eglandular

Salesses and Al-Kai (1985)

Monet and Massonié (1994)

7

6–8

Incomplete dominance

Connors (1921)

Genetics and Breeding

Graft incompatibility with Damas 1869 plum (I) Corky triangle (T)

High susceptibility to powdery mildew; serrate leaf margin Red incompletely dominant over green in leaves Blake (1937) and fruit skin ground colour Plant does not survive Bailey and French (1932) Scott and Cullinan (1942) Associated with very oblate fruit shape Ledbetter (1996) Chaparro et al. (1994) (Continued) 63

64

Table 3.1.

continued

Genotype

Flower Non-showy (Sh)

Sh/–

Large size (L)

L/-

Double (D1)

d1/d1

Fewer extra petals (Dm1, Dm2) Dark pink petal (P)

dm1/dm1 dm2/dm2 P/–

Red petal (R) Male sterility (from ‘J.H. Hale’) (Ps)

r/r ps/ps

Linkage groupa Note

1

2

More than five petals; often incompletely dominant; number of extra petals controlled by one or two recessive genes Dm1 and Dm2 are independent and additive

sr/sr S/– af/af Bf/–

Rough skin (Rs) Glabrous skin (nectarine) (G) Full red skin (Fr) Highlighter (H) White flesh (Y)

rs/rs g/g fr/fr h/h Y/–

Connors (1920); Bailey and French (1942); Lammerts (1945) Connors (1920); Lammerts (1945); Bailey and French (1949) Lammerts (1945)

Lammerts (1945); Yamazaki et al. (1987) Lammerts (1945)

6

Sometimes has some viable pollen

6 6

S/S is lethal (Guo et al., 2002)

Male sterility (from ‘White Glory’) (Ps2) ps2/ps2 Fruit Slow ripening (Sr) Saucer (flat) shape (S) Aborting fruit (Af)b Blood red flesh (Bf)

Reference

5

1

Pigment appears in immature fruit and main leaf vein; often smaller trees Matte skin surface; glabrous flower buds Fuzzless Only on fruit Red colour suppression on fruit skin Also affects calyx cup and leaf colour

Lammerts (1945); Chaparro et al. (1995) Connors (1926); Blake and Connors (1936); Scott and Weinberger (1944) Blake (1932); Werner and Creller (1997)

Ramming (1991) Lesley (1940) Dirlewanger et al. (2006) Blake (1932); Werner et al. (1998) Okie and Prince (1982); Okie (1988b) Blake (1932); Blake and Connors (1936) Beckman and Sherman (2003) Beckman et al. (2005) Connors (1920)

R. Monet and D. Bassi

Phenotype and symbol

Flesh texture and pit adherence (F)c Melting freestone Melting clingstone

Non-melting clingstone

Stony hard flesh (Hd)d

aDirlewanger

4

Bailey and French (1932, 1949); Monet (1989); Peace et al. (2005) Peace et al. (2005)

f/f f/f1 f/n f1/f1 f1/n n/n hd/hd hdhd/F hdhd/f1f1 D/– Sk/sk

Peace et al. (2005)

7

Stony hard, melting Stony hard, non-melting D for douce (sweet, in French)

Yoshida (1976); Scorza and Sherman (1996) Haji et al. (2005) Haji et al. (2005) Monet (1979) Werner and Creller (1997)

et al. (2004). ‘aborting fruit’ has been reported as a recessive trait causing the abortion of all fruits within 2 months after full bloom; since it co-segregates with flat fruit shape at the homozygous level (S/S), it is still not clear whether the ‘aborting fruit’ phenotype is regulated from the same locus or from a novel gene (Af). cFour alleles at the same locus controlling both flesh texture (endopolygalacturonase enzyme expression) and pit adherence; the fourth, null allele (n), has the same effect as the f1 allele (non-melting clingstone) (Peace et al., 2005). dThe independent inheritance of this trait was demonstrated, also suggesting an epistatic influence on the F locus, since the stony-hard, melting (hdhd/f–) phenotype is induced to soften when exogenous ethylene is applied (Haji et al., 2005). bThe

Genetics and Breeding

Low-acid flesh (D) Sweet kernel (Sk)

F/–

65

66

R. Monet and D. Bassi

markers have permitted establishment of these groups and the position of some of these genes on them (see Chapter 4). Nevertheless, the observation of characters in F2 families allowed determination in some cases of independent disjunction or linkage (Table 3.2) (Bailey and French, 1949; Monet, 1967; Monet and Bastard, 1972, 1983; Monet et al., 1985, 1988; Chaparro et al., 1995). Quantitative characters Characters with quantitative inheritance have great importance in selection, because they are often related to the economic value of the harvested fruit. Traits such as fruit size, fruit colour, ﬁrmness and taste were considered at the beginning of peach classical breeding. These traits have polygenic control and are inﬂuenced by environment changes. Within a population, their variation is not discrete but continuous. Thus, it is difﬁcult to know precisely the number of minor genes involved that control expression of the character. Quantitative genetics, which takes into account all of these speciﬁcities, is essentially mathematics. It works on population distribution graphs from which are compared the characteristics of central values (means) and the characteristics of dispersion (variances). It evaluates, for one character, the share that is attributable to gene function and that due to environmental effect. It also tries to predict the effect of one reproductive cycle on the character evolution. Finally, it provides a mathematical basis for selection to help breeders. Heritability (h) is one of them; it is deﬁned by the ratio of the variance attributable to additive effects of genes on the character (VA) to the phenotypic variance (VP), i.e. heritability in the narrow sense: h2 = VA/VP.

In some situations, the heritability of a character can be estimated by the coefﬁcient of regression between offspring to midparent: h2 = bPE.

In this case, if S is the applied level of selection on a quantitative character, the response

R is proportional to the regression coefﬁcient and then to heritability: R = bPE S = h2S.

If heritability is small, near zero, there will be no response. If it is near one, the response will be strong. Thus, for a breeder, the knowledge of the heritability of one character under selection is of major importance because it indicates if selection will be efﬁcient or not. For peach, Hansche et al. (1972) and Hansche and Boyton (1986a,b) estimated heritability of the main agronomic characters. The values they obtained are reported in Table 3.3.

Ploidy Peach is a diploid plant with 2n = 16 chromosomes. Sometimes in this species one can ﬁnd monoploids (or haploids) in progenies that have received only the basic chromosome number (n = 8). This set comes from the female parent, from which a cell of its embryo sac (oospore, generally) divides without fertilization and gives an embryo. Hesse (1971) made a detailed description of two monoploids obtained, by chance, in a progeny resulting from a cross between a nectarine and a canning clingstone peach. These trees were dwarf and possessed all the recessive characters of the female parent. Moreover, shoots were slender, with short internodes; leaves were narrow and long; ﬂowers and fruits were small. In ageing, the shoot cambium developed outgrowths which gave them a knotty appearance. Hesse (1971) also observed the pollen grain germination of these monoploids. The percentage of grains able to germinate was low (less than 7%). These viable grains would have the normal basic chromosome number. Toyama (1974) searched systematically for monoploids in peach seedlings, trying to isolate them before their germination. He focused on seeds with two embryos (one of which may have proceeded from a monoploid nonfertilized cell of the embryo sac). He obtained 16 monoploids, ﬁve of them from seeds with two embryos. For this result, he examined 20,053 seedlings which gave a relatively high

Table 3.2.

Linkages and independent disjunctions in peach. Corky Red Anthocyanin AnthoFoliar Non-showy/ Male White flesh/ Melting flesh/ Flat Weeping triangle leaves deficicient cyaninless glands showy flower sterility Nectarine yellow flesh non-melting flesh fruit

Low-acid Sweet Myzus flesh kernel resistance

Weeping Corky triangle Red leaves

Indt ??

Anthocyanin ?? deficient Antho?? cyaninless Foliar glands ??

??

??

??

Indt

??

??

??

??

??

Non-showy/ Indt showy flower Male sterility ??

??

??

Indt

??

Indt

??

??

??

??

Indt

??

Nectarine

??

??

??

??

??

Indt

??

White flesh/ Indt yellow flesh Melting flesh/ ?? non-melting flesh Flat fruit ??

Indt

??

??

??

Indt

Indt

Indt

Indt

??

??

Indt

??

Indt

Indt

??

??

Indt

??

??

??

??

??

??

Indt

??

Indt

??

Low-acid ?? flesh Sweet kernel ??

??

??

??

??

??

??

Indt

??

Indt

??

??

??

??

??

??

??

??

Link 12 cM ??

??

Link 30 cM ?? ??

Myzus resistance

Indt

??

??

??

??

Indt

??

??

??

??

??

Indt

Genetics and Breeding

??

Indt

??

??

Indt, independent; Link, linkage; ??, not observed.

67

68

Table 3.3.

R. Monet and D. Bassi

Estimates of heritability of major quantitative traits in peach.

Trait

Heritability

Full bloom Amount of ripening Ripening date Crop Fruit length Fruit cheek Fruit suture Fruit firmness Fruit acidity Soluble solids Juvenility (flower number) Intensity of browning

ratio (approximately 8 out of 10,000). Toyama obtained pure lines by doubling the chromosome number of some of these monoploids with colchicine. Pooler and Scorza (1995) observed the pollen grains of monoploid peach trees. Some of them, not reduced, were diploids and capable of germination. Thus it is possible to obtain triploid peach trees. We observed (R. Monet, unpublished results) that monoploid peach trees can give some fruits (Fig. 3.1/Plate 35). The seeds associated with these fruits were able to germinate and some were triploids; others were diploids and aneuploids. Triploids were vigorous but with little fertility; diploids, if they resulted from self-pollination (the monoploid parent was maintained in a greenhouse during ﬂowering but without protection), were pure lines; aneuploids, which have a chromosome in excess or in deﬁcit, were small plants with a very slow rate of development.

3.2 Peach Breeding First steps The ﬁrst peach cultivars to be developed resulted from chance seedlings that were isolated and propagated by grafting. In this way, each country has constituted a cultivar pool

0.39 0.38 0.84 0.08 0.31 0.26 0.29 0.13 0.19 0.01 0.16 0.35

Reference Hansche et al. (1972) Hansche et al. (1972) Hansche et al. (1972) Hansche et al. (1972) Hansche et al. (1972) Hansche et al. (1972) Hansche et al. (1972) Hansche et al. (1972) Hansche et al. (1972) Hansche et al. (1972) Hansche and Boyton (1986a) Hansche and Boyton (1986b)

whose richness has increased continually with new discoveries and germplasm exchanges. By the 18th century, ‘physiocrats’ of a French economics school considered agriculture as a unique source of ‘net product’. They originated important literature to describe the best agricultural practices and make inventories of the best productive genetic material. The ﬁrst pomologies were compilations of all the available fruit cultivars with their main characters, their agronomical interest and their organoleptic qualities. Each country with an orcharding tradition has established cultivar records whose content has increased continually. In France, the Duhamel du Monceau (1768) pomology book described 42 peach cultivars; one century later, the one of Leroy (1879) described 143 cultivars. Attempts at classiﬁcation based on the main botanical characters were also made. For example, De Mortillet (1865) made a dichotomous classiﬁcation of peach cultivars depending on whether they had epidermal fuzz or not, whether they were freestone or clingstone, whether their ﬂowers were large, medium or small and whether their foliar glands were reniform, circular or absent. In the USA, Downing’s pomology (1866) described 136 cultivars. It mentioned, probably for the ﬁrst time in fruit culture, hybridization as a new method to obtain varieties: Cross-breeding is then nothing more than removing out of the blossom of the fruit tree

Genetics and Breeding

Fig. 3.1.

69

A monoploid peach with some fruits.

the stamens, or male parent, and bringing those of another, and different variety of fruit, and dusting the pistil of female parent with them, – a process sufﬁciently simple, but which has the most marked effect on the seeds produced. It is only within about ﬁfty years that cross breeding has being practiced.

Hedrick’s pomology (1917) describes cultivars such as ‘J.H. Hale’, ‘Elberta’ and ‘Chinese Cling’, which were extensively used in the ﬁrst peach breeding programmes. Pomological records provide the ﬁrst step in the search and inventory of the best fruit genetic material, but they do not have innovative capacity. When Hedrick published his pomology in the USA, the ﬁrst peach breeding programmes were already initiated (Connors, 1917), and their contribution signiﬁcantly modiﬁed the available cultivar assortment worldwide.

Objectives One can criticize the ﬁrst generation of breeders for their emphasis on improvement of commercial characteristics of the fruit such as

colour, ﬁrmness and attractiveness while not focusing on taste, hardiness or their adaptation to economically efﬁcient growing systems. The improvement of commercial characteristics was nevertheless necessary, because old cultivars were not very attractive, unsuitable for handling and shipping and did not satisfy commercial requirements. Today one can consider these defects almost completely corrected. Some 30 years ago, breeders developed objectives which had interest for consumers and growers. These innovative objectives are presented below (Childers, 1975; Monet, 1995; see also Chapters 5, 6 and 7). Reduction of production costs A cultivar has low production costs if it is well adapted to the place where one cultivates it. If it is not adapted, conditions favourable to its culture must be obtained artiﬁcially, and that will increase costs. Adaptation to climatic factors has been and continues to be an objective of some breeding programmes, like obtaining hardiness of dormant buds for northern-limit zones of peach culture as in

70

R. Monet and D. Bassi

the Great Lakes region in Canada (Layne, 1982) and Michigan and New York in the USA (Callahan et al., 1991), or creating low-chill cultivars for subtropical regions as in Florida, Texas (Sherman and Rodriguez-Alcazar, 1987) and Georgia (Krewer et al., 1997) in the USA and Rio Grande do Sul in Brazil (Nakasu et al., 1981). Also interesting are the projects whose goal is to improve disease and pest resistance. The reduction of spray applications is desirable because they reduce production costs and environmental contamination. Indeed genetic engineering could bring, in the near future, original and rapid solutions for problems of pest and disease resistance. However, consumers are still reluctant in using food products derived from transformed plants, the so-called ‘genetically modiﬁed organisms’. Using a classical approach, many breeding programmes have attempted to improve peach pest and disease resistance. ●

●

Bacterial leaf spot (Xanthomonas campestris) in the USA (Werner et al., 1986). Brown rot (Monilinia fruticola Aderh. et Ruhl. (Honey)) in the USA (Gradziel et al.,

Fig. 3.2.

A weeping tree trained in central axis.

●

●

●

●

1997) and Europe (Pascal et al., 1994; Bassi et al., 1998). Cytospora canker (Leucostoma personii and Leucostoma cincta) in the USA (Chang et al., 1989) and Italy (Liverani and Fideghelli, 1993). Green peach aphid (Myzus persicae) in France (Monet et al., 1997; Pascal et al., 1997) and Italy (Liverani and Fideghelli, 1993; Bassi et al., 1994). Leaf curl (Taphrina deformans) in the USA (Scorza, 1992) and Italy (Bellini et al., 1993). Powdery mildew (Spherotheca pannosa) in France (Pascal, 1990) and Italy (Liverani and Fideghelli, 1993).

One can reduce production costs with the use of cultivars whose tree size and shape are naturally adapted to the growing system. Thus, breeding efforts to develop dwarf trees for high-density plantings (Fideghelli et al., 1979; Hansche, 1988; Liverani and Fideghelli, 1993), ‘pillar’ (columnar) trees for tree–wall systems (Scorza et al., 1989) and weeping trees (Fig. 3.2/Plate 36) for central leader pruning (Monet et al., 1988) have been explored.

Genetics and Breeding

Diversification for the consumer Consumers like variation in their food choices. To bring diversity, peach breeders draw on Mendelian genetic variability. In the past, white- or yellow-ﬂeshed peaches only could be found in markets but now both are available. Then, from the 1960s, came nectarines. New Mendelian characters that modify other fruit attributes and taste are being introduced. The ﬂat peach character has been the object of several breeding programmes, e.g. in the People’s Republic of China, France (Monet et al., 1985), Italy and the USA (Sherman and Lyrene, 2001). Bloodﬂeshed peaches and nectarines are being developed in France (T. Pascal, Avignon, 1995, personal communication) and in the USA (Okie, 1988a). Conversely, anthocyaninless

71

nectarines have been created in the USA (Okie, 1988a). Canning clingstone anthocyaninless nectarines are also the objective of a breeding programme in Italy (Bellini et al., 1994) and the USA. All of these Mendelian characters can be recombined. For example, the ‘honey’ character (low-acid), very popular only in the Far East countries, has been introduced also in breeding programmes in Europe and the USA. It permits the harvest of fruit earlier without adversely affecting the taste. Combining ﬂat, low-acid and nectarine, a sweet, ﬂat nectarine (‘platerine’) has been obtained (Fig. 3.3/Plate 37). In the same way, the introduction of the nonmelting ﬂesh character in cultivars for the fresh market gives the possibility of harvesting the fruits near maturity at their optimal

Fig. 3.3. Flat nectarines (‘platerines’ in French).

72

R. Monet and D. Bassi

quality and taste with greater durability for handling and transport to distant markets. Finally, these numerous projects are likely to bring innovations in peach culture with more interest for growers and consumers. This represents a change in emphasis compared with the breeding for commercial and horticultural objectives only.

Floral biology and selection cycles Although peach is preferentially autogamous, there is no impediment to intraspeciﬁc crossing. The breeder can include in a selection scheme self-pollination and intraspeciﬁc crosses. This is an ideal situation; the sole break of progression is the 3-year sexual cycle. Seedlings bear their ﬁrst harvest from 2 to 3 years after obtaining the seeds, depending on climatic and cultivation conditions. For further details also see Chapter 1.

Parental choice: phenotypic This very simple method is always used in private breeding programmes. It consists of crossing two individuals which present complementary phenotypic characters. For example, one can cross a cultivar with soft-ﬂeshed fruit but whose epidermis is very coloured with a cultivar with ﬁrm-ﬂeshed fruit but whose epidermis is little coloured in the hope of obtaining, in the progeny, individuals with ﬁrm ﬂesh and very coloured skin. This method has led to improvement of most of the fruit characters, especially those in relation to their commercial attributes. Some breeders also cross the best cultivars available at the time to obtain better recombinations. This method has several advantages. ●

●

●

Methodology

It is simple and fast, since it does not use long-term schemes. The majority of characters of interest have quantitative inheritance with high heritability. Working with large families increases one’s chance to obtain favourable combinations.

Nevertheless, it has some disadvantages. Peach cultivars are clones, propagated by grafting. Thus, the simplest selection methods can give results as good as the more complex. An exceptional recombination may occur by chance, resulting in a tree that possesses the required commercial attributes. This tree then can become the mother tree, from which one can cut scions necessary for its multiplication to be perpetuated in space and time. To obtain this mother tree, one can utilize mutagenesis, polyploidization or character recombination by inter- or intraspeciﬁc sexual reproduction. Mutagenesis, polyploidization and interspeciﬁc sexual reproduction have been used very little in peach breeding; results obtained by these methods have been largely unsatisfactory. Alternatively, recombinations obtained by intraspeciﬁc cross-breeding have allowed noteworthy improvements of the species and continue to supply most of the replacement cultivars. The general breeding schemes (see Monet, 1995; Scorza and Sherman, 1996) are more or less complicated and are presented below.

●

●

The repeated use of the best cultivars leads to phenotypic homogeneity (e.g. in the market, peaches become more and more similar). This is the result of their genotypic homogeneity, a consequence of the close parentage of their progenitors. A phenotype results from the additive effect of genes plus the genetic interactions (dominance and epistasis effects), so that the choice of two parents on their phenotypic value alone can result in progenies without interest. While individual breeders may gain empirical experience after the observation of many crosses, they may not like to share this information with other breeders (particularly in the private sector).

Parental choice: genotypic To really know the genetic value of a parent, it is necessary to observe its progeny. In peach, the possibility to do self-pollination permits an accurate evaluation of this value. It provides

Genetics and Breeding

valuable information on its heterozygous state (the more the progeny is heterogeneous, the more the parent is heterozygous). It informs also on its capacity to transmit important horticultural characters. To conduct self-pollination of progenitors before crossing could permit a better choice of parents. In fact this is not often done because it lengthens the breeding process by a new sexual cycle. Monet (1995) tried to obtain pure lines with peach using a genotypic choice of the parents. The method is as follows. Many cultivars of great interest are selfpollinated simultaneously; the observation of the obtained families permits the elimination, between these parents, of those with insufﬁcient value. In each of the remaining progenies, two of the best individuals are chosen (or more,

●

●

Starting parents

A

●

73

but it increases the work load), which are self-pollinated; the comparison of the two obtained families permits an elimination of the less interesting individual and its family. In the family resulting from the bestperforming individual, the two best individuals are self-pollinated to choose the parents of the next generation, and so on.

This process (Fig. 3.4/Plate 38) has been followed during six generations for one parent and less (three to ﬁve) for eight others. After six self-pollination cycles, the resemblance between individuals is more and more strong and shows that we are near the pure line. The inbreeding depression is light probably because peach is preferentially an autogamous species. The cross between individuals taken from

B

C

Self-pollination

G1 Parent eliminated

Self-pollination

Self-pollination

Family treated like A to obtain a new pure line

G2 Parent eliminated

Self-pollination

Self-pollination

G3

Self-pollination

Self-pollination

Parent eliminated

G4 Fig. 3.4. Scheme based on genotypic choice of parents to obtain pure lines. In each generation, parents giving progenies with low horticultural value are eliminated.

74

R. Monet and D. Bassi

families with three self-pollination cycles gave families with good agronomic performances and this process led to the elimination of individuals without agronomic interest. However, intercrossing pure lines obtained by repeated self-pollination (Lesley, 1957) or pure lines obtained by doubling the chromosome number of monoploids (Scorza and Pooler, 1993) shows that there are no important heterosis effects with peaches. Therefore, the use of pure lines can be reserved for theoretical research but has little agronomic interest. Character of Mendelian inheritance The goal of many current breeding programmes is to create cultivars which possess a particular character with Mendelian inheritance. These characters do not change from one generation to the next. If they are dominant they are present in each generation; if they are recessive, they can disappear by cross-breeding, but they will reappear after self-pollination. The breeder is in a particularly comfortable situation. The main difﬁculty in these programmes results from the fact that the parent that brings the Mendelian character could be near the wild state and produce fruits that are neither edible nor marketable and also can present important horticultural defects. It is only after several recurrent crosses with an improved cultivar that these defects will be eliminated. Self-pollination exploits recombinations and recessive characters, while intra- and interspeciﬁc crossing permits the introduction of new characters within the genetic pool under selection. Figure 3.5 shows a breeding scheme used to introduce the resistance to green aphid using a monogenic dominant resistance found in a weeping ornamental peach. It employs alternation of self-pollination and crossing. Five generations were required to obtain the ﬁrst marketable selections, more than 20 years after the beginning of the programme.

Technique Breeding techniques have been described in detail by Hesse (1975); below we recall only the main operations followed in peach.

Operations during flowering Peach ﬂowers, being hermaphroditic and self-fertile, require emasculation of the ﬂowers of the female parent before pollination. Emasculation takes place at balloon stage, i.e. some days before ﬂower opening (for non-showy ﬂowers, because anthers emerge beyond the petals, it should be ensured that none of them are open before emasculation is initiated). With tweezers, the part of the ﬂoral receptacle that bears the anthers, sepals and petals is eliminated (Fig. 3.6/Plate 39). After emasculation, all that remains is the pistil and a little piece of the ﬂoral receptacle. An emasculated ﬂower does not attract insects; thus out-crossing is rare and usually it is not necessary to protect a tree where all ﬂowers are emasculated. However, for genetic studies, to be sure that there are no accidental pollinations by wind or insects (i.e. honeybees; Fig. 3.7/Plate 40), a cage with a ﬁne grid can be placed over the tree, which will be maintained during ﬂowering of the neighbouring trees. The male parent will provide the desired pollen. Flowers are harvested at the balloon stage (when anthers are not dehiscent). With tweezers the ﬂowers are opened; the anthers are removed and placed in a Petri dish which is maintained in a dry place or in a desiccator with anhydrous calcium sulfate to obtain dehiscence. Dry pollen can be stored for up to 2 years in a refrigerator at –30°C or for many years at –80°C. Pollination of the female parent can be done 24–48 h after emasculation. Pollen, collected from the anthers of the male parent (Fig. 3.8/Plate 41), is brought with a brush (or by ﬁngertip) (Fig. 3.9/Plate 42) and applied to the stigmas of emasculated ﬂowers. To save pollen, glass rods could be used to apply pollen on to pistils.

CROSSING PROCEDURES.

SELF-POLLINATION. This results from the natural transfer of pollen from dehiscent anthers to the stigma of the same ﬂower. It is not necessary to intervene by hand to obtain self-pollination, even if it could improve pollen transport on to the stigma and then fruit yield. Before ﬂowering, branches can be wrapped with waterproof paper bags (Fig. 3.10/Plate 43) or the

Genetics and Breeding

Starting parents

Redhaven

75

Weeping ornamental peach

clone S1161

clone S2678

Self-pollination

Self-pollination

F0 Family (1971)

S1161: (167 trees)

S2678: (55 trees)

Parents of 1st cycle

S1161: 12

S2678: 47

Cross-pollination F1 Family (1975)

S(1161:12 x 2678:47) (2 trees)

Parent of 2nd cycle

S(1161:12 x 2678:47)1

Self-pollination F2 Family (1981)

Parents of 3rd cycle

S(1161:12 x 2678:47)1: (55 trees)

S(1161:12 x 2678:47)1: 55

Early Sungrand clone S3965

Cross-pollination F3 Family (1987)

S[(1161:12 x 2678:47)1: 55 x 3965] (64 trees)

Parent of 4th cycle

S[(1161:12 x 2678:47)1: 55 x 3965] 56

Self-pollination F4 Family (1991)

S[(1161:12 x 2678:47)1: 55 x 3965] 56: (64 trees)

In 1994, two selections (trees nr. 5 and nr. 14) were retained in this F4 family for evaluation

Fig. 3.5. Scheme used for the development of cultivars resistant to green aphid, Myzus persicae. (From Monet, 1995.)

whole tree can be protected by an insect-proof cage. These barriers against accidental pollinations are removed when ﬂowering is completed. Raising seedlings Pollinated ﬂowers give fruits and seeds. When these seeds have a normal development, as in

medium- and late-ripening trees, germination can be easily attained without difﬁculty by humid stratiﬁcation at 0–4°C for 3 months, in order to overcome dormancy. Seeds are placed (better without the pit, to improve and speed germination) in moist sand, poured into bags (alternatively, into sealed Petri dishes with moist paper) and stored in a cold room at 0–4°C. After 3–5 months, germination occurs,

76

R. Monet and D. Bassi

Fig. 3.6.

Emasculated flower (on left). (Courtesy of W.R. Okie, Byron, Georgia, USA.)

Fig. 3.7.

Pollination by honeybee. (Courtesy of D.R. Layne, Clemson, South Carolina, USA.)

Genetics and Breeding

77

Fig. 3.8. Dehydrated stamens ready for artificial pollination: anthers and filaments render the pollen less sticky.

Fig. 3.9.

Emasculated flower pollinated by finger, a fast way for cross-breeding.

78

R. Monet and D. Bassi

Fig. 3.10.

Self-pollination with waterproof paper bags.

a young root appears out of the seeds and the germinated seeds are transplanted in the greenhouse. When seeds are insufﬁciently developed (for seeds obtained from mother parents which ripen their fruits less than about 110–120 days after ﬂowering), embryos of these seeds have little reserves and are too weak to germinate in normal stratiﬁcation; embryo culture should be used to germinate them. Embryo culture in vitro avoids bacterial or fungal contamination, prevents rapid dehydration, and provides essential nutrients to the embryo. In practice, the different steps of this technique are as follows. ●

●

Fruits are harvested at the veraison stage (before physiological ripening), their ﬂesh is removed, seeds are removed from the pits and their integuments are sterilized in a solution of calcium hypochlorite (8 g calcium hypochlorite in 20 ml water, 20 min of stirring, ﬁltration) for 10 min and then washed in sterile water. Inside a sterile room the embryo is extracted from the seed; with a sterile pair of tweezers, the integuments of the seed are removed and the embryo is separated from the endosperm, then it is placed in a ﬂask or test-tube with the nutritive medium.

●

●

The ﬂasks containing the embryos are placed in a cold room at 0°C for 1 month to eliminate dormancy and then taken to a growing room (at 22–24°C). When their development is sufﬁcient (Fig. 3.11/Plate 44), they are transplanted in a greenhouse.

A comprehensive review on embryo culture in fruit breeding was given by Ramming (1990). Obtained by classical stratiﬁcation or by embryo culture, seedlings continue their growth in a greenhouse during winter. At the end of the dormant season, they can be transplanted in the orchard. Plantation distances vary from one breeder to another. Some prefer high densities of 0.5 m × 1 m, others prefer a wider spacing of 2 m × 5 m. High density induces competition between trees and reduces fruit quality, making it more difﬁcult for the breeder to choose the best individuals (Fig. 3.12/Plate 45). Seedling evaluation and selection Sexual reproduction results in the genetic recombination of characters. Thus, between individuals from the same family issued from a cross or a self-pollination, there is a variability

Genetics and Breeding

79

Fig. 3.11. Young seedling at the end of embryo culture.

Fig. 3.12.

Seedling orchard at first flowering.

80

R. Monet and D. Bassi

associated with genetic effects and, for quantitative characters, there is also a variability associated with environmental effects. The problem for the breeder is how to choose the best recombinant. For Mendelian characters, selection in a progeny is straightforward; the breeder has two simple options: presence or absence of the character. For quantitative characters, the choice is more difﬁcult, and a good deﬁnition of selection criteria is fundamental. Measuring the character is, in this case, a great advantage because it suppresses all subjective inﬂuences. Finally, for pest and disease resistance, there is a need for careful evaluation of tree contamination and damage assessment that is speciﬁc for each pest and disease. The selection criteria depend on the breeder’s objectives but some must be considered intangible. A cultivar has no chance to have great success if it does not respond to them. They can be of horticultural importance like the degree of fertility (yield). Overall, commercial attributes are essential: fruits should be attractive, ﬁrm and have good taste. To these basic objectives are associated speciﬁc objectives (introduction of a new character, a disease resistance, etc.) that justify the breeding programme. For individuals of families under selection, it is essential to record the value for each important character. The simplest method is recording in a notebook; but, today, many electronic devices are available that permit transfer of data to the computer for data processing. A breeder has the tendency to focus on some characters more than others and may forget that a cultivar is a compromise between horticultural and commercial attributes. To avoid this drawback, a selection index (I) could be established. The simplest is to calculate, for each tree of the family, the sum of products of the value given to each character (C) included in the index by a coefﬁcient (n) reﬂecting its importance: I = C1n1 + C2n2 + . . .

Trees with the highest index will be selected for in the next generation (or eventually assessed as potential new cultivars).

Release of a new cultivar When the level of improvement is sufﬁcient, the breeder possesses within his families individuals with the potential to become new cultivars. Trees can be propagated by grafting for a comparative test with cultivars of the same period of maturity. This test is essential to avoid mistakes because a judgement based on one individual within a family is not the same as when this individual is grafted. The comparative test must be simple; a statistical plan is not necessary. For example, two grafted trees from each advanced selection will be placed side by side with two grafted trees of the reference cultivar. The new advanced selection can be easily compared with the reference trees. At the present time, it is also important to evaluate the sanitary state of the future new cultivar. Bud sticks or leaves should be taken from the original tree and used for laboratory tests to detect viruses and phytoplasmas that can be transmitted by grafting. For peach, the tests may search specially for: Plum pox virus, the family of Isometric Labile Ringspot virus, Nematode polyhedric virus and European stone fruit yellows phytoplasma. If the plant is healthy, it is recommended to keep some copies of it inside an insect-proof repository to preserve a source of buds with their original qualities. If it is contaminated, it is better to eliminate it because the success of virus or phytoplasma therapies is not assured, even though for selections of particular interest efforts could be justiﬁed in order to obtain a healthy tree. However, the basis of vegetative propagation of the new cultivar will come from healthy plants. To create a new variety is expensive and justiﬁes a return on the investment. This needs legal protection. In the past, commercial patenting was done only by private breeders. Today, cultivars from public programmes are also being patented. The conditions of patenting are different from one country to another. In the USA patenting a cultivar has the same value as patenting an industrial process. In Europe, a new cultivar receives a certiﬁcate (Certiﬁcat d’Obtention Varietale) that has approximately the same value as a patent. To be patented a cultivar

Genetics and Breeding

must be original (not a copy of another existing cultivar) and healthy. The legal protection lasts 20 years; it covers its phenotype only but there is a strong demand for an extension to the genotype. The release of a new cultivar is always a point of satisfaction for the breeder because it gives evidence of the success of the project. However, the commercial success of a new cultivar depends on many factors: its agronomic value can be negated by a defect that may become evident only in the orchard. New peach cultivars have a short lifespan: 10 to 20 years approximately. If we compare this duration with that needed to create a truly innovative cultivar (20 years on average), one can say that it is an ungrateful job. However,

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some cultivars retain their commercial usefulness for many years, e.g. ‘Redhaven’, but they tend to be the exception rather than the rule. The problem lies in the fact that the breeder is often aiming at a moving target. While the new cultivar may have successfully combined the desired characters that were sought when the programme was initiated, the cultivar requirements of the market may have changed during the 15–20-year period in which the cultivar was being developed. Thus, the new cultivar may not meet the existing market requirements when released. This is an inherent risk in peach breeding, but the evidence of genetic advancement in new peach cultivars compared with older ones shows that it is a risk well worth taking.

References Bailey, J.S. and French, A.P. (1932) The inheritance of certain characters in the peach. Proceedings of the American Society for Horticultural Science 29, 127–130. Bailey, J.S. and French, A.P. (1942) The inheritance of blossom type and blossom size in the peach. Proceedings of the American Society for Horticultural Science 40, 248–250. Bailey, J.S. and French, A.P. (1949) The inheritance of certain fruit and foliage characters in the peach. Massachusetts Agricultural Experiment Station Bulletin 452. Bassi, D. and Rizzo, M. (2000) Peach breeding for growth habit. Acta Horticulturae 538, 411–414. Bassi, D., Liverani, A. and Rizzo, M. (1994) Il miglioramento genetico del pesco in Emilia Romagna: risultati e prospettive. Rivista di Frutticoltura 1, 11–23. Bassi, D., Rizzo, M. and Cantoni, L. (1998) Assaying brown rot (Monilinia laxa Aderh. et Ruhl. (Honey)) susceptibility in peach cultivars and progeny. Acta Horticolturae 465/2, 715–721. Beckman, T.G. and Sherman, W.B. (2003) Probable qualitative inheritance of full red skin color in peach. HortScience 38, 1184–1185. Beckman, T.G., Rodriguez Alcazar, J., Sherman, W.B. and Werner, D.J. (2005) Evidence for qualitative suppression of red skin color in peach. HortScience 40, 523–524. Bellini, E., Surico, G., Mugnai, L., Natarelli, L. and Nencetti, V. (1993) Osservazioni su una progenie di pesco resistente a Taphrina deformans (Berck. Tul.). Italus Hortus 1, 11–13. Bellini, E., Giannelli, G., Giordani, E. and Sabbatini, I. (1994) Costituzione di nettarine a polpa bianca e di percoche a buccia liscia. Rivista di Frutticoltura 4, 23–37. Bielenberg, D.G., Wang, Y., Fan, S., Reighard, G.L., Scorza, R. and Abbott, A.G. (2004) A deletion affecting several gene candidates is present in the evergrowing peach mutant. Journal of Heredity 95, 436–444. Blake, M.A. (1932) The J.H. Hale peach as a parent in peach crosses. Proceedings of the American Society for Horticultural Science 29, 131–136. Blake, M.A. (1937) Progress in peach breeding. Proceedings of the American Society for Horticultural Science 35, 49–53. Blake, M.A. and Connors, C.H. (1936) Early results of peach breeding in New Jersey. New Jersey Agricultural Experiment Station Bulletin 599. Callahan, A., Scorza, R., Morgens, P., Mante, S., Cordts, J. and Cohen, R. (1991) Breeding for cold hardiness: searching for genes to improve fruit quality in cold-hardy peach germplasm. HortScience 26, 522–526. Chang, L.S., Lezzoni, A., Adams, G. and Howell, G.S. (1989) Leucostoma personii, tolerance and cold hardiness among diverse peach genotypes. Journal of the American Society for Horticultural Science 114, 482–485. Chaparro, J.X., Werner, D.J., O’Malley, D. and Sederoff, R.R. (1994) Targeted mapping and linkage analysis of morphological, isozyme, and RAPD markers in peach. Theoretical and Applied Genetics 87, 805–815.

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Chaparro, J.X., Werner, D.J., Whetten, R.W. and O’Malley, D.M. (1995) Inheritance, genetic interaction, and biochemical characterisation of anthocyanin phenotypes in peach. Journal of Heredity 86, 32–38. Childers, N.F. (1975) The Peach. Horticultural Publications, New Brunswick, New Jersey, 659 pp. Connors, C.H. (1917) Methods in breeding peaches. Proceedings of the American Society for Horticultural Science 14, 126–127. Connors, C.H. (1920) Some notes on the inheritance of unit characters in the peach. Proceedings of the American Society for Horticultural Science 1919 16, 24–36. Connors, C.H. (1921) Inheritance of foliar glands of the peach. Proceedings of the American Society for Horticultural Science 18, 20–26. Connors, C.H. (1926) The sterility of ‘J.H. Hale’. New Jersey Agriculture Experimental Station Annual Report (1925) 46, 90–91. De Mortillet, M.P. (1865) Les meilleurs fruits. Le pêcher. Prudhomme et Giroud, Grenoble, France. Dirlewanger, E., Graziano, E., Joobeur, T., Garriga-Caldere, F., Cosson, P., Howad, W. and Arùs, P. (2004) Comparative mapping and marker-assisted selection in Rosaceae fruit crops. Proceedings of the National Academy of Sciences USA 101, 9891–9896. Dirlewanger, E., Cosson P., Boudehri, K., Renaud, C., Capdeville, G., Tauzin, Y., Laigret, F. and Moing, A. (2006) Development of a second generation genetic linkage map for peach [Prunus persica (L.) Batsch.] and characterization of morphological traits affecting flower and fruit. Tree Genetics & Genome 1, 1–13. Downing, C. (1866) The Fruits and Fruit Trees of America. Wiley, New York. Duhamel du Monceau, M. (1768) Traité des arbres fruitiers. Tome 2. Le pêcher. Saillant, Paris. Fideghelli, C., Della Strada, G., Quarta, R. and Rosati, P. (1979) Genetic semi-dwarf peach selections. In: Proceedings of Eucarpia Fruit Section Symposium, Tree Fruit Breeding. INRA, Angers, France, pp. 3–7. Gradziel, T.M., Thorpe, M.A., Bostock, R.M. and Wilcox, S. (1997) Breeding for brown rot (Monilinia fructicola) resistance in clingstone peach with emphasis on the role of fruit phenolics. Acta Horticulturae 465, 161–170. Guo, J., Jang, Q., Zhang, K., Zhao, J. and Yang, Y. (2002) Screening for molecular marker linked to saucer gene of peach fruit shape. Acta Horticulturae 592, 267–271. Haji, T., Yaegaki, H. and Yamaguchi, M. (2005) Inheritance and expression of fruit texture melting, non-melting and stony hard in peach. Scientia Horticulturae 105, 241–248. Hansche, P.E. (1988) Two genes that induce brachytic dwarfism in peach. HortScience 23, 604–606. Hansche, P.E. and Boynton, B. (1986a) Heritability of juvenility in peach. HortScience 21, 1195–1197. Hansche, P.E. and Boynton, B. (1986b) Heritability of enzymatic browning in peaches. HortScience 21, 1197– 1198. Hansche, P.E., Hesse, C.O. and Beres, V. (1972) Estimate of genetic and environmental effects on several traits in peach. Journal of the American Society for Horticultural Science 97, 9–12. Hedrick, U.P. (1917) The Peaches of New York. J.B. Lyon Company, Albany, New York. Hesse, C.O. (1971) Monoploid peaches, Prunus persica L. Batsch: description and meiotic analysis. Journal of the American Society for Horticultural Science 96, 326–330. Hesse, C.O. (1975) Peaches. In: Janick, J.J. and Moore, J.N. (eds) Advances in Fruit Breeding. Purdue University Press, West Lafayette, Indiana, pp. 285–335. Krewer, G., Beckman, T.G. and Sherman, W.B. (1997) Moderate chilling peach and nectarine breeding and evaluation program at Attapulgus, Georgia. Acta Horticulturae 465, 171–175. Lammerts, W.E. (1945) The breeding of ornamental edible peaches for mild climates. I. Inheritance of tree and flower characters. American Journal of Botany 32, 53–61. Layne, R.E.C. (1982) Cold hardiness of peaches and nectarines following a test winter. Fruit Varieties Journal 36, 90–98. Ledbetter, C.A. (1996) Characterization and inheritance of the crinkle-leaf trait in peach and peach–almond hybrids. Journal of Genetics and Breeding 50, 5–60. Leroy, A. (1879) Dictionnaire de pomologie. Tome VI. Fruits à noyau. Goin, Paris. Lesley, J.W. (1940) A genetic study of saucer fruit shape and other characters in the peach. Proceedings of the American Society for Horticultural Science 37, 218–222. Lesley, J.W. (1957) A genetic study of inbreeding and of crossing inbred lines in peaches. Proceedings of the American Society for Horticultural Science 70, 93–103. Liverani, A. and Fideghelli, C. (1993) Il miglioramento genetico del pesco: risultati e prospettive. Rivista di Frutticoltura 5, 11–21. Lownsberry, B.F. and Thomson, I.J. (1959) Progress in nematology related to horticulture. Proceedings of the American Society for Horticultural Science 74, 730–746.

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Lu, Z.X., Reighard, G.L., Nyczepir, A.P., Beckman, T.G. and Ramming, D.W. (2000) Inheritance of resistance to root-knot nematodes (Meloidogyne sp.) in Prunus rootstocks. HortScience 35, 1344–1346. Mehlenbacher, S.A. and Scorza, R. (1986) Inheritance of growth habit in progenies of ‘Com-Pact Redhaven’ peach. HortScience 21, 124–126. Monet, R. (1967) Contribution à l’étude génétique du pêcher. Annales de l’Amélioration des Plantes 17, 5–11. Monet, R. (1979) Transmission génétique du caractère ‘fruit doux’ chez le pêcher. Incidence sur la sélection pour la qualité. In: Proceeedings of Eucarpia Fruit Section Symposium. Tree Fruit Breeding. INRA, Angers, France, pp. 273–276. Monet, R. (1989) Peach genetics: past, present and future. Acta Horticulturae 254, 49–57. Monet, R. (1995) Il miglioramento genetico del pesco. In: Bellini, E. (ed.) Proceeding of the International Symposium ‘State of the Art and Perspectives of World Genetic Improvement of Fruit Tree Species’. ERSO, Faenza, Italy, pp. 13–27. Monet, R. and Bastard, Y. (1972) Contribution à l’étude du contrôle génétique de quelques caractères morphologiques chez le pêcher. Annales de l’Amélioration des Plantes 22, 399–403. Monet, R. and Bastard, Y. (1982) Une anomalie du fonctionnement de l’apex à hérédité mendélienne chez le pêcher (Prunus persica (L.) Batsch). Agronomie 2, 103–106. Monet, R. and Bastard, Y. (1983) Nouveaux cas de ségrégation indépendante de caractères mendéliens chez le pêcher. Agronomie 3, 387–390. Monet, R. and Massonié, G. (1994) Déterminisme génétique de la résistance au puceron vert (Myzus persicae) chez le pêcher. Résultats complémentaires. Agronomie 2, 177–182. Monet, R. and Salesses, G. (1975) Un nouveau mutant de nanisme chez le pecher. Annales de l’Amélioration des Plantes 25, 353–359. Monet, R., Bastard, Y. and Gibault, B. (1985) Etude génétique et amélioration des pêches plates. Agronomie 5, 727–731. Monet, R., Bastard, Y. and Gibault, B. (1988) Etude génétique du caractère ‘port pleureur’ chez le pêcher. Agronomie 8, 127–132. Monet, R., Guye, A. and Massonié, G. (1997) Breeding for resistance to green aphid, Myzus persicae Sulzer. Acta Horticulturae 465, 171–175. Nakasu, B., Bassols, M. and Feliciano, A. (1981) Temperate fruit breeding in Brazil. Fruit Varieties Journal 35, 114–122. Okie, W.R. (1988a) USDA peach and nectarine breeding at Byron, Georgia. In: Childers, N. and Sherman, W. (eds) The Peach. Horticultural Publications, Gainesville, Florida, pp. 51–56. Okie, W. R. (1988b) Preliminary descriptions of five new peach genes. Acta Horticulturae 465, 107–110. Okie, W.R. and Prince, V.E. (1982) Surface features of a novel peach × nectarine hybrid. HortScience 17, 66–67. Pascal, T. (1990) Etude de la résistance à l’oïdium (Spherotheca pannosa) chez le pêcher (Prunus persica L. Batsch). MSc. thesis, University of Montpellier, Montpellier, France. Pascal, T., Levigneron, A., Kervella, J. and Nguyen-The, C. (1994) Evaluation of two screening methods for resistance of apricot, plum and peach to Monilinia laxa. Euphytica 77, 19–23. Pascal, T., Kervella, J., Pfeiffer, F.G., Sauge, M.H. and Esmenjaud, D. (1997) Evaluation of the interspecific progeny Prunus persica cv. Summergrand × Prunus davidiana for disease resistance and some agronomic features. Acta Horticulturae 465, 185–191. Peace, C.P., Crisosto, C.H. and Gradziel, T.M. (2005) Endopolygalacturonase: a candidate gene for freestone and melting flesh in peach. Molecular Breeding 16, 21–31. Pooler, M.R. and Scorza, R. (1995) Occurrence of viable eggs in haploid peach. Fruit Varieties Journal 49, 239–241. Ramming, D.W. (1990) The use of embryo culture in fruit breeding. HortScience 25, 393–398. Ramming, D.W. (1991) Genetic control of a slow-ripening fruit trait in nectarine. Canadian Journal of Plant Science 71, 601–603. Rodriguez, A.J., Sherman, W.B., Scorza, R. and Wisniewski, M. (1994) ‘Evergreen’ peach, its inheritance and dormant behavior. Journal of the American Society for Horticultural Science 119, 789–792. Salesses, G. and Al-Kai, N. (1985) Simply inherited grafting incompatibility in peach. Acta Horticulturae 173, 57–62. Sansavini, S., Bassi, D. and Gamberini, A. (2006) Peach breeding, genetic and new cultivar trends. Acta Horticulturae 713, 23–52. Scorza, R. (1992) Evaluation of foreign peach and nectarine introductions in the US for the resistance of leaf curl (Taphrina deformans Berck. Tul.). Fruit Varieties Journal 46, 141–145.

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Scorza, R. and Pooler, M. (1993) Development and testing of F1 hybrid peaches as an alternative peach production strategy. HortScience 28, 455. Scorza, R. and Sherman, W.B. (1996) Peaches. In: Janick, J. and Moore, J.N. (eds). Fruit Breeding. Vol. I. Tree and Tropical Fruits. Wiley, New York, pp. 325–440. Scorza, R., Lightner, G.W. and Liverani, A. (1989) The Pillar peach tree and growth habit analysis of compact × Pillar progeny. Journal of the American Society for Horticultural Science 114, 991–995. Scorza, R., Bassi, D. and Liverani, A. (2002) Genetic interaction of pillar (columnar), compact and dwarf peach tree genotypes. Journal of the American Society for Horticultural Science 127, 254–261. Scott, D. and Cullinan, F. (1942) The inheritance of wavy leaf character in the peach. Journal of Heredity 33, 293–295. Scott, D.H. and Weinberger, J.H. (1944) Inheritance of pollen sterility in some peach varieties. Proceedings of the American Society for Horticultural Science 45, 229–232. Sharpe, R.H., Hesse, C.O., Lownsberry, B.F., Perry, V.G. and Hansen, C.J. (1970) Breeding peaches for root-knot nematode resistance. Journal of the American Society for Horticultural Science 94, 209–212. Sherman, W.B. and Lyrene, P.M. (2001) ‘UFO’, a saucer or donut peach. Journal of the American Pomological Society 55, 2–3. Sherman, W.B. and Rodriguez-Alcazar, J. (1987) Breeding of low chill peach and nectarines for mild winters. HortScience 22, 1233–1236. Toyama, T.K. (1974) Haploidy in peach. HortScience 9, 187–188. Weinberger, J.H., Math, P.C. and Scott, D.H. (1943) Inheritance study of root-knot nematode resistance in certain peach varieties. Proceedings of the American Society for Horticultural Science 42, 321–325. Werner, D.J. and Chaparro, J.X. (2005) Genetic interaction of pillar and weeping peach genotypes. HortScience 40, 18–20. Werner, D.J. and Creller, M.A. (1997) Inheritance of sweet kernel and male sterility. Journal of the American Society for Horticultural Science 122, 215–217. Werner, D.J., Creller, M.A. and Chaparro, J.X. (1998) Inheritance of the blood-flesh trait in peach. HortScience 33, 1243–1246. Werner, D., Ritchie, D., Cain, D. and Zehr, E. (1986) Susceptibility of peaches and nectarines, plant introductions, and other Prunus species to bacterial leaf spot. HortScience 21, 127–130. Yamazaki, K., Okabe, M. and Takahashi, E. (1987) Inheritance of some characteristics and breeding of new hybrids in flowering peaches. Bulletin of Kanagawa Horticultural Experimental Station 34, 46–53. Yoshida, M. (1976) Genetical studies on the fruit quality of peach varieties. III. Texture and keeping quality. Bulletin of the Fruit Tree Research Station, Series A 3, 1–16.

4

Genetic Engineering and Genomics A.G. Abbott,1 P. Arús2 and R. Scorza3 1Clemson

2Institut

University, Clemson, South Carolina, USA de Recerca i Tecnologia Agroalimentàries (IRTA), Cabrils, Spain 3USDA-AFRS, Kearneysville, West Virginia, USA

4.1 Peach Molecular Genetics Brief description of peach genetics Application of molecular genetic mapping approaches to peach genetics Comparative mapping of peach and other Prunus species Comparative mapping of peach to Arabidopsis 4.2 Peach Genomics and Gene Discovery Construction of the peach physical map and its use in gene discovery Summary of current peach expressed sequence tags projects and data Comparative physical mapping of peach and other model genome species The peach genome database and gene discovery Rosaceae genome database and peach as a model genome species 4.3 Transformation in Peach 4.4 Conclusions and Perspectives

4.1 Peach Molecular Genetics Brief description of peach genetics The cultivated peach is a diploid species (2n = 2x = 16) that belongs to the Rosaceae family, subfamily Prunoideae, genus Prunus and subgenus Amygdalus. The peach karyotype has been studied during meiosis (Jelenkovic and Harrington, 1972) and mitosis (Salesses and Mouras, 1977) and consists of a clearly identiﬁable, large submetacentric chromosome and seven more chromosomes of smaller size, two of them acrocentric. Recent results with ﬂuorescence in situ hybridization in the closely related almond (Prunus dulcis) have enabled

85 85 86 88 92 92 93 94 96 97 97 97 100

detection of each chromosome individually based on chromosome length and the positions of the rDNA genes (Corredor et al., 2004). The size of the Prunus genome is one of the smallest among cultivated species, with an estimated length of 290 Mbp in peach (Baird et al., 1994), approximately twice the size of Arabidopsis. Most of the crosses between peach and species included in the subgenus Amygdalus are possible and produce fertile hybrids, like those obtained with the peach-like Prunus ferganensis, Prunus mira, Prunus davidiana and Prunus kansuensis, or the cultivated almond. Crosses with species of other subgenera (Prunophora and Cerasus) such as apricot (Prunus

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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armeniaca), Myrobalan plum (Prunus cerasifera), European plum (Prunus domestica), Japanese plum (Prunus salicina) or sour cherry (Prunus cerasus) are also possible, but fertile hybrids are produced only occasionally (Scorza and Sherman, 1996). In all, these results suggest that there is an enormous gene pool available for the development of improved cultivars, although this variability has so far been underexploited. One of the distinctive characteristics of peach is its self-compatible mating behaviour, unlike the majority of its congeneric species, which have a gametophytic self-incompatibility system. Selﬁng (Miller et al., 1989), plus important bottlenecks in its recent breeding history (Scorza et al., 1985), have resulted in a lower level of genetic variability in peach compared with the other Prunus crops (Byrne, 1990). The high economic interest of peach, its self-compatible nature that allows the development of F2 progenies and the possibility of shortening the juvenile period to 1–2 years after planting (Scorza and Sherman, 1996) make peach a more adequate organism for genetic analysis than other Prunus crops, resulting in more detailed studies. A total of 42 morphological characters of simple Mendelian inheritance were discovered during the last century (Dirlewanger and Arús, 2008) but, until the recent development of molecular marker maps, only a few linkage relationships among them could be established. Five linkage groups involving 11 major genes were reported by Monet et al. (1996).

Application of molecular genetic mapping approaches to peach genetics The ﬁrst map constructed in fruit trees was reported by Chaparro et al. (1994) using 83 random ampliﬁed polymorphic DNA (RAPD) markers, one isozyme and four morphological characters in a peach intraspeciﬁc F2 progeny. Two more maps based on restriction fragment length polymorphism (RFLP) markers were published shortly thereafter; the ﬁrst constructed in a peach × peach F2 progeny (Rajapakse et al., 1995) and the second in a peach × almond F2 progeny (Foolad et al.,

1995). The peach maps that followed integrated dominant RAPD and ampliﬁed fragment length polymorphism (AFLP) markers with co-dominant (RFLP) and morphological markers (Dirlewanger et al., 1998) or were constructed almost entirely with AFLP markers (Lu et al., 1998). These maps can be considered incomplete, as they generally detected a number of linkage groups different from the eight expected, had a low average marker density (4.5–8.5 cM/marker), included large gaps without markers and many of the markers identiﬁed (8–28%) were unlinked. The ﬁrst saturated linkage map, constructed exclusively with transferable markers (11 isozymes and 226 RFLPs, most of them detected with Rosaceae DNA probes) in a ‘Texas’ almond × ‘Earlygold’ peach F2 population, was published by a European consortium (Joobeur et al., 1998). All these markers were distributed into eight linkage groups with a total distance of 491 cM, representing an average density of 2.0 cM/marker, and with all gaps between markers shorter than 12 cM. This map (abbreviated as the T × E map) has recently been improved by the addition of 176 simple sequence repeat (SSR) markers (Aranzana et al., 2003; Dirlewanger et al., 2004) and 123 RFLPs (Dominguez et al., 2003), most of them obtained with Arabidopsis DNA probes. From the 536 markers currently placed on the T × E map, 466 (87%) are based on known, publicly available DNA sequences, with 198 (37%) of these sequences corresponding to a putative protein. The Prunus scientiﬁc community has adopted the T × E map as the reference map for the genus. It provides a set of transferable markers that can be used as anchors for map construction in other progenies, a common linkage group terminology and marker order within each linkage group, and a highly polymorphic population that allows mapping markers that would not segregate in most peach intraspeciﬁc crosses. Several inter- or intraspeciﬁc peach maps anchored with the T × E map have been obtained and their characteristics are summarized in Table 4.1. The network of maps interconnected with T × E constitutes a resource from which many markers can be found to saturate speciﬁc genomic regions of any progeny or to

Table 4.1.

Peach linkage maps and anchor markers with the ‘Texas’ × ‘Earlygold’ (T × E) reference map. No. of markers

Anchors with T × E

No. of linkage groups

Species

Type

‘Texas’ × ‘Earlygold’

Almond × peach

F2

536

536

8

NC174RL × ‘Pillar’ ‘N.J. Pillar’ × KV77119 ‘Padre’ × ‘54P455’ ‘Ferjalou Jalousia®’ × ‘Fantasia’

Peach Peach Almond × peach Peach

F2 F2 F2 F2

84 47 161 69

0 2 38 48

15 8 8 8

‘Lovell’ × ‘Nemared’ ‘Garfi’ × ‘Nemared’ IF731 × Prunus ferganensis ‘Akame’ × ‘Juseitou’ ‘Summergrand’ × P1908

Peach Almond × peach Peach × P. ferganensis Peach Peach × Prunus davidiana

F2 F2 BC1 F2 F2

153 51 141 120 153

0 50 32 56 62

15 7b 10 7b 8

aWhere

Referencea Joobeur et al. (1998); Aranzana et al. (2003); Dominguez et al. (2003); Dirlewanger et al. (2004) Chaparro et al. (1994) Rajapakse et al. (1995) Foolad et al. (1995); Bliss et al. (2002) Dirlewanger et al. (1998); Etienne et al. (2002) Lu et al. (1998) Jáuregui et al. (2001) Dettori et al. (2001) Yamamoto et al. (2001, 2005) Foulongne et al. (2003a)

Genetic Engineering and Genomics

Population

more than one reference is given the data presented are either from the most recent publication or from the combination of the data from all publications. groups 6 and 8 of these maps were mapped as a single group due to the effects of a reciprocal translocation.

bLinkage

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search for markers covering the whole genome adequate for quantitative trait locus (QTL) or other genetic analyses. Given that peach has a low level of intraspeciﬁc variation, a very dense ‘consensus’ map with highly polymorphic markers well distributed in all genomic regions is necessary to ensure that segregating markers are found where needed in the population of interest. To reach this goal, a supplementary effort will be required to increase the number of SSRs mapped (Aranzana et al., 2003) in parallel with targeted strategies to ﬁll regions with low SSR density (Wang et al., 2001, 2002; Georgi et al., 2002). The existence of a single reference map has made it possible to locate the major genes and QTLs that segregated in different populations (Table 4.2). In total, 21 major genes have been assigned to speciﬁc positions on the T × E map, 18 of these major genes described in peach plus three more affecting ﬂower or kernel characteristics that segregated in almond × peach crosses. Joint analysis between markers and quantitatively inherited characters has also been undertaken for bloom and maturity date, fruit quality, tree architecture and disease resistance (Abbott et al., 1998; Viruel et al., 1998; Dirlewanger et al., 1999; Etienne et al., 2002; Verde et al., 2002; Foulongne et al., 2003b). In addition, QTLs with major effects or consistently found in different years have been detected for all of the above characters, enabling the approximate positioning of 28 QTLs on the T × E map. Most of the major genes located on the Prunus general map can be selected with neighbouring markers. Other strategies for gene tagging that do not require knowledge of the map position, such as bulked segregant analysis (Michelmore et al., 1991), have also been used successfully in peach (Chaparro et al., 1994; Warburton et al., 1996; Lu et al., 1998). In spite of this information being available, the use of markers for commercial breeding is still in its infancy. Marker-assisted selection is currently used in a rootstock breeding programme to pyramid a root-knot nematode (Meloidogyne spp.) resistance gene coming from ‘Nemared’ peach (Lu et al., 1998; Yamamoto and Hayashi, 2002; Arús et al., 2004) with another independent root-knot nema-

tode resistance gene coming from Myrobalan plum (Claverie et al., 2004). However, selections using markers of other well-characterized genes affecting fruit characters (i.e. ﬂesh colour, skin pubescence, fruit shape, fruit sweetness) have not been reported. This is undoubtedly due to the fact that the variability of major traits of interest to breeders (i.e. ripening time, fruit quality and other characters) is quantitatively inherited. There is information on some of these traits (Dirlewanger et al., 1999; Etienne et al., 2002), but a more detailed knowledge of the number, effects and map positions of the QTLs affecting them is necessary before QTL-associated markers can be routinely integrated in selection programmes. Additional candidates for marker-assisted selection in peach are genes or QTLs that can be introgressed into peach from other wild or cultivated species, such as disease or pest resistance. Examples include resistance to sharka (Plum pox virus) from apricot, mapped by Vilanova et al. (2003) in linkage group 1 of Prunus, and other disease resistance QTLs (mildew, leaf curl, aphids, sharka) from P. davidiana identiﬁed by Viruel et al. (1998) and Foulongne (2002). Introgression from wild species is facilitated with markers using whole genome selection approaches (Tanksley et al., 1989) that reduce the number of generations needed for recovery of the genome of the cultivated species or elite genotype. Comparative mapping of peach and other Prunus species The transferable markers (RFLPs, SSRs and isozymes) mapped in the T × E population have been used for the construction of linkage maps in other Prunus species. Detailed comparisons can be made between this map and those of almond (Joobeur et al., 2000), apricot (Lambert et al., 2004), P. davidiana (Foulongne et al., 2003a), cherry (Dirlewanger et al., 2003) and P. cerasifera (E. Dirlewanger, INRA Bordeaux, 2004, personal communication). The order and distribution of the markers into the eight linkage groups was generally identical between species, suggesting a high degree of synteny (see Fig. 4.1/Plate 46 below). Occasional marker position discrepancies

Table 4.2. Description of the major genes (21) and quantitative trait loci (QTLs; 28) affecting morphological or agronomic characters in peach that can be placed on the Prunus reference map.

Character

Linkage groupa

Population

Reference Warburton et al. (1996); Bliss et al. (2002) Wang et al. (2002) Verde et al. (2002) Foulongne et al. (2003b) Jáuregui (1998) Jáuregui (1998); Lu et al. (1998); Yamamoto et al. (2001); Bliss et al. (2002); Claverie et al. (2004) Verde et al. (2002)

Flesh colour (white/yellow) Evergrowing Internode length Powdery mildew resistance Flower colour Root-knot nematode resistance

G1 G1 G1 G1 G1 G2

Y Evg QTL QTL B Mi c

Ripening time, fruit skin colour, soluble solids content Double flower Broomy (or pillar) growth habit Flesh colour around the stone Anther colour (yellow/anthocyanic) Leaf curl resistance Fruit weight, fruit diameter, glucose content Polycarpel Flower colour Blooming time, ripening time, fruit development period Soluble solids content, fructose, glucose Flesh adhesion (clingstone/ freestone) Non-acid fruit

G2

QTL

‘Padre’ × ‘54P455’ ‘Empress op op dwarf’ × PI442380 (Prunus ferganensis × ‘IF310828’)BC1 ‘Summergrand’ × P1908 ‘Garfi’ × ‘Nemared’ ‘P.2175’ × ‘GN22’, ‘Akame’ × ‘Juseitou’, ‘Lowell’ × ‘Nemared’, ‘Garfi’ × ‘Nemared’, ‘Padre’ × ‘54P45’ (P. ferganensis × ‘IF310828’) BC1

G2 G2 G3 G3 G3 G3

Dl Br Cs Ag QTL QTL

‘NC174RL’ × ‘PI’ Various progenies ‘Akame’ × ‘Jusetou’ ‘Texas’ × ‘Earlygold’ ‘Summergrand’ × P1908 ‘Suncrest’ × ‘Bailey’

Chaparro et al. (1994) Scorza et al. (2002) Yamamoto et al. (2001) Joobeur (1998) Viruel et al. (1998) Abbott et al. (1998)

G3 G3 G4

Pcp Fc QTL

Bliss et al. (2002) Yamamoto et al. (2001) Etienne et al. (2002); Verde et al. (2002)

G4

QTL

‘Padre’ × ‘54P455’ ‘Akame’ × ‘Jusetou’ ‘Ferjalou Jalousia®’ × ‘Fantasia’, (P. ferganensis × ‘IF310828’)BC1 ‘Ferjalou Jalousia®’ × ‘Fantasia’

G4

F

G5

D

(P. ferganensis × ‘IF310828’) BC1, ‘Akame’ × ‘Juseitou’ ‘Ferjalou Jalousia®’ × ‘Fantasia’

Dettori et al. (2001); Yamamoto et al. (2001); Verde et al. (2002) Dirlewanger et al. (1998, 1999); Etienne et al. (2002)

Genetic Engineering and Genomics

Symbolb

Etienne et al. (2002)

89

(Continued)

90

Table 4.2.

Continued

Character

Linkage groupa

Symbolb

Population

Reference

G5

QTL

‘Ferjalou Jalousia®’ × ‘Fantasia’

Etienne et al. (2002)

Skin hairiness (nectarine/peach)

G5

G

Kernel taste (bitter/sweet) Ripening time, fruit skin colour, soluble solids content Plant height (normal/dwarf) Leaf shape (narrow/wide) Male sterility Powdery mildew resistance Leaf curl resistance Fruit shape (flat/round) Leaf colour (red/yellow) Fruit skin colour Leaf gland (reniform/globose/ eglandular) Resistance to mildew Powdery mildew resistance Quinase

G5 G6

Sk QTL

‘Ferjalou Jalousia®’ × ‘Fantasia’; ‘Padre’ × ‘54P455’ ‘Padre’ × ‘54P455’ (P. ferganensis × ‘IF310828’)BC1

Dirlewanger et al. (1998, 1999); Bliss et al. (2002) Bliss et al. (2002) Verde et al. (2002)

G6 G6 G6 G6 G6 G6 G6–G8 G6–G8 G7

Dw Nl Ps QTL QTL S* Gr Sc E

‘Akame’ × ‘Juseitou’ ‘Akame’ × ‘Juseitou’ ‘Ferjalou Jalousia®’ × ‘Fantasia’ ‘Summergrand’ × P1908 ‘Summergrand’ × P1908 ‘Ferjalou Jalousia®’ × ‘Fantasia’ ‘Garfi’ × ‘Nemared’, ‘Akame’ × ‘Juseitou’ ‘Akame’ × ‘Juseitou’ (P. ferganensis × ‘IF310828’)BC1

Yamamoto et al. (2001) Yamamoto et al. (2001) Dirlewanger et al. (1998) Foulongne et al. (2003b) Viruel et al. (1998) Dirlewanger et al. (1998, 1999) Jáuregui (1998); Yamamoto et al. (2001) Yamamoto et al. (2001) Dettori et al. (2001)

G7 G8 G8

QTL QTL QTL

(P. ferganensis × ‘IF310828’)BC1 ‘Summergrand’ × P1908 ‘Ferjalou Jalousia®’ × ‘Fantasia’

Verde et al. (2002) Foulongne et al. (2003b) Etienne et al. (2002)

aG6–G8

genes located close to the translocation breakpoint between these two linkage groups. are included if they have been consistently found (at least in two independent measurements) in the indicated populations. cOne or two genes of nematode resistance with different notations and one QTL with ? have been described in this linkage group. bQTLs

A.G. Abbott et al.

Sucrose, malate, titrable acidity, pH, sucrose

Genetic Engineering and Genomics

91

Chromosome 1 Contigs

–1

–2 –3

–4

–5 –6

–7

–8

2.5: AG53 4.3: AC24, FG81, FG83 5.1: AG109 6.8: EPPCU3062 8.7: AG102 10.8: HDL 12.6: AG51 16.2: AG116 25.8: AC32, AC47 27.9: AG29 35.7: FG28

–9 11

Frameworks

–10 –12

13

–14

–15

–16

40.5: 41.3: 42.8: 48.0: 49.6: 49.8:

FG5, PC7 AC7, AG113 EPPCU1589, EPPCU3088, pchgme56 AG105 AG44 TSA2

65.1: FG36, FG228 65.7: AC18, AC23 72.9: PC32A 77.4: BPPCT028

–17

87.0: AG36

[17 contigs] [31 markers] FPC file date: 00:02 Wed 23 May 2007 Fig. 4.1. Initial physical map of linkage group 1 of peach depicted in the Prunus genome web site (http://www.bioinfo.wsu.edu/gdr/, accessed August 2007).

among species maps are attributed to the mapping of different duplicated loci detected by the same RFLP probe or SSR primer pair. These results strongly indicate that the group of Prunus species studied to date shares a nearly identical genome. Therefore, the information on gene sequence and position obtained in one Prunus species would be generally useful for the rest. An exception to the full collinearity observed within Prunus was reported by Jáuregui et al. (2001), who demonstrated the presence of a reciprocal translocation between linkage

groups 6 and 8 in an F2 progeny of ‘Garﬁ’ almond × ‘Nemared’ peach, and established the approximate position of the translocation breakpoint. Although it was not possible to determine the chromosomal conﬁguration of the parents of this cross, the fact that previous maps involving peach, almond or both species never detected the translocation suggested that this mutation occurred only in part of the germplasm of either peach or almond. The same translocation was found in the F2 progeny derived from a cross of the peach cultivars ‘Akame’ and ‘Juseitou’ (Yamamoto et al., 2001,

92

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2005), suggesting that it occurs within peach. Since one of the parents of each cross, ‘Nemared’ and ‘Juseitou’, is a red-leaved cultivar, and the translocation breakpoint is located in the same chromosomal region as the gene that determines red versus green leaf colour (Gr/gr), perhaps there is a relationship between the translocation and the leaf colour trait. This observation is worthy of further study.

Comparative mapping of peach to Arabidopsis The Prunus map and the Arabidopsis thaliana genome sequence have been compared using a set of RFLP markers mapped in T × E obtained either with probes of different species (mainly Prunus and apple) that had a high level of sequence conservation with Arabidopsis (TBLASTX values lower than 10−15) or with Arabidopsis probes that hybridized well to Prunus DNA (Dominguez et al., 2003). The position of 227 Prunus loci (map average density of 2.6 cM/marker) could be compared with that of 703 Arabidopsis homologous sequences. The criterion for declaring a syntenic region was that three or more homologous markers had to be located within 1% of the Prunus map distance (6 cM) and within 1% of the Arabidopsis genome (1.2 Mb). In addition, blocks with gaps longer than 1% of either genome were rejected. With these stringent criteria it was possible to detect 37 syntenic regions, covering 23% and 17% of the Prunus and Arabidopsis genomes, respectively. The longest of these regions included 13 markers for a distance of 25 cM in linkage group 2 of Prunus and 16 homologous sequences spanning 5.4 Mb in chromosome 5 of Arabidopsis. Dominguez et al. (2003) used the same approach to compare Arabidopsis with the genomes of other dicotyledonous species belonging to three different families (sugarbeet, sunﬂower and potato). These results indicated a similar level of synteny to that found between Prunus and Arabidopsis. Although map comparisons between the four crop species were not directly possible, common syn-

tenic regions with Arabidopsis were frequent: 20 of the 37 syntenic Prunus–Arabidopsis blocks were also common to two or three of the other species, indicating that synteny between these species is important. Interestingly, three regions of Arabidopsis (in chromosomes 1, 2 and 3) were syntenic to all species studied, suggesting that they are of evolutionary signiﬁcance. The sequence of peach bacterial artiﬁcial chromosomes (BACs) and BAC ends located in the proximity of the region around the evergrowing gene in linkage group 1 was compared with that of Arabidopsis by Georgi et al. (2003). Predicted genes in these sequences were homologous to genes scattered along the ﬁve chromosomes of Arabidopsis, although some of them were placed in close positions in both genomes. Macro- and microsynteny results coincide in detecting a fragmentary but still existing synteny between these two genomes. This indicates that the sequence of Arabidopsis is a resource that may be useful for characterizing speciﬁc regions of the Prunus genome to search for genes of interest or markers for their selection.

4.2 Peach Genomics and Gene Discovery Although Prunus is an economically and biologically important genus, little was known about the genome structure and organization of its members up until the advent of DNA marker technologies. With respect to the application of DNA marker technologies to the problem of developing genetic resources in trees, peach has distinct advantages that make it suitable as a model species for structural and functional genomics studies. It is diploid with a small genome and a large number of genes controlling fundamentally important traits that have been genetically described (Moore and Janick, 1975; Mowrey et al., 1990). These include genes controlling ﬂower development, fruit development, tree growth habit, dormancy, cold hardiness, and disease and pest resistance. As described above, extensive and detailed molecular genetic mapping efforts have positioned many of these traits (both single gene and QTL) on saturated genetic linkage maps.

Genetic Engineering and Genomics

In order to bridge the gap between the map position of important traits and candidate gene identiﬁcation, the International Rosaceae Genome Consortium (IRGC) was created to promote the development of the peach as an index genome for the identiﬁcation, characterization and cloning of important rosaceous species genes using structural and functional genomics technologies. The current status of this programme is outlined below.

Construction of the peach physical map and its use in gene discovery Large-insert libraries and physical maps are important tools for map-based cloning of Mendelian loci (Arondel et al., 1992) and QTLs (Frary et al., 2000). In cooperation with the Clemson University Genomics Institute, separate peach BAC libraries were constructed for ‘Nemared’ rootstock and a haploid of ‘Lovell’. The restriction enzymes used were HindIII and Sau3A1, respectively. The ‘Nemared’ library consists of approximately 40,000 clones with average inserts approximately 60 kb in size. The theoretical coverage of the genome is eight- to tenfold but in practice it is approximately four- to ﬁvefold. The haploid ‘Lovell’ library consists of approximately 35,000 clones with an approximate average insert size around 80 kb, yielding a theoretical tenfold coverage of the genome. Utilizing these BAC library resources the IRGC is constructing a complete physical map of the peach genome anchored on the general Prunus genetic map (Joobeur et al., 1998), essentially following strategies utilized to develop the Drosophila physical map and others (Marra et al., 1999; Hoskins et al., 2000; Tao et al., 2001; Cone et al., 2002). The approach utilizes a combination of hybridizing mapped markers, BAC ﬁngerprinting and in our case hybridizing expressed sequence tag (EST) sequences. With the current Prunus molecular marker map resources, 210 low-copy mapped RFLP markers, 3700 peach fruit ESTs, 80 resistance gene analogues, 200 speciﬁc cDNAs and numerous speciﬁc AFLP markers have been hybridized to the BAC libraries. We completed BAC ﬁngerprinting approximately

93

20,000 BACs (15,000 from the ‘Nemared’ library and 5000 from the haploid ‘Lovell’ library), from which approximately 15,000 have been used to construct an initial physical map (see map speciﬁcs in Table 4.3 and Fig. 4.1/Plate 46). Physical mapping software (FPC (FingerPrinted Contigs) version 4.7; Soderlund et al., 2000) was used to construct an initial physical map of the peach genome following strategies employed by others (Marra et al., 1999, Tao et al., 2001) to construct physical maps in other crops. Initially, the map was constructed at a cut-off from e−10 to e−12 and tolerance of 5 to obtain all high-conﬁdence overlapping BAC inserts (contigs). These were then merged by testing end clones at a cut-off value ranging from e−8 to e−11. Since there was a signiﬁcant amount of hybridization data, merges were often achieved based on common hybridization of BACs in different contigs. However, if only BAC ﬁngerprint data existed, we noted the merge points for further testing. Presently, the framework map is composed of about 1000 contigs containing approximately 8000 clones (see Table 4.3 and Fig. 4.1). Based on estimates of an average BAC insert size of 60 kb and an average of 60% degree of overlap in contigs, 80% or better of the peach genome should be in highconﬁdence contigs. Currently adding in orphan singleton BACs (approximately 7000, not in contigs from initial map construction) and merging contigs at lower cut-off scores is under way to ﬁnalize the initial peach physical map. Preliminary estimates from trial merges of contigs suggest that the initial map will consist of 800–900 contigs with an average of 12 clones per contig upon completion of the analysis. Since the map includes marker hybridization data from the general Prunus genetic map, the developing physical map is directly anchored to the genetic map. From initial analysis of the integrated genetic/ physical map, there is already evidence for duplication of some regions of the peach genome. The developing physical map is located at the Prunus genome web site within the Genome Database for Rosaceae (GDR) (www.bioinfo.wsu.edu/gdr). This database is under ongoing development (for details see below).

94

A.G. Abbott et al.

Table 4.3.

Peach physical map data.

BACs fingerprinting information No. of bands per fingerprint Class

Contig

Single

Avg.a

<5

<15

<25

<35

<45

<55

≥55

BAC

8360

6419

18.6

0.0b

33.5

45.9

16.9

3.2

0.4

0.1

Contig information Size distribution

Contig Anchored

max

>200

296 43

1 0

200:100 100:50 0 0

0 0

50:25

25:10

9:3

2

Total

8 1

232 74

726 91

303 0

1270 176

Marker information No. of contigs

No. of clones

Class

Total

Avg.

0

1

2

>2

Avg.

1

<5

<10 ≥10

Probe

863

1.2

207

429

129

98

2.9

322

389

124

28

BAC, bacterial artificial chromosome. number of bands analysed per fingerprint. bPercentage of clones containing the specified number of fragments. aAverage

Summary of current peach expressed sequence tag projects and data Peach expressed sequence tag functional genomics database development With the support of the US Department of Agriculture (USDA), the IRGC initiated a peach EST project with the central goal of developing the unique expressed gene set (unigene set) for peach. The current efforts are centred on sequencing 30,000–40,000 cDNAs from libraries of developing fruit, shoot and seeds. Original expectations were that these would resolve into 3000–4000 unigenes; however, this number was obtained from the ﬁrst 15,000 sequences ﬁnished. The data summary for the completed analysis of 15,000 cDNAs from developing peach fruit and almond seed libraries is available at www.bioinfo.wsu. edu/gdr/. Sequencing of developing shoot and root cDNAs is in progress. We have also begun mapping peach ESTs on the developing physical/genetic peach map and have determined that a signiﬁcant

portion of ESTs (11%) hybridized on our BAC libraries are placed directly on genetically mapped anchored contigs in the physical map (Fig. 4.2/Plate 47 and Table 4.3). From the current 15,000 sequences, a peach/almond unigene set has been initiated. This unigene set consists of 3842 putative unique genes. Transcript map One hundred and eighty ESTs (11%) have been localized in 86 locations (involving 80 core markers) on the general Prunus genetic map by common hybridization with RFLP markers to BACs in the ‘Nemared’ library. This EST resource will provide candidate genes for marked regions of the Prunus maps containing traits of interest and will be available online through the Prunus genome database noted before. From the initial fruit unigene set, we have completed hybridizing in excess of 1700 ESTs on to the ‘Nemared’ BAC library. From this set, 184 ESTs have been directly located on the general Prunus genome map through common hybridization

Peach – Transcript map (180 ESTs, 86 locations – 12-01-03) G1 0

MC013

2

AG53 FG81A,

5 6

10

G2 1 4 3 5 4

FG83 AC24 AG109 AG102

2

}

2

5 3

1 1

PC26

27 28 29

6 AG32C AC32 AC47, PC30

31

6 AG23 (T) 30 AG29A AG25B (T,JxF) 12 CC6A 1 PC85, FG16, AG22A, AG36A 5

51

} 5 }2 }2

7 7

FG9A, LY5B, MC044, FG28

4

MC001, PC35A PC15 10 PC7 3 AC7A, AG113, FG5 Pgm-2 AG47 , AG30

5

AG105A AG44

58

TSA2

14

}

0

18 19 20

AG20A+ AG35+, AG107A+ PC5+

22 23

2 FG220+ AG52A+, PC9A+

26

AC27A+, CC135B

10

3 8 9

MC004A CC115+, AC19+, MC045, PC32B AC21B+, Ole1+

Pgm-1+ FG201A+

3

1

6

3

6

AG32A

1

2

CC129

14

PC70, CC124

16

PLG17

B4A9

20

CC116, LY5A

23

AG57A+

}

2 2

25 26

CC2+ CC69+

29 30

CC12A+, AG110+ MC007+, AG1A+

32

PC67A +, CC8+

37 39 40

5

1 2

28

AG6, FG205, MC030A CC3A

30

CC59, AG62

5

26

3

1 7

1

15 B7A5A+, PC13+, Aco-2+, AG50A, 2 CC11B 3 AG106+, Pgd-2+ FG38+ FG22A, AG45, 9 6 CC56 1 PLG39B, AC51

AG37

}

5

Lap-1+, LY16A+

6

}

4

2

3

3 5

}

1

4

8

AG63B AG21B, AC9 AC55B 2 AC49, AG114 4 AC53 (D)

4 2

20

AG25A

12

22 23 24

Tip1 PLG2 PC14

8

26

6Pgd-1

5

}

3 2

15

1

35

4 2

37

FG3

40

CC133B

2

FG202, AG46

1

1

3 1

3 2 7 9

AC42 (F) AC50, FG1A 5

}

AC43A CC133A

AC8 Sdh-1

9

PC6A+, FG6

54

PC1, CC52 MC024A AG12B, AG16B

12 2

3 47 50

AG61A, 4 AG108A AG33, 13 MC011A

9

1 3

}

45

FG4

1

3

7

AG112A

13

LY29, FG230A CC131A

5 1

FG84A, 2 MC003B B4G3 Ma1 (Myrobalan)

15

1

1

PC12

2 2

23

CC63, MC225

25

AG104

31

PC34A

2 18

}

1

1 3

AC22A

1

1

6

4

1 22 23 25

PC101+ AG4A+, 11 10 TubA2 Pyk1 1

1

32

FG37

38

AC48A+

41

FG119A

47

AG49

2

52

AC26

2

54

Pru1, AG14A, Adf1, MC043 PC36+

2 5

4

35 36

AG39B AG60A

40

Aco-1, MC003A

1 2

49 51

3

9

Prp1 PC21 FG14

2

2

TSA3+

8

51

FG42+

55

FG27

57

AG63A

2

1

59

AG17A

62

CC132

66

FG24

5 8 4

1 11 2

FG104 (PxF) AG10 (D, T, PxF)

}

1

2 59

PC73

1

10

65

PC28A

67

2 PC60, PC105A

73 74

Pgl1 Ltp2

79 80

PLG39C, FG209A AG111A

1

6 5 1

1 6

1

}

13

46

2

4

Ext1

5

3 3

AG2A

4

1 4

3

3

61

1

MC023B

1

}

G8 0

1 1

3

1

1

3

AG26A,

FG53 (PxF, S) FG78 (PxF)

1

}

10

AG58 (T,F) FG49 (PxF)

PC29A

4

1 1 6

3

18

50

AG101A PLG26C

PLG39D

2

1 46 47

3

3

3

CC138+, CC135A, AG8A

AC44 AC52A,

18 21

1

0 1

4

5

29 30

1

1

38 11

1

1

CC110, PLG26A, TubA3 10 PCsl104 (PxA) 9 AG36B

1

2

6

1 AG8C, PC32A FG8A

5

9

1

AC3, B6H11 (T)

AC23+, AC18

AG8B PLG26B

33

57 58

65

71

1

G7

TSA4 CC135C 2 PC104A AG54, AG13, FG54A FG215, AG40 PLG59 , CC11A

7

Lap-2+

FG228+, FG36

1

7

2

7

69

7

0 1 2 3

3

43 46

CC125+

4

PLG35

9 12 13 14 15

2

Omt1+

47

9

G6

3

FG26A

9

18

34 35

2

4 2 2 5

5

17 AC43B+ CC47+, AC41A

11

5

1 15

2

40 41

AG7, Me-1

1

37

G5 0

2

FG13

2

2

34 35

AC55A

3

1

7

12

3

FG98, FG106 (PxF) LY37+, MC022+

81

4

38

G4 1

CC127, MC115, MC028A, Idh-2, AG56 1

3 7 8

63

85

2

4 14

1

Pij1+ 4 AG21A+ FG10 (JxF) 3 CC131B+

AT/CTC2 (SCxB) 6

1

60

77 78

5

1

1 evg

LY21

55 56

AG43A+, AC37A+ AC13+ 3

G3 0

Genetic Engineering and Genomics

25

47 48 49

2

6

2

AG51 3 CC23, PC78 15 AC45 (T, F) AG116A 5 PLG39A PC102

42 43 44

AC31+, AC10+,

5

12 13

Mdl1

37 38

4

2

5

15 16

35

1

4

1

13

18 19 20

2

1 AC33A+

0

1

18

3

95

Fig. 4.2. General Prunus genetic map (Joobeur et al., 1998) and developing peach physical/expressed sequence tag (EST) map. Markers depicted in bold have been used to develop contigs of peach bacterial artificial chromosomes (BACs), which are depicted as light-coloured circles with the number of BACs detected by each marker inscribed in the circle. Green circles denote two adjacent markers detecting the same BACs. Black flags depict peach and tomato EST positions, with the number of ESTs at this location posted above the flags.

96

Table 4.4.

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Current peach EST database.

EST probes 1552 (PP_LE) 68 (LF) Total: 1620

BACs identified 5920 209 6129

Average no. of BACs detected 3.8 3.1 3.8

of mapped molecular markers and ESTs. BACs have been identiﬁed in the ‘Nemared’ library for nearly 85% of these ESTs. Initial hybridizations on the haploid ‘Lovell’ BAC library of about 100 ESTs failing to detect BACs in the ‘Nemared’ library have been 60% successful. Thus, upon completion of the physical map, virtually all unigene EST locations will be identiﬁed. In cooperation with Dr V. Decroocq (INRA, Bordeaux, France), we are also mapping resistance gene analogues (RGAs) and resistanceassociated genes (RAGs). We have completed hybridizing over 80 different RGAs/RAGs and are currently positioning these on the physical map. We have already positioned one RAG in a contig that maps to a putative resistance gene location for Plum pox virus (V. Decroocq and D. Abernathy, unpublished results), demonstrating the potential for the transcript map of peach to provide candidate genes. The structural and functional genomics databases of peach serve as tools for microsynteny analysis of regions of interest and for gene cloning investigations. With the integration of sequenced cDNA loci (EST loci), the physical map database immediately provides candidate genes located in the genetically marked intervals containing traits of interest. These associations provide the potential to greatly speed the process of gene discovery and characterization.

Comparative physical mapping of peach and other model genome species One of the most important contributions of DNA marker technology to fundamental studies in plant biology is the ability to rapidly compare genome organization in closely related as well as diverse species. Compara-

tive mapping studies can identify highly conserved genome blocks and regions of lesser conservation. Identiﬁcation and molecular dissection of these evolutionarily conserved regions may uncover genetic associations that, by virtue of their preservation, are implicated as important for plant development. In addition, comparative mapping information can serve as a starting point for initial mapping and gene cloning investigations in poorly characterized species. The comparative genome sequence organization of plant genomes has not been examined as extensively as chromosomal mapping level studies; however, some reports suggest that within families there is a signiﬁcant preservation of gene repertoire and order among plants with quite different genome sizes (Dunford et al., 1995; Bennetzen et al., 1996; Chen et al., 1997; Kilian et al., 1997; Avramova et al., 1998). Initial comparative sequencing studies between Arabidopsis and rice have revealed some conservation of genomic structure in deﬁned regions. The data suggest, however, that genes are being dispersed into and out of regions by mechanisms such as transposition, thus obscuring microsynteny across great evolutionary distances (van Dodeweerd et al., 1999). Future research is necessary to examine the degree of microsynteny within and among plant families. As discussed in the genetic mapping section above, limited comparative mapping between peach and other model genome species was done utilizing molecular marker technologies (Dominguez et al., 2003). This lack of comparative data is also evident at the highresolution level; however, there are several reports suggesting that speciﬁc regions of the peach genome maintain a very limited microsynteny with the Arabidopsis genome (Georgi et al., 2002). These initial studies demonstrate that substantial genome rearrangements have occurred, thus limiting the value of interfamily comparative genomics as a tool for gene discovery. However, within the Prunus genus, the high level of genome preservation at the low-resolution scale suggests that utilization of the peach genome as an anchor for identiﬁcation of important genes in other species is more promising. Initial high-resolution comparative studies of peach with plum and

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apricot suggest that the peach genome database will serve as an excellent source of candidate genes for traits in these species (M. Badenes, IVIA, Valencia, Spain, 2004, personal communication; D. Esmenjaud, INRA Antibes, France, 2004, personal communication). The peach genome database and gene discovery As peach genomic resources are generated, utilization of these resources is now occurring. Peach genome resources are being used for identiﬁcation of genes important to deciduous tree life history traits. A non-dormant genotype (‘Evergrowing’, USDA PI442380) of peach was previously identiﬁed in southern Mexico, where killing frosts do not occur. In Mexico, terminal growth on ‘evergrowing’ trees is continuous under favourable environmental conditions and leaves are retained until they are lost due to drought and/or disease (Diaz, 1974). At more northern latitudes, the ‘Evergrowing’ peach does not appear to respond to winter dormancy cues, exhibiting persistence of shoot growth and a lack of leaf abscission in response to short days and low temperatures in the autumn until these tissues are killed by freezing temperatures (Rodriguez et al., 1994). A number of crosses with evergreen (non-dormant) trees using different deciduous trees were made and all nine of the F2 progenies ﬁt a 3:1 (deciduous:nondormant) ratio, suggesting that the ‘Evergrowing’ phenotype is controlled by a single recessive gene (Rodriguez et al., 1994). Thus, ‘Evergrowing’ trees provide a model system to examine the genetic control of winter dormancy through the cloning and functional analysis of a major gene known to be required for dormancy. In order to map the evergrowing gene locus in peach, crosses were performed between the peach cultivar ‘Empress’ and the non-dormant peach selection PI442380 (Werner and Okie, 1998). Two F1 trees from this cross were selfpollinated to produce an F2 population. F2 seeds were germinated in the greenhouse in winter and transplanted to the ﬁeld in June. The growth characteristics of the progeny were evaluated at the USDA-ARS Appalachian Fruit Research Station in Kearneysville, WV. One

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hundred and nine of 314 F2 trees exhibiting consistent phenotypes in 1997 and 1998 were randomly selected for the genetic mapping of the recessive evg gene (Wang et al., 2002). Bulk segregant AFLP analysis was performed to identify AFLP markers linked to the evg gene, and a local molecular linkage map covering a total genetic distance of 79.3 cM was constructed (Wang et al., 2002). Four ﬂanking AFLP markers were cloned, sequenced and converted into sequence tagged site (STS) markers (Wang et al., 2002). A localized physical map of the evergrowing region was initiated from the closest STS marker utilizing the peach physical map resources. A chromosomal walk in both directions was initiated from the BAC PpN18F12 (Prunus persica ‘Nemared’ 18F12), which contained the closest STS marker EAT/ MCAC. Identiﬁcation of markers from the contig developed from this walk suggested that the evergrowing region was contained within a limited number of BACs, which were then subjected to BAC sequencing (Bielenberg et al., 2004). Gene candidates were identiﬁed of the MADS box transcription factor class. Southern hybridization analysis of this region demonstrated a deletion spanning the putative evergrowing region in the evg mutant. Candidate genes in this region and their homologues in other tree systems (poplar, plum) are currently under characterization. Rosaceae genome database and peach as a model genome species We have taken a worldwide cooperative approach to develop the peach as a reference genome for fruiting trees. All the structural and functional genomics resources are incorporated in the Genome Database for Rosaceae (GDR) to serve as the repository for Rosaceae genomics data worldwide. The Prunus genomics data set, as well as data of other important Rosaceae species, are included in the GDR (http://www.bioinfo.wsu.edu/gdr).

4.3 Transformation in Peach Peach (P. persica) and its smooth-skinned sport, nectarine, is one of the most commercially

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important stone fruit species (a group that also includes apricot, cherry and plum). World production of peach and nectarine is about 17 million t (FAO, 2007). Biotic and abiotic stress factors such as pests, diseases, drought and postharvest losses reduce stone fruit production worldwide. New improved cultivars have been released but many production problems have yet to be solved by conventional plant breeding (Scorza and Sherman, 1996; Srinivasan and Scorza, 1999). Genetic transformation is an alternative method of stone fruit improvement that may be particularly useful to increase biotic and abiotic stress resistance and fruit quality (Scorza, 1991, 2001; Scorza et al., 1995a; Srinivasan et al., 2004). Plant genetic transformation generally involves the transfer of DNA with the desired gene(s) into cells and the regeneration of transgenic plants from the transformed cells through in vitro culture. While genetic transformation is an important tool for peach improvement, a reliable and reproducible transformation and regeneration system from somatic tissue has yet to be developed. The following summarizes the reports of work in peach transformation and regeneration. Although induction of somatic embryogenesis has been reported for peach, conversion of these somatic embryos into plants is far from routine (Scorza, 2001). Raj Bhansali et al. (1990) induced somatic embryos from 1–3 mm long immature zygotic embryos of peaches and nectarines. To induce embryogenic callus, the zygotic embryos were cultured on Murashige and Skoog (MS) basal medium (Murashige and Skoog, 1962) containing glutamine, myo-inositol and casein hydrolysate (each 500 mg/l), 2,4-dichlorophenoxyacetic acid (2,4-D) (5 mg/l), kinetin (2 mg/l) and 6-benzylaminopurine (BAP) (2 mg/l). The zygotic embryo cultures were initially incubated for 10 days in the dark and then exposed to continuous light for 20 days at 23°C. To produce somatic embryos, these calli were transferred on to MS basal medium containing glutamine, myo-inositol and casein hydrolysate (each 500 mg/l), MES (2-(N-morpholino) ethanesulfonic acid) (976 mg/l) and activated charcoal (2.5 g/l). No growth regulators were added to the medium. Somatic embryos were

produced on this medium after three to ﬁve transfers at 3-week intervals. Plant development from embryos was on basal medium supplemented with BAP (1.0 mg/l), a-naphthalene acetic acid (NAA) (0.1 mg/l) and 0.03% activated charcoal. Efforts to produce long-term embryogenic callus yielded embryos with abnormal morphologies. Guohua and Yu (2002) produced embryogenic callus from immature cotyledons of four Chinese peach cultivars using a two-step process. Culture on MS-based basal medium supplemented with BAP (0.1 mg/l) and 2,4-D (1.0 mg/l) for 6 weeks (transferred to fresh medium after 3 weeks) was followed by culture on the same basal medium with the addition of BAP (0.01 mg/l) and 2,4-D (0.1 mg/l). This procedure induced up to 95% of the immature embryos to produce callus with up to eight somatic embryos per explant. Up to 75% of these somatic embryos produced shoots. While BAP has been generally used for peach regeneration, Guohua and Yu (2002) found thidiazuron (TDZ) (0.1–2.5 mg/l), in combination with NAA (0.01 mg/l), to more effectively induce adventitious shoots directly from immature cotyledons of ‘Jingyan’ peach when compared with BAP, kinetin, zeatin and CPPU (N-(2-chloro-4-pyridinyl)-N′-phenylurea). Scorza et al. (1990a) produced somatic embryogenic cultures from immature (45–50 days post bloom) embryos. Following a 6-month culture period on the media of Hammerschlag et al. (1985), these cultures became growth regulator-independent (habituated) and continually produced somatic embryos for up to 4 years. These embryogenic cultures only rarely germinated to produce viable shoots even when exposed to a number of treatments including cold treatment and various growth regulators. Direct adventitious shoot regeneration without intervening somatic embryo production has been induced from callus derived from immature zygotic peach embryos (Hammerschlag et al., 1985). To produce a white nodular shoot regenerative callus, immature zygotic embryos were excised from 70-dayold ‘Sunhigh’ and ‘Suncrest’ peach fruits. These were ﬁrst cultured in MS basal medium supplemented with 2.4 mM 2,4-D and 0.44 mM BAP and then transferred to medium containing

Genetic Engineering and Genomics

0.27 mM NAA and 2.2 mM BAP. Shoots were regenerated from these calli after transferring to a medium containing 2.2 mM BAP and 1.35 mM NAA. Regenerated shoots were rooted in the dark on a medium containing 28.5 mM indole-3-butyric acid (IBA). Direct shoot organogenesis has also been induced from immature cotyledons excised from 70-day-old fruits of peach cultivars ‘Bailey’, ‘Boone County’, ‘Suncrest’ and ‘Hann’ after 4–6 weeks’ culture on MS medium containing 2.5 mM IBA and 7.5 mM TDZ (Mante et al., 1989). Roots were produced in 50–70% of the regenerated shoots cultured under light on half-strength MS medium with 2.5 or 5 mM IBA. The use of immature zygotic explants limits source material availability to only a few months out of the year. Pooler and Scorza (1995) demonstrated adventitious shoot production from mature cotyledons of peach rootstock (‘Nemaguard’, ‘Flordaguard’ and ‘Nemared’) seeds that had been cold-stored at 4°C for 1–3 years. Cotyledons were cultured in the dark on MS medium containing 1.25, 2.5, 6.25 or 12.5 mM IBA. The regenerated shoots were maintained on medium containing 0.1 mM IBA and 1.0 mM BAP and shoots were rooted in half-strength MS basal medium supplemented with 5 mM IBA. This procedure provides a relatively simple method for peach regeneration that can be used year-round on responsive genotypes. As with all peach regeneration systems developed to date, successful regeneration is highly genotypedependent. Most of the preceding reports of regeneration from peach have focused on the use of zygotic tissues, and most from immature zygotic embryos. In contrast, Gentile et al. (2002) reported adventitious shoot regeneration from callus cultures of young leaves (1–2 mm long) from in vitro-grown peach shoots in a medium containing 9 mM BAP and 0.54 mM NAA. Regeneration rates of 13–28% were obtained using three cultivars from diverse origins and two seedling selections. Most regeneration was obtained from leaf petioles. Preconditioning the in vitro shoots that were the sources of leaf explants in medium containing 2 mg BAP/l and ≤0.2 mg NAA/l for up to 4 months was a critical step in the regeneration process.

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Clearly, it is possible to regenerate peach plants in vitro. This has been achieved for the most part by using zygotic tissues. These explant sources have generally not been favoured for tree fruit transformation because the ability to improve established cultivars is lost. Each seed-derived genotype is unique and not a clone of the parent. Transformation of zygotic tissues would be useful for providing unique and useful genes to breeding programmes where they could be incorporated into new germplasm. Given the facts that: (i) the generation cycle for peach is approximately 3 years (a short cycle compared with most tree fruit species; Sherman and Lyrene, 1983); (ii) most new peach cultivars are produced by breeding programmes versus the selection of sports of established cultivars; and (iii) peach varieties are continually replaced at a fairly rapid pace (10–12 years or less in some areas), the efﬁcient transformation of peach germplasm can be of great beneﬁt to the genetic improvement of this species. While the production of transgenic Prunus currently depends largely on the efﬁciency of regeneration of plants from transformed cells, the efﬁciency of transformation itself is also an important factor, one that takes on an even greater level of importance in the case of low regeneration rates. Several reviews have been published on transformation of Prunus species, including peach (Scorza and Hammerschlag, 1992; Scorza et al., 1995a; Rugini and Gutierrez-Pesce, 1999; Srinivasan and Scorza, 1999; Srinivasan et al., 2004). Transformation efﬁciency is affected by many factors including the method of transformation (e.g. Agrobacterium tumefaciens or biolistics), the transformation environment and the antibiotic selection pressure. In most published reports, A. tumefaciens has been used to transfer the DNA plasmids carrying the gene(s) of interest to peach cells. Neomycin phosphotransferase II (NPTII) has been used as the selectable marker and, in some cases, b-glucuronidase (GUS) as a visual marker of transformation. Although peach is infected by wild A. tumefaciens and crown gall disease is common in Prunus (Scorza and Sherman, 1996), the transformation efﬁciency of peach cells in vitro with disarmed A. tumefaciens is relatively low. To date, there is only one report of the

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development of transgenic peach plants (Smigocki and Hammerschlag, 1991). In that study, transgenic ‘Redhaven’ peach plants expressing the A. tumefaciens ipt (isopentenyl phosphotransferase) gene were regenerated from immature zygotic embryogenic calli. This ‘Redhaven’ peach was transformed with a shooty mutant strain of A. tumefaciens, tms328::Tn5, which carries an octopine type Ti plasmid with a functional cytokinin gene and a mutated auxin gene. The use of this cytokinin-producing shooty-mutant strain of A. tumefaciens may have been responsible for the successful regeneration of transformed shoots. The levels of endogenous cytokinins in the few regenerated shoots that were produced were reported to be 50-fold higher than the levels in untransformed controls. The transgenic plants showed alterations in growth habit compared with untransformed controls. These included dwarf stature, increased branching and delayed leaf senescence (Hammerschlag et al., 1997; Hammerschlag and Smigocki, 1998). These growth characteristics are indicative of high cytokinin levels and were apparently due to the expression of the ipt gene in the transgenic peach lines. Scorza et al. (1990b) reported the transformation of peach leaf segments, immature embryos and long-term embryonic callus using A. tumefaciens strain A281 carrying plasmid pGA472 with the NPTII selectable marker. Transformation rates of 5% of immature embryos and up to 64% of leaf segments were observed. These explant sources did not undergo organogensis, thus no transgenic shoots were obtained from that work. In contrast to A. tumefaciens-based transformation studies, particle bombardment (biolistics) has also been used to produce stably transformed embryogenic peach callus (Ye et al., 1994). Embryogenic callus derived from immature embryos was used as the starting material. A high frequency of subculture (3 days to 2 weeks) prior to bombardment was considered important in order to maintain actively dividing cells, which tend to be most receptive to biolistic transformation. From 114 callus lines, 65 were putatively transformed. Seven lines were conﬁrmed as transformants by PCR and GUS histological assays. No regeneration was obtained from

the transformed embryogenic callus produced in the study. Transient expression tests of biolistic transformation of embryogenic callus, embryonic axes, cotyledons, immature embryos, leaf discs and shoot tips demonstrated high levels of transformation efﬁciency. However, shoot tip explant transformation showed efﬁciency (number of GUS-positive spots/sample) that was approximately 80% lower than the average of the other explants. The ability to transform peach embryogenic callus, embryonic axes and cotyledons was considered to be signiﬁcant because regeneration from these tissues had been previously reported. Peach is not unique in the Prunus in its recalcitrance to transformation and regeneration. There are few reports of the successful production of transgenic Prunus species. Those species that have been transformed include apricot (P. armeniaca) (Laimer da Camara Machado et al., 1992), sweet cherry (Prunus avium) (Brasileiro et al., 1991), sweet × sour cherry (Dolgov and Firsov, 1999), almond (Prunus amygdalus) (Miguel and Oliveira, 1999), P. avium × Prunus pseudocerasus cv. Colt (Gutierrez-Pesce et al., 1998), Prunus subhirtella autumno rosa (da Câmara Machado et al., 1995) and P. domestica (European or prune plum) (Mante et al., 1991). For most of these species there exists a single report of the development of only a few transgenic plants. The P. domestica system, which uses mature seeds as the explant source, has been used repeatedly to develop transgenic trees (Mante et al., 1991; Scorza et al., 1994, 1995b; Padilla et al., 2003) and presents what can be considered a reliable and routine system. It is such a system that remains a goal for peach and one that will advance the utilization of gene transfer for peach improvement.

4.4 Conclusions and Perspectives Signiﬁcant progress has been made in recent years to understand the genome organization in peach and its close relatives. The genome organization of Prunus species is highly collinear; there is signiﬁcant progress towards the completion of a physical map/genetic

Genetic Engineering and Genomics

map resource and signiﬁcant numbers of genes have been identiﬁed through EST and genomic sequencing projects in peach. These gene sequences are mapped on the physical/ genetic map database and this information is publicly available in the GDR. This work paves the way for future identiﬁcation and cloning of important genes in cultivation of peach and other Prunus species. Recent reports utilizing these resources have demonstrated the importance of this database for identiﬁcation and study of important fruit

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tree genes. Manipulation of these genes in peach awaits the development of a reliable transformation system for peach. Future work will focus on the utilization of this gene information and marker systems for manipulation of important characters in the breeding schemes. Integration of the molecular genetic resources for peach with traditional breeding programmes promises to streamline the breeding process and provide new and improved varieties for the global market.

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Georgi, L.L., Wang, L., Reighard, G.L., Mao, L., Wing, R.A. and Abbott, A.G. (2003) Comparison of peach and Arabidopsis genomic sequences: fragmentary conservation of gene neighborhoods. Genome 46, 268– 276. Guohua, Y. and Yu, Z. (2002) Plant regeneration from excised immature embryos of peach (Prunus persica L.). Acta Horticulturae Sinica 29, 480–482. Gutierrez-Pesce, P., Taylor, K., Muleo, R. and Rugini, E. (1998) Somatic embryogenesis and shoot regeneration from transgenic roots of the cherry rootstock Colt (Prunus avium × Prunus pseudocerasus) mediated by pRi 1855 T-DNA of Agrobacterium rhizogenes. Plant Cell Reports 17, 574–580. Hammerschlag, F.A. and Smigocki, A.C. (1998) Growth and in vitro propagation of peach plants transformed with the shooty mutant strain of Agrobacterium tumefaciens. HortScience 33, 897–899. Hammerschlag, F.A., Bauchan, G. and Scorza, R. (1985) Regeneration of peach plants from callus derived from immature embryos. Theoretical and Applied Genetics 70, 248–251. Hammerschlag, F.A., McCanna, I.J. and Smigocki, A.C. (1997) Characterization of transgenic peach plants containing a cytokinin biosynthesis gene. Acta Horticulturae 447, 569–574. Hoskins, R.A., Nelson, C.R., Berman, B.P., Laverty, T.R., George, R.A., Ciesiolka, L., Naeemuddin, M., Arenson, A.D., Durbin, J., David, R.G., Tabor, P.E., Bailey, M.R., DeShazo, D.R., Catanese, J., Mammoser, A., Osoegawa, K., de Jong, P.J., Celniker, S.E., Gibbs, R.A., Rubin, G.M. and Scherer, S.E. (2000) BACbased physical map of the major autosomes of Drosophila melanogaster. Science 287, 2271–2274. Jáuregui, B. (1998) Localización de marcadores moleculares ligados a caracteres agronómicos en un cruzamiento interespecífico almendro × melocotonero. PhD thesis, Universitat de Barcelona, Barcelona, Spain. Jáuregui, B., de Vicente, M.C., Messeguer, R., Felipe, A., Bonnet, A., Salesses, G. and Arús, P. (2001) A reciprocal translocation between ‘Garfi’ almond and ‘Nemared’ peach. Theoretical and Applied Genetics 102, 1169–1176. Jelenkovic, G. and Harrington, E. (1972) Morphology of the pachytene chromosomes in Prunus persica. Canadian Journal of Genetics and Cytology 14, 317–324. Joobeur, T. (1998) Construcción de un mapa de marcadores moleculares y análisis genético de caracteres agronómicos en Prunus. PhD thesis, Universitat de Lleida, Lleida, Spain. Joobeur, T., Viruel, M.A., de Vicente, M.C., Jáuregui, B., Ballester, J., Dettori, M.T., Verde, I., Truco, M.J., Messeguer, R., Batlle, I., Quarta, R., Dirlewanger, E. and Arús, P. (1998) Construction of a saturated linkage map for Prunus using an almond × peach F2 progeny. Theoretical and Applied Genetics 97, 1034– 1041. Joobeur, T., Periam, N., de Vicente, M.C., King, G. and Arús, P. (2000) Development of a second generation linkage map for almond using RAPD and SSR markers. Genome 43, 649–655. Kilian, A., Chen, J., Han, F., Steffenson, B. and Kleinhofs, A. (1997) Towards map-based cloning of the barley stem rust resistance genes Rpg1 and rpg4 using rice as an intergenomic cloning vehicle. Plant Molecular Biology 35, 187–195. Laimer da Camara Machado, M., da Camara Machado, A., Hanzer, V., Weiss, H., Regner, F., Steinkellner, H., Mattanovich, D., Plail, R., Knap, E., Kalthoff, B. and Katinger, H. (1992) Regeneration of transgenic plants of Prunus armeniaca containing the coat protein gene of plum pox virus. Plant Cell Reports 11, 25–29. Lambert, P., Hagen, L.S., Arús, P. and Audergon, J.M. (2004) Genetic linkage maps of two apricot cultivars (Prunus armeniaca L.) compared with the almond ‘Texas’ × peach ‘Earlygold’ reference map for Prunus. Theoretical and Applied Genetics 108, 1120–1130. Lu, Z.X., Sosinski, B., Reighard, G.L., Baird, W.V. and Abbott, A.G. (1998) Construction of a genetic linkage map and identification of AFLP markers for resistance to root-knot nematodes in peach rootstocks. Genome 41, 199–207. Mante, S., Scorza, R. and Cordts, J. (1989) Plant regeneration from cotyledons of Prunus persica, Prunus domestica, and Prunus cerasus. Plant Cell, Tissue and Organ Culture 19, 1–11. Mante, S., Morgens, P., Scorza, R., Cordts, J. and Callahan, A. (1991) Agrobacterium-mediated transformation of plum (Prunus domestica) hypocotyl slices and regeneration of transgenic plants. Biotechnology 9, 853–857. Marra, M., Kucaba, T., Sekhon, M., Hillier, L., Martienssen, R., Chinwalla, A., Crokett, J., Fedele, J., Grover, H., Gund, C., McCombie, W.R., McDonald, K., McPherson, J., Mudd, N., Parnell, L., Schein, J., Seim, R., Shelby, P., Waterston, R. and Wilson, R. (1999). A map for sequence analysis of the Arabidopsis thaliana genome. Nature Genetics 22, 269–270. Michelmore, R.W., Paran, I. and Kesseli, R.V. (1991) Identification of markers linked to disease-resistance genes by bulked segregant analysis: a rapid method to detect markers in specific genomic regions by using segregating populations. Proceedings of the National Academy of Sciences USA 88, 1212–1217.

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Miguel, C. and Oliveira, M.M. (1999) Transgenic almond (Prunus dulcis Mill.) plants obtained by Agrobacterium-mediated transformation of leaf explants. Plant Cell Reports 18, 387–393. Miller, P.J., Parfitt, D.E. and Weinbaum, S.A. (1989) Outcrossing in peach. HortScience 24, 359–360. Monet, R., Guye, A., Roy, M. and Dachary, N. (1996) Peach Mendelian genetics: a short review and new results. Agronomie 16, 321–329. Moore, J. and Janick, J. (eds) (1975) Advances in Fruit Breeding. Purdue University Press, West Lafayette, Indiana. Mowrey, B.D., Werner, D.J. and Byrne, D.H. (1990) Inheritance of isocitrate dehydrogenase, malate dehydrogenase, and shikimate dehydrogenase in peach and peach × almond hybrids. Journal of the American Society of Horticultural Science 115, 312–319. Murashige, T. and Skoog, F. (1962) A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiologia Plantarum 15, 473–497. Padilla, I.M.G., Webb, K. and Scorza, R. (2003) Early antibiotic selection and efficient rooting and acclimatization improve the production of transgenic plum plants (Prunus domestica L.). Plant Cell Reports 22, 38–45. Pooler, M.R. and Scorza, R. (1995) Regeneration of peach [Prunus persica (L.) Batsch] rootstock cultivars from cotyledons of mature stored seed. HortScience 30, 355–356. Rajapakse, S., Bethoff, L.E., He, G., Estager, A.E., Scorza, R., Verde, I., Ballard, R.E., Baird, W.V., Callahan, A., Monet, R. and Abbott, A.G. (1995) Genetic linkage mapping in peach using morphological, RFLP and RAPD markers. Theoretical and Applied Genetics 90, 503–510. Raj Bhansali, R., Driver, J.A.A. and Durzan, D.J. (1990) Rapid multiplication of adventitious somatic embryos in peach and nectarine by secondary embryogenesis. Plant Cell Reports 9, 280–284. Rodriguez, J., Sherman, W.B., Scorza, R., Wisniewski, M. and Okie, W.R. (1994) Evergreen peach, its inheritance and dormant behavior. Journal of the American Society for Horticultural Science 119, 789–792. Rugini, E. and Gutierrez-Pesce, P. (1999) Transgenic Prunus fruit species (almond, apricot, cherry rootstocks, sour cherry and sweet cherry, peach and plum). In: Bajaj, Y.P.S. (ed.) Biotechnology in Agriculture and Forestry. Vol. 44. Transgenic Trees. Springer, Berlin, pp. 245–262. Salesses, G. and Mouras, A. (1977) Tentative d’utilisation des protoplastes pour l’etude des chromosomes chez les Prunus. Annals de l’Amelioration des Plantes 27, 363–368. Scorza, R. (1991) Gene transfer for the genetic improvement of perennial fruit and nut crops. HortScience 26, 1033–1035. Scorza, R. (2001) Progress in tree fruit improvement through molecular genetics. HortScience 36, 855–857. Scorza, R. and Hammerschlag, F. (1992) Emerging technologies for the genetic improvement of stone fruits. In: Hammerschlag, F.A. and Litz, R.E. (eds) Biotechnology of Perennial Fruit Crops. CAB International, Wallingford, UK, pp. 277–302. Scorza, R. and Sherman, W.B. (1996) Peaches. In: Janick, J. and Moore, J.N. (eds) Fruit Breeding. Vol. I. Tree and Tropical Fruit. Wiley, New York, pp. 325–440. Scorza, R., Mehlenbacher, S.A. and Lightner, G.W. (1985) Inbreeding and co-ancestry of freestone peach cultivars of the eastern United States and implications for peach germplasm improvement. Journal of the American Society of Horticultural Science 110, 547–552. Scorza, R., Cordts, J. and Mante, S. (1990a) Long-term somatic embryo production and plant regeneration from embryo-derived peach callus. Acta Horticulturae 280, 183–190. Scorza, R., Morgens, P., Cordts, J.M., Mante, S. and Callahan, A. (1990b) Agrobacterium-mediated transformation of peach [Prunus persica (L.) Batsch] leaf segments, immature embryos, and long-term embryogenic callus. In vitro Cellular and Developmental Biology 26, 829–834. Scorza, R., Ravelonandro, M., Callahan, A., Cordts, J.M., Fuchs, M., Dunez, J. and Gonsalves, D. (1994) Transgenic plums (Prunus domestica L.) express the plum pox virus coat protein gene. Plant Cell Reports 14, 18–22. Scorza, R., Hammerschlag, F.A. and Zimmerman, T.W. (1995a) Genetic transformation in Prunus persica (peach) and Prunus domestica (plum). In: Bajaj, Y.P.S. (ed.) Biotechnology in Agriculture and Forestry, Vol. 34. Springer, Berlin, pp. 255–268. Scorza, R., Levy, L., Damsteegt, V., Yepes, M., Cordts, J., Hadidi, A., Slightom, J. and Gonsalves, D. (1995b) Transformation of European plum (Prunus domestica L.) with the papaya ringspot virus coat protein gene and reaction of transgenic plants to inoculation with plum pox virus. Journal of the American Society of Horticultural Science 120, 943–952. Scorza, R., Melnicenco, L., Dang, P. and Abbott, A.G. (2002) Testing a microsatellite marker for selection of columnar growth habit in peach (Prunus persica (L.) Batsch). Acta Horticulturae 592, 285–289.

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5

Low-chill Cultivar Development B.L. Topp,1 W.B. Sherman2 and M.C.B. Raseira3

1Queensland

Department of Primary Industries & Fisheries, Nambour, Queensland, Australia 2Horticultural Science Department, University of Florida, Gainesville, Florida, USA 3Empresa Brasileira de Pesquisa Agropecuaria/Embrapa Clima Temperado, Pelotas, Rio Grande do Sul, Brazil

5.1 Introduction Reasons for breeding low-chill cultivars History of low-chill cultivar development 5.2 Current Low-chill Breeding Programmes Australia, New South Wales Australia, Queensland Brazil, Pelotas Brazil, Sao Paulo Mexico, Chapingo Mexico, Queretaro South Africa, Stellenbosch Taiwan, Taichung Thailand, Angkhang USA, California, Sun World USA, California, Zaiger Genetics USA, Florida, University of Florida USA, Texas, Texas A&M University 5.3 Common Objectives in Low-chill Peach Breeding Low chilling requirement Time of ﬂowering Flower bud density Blind nodes and bud drop Fruit development period Fruit shape Fruit ﬁrmness Disease resistance 5.4 Management of Low-chill Breeding Populations Hybrid seed production Seedling populations Testing advanced selections 5.5 Conclusions 106

107 107 108 110 113 113 117 118 118 118 119 119 119 119 120 120 121 121 121 122 123 123 123 125 126 127 129 129 132 133 133

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Low-chill Cultivar Development

5.1 Introduction When Professor R.E. Smith commenced planning for pathological work in southern California about 1904, one of the troubles to be studied and, if possible, prevented, was a rather vague disease of peaches, in which there was delayed blooming and foliation, with loss of crop. . . . Among other things undertaken in connection with the peach problem was a breeding project in which the adaptability of certain South China peaches to the climate of southern California was to be combined with the desired commercial qualities of ordinary varieties. (Horne et al., 1926)

So began the ﬁrst attempts in US public breeding aimed at developing low-chill peach cultivars. The term ‘low-chill’, used to describe peach cultivars, is a relative and somewhat artiﬁcial term. Chilling refers to the amount of low temperatures required by leaf and ﬂower buds during winter to break dormancy and commence normal growth and development each growing season. Chilling has traditionally been quantiﬁed as chill-hours, measuring the number of hours below 7°C (Weinberger, 1950), and more recently as chill units (CU), which allow for partial chill-hour accumulation and chill negation (Dennis, 2003). The distinction of cultivars as low-, medium- and high-chill provides broad categories rather than exact deﬁnitions, as there is actually a continuum of chilling requirements. As a general rule, low-chill cultivars are those adapted to subtropical environments, high-chill cultivars are those adapted to temperate environments and medium-chill cultivars are intermediate in adaptation. In this chapter we focus on the breeding of low-chill peach cultivars adapted to the subtropics, even though they may be grown in temperate environments (in the absence of spring freezes that kill the bloom) or in tropical highlands.

Reasons for breeding low-chill cultivars Low-chill peach cultivars are economically important for a number of reasons. In subtropical regions, they provide a fresh supply

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of fruit for local markets and the potential to transport fruit to more distant markets not producing peaches at that time. The low chilling requirement of these cultivars means that the trees ﬂower in mid- to late winter. In warm environments the fruit develop rapidly, resulting in harvests that are up to 2 months earlier than cultivars grown in cooler, temperate regions. Fruit prices are usually high at this time. Globalization and reduction in trade barriers between northern and southern hemisphere countries will impact on lowchill cultivar development. Old markets that supplied low-chill cultivars because they were early, but lacked fruit quality, will be rendered obsolete by the importation of lateseason, high-quality, high-chill fruit from opposite hemispheres. In Australia, the only peaches on the market in September are from the low-chill cultivar ‘Flordaprince’, but California has applied to export peaches to Australia. If this occurs, then late-season Californian cultivars such as ‘August Red’, ‘Autumn Flame’ and ‘September Sun’ will be on Australian markets in September and may out-compete ‘Flordaprince’ fruit in terms of size, colour, ﬁrmness and ﬂavour. New markets are also likely to develop for low-chill cultivars, but this will require improvements in ﬂesh ﬁrmness, transportability and speciﬁc fruit quality characteristics tailored to new markets. Finally, low-chill cultivars may become more widely planted if global warming trends continue. The Intergovernmental Panel on Climate Change reported projected increases in global average surface temperatures of 0.8–2.6°C by 2050, with minimums increasing at twice the rate of maximums (Watson et al., 2001). Increases of this magnitude would result in less winter chilling in many locations. Hennessy and Clayton-Greene (1995) modelled an increase of 1.5–2.0°C and found it would increase the risk of prolonged dormancy for stone fruits at many temperate fruit-growing regions in southern Australia. Using a modiﬁed Utah chill model, chilling at key Australian fruit-growing regions was shown to decrease (Table 5.1). Under these conditions, the demand for low-chill cultivars would increase considerably.

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Table 5.1. Annual average chilling (chill units, CU) accumulated in 1995 and predicted for 2030 at sites in Australian peach-growing regions. The range of values for 2030 represents the effect of a low and high global warming scenario. (Adapted from Hennessy and Clayton-Greene, 1995.) Location

Average chilling (CU), 1995

Predicted chilling (CU), 2030

1409 1187 1486 1316 1608

671–1159 529–983 944–1316 888–1185 898–1397

Bridgetown, Western Australia Renmark, South Australia Griffith, New South Wales Stanthorpe, Queensland Swan Hill, Victoria

History of low-chill cultivar development From its original home in China, the peach has been widely distributed through Europe, Asia, South Africa, Australia and the Americas, and over the centuries there has been selection of locally adapted cultivars (Cullinan, 1937). The honey and peento peaches from southern China are adapted to the subtropics and were the original source of lowchill adaptation used in early low-chill peach breeding in southern California (Cullinan, 1937). The European or Persian peaches were introduced from China to the Mediterranean, west Asia, Italy, Spain, Iran and Turkey (Li, 1984). This germplasm, including non-melting, yellow-ﬂeshed clingstones, was introduced to the New World by Spanish and Portuguese explorers in the 16th century. This peach group provided source material used in low-chill peach development in South and Central America. While the original source of low-chill requirement is from southern China, it reached the subtropics by varied routes. In Australia, subtropical peaches are thought to have been introduced by Chinese immigrants in the 1800s and gave rise to cultivars such as ‘China Flat’, ‘Bell’s November’, ‘Beauty of Booroodabin’, ‘Watt’s Early Champion’ and strains of ‘Dwarf Peach’ (Ward, 1952). The ‘China Flat’ was imported as seed into the USA from Australia in 1869 and named ‘Australian Saucer’ (Hume, 1902; Price, 1905; Lammerts, 1941). The heterozygous nature of the ﬂat or peento shape (because homozygous peento is lethal) would have ensured segregation for both regular and ﬂat-shaped peaches from this

imported seed. Hume (1902) reported that 24 varieties belong to this peento group including ‘Angel’, ‘Jewel’, ‘Bidwell Early’, ‘Waldo’ and ‘Peen-to’ and that they were adapted to subtropical conditions, especially in Florida. In the USA, low-chill breeding began in 1907 at the University of California Citrus Experiment Station at Riverside, and not long after at the Chaffee Junior College. Low-chill adaptation was obtained from cultivars from the southern Chinese and peento groups of peaches including ‘Peento’ and ‘Lukens Honey’. These were intercrossed and also combined with high-chill cultivars such as ‘Elberta’ and ‘Mayﬂower’ to produce a range of white- and yellow-ﬂeshed, melting and non-melting cultivars. In 1933, these programmes jointly released ‘Babcock’, a 350 CU peach described as an early-ripening, white-ﬂeshed freestone of fair size and good quality (Cullinan, 1937). ‘Babcock’ and its derivates ‘Giant Babcock’ and ‘Early Babcock’ were still being grown in California in the 1990s and exported to Asia where low-acid types are popular. Between 1933 and 1958 these breeding programmes released 23 cultivars adapted to the mild winters of southern California with 350 to 450 CU required (Table 5.2). ‘Babcock’ was also used extensively in later breeding programmes as a source of low-chill adaptation. In the late 1940s and early 1950s, lowchill breeding commenced in the USA at the University of Florida (UF) and in Brazil at Sao Paulo and Pelotas. All three programmes used the south China-derived ‘Peento’ and ‘Hawaiian’ as founding parents for low-chill adaptation (Byrne, 2003). In addition, the Brazilian programmes used a number of local cultivars

Table 5.2. Characteristics and parentage of peach cultivars released from the University of California, Riverside (1907–1961) and Chaffey Junior College (1919–1947) breeding programmes in southern California. (From Okie, 1998.) Cultivar

aFlesh

Chill (CU)

1933 1933 1939 1939 1939 1939 1939 1939 1939 1943 1945 1948 1948 1948 1948 1948 1948 1948 1948 1949 1951 1958 1958

350 450 450 450 450 450 350 450 450 450 100 450 450 450 450 450 450 450 450 350 450 450 350

Flesh coloura

Origin

Female parent

Male parent

W W W Y Y W W Y Y Y Y W W Y Y Y W W Y Y Y Y Y

UC–Riverside UC–Riverside Chaffey Jr Coll. Chaffey Jr Coll. UC–Riverside UC–Riverside UC–Riverside UC–Riverside Chaffey Jr Coll. UC–Riverside UC–Riverside Chaffey Jr Coll. Chaffey Jr Coll. Chaffey Jr Coll. Chaffey Jr Coll. Chaffey Jr Coll. Chaffey Jr Coll. Chaffey Jr Coll. Chaffey Jr Coll. UC–Riverside UC–Riverside UC–Riverside UC–Riverside

‘Strawberry’ × ‘Peento’ ‘Strawberry’ × ‘Peento’ ‘Lukens Honey’ ‘Sims’ ‘Paragon’ ‘J.H. Hale’ ‘J.H. Hale’ ‘7-2’ ‘Babcock’ ‘Prenda’ ‘Babcock’ ‘Babcock’ ‘Chaffey’ ‘Babcock’ ‘Lukens Honey’ ‘Imperial’ ‘Mayflower’ ‘Mayflower’ ‘Weldon’ Unknown ‘Hermosa’ ‘Peento Hybrid’ Unknown

F2 F2 ‘Elberta’ ‘Feicheng’ × ‘Bolivian Cling’ ‘BH7-7-4’ ‘Babcock’ ‘11-May’ ‘OP’ ‘Elberta’ ‘Sunglow’ ‘Quetta’ ‘Weldon’ ‘Weldon’ ‘Elberta’ ‘Elberta’ ‘Paragon’ ‘Weldon’ ‘Weldon’ ‘Elberta’ Unknown ‘71-9’ (‘Rochester’ × ‘Peento’) Unknown

Low-chill Cultivar Development

‘Babcock’ ‘C.O. Smith’ ‘Chaffey’ ‘Fontana’ ‘Golden State’ ‘Hermosa’ ‘Prenda’ ‘Ramona’ ‘Weldon’ ‘Bonita’ ‘Banquet’ ‘Babdon’ ‘Chadon’ ‘Gloribloom’ ‘Honeyberta’ ‘Impon’ ‘Maydon’ ‘Maywel’ ‘Welberta’ ‘Rubidoux’ ‘Ventura’ ‘Rochon’ ‘Tejon’

Year of release

colour: W, white; Y, yellow. 109

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imported by the Portuguese in the 16th century (Byrne and Bacon, 1999). Byrne and Bacon (1999) analysed pedigrees of cultivars released from 1976 to 1997 to determine the founding parents of lowchill breeding programmes in Brazil, Mexico and the USA. ‘Peento’ was identiﬁed as a primary source in all breeding programmes and is in the pedigree of the UF cultivars ‘Sunred’, ‘Sunlite’ and ‘Maravilha’. Other important founding clones, as sources of the low-chilling trait, are ‘Okinawa’ and ‘Hawaiian’. All three cultivars produce fruit with a long fruit development period (FDP; days from ﬂowering to harvest) that is white-ﬂeshed, soft and poor quality, but have provided a source of adaptation to subtropical environments. Lack of genetic diversity in breeding populations may limit cultivar improvement and prevent development of novel gene combinations for future progress. High levels of inbreeding and co-ancestry have been reported for high-chill peaches (Scorza et al., 1985). While all low-chill breeding programmes have used high-chill germplasm for high fruit quality, the inclusion of native low-chill parents in the breeding means they are genetically distinct. Scorza et al. (1988) studied 32 cultivars released by UF and found that the level of inbreeding was 0.039, assuming open pollination equated to outcrossing by unrelated males, but 0.286 with an assumption of open pollination equating to selﬁng. The second case is a relatively high level of inbreeding, considering that the inbreeding coefﬁcient will be 0.125 for half-sib mating and 0.250 for full-sib mating, and is comparable with the levels of inbreeding in eastern US high-chill peaches. Scorza et al. (1988) concluded that although unique and unrelated germplasm had been incorporated into the UF cultivars, a certain level of inbreeding had been required to concentrate the tree and fruit quality traits necessary for commercialization.

5.2 Current Low-chill Breeding Programmes Eleven public and two private breeding programmes across seven countries are currently

developing new low-chill peach and nectarine cultivars (Table 5.3). Most of these programmes have a primary focus on breeding low-chill cultivars although some, such as Zaiger Genetics, Inc., breed predominately for high-chill but have released several lowchill cultivars. Low-chill breeding programmes are located where the average temperature of the coldest month ranges from 12 to 16°C (Table 5.3). This corresponds to an average winter chilling of 250 to 650 CU using the Sharpe– Weinberger model (Sherman and RodriquezAlcazar, 1987; Sharpe et al., 1990). Low-chill breeding programmes are located between latitudes of 19° and 30°. Programmes located at the lower tropical latitudes are at high elevation, thus providing winter chill (Table 5.3). Low-chill breeding programmes are established in environments ranging from dry deserts, humid subtropics and tropical highlands to temperate locations (Table 5.4). Cultivars released from these programmes provide orchardists with adaptation to varying climatic, disease and pest pressures. The oldest of the current programmes are in the USA (Gainesville), Brazil (Pelotas and Campinas) and South Africa (Stellenbosch). The number of programmes has increased in the past 25 years with ﬁve programmes commencing in the 1980s and another three commencing in the 1990s (Table 5.4). It is interesting to speculate on the reasons for the increased effort in low-chill breeding over the past 25 years. Part of the increase is probably due to demand for cultivars adapted to local environments and local markets that were not being ﬁlled by imported cultivars. For example, the breeding programmes in Mexico select speciﬁcally for non-melting, yellow-ﬂeshed peaches that have a small amount of red blush. Mexican consumers associate this type of fruit with the high eating quality of native criollo peaches and so the Mexican breeders have market forces directing their breeding efforts in this direction; this is quite different to the objectives of many other breeding programmes that concentrate on highly coloured, meltingﬂesh types. Increased activity is probably also due to the inﬂuence of the UF breeding programme. New UF cultivars have been spread

Table 5.3. Location, latitude, altitude, coldest month mean temperature and winter chilling of 13 breeding programmes that have released low-chill peach and nectarine cultivars.

Institution or company

Australia

Department of Primary Industries and Fisheries, Nambour, Queensland University of Western Sydney, Richmond, New South Wales Empressa Brasileira de Pesquisa Agropecuaria/Centro Nacional de Pesquisa de Fruteiras de Clima Temperado (EMBRAPA/CPACT), Pelotas, Rio Grande do Sul Instituto Agronomico (IAC), Campinas, Sao Paulo Centro de Fruiticultura, Colegio de Postgraduidos, Chapingo, Mexico State Universidad Autonoma de Queretaro, Area Agricola, Queretaro, Queretaro Agricultural Research Council Infruitec–Nietvoorbij, Stellenbosch Taiwan Agricultural Research Institute, Wufeng, Taichung Royal Project Foundation, Kasetsart University, Angkhang Royal Agricultural Station, Angkhang Sun World International, Inc., Coachella, California Zaiger Genetics, Inc., Modesto, California University of Florida, Gainesville, Florida Texas A&M University, Weslaco, Texas

Australia Brazil

Brazil Mexico Mexico South Africa Taiwan Thailand USA USA USA USA aWinter

Latitude (°)

Altitude (m)

Mean temperature of coldest month (°C)

Mean winter chilling (CU)a

26

25

15.0

200

33 32

113 60

10.2 12.3

540 370

23 19

669 2245

17.0 12.9

100 320

20

1876

14.8

210

33

91

12.4

360

24 19

85 1400

15.7 13.0

160 320

33 37 29 26

−22 27 29 22

12.3 7.5 12.7 14.2

370 870 340 240

Low-chill Cultivar Development

Country

chill units (CU) of each location calculated using mean temperature of coldest month as per George and Nissen (1998).

111

112

Table 5.4.

B.L. Topp et al.

Low-chill peach breeding programmesa arranged by starting year and climate type. Climate type

Starting year

Dry

1937–1953

1980–1990 1990–2000

Weslaco, USA Coachella, USA

Humid subtropics

Temperate

Pelotas, Brazil Sao Paulo, Brazil Gainesville, USA Taichung, Taiwan

Stellenbosch, South Africa

Nambour, Australia

Richmond, Australia

Tropical highland

Chapingo, Mexico Queretaro, Mexico Angkhang, Thailand

aCountry,

town, institution/company responsible for the breeding programme: Australia, Nambour, Department of Primary Industries and Fisheries; Australia, Richmond, University of Western Sydney; Brazil, Sao Paulo, Instituto Agronomico (IAC); Brazil, Pelotas, Empressa Brasileira de Pesquisa Agropecuaria/Centro Nacional de Pesquisa de Fruteiras de Clima Temperado (EMBRAPA/CPACT); Mexico, Chapingo, Colegio de Postgraduados; Mexico, Queretaro, Instituto Nacional de Investigaciones Forestales y Agropecunarias; South Africa, Stellenbosch, Agricultural Research Council Infruitec; Taiwan, Taichung, Taiwan Agricultural Research Institute; Thailand, Angkhang, Royal Foundation and Kasetsart University; USA, Coachella, Sun World International, Inc.; USA, Gainesville, University of Florida; USA, Weslaco, Texas A&M University.

far and wide, particularly up until 1992, when all material was in the public domain. UF cultivars are grown commercially and are the mainstay of low-chill industries in many countries. In Australia, for example, although there was a small low-chill industry prior to 1980, the industry only expanded with the introduction of UF cultivars. The industry has now moved on to the next phase of development where it requires new cultivars that are tailored for the local environment and market. However, without the importation of the UF cultivars, the local industry would not have developed and be in a position to sponsor new breeding. Of the 842 new peach and nectarine cultivar descriptions published internationally between 1980 and 1992, approximately 16% (135 cultivars) were low-chill (Della Strada et al., 1996). In the next decade (1991–2001) 1126 new peach and nectarine cultivar descriptions were published, of which 71 (6%) were classiﬁed as low-chill (Della Strada and Fideghelli, 2003). The majority of low-chill cultivar releases are from the three longest-running public breeding programmes located in the USA (Gainesville, Florida) and Brazil (Pelotas and Sao Paulo) (Fig. 5.1/Plate 48). These programmes have been operating for about 50 years and

released over 100 cultivars from 1980 to 2004 (Table 5.5). They have the common objective of breeding for adaptation to subtropical environments, but differ in other ways. The Brazilian programmes are supplying cultivars for the full stone fruit season and so release cultivars with FDP up to 180 days. In the USA, the bulk of peach production is from temperate high-chill locations with fruit available from late May; hence the Florida programme aims to produce only short FDP cultivars that are harvested before this time. In the following sections low-chill breeding programmes are described in terms of objectives and outputs. There are sources of low-chill cultivars other than the breeding programmes described here. Some high-chill breeding programmes develop low-chill cultivars for speciﬁc purposes. In California, private breeding programmes located in temperate environments select low-chill cultivars for early production in the southern part of the Central Valley. In Japan, low-chill peaches are being created for use in protected culture (I. Kataoka and K. Beppu, Japan, 2004, personal communication). Traditional Japanese highchill cultivars such as ‘Hakuho’ are hybridized with low-chill cultivars ‘Flordaprince’, ‘Flordaglo’, ‘TropicSnow’ and ‘Earligrande’.

Low-chill Cultivar Development

113

70 Canning peach Nectarine Peach

No. of cultivar releases

60 50 40 30 20 10 0 Brazil

Mexico

South Africa

USA

Fig. 5.1. Numbers of new low-chill peach and nectarine cultivars released from four countries, 1980–1992. These countries accounted for 94% of low-chill cultivars released in this period. (Adapted from Della Strada et al., 1996.)

Low-chill cultivars can be forced to ﬂower in heated plastic tunnels earlier than high-chill cultivars and so ripen earlier. In China, there is breeding for low-chill ornamental peach cultivars with attractive ﬂowers that can be used for peach ﬂower festivals during Chinese New Year (Wang et al., 2002) but there is only limited breeding for low-chill cultivars for fresh fruit (L. Wang, China, 2004, personal communication).

Australia, New South Wales In Australia, low-chill cultivars are used to extend the early season. Currently the earlyripening UF cultivars are the mainstay of this industry. Tree sales from the Australian Nurserymen’s Fruit Improvement Company in 2001–2003 ranked ‘TropicBeauty’, ‘Flordaprince’ and ‘UFGold’ as the most planted peach cultivars and ‘SunWright’ and ‘SunBest’ as the most planted nectarine cultivars (G. Porter, Australia, 2004, personal communication). The University of Western Sydney began breeding low- and medium-chill peaches in the early 1990s. The programme is located at Richmond, New South Wales, in a temperate location that receives annual winter chilling of 400–600 CU. New selections are protected and commercialized through the Phytonova

company (McPhee, 2003). One of the selection strategies for obtaining high eating quality is to develop cultivars with FDP of 120 days. The programme has released ten peach and nectarine selections in the 300–400 CU range.

Australia, Queensland The Queensland Department of Primary Industries and Fisheries commenced breeding low-chill peaches at Maroochy Research Station at Nambour in the mid-1990s. The aim of the programme is to produce highquality peach and nectarine cultivars requiring 100–400 CU but with emphasis in the 100–150 CU range. Breeding is partly sponsored by grower organizations and has developed in response to their requirements for new cultivars with local adaptation and with their input into the breeding objectives and commercialization of the new cultivars. Domestically, it is important that quality fruit are produced by the low-chill sector of the industry in order to start consumers enjoying their spring purchases of peaches. There is also the prospect of expanding Australia’s export to South-east Asia from September to December as there is a marked reduction in peach volume in Asia at this time (Nissen et al., 2000; Wei, 2001). Initial hybridizations

114

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Table 5.5. Low-chill (<400 CU) peach and nectarine cultivars released from 1980 to 2004. Cultivars are arranged alphabetically by the breeding programme from which they were released and then by cultivar name.

Cultivar

Year of introduction

Cropa

Chillb (CU)

Flesh typec

Flesh colourd

FDPe (days)

Purposef

Colegio de Postgraduados, Chapingo, Mexico ‘Diamante Mejorado’ 1995 P 250 NM Y 110 ‘Oro Mex’ 1995 P 350 NM Y 130 ‘Oro-Azteca’ 1992 P 275 NM Y 130 ‘Oro-B’ 1995 P 275 NM Y 105 Empressa Brasileira de Pesquisa Agropecuaria (EMBRAPA), Pelotas, Rio Grande do Sul, Brazil ‘Ametista’ 1994 P 400 NM Y 131 ‘Anita’ 1999 N 375 NM W 97 ‘Atenas’ 2004 P 250 NM Y 125 ‘Bolinha’ 1986 P 400 NM Y 151 ‘BR-2’ 1981 P 300 NM O–Y 160 ‘BR-6’ 1981 P 350 NM Y 151 ‘Branca’ 1989 N 350 M W 90 ‘Charme’ 2000 P 350 M W 105 ‘Chimarrita’ 2000 P 350 M W 115 ‘Chinoca’ 1987 P 275 M W 106 ‘Chirua’ 1995 P 250 M W 113 ‘Chula’ 1995 P 400 M W 122 ‘Della Nona’ 1992 P >300 M W 121 ‘Dulce’ 1992 N 400 M W 103 ‘Eldorado’ 1989 P 300 NM Y 143 ‘Esmeralda’ 1987 P 350 NM Y 126 ‘Granada’ 1995 P 300 NM Y 98 ‘Granito’ 1993 P 400 NM O–Y 112 ‘Guaiaca’ 1993 P 250 M Y 99 ‘Jade’ 1987 P 300 NM Y 124 ‘Jubileu’ 1998 P 300 NM Y 127 ‘Leonense’ 1998 P 275 NM Y 128 ‘Linda’ 1989 N 400 M Y 95 ‘Maciel’ 1992 P <300 NM Y 136 ‘Marfim’ 1999 P 350 M W 120 ‘Marli’ 1984 P 300 M W 108 ‘Olimpia’ 2004 P 300 NM Y 150 ‘Onix’ 1985 P 300 NM Y 122 ‘Pampeano’ 1993 P 175 M W 86 ‘Pepita’ 2000 P 150 NM Y 91 ‘Pilcha’ 1985 P 400 M Y 116 ‘Planalto’ 1992 P 400 NM W 101 ‘Precocinho’ 1981 P 150 NM Y 101 ‘Riograndense’ 1991 P <300 NM Y 113 ‘Santa Aurea’ 2004 P 400 NM Y 122 ‘Sensacao’ 2004 P 200–300 NM Y 107 ‘Sentinela’ 1985 P 150 M W 98 ‘Turmalina’ 1999 P 350 NM Y 111 ‘Vanguarda’ 1989 P <150 NM Y 102 Infruitec, Stellenbosch, South Africa 1997 N L M Y Late Nov ‘Alpine’ (p)g ‘Classic’ (p) 1994 P M NM Y Early Dec ‘Crimson Giant’ (p) 1995 N L M Y Mid-Dec

FR FR FR FR PR FR DU PR PR PR FR FR FR FR FR FR FR FR DU PR PR PR FR PR PR PR FR DU FR FR DU PR FR PR FR FR PR DU DU DU FR PR PR FR FR FR

(Continued)

Low-chill Cultivar Development

Table 5.5.

Cultivar

115

continued Year of introduction

Cropa

Chillb (CU)

Flesh typec

Flesh colourd

‘Donnarine’ (p) 1987 N L M Y ‘Elandia’ (p) 1998 P L-M M Y ‘Escellence’ (p) 1995 P L-M M Y ‘Marg. Pride’ (p) 1991 N L M Y ‘Novadonna’ (p) 1990 P L-M NM Y ‘Olympia’ (p) 1985 N M M Y ‘Oribi’ (p) 1993 P M M Y ‘Summersun’ (p) 1995 P L NM Y ‘Transvalia’ (p) 1987 P L NM O-Y ‘Unico’ (p) 1996 N L M Y ‘Western Cling’ (p) 1994 P L NM Y Instituto Agronomico (IAC), Sao Paulo, Brazil ‘Arlequim’ 1981 P <50 M W ‘Aurora-1’ 1987 P <50 NM Y ‘Aurora-2’ 1987 P <50 NM Y ‘Branca De Guapiara’ 1984 N <50 M W ‘Canario’ 1982 P <50 M Y ‘Catita’ 1982 P <50 M W ‘Catuiba’ 1982 P <50 M Y ‘Centenaria’ 1987 N <50 M Y ‘Centenario’ 1987 P <50 M Y ‘Delioso Precoce’ 1987 P <100 M W ‘Docura’ 1980 P <50 M W ‘Docura-2’ 1983 P <50 M W ‘Docura-3’ 1983 P <50 M W ‘Docura-4’ 1987 P <50 M W ‘Douradão’ 1998 P <100 M Y ‘Dourado-1’ 1985 P <50 M Y ‘Dourado-2’ 1985 P <50 M Y ‘Joia-1’ 1983 P <50 M W ‘Joia-2’ 1983 P <50 M W ‘Joia-3’ 1987 P <50 M W ‘Joia-4’ 1987 P <50 M W ‘Joia-5’ 1987 P <50 M W ‘Josefina’ 1986 N <50 M W ‘Momo’ 1981 P <50 NM Y ‘Ouromel-2’ 1983 P <50 M Y ‘Ouromel-3’ 1983 P <50 M Y ‘Ouromel-4’ 1983 P <50 M Y ‘Perola De Mairinque’ 1980 P <50 M W ‘Petisco-2’ 1983 P <50 M Y ‘Precoce De Itupeva’ 1984 N <50 M W ‘Regis’ 1987 N <50 M Y ‘Rosalina’ 1984 N <50 M Y ‘Sol Do Vale’ 1982 P <50 M W ‘Somel’ 1984 N <50 M W ‘Tropical’ 1989 P <50 M Y ‘Tropical-2’ 2002 P <50 M Y Instituto Nacional de Investigaciones Forestales y Agropecuarias (INIFAP), Mexico ‘Cengua-Guia’ 1990 P 250 M W ‘Comonfort’ 1992 P 250 NM Y

FDPe (days)

Purposef

Mid-Dec Late Jan Late Dec Mid-Dec Late Nov Mid-Dec Late Feb Late Nov Mid-Nov Mid-Nov Early Dec

FR FR FR FR FR DU DU DU FR FR FR

180 110 118 115 128 150 125 108 115 107 135 115 120 120 105 108 115 100 105 110 103 105 112 185 110 108 112 160 145 115 95 120 145 120 80 78

FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR DU FR FR FR FR FR FR DU DU FR FR FR FR

160 130

RO FR (Continued)

116

Table 5.5.

Cultivar

B.L. Topp et al.

continued Year of introduction

Cropa

Chillb (CU)

‘Dorado’ 1992 P 250 ‘Regio’ 1992 P 200 ‘Rendidor’ 1992 P 300 ‘Seleccion 165’ 1980 P 300 Sun World International, Inc., Bakersfield, California, USA ‘Supechfifteen’ (p) 2002 P 150 ‘Supechthirteen’ (p) 2002 P 150 Taiwan Agricultural Research Institute, Taichung, Taiwan ‘SpringHoney’ 2003 P 180 Texas A&M University, Weslaco, Texas, USA ‘Earligrande’ 1979 P 250 ‘TropicPrince’ (p) 2001 P 150 ‘ValleGrande’ 1990 P 250 University of Florida, Gainesville, Florida, USA ‘Carolina’ 1990 N 325 ‘Desertred’ 1983 P 250 ‘Diamante Especial’ 1995 P 250 ‘Fla.85-1’ 1995 P 400 ‘Flordadawn’ 1989 P 250 ‘Flordagem’ 1983 P 250 ‘Flordaglo’ 1988 P 150 ‘Flordaguard’ 1991 P 300 ‘FlordaMex 1’ 1989 P 400 ‘Flordaprince’ 1982 P 150 ‘FlordaRio’ 1994 P 400 ‘Flordastar’ 1988 P 225 ‘Forestgold’ 1991 P 350 ‘Hermosillo’ 1984 P 300 ‘Newbelle’ 1984 P 150 ‘Opedepe’ 1982 P 150 ‘Oro A’ 1989 P 250 ‘Rayon’ 1982 P 175 ‘Sherman’s Red’ 1985 P 300 ‘SunBest’ (p) 2002 N 225 ‘Sunblaze’ 1985 N 250 ‘Sunbob’ 1989 N 200 ‘Suncoast’ 1994 N 400 ‘Sundollar’ 1989 N 400 ‘Sundowner’ 1987 N 250 ‘Sunhome’ 1985 N 300 ‘Sunmist’ 1994 N 300 ‘Sunraycer’ 1994 N 275 ‘Sunsnow’ 1990 N 250 ‘Sunsplash’ 1993 N 400 ‘SunWright’ 1991 N 200 ‘UF2000’ (p) 2000 P 300 ‘UFBeauty’ (p) 2003 P 200 ‘UFCharm’ (p) 2000 P 250 ‘UFGold’ (p) 1996 P 225 ‘UFO’ (p) 2000 P 250

Flesh typec

Flesh colourd

FDPe (days)

Purposef

NM NM NM NM

Y Y Y Y

110 130 160 150

FR FR FR GE

M M

Y Y

5 Apr 1 Apr

FR FR

M

W

82

FR

M M M

Y Y Y

75 <90 85

FR FR FR

M M NM M M M M M M M M M M M M M NM M M M M M M M M M M M M M M NM NM NM NM NM

Y Y Y Y Y Y W Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y W Y W Y Y Y Y Y Y Y

90 90 120 67 60 85 85 130 95 80 92 72 95 108 105 85 83 105 75 90 90 100 77 70 90 88 80 85 90 74 80 95 83 80 80 95

FR FR FR GE FR FR FR RO FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR FR (Continued)

Low-chill Cultivar Development

Table 5.5.

Cultivar

117

continued Year of introduction

Cropa

Chillb (CU)

Flesh typec

Flesh colourd

‘UFQueen’ (p) 1998 N 250 NM Y ‘UFSun’ (p) 2003 P 100 NM Y ‘White Opal’ 1998 P 200 M W ‘White Satin’ 2000 P 250 M W ‘Zorrito’ 1985 P 275 M Y University of Florida and Texas A&M University, USA ‘FlordaGrande’ 1985 P 50 M Y ‘Tropic Blush’ 1990 P 200 M Y ‘TropicBeauty’ 1988 P 150 M Y ‘TropicSnow’ 1988 P 250 M W ‘TropicSweet’ 1986 P 175 M Y University of Georgia, US Department of Agriculture and University of Florida, USA ‘Gulfking’ (p) 2004 P 350 NM Y ‘Gulfprince’ (p) 2000 P 375 NM Y University of Western Sydney, Richmond, New South Wales, Australia ‘Dawn Gold’ (p) 2003 N 200–300 M Y ‘December Ice’ (p) 2003 N 350 M W ‘Hail’ (p) 2003 N 200–300 M W ‘Honey Ice’ (p) 2003 N 400 M W ‘Pale Ice’ (p) 2003 N 250–300 M W Zaiger Genetics, Inc., Modesto, California, USA ‘April Glo’ (p) 1990 N 150 M Y ‘Earliglo’ (p) 1990 N 150 M Y ‘Earlitreat’ (p) 1997 P 300 M Y ‘Evas Pride’ (p) 1991 P 250 M Y ‘Mayglo’ (p) 1984 N 200 M Y ‘Red Roy’ (p) 2001 N 300 M Y ‘Snow Angel’ (p) 2004 P 250 M W ‘Zee Fire’ (p) 2003 N 250 M Y

FDPe (days)

Purposef

97 103 75 75 95

FR FR FR FR OR

105 90 85 93 90

FR FR FR FR FR

73–80 94

FR FR

109 129 106 128 113

FR FR FR FR FR

<90 <90 <90 <90 <90 <90 <90 <90

FR FR FR FR FR FR FR FR

aCrop:

P, peach; N, nectarine. chilling requirement in chill units (CU); or L, low-chill; M, moderate-chill. cFlesh type: M, melting; NM, non-melting. dFlesh colour: O, orange; W, white; Y, yellow. eFDP: fruit development period in days; or harvest date at place of origin. fPurpose: DU, dual purpose of fresh and processing; FR, fresh; GE, germplasm; OR, ornamental; PR, processing; RO, rootstock. g(p), patented. bCultivar

have drawn heavily on parents from UF but have also incorporated local subtropical peaches (Ward, 1952) and germplasm from Brazil, Mexico, California, Georgia, Vietnam and China. Brazil, Pelotas The breeding programme of the Brazilian Agricultural Research Enterprise (Embrapa Clima

Temperado) is located at the Agriculture Research Centre of Temperate Crops (CPACT) at Pelotas, Rio Grande do Sul. It began in 1953 and has released 21 fresh market peach, six nectarine and 25 dual-purpose (fresh and processing) peach cultivars requiring 150–500 CU. The peach harvest in Rio Grande do Sul has been extended from 15 days in 1963, when there were only two cultivars (‘Aldrighi’, a seed-propagated clingstone and ‘Delicioso’, a

118

B.L. Topp et al.

white-ﬂeshed peach) grown, to over 100 days with the current releases (Raseira et al., 1992). The main objectives are for adaptation to 150– 500 CU but with emphasis on 200–300 CU, productivity, resistance to brown rot, bacterial spot and frost, and acceptable fruit size, shape, ﬁrmness and ﬂavour (Raseira et al., 2003). Temperatures during the winter bloom period are highly variable in southern Brazil and this contributes to variation in yield. Cultivars such as ‘Esmeralda’ consistently produce heavy crops despite these conditions; the reason for this cultivar’s speciﬁc yield stability is an area of ongoing research.

Brazil, Sao Paulo This programme began in 1950 at the Instituto Agronomico (IAC) in Sao Paulo. The aim of the programme is to produce peaches requiring 50–150 CU. Initial germplasm included ‘Jewel’, ‘Suber’, ‘Hall’s Yellow’, ‘Lake City’ and ‘Angel’ imported from the USA, plus a number of locally selected seedlings probably derived from Portuguese introductions from the 16th century (Barbosa et al., 1997). These were crossed with medium-chill North American germplasm. From 1970 to 2000 the best IAC cultivars were intercrossed with selections from UF. Emphasis has been on fresh market fruit or fruit that can serve the dual purpose of canning and fresh market. Fifty-eight cultivars have been released, all needing 50–200 CU, and account for about 1.2 million of the 1.9 million trees grown in the state of Sao Paulo. The remaining cultivars are releases from UF and EMBRAPA. IAC cultivars cover the full harvest season with FDP of 80–180 days. Future breeding will aim to produce compact tree structure, ultra-early ripening, extra-large fruit size, very attractive and ﬁrm fruit, improved disease and pest resistance and tolerance to warmer climates.

Mexico, Chapingo The breeding programme of the Centro de Fruiticultura, Colegio de Postgraduidos at

Chapingo started in 1985 with the main objective being to develop low-chill peaches over a wide range of FDP with resistance to powdery mildew. Breeders at UF and Chapingo have cooperated closely, sharing and testing germplasm and jointly releasing the full yellow-skin, non-melting ﬂesh peach ‘Oro A’ in 1989 (this cultivar has found a niche in Australia, where it is marketed as a ‘peachcot’ owing to its colour, size and low fuzz). The Chapingo programme almost exclusively produces non-melting peaches for the fresh market. Mexican consumers associate high sugar and good ﬂavour with mostly yellowskinned criollo peaches that have only a small amount of red blush and so the breeding programme has selected for this appearance. A series of mildew-resistant peaches has been released and now the programme is focusing on developing resistance to Monilinia (particularly the blossom blight phase of the disease). Adaptation is sought mainly in the 150–450 CU range, but since 1993 there has been some breeding for 500–700 CU genotypes for the peach industry in the Aguascalientes and Zacatecas regions. Mexico, Queretaro Salvador Perez at the Universidad Autonoma de Queretaro has studied the phenology and adaptation of feral Mexican and imported peach seedling populations across Mexico in order to deﬁne breeding strategies for the subtropics (Perez, 1989, 2003, 2004; Perez et al., 1993; Perez-Gonzalez, 2001, 2002). Several cultivars were released from the Instituto Nacional de Investigaciones Forestales y Agropecuarias (INIFAP) breeding programme (Table 5.5) with emphasis on developing resistance to powdery mildew in non-melting ﬂesh peach needing 50–450 CU. The focus now is on fruit quality in non-melting ﬂesh types for the fresh market, in both yellow and white ﬂesh. Fruit must have low to medium acidity with <0.6 mEq malic acid, high sugar with >15% total soluble solids (TSS), medium size (120–180 g), round to ﬂat shape and from bright orange to red skin covering 80% of the surface. Seedlings are grown on commercial orchards rather than at a research station, as

Low-chill Cultivar Development

occurs with most other programmes. This was done because the university research plot was located far from the commercial sites and it allows screening of higher-chilling seedling populations at high-elevation orchards. From 100 to 2000 seedlings are produced each year. Advanced selections are tested for 5 years prior to public release. The most recent release is ‘Fred’ (‘Lucero’ × ‘Springcrest’) in 2000, which is a 450 CU, non-melting peach with excellent quality and resistance to ﬂesh browning.

South Africa, Stellenbosch The Agricultural Research Council (ARC) Infruitec–Nietvoorbij breeding programme started in 1937 and caters for the South African canning industry, dried fruit industry and fresh market, both domestic and export. Inadequate chilling of traditional high-chill peach cultivars is a problem in the early-maturing region in South Africa and so breeding has concentrated on developing cultivars with a chilling requirement of <400 CU. Speciﬁc breeding objectives are high skin over-colour, development of >80% red blush, round fruit with no tip or suture, high ﬂesh ﬁrmness, high sugar to acid ratio, >13% TSS, ﬁne texture, absence of split pits and a minimum cold storage life of 4 weeks. Approximately 3000 hybrid seedlings are produced each year, with about two-thirds being low-chill (<400 CU) early types. Selection is for peach and nectarine, yellow and white ﬂesh and both melting and non-melting ﬂesh. Advanced selections are planted in semi-commercial trials prior to release. This programme accounts for 95% of all processed peach, 90% of fresh market peach and 60% of fresh market nectarine cultivars grown in South Africa.

119

were introduced to the highlands (>1500 m above sea level) in the 1950s, but soil erosion on the steep slopes led the Taiwan government to commence breeding for low-chill cultivars that could be grown at lower elevations (locations receiving <250 CU). New cultivars must be white-ﬂeshed, low- or sub-acid, with high juiciness and high sugar level. The stonyhard ﬂesh ‘Ing-go’ is being used as a standard for ﬁrmness as are the non-melting ﬂesh genotypes from Brazil and Florida (Wen and Sherman, 2002). ‘Tainung No. 1’ peach was selected from a cross between the Brazilian peach ‘Premier’ and the Florida peach ‘Flordaking’ and named in 2001. More recently ‘SpringHoney’ peach was released to ﬁll the need for a lowland, subtropical cultivar that produces early-ripening, low-acid, white, melting-ﬂesh fruit (Ou and Wen, 2003). It was derived from a population of ‘Premier’ × ‘Flordabelle’.

Thailand, Angkhang Low-chill peach breeding by the Royal Project Foundation and Kasetsart University commenced in 1997. Test plots are located in the mountainous regions of northern Thailand at the Royal Angkhang Research Station and also at Khunwang. The tropical highland peach-growing regions are characterized by long growing season, high rainfall and mild winters. Objectives are for 100–300 CU cultivars, ripening during the dry season from March to June, and fruit with bright red skin, round shape, white and yellow ﬂesh and intense ﬂavour including both low- and highacid types. The breeder works closely with and is testing advanced selections from the Texas A&M University (TAMU) programme.

USA, California, Sun World Taiwan, Taichung The Taiwan Agricultural Research Institute began breeding in 1980 for peach, nectarine and now peento cultivars for the local market. High-chill peach cultivars from Japan

Sun World International, Inc. has been actively involved in low-chill peach breeding since 1987 when the ﬁrst large-scale seedling populations were planted in the Coachella Valley of southern California. In this region there is often less than 300 CU and trees are exposed

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to prolonged periods above 38°C during much of summer and into autumn. The goal was to develop cultivars adapted to these conditions that ripen in the ﬁrst half of April, before the lower San Joaquin Valley harvest begins. The programme initially used UF selections as parents both in combination with commercial Californian cultivars and mated inter se. About 3000 seedlings from low-chill × low-chill crosses are planted annually in the Coachella Valley and about 2500 seedlings annually from lowchill × medium-chill crosses are planted near Bakersﬁeld. Sun World also has an active breeding programme for low-chill plums and a small effort for low-chill apricot and rootstocks. High temperatures in spring in the Coachella Valley result in FDPs up to 20 days less than for Bakersﬁeld in the San Joaquin Valley. The short FDP and high temperatures in Coachella mean that small fruit size, low fruit ﬁrmness, prominent tips and low or inconsistent bloom require high selection pressure in the breeding programme. New cultivars are patented if they are to be grown commercially in the USA or distributed to other countries where they are licensed to growers on a production–royalty basis. ‘Supechthirteen’ and ‘Supechﬁfteen’ are patented peach cultivars grown commercially by Sun World in the Coachella Valley.

USA, California, Zaiger Genetics Zaiger Genetics, Inc. has released a number of low-chill peach and nectarine cultivars, with ‘Mayglo’ nectarine in 1984 being one of their ﬁrst. Low-chill seedlings are selected at highchill test plots at Modesto, California. The primary goal of these selections is for very early ripening in California. Creating earlier ripening through earlier ﬂowering (lower chill) is possible in temperate climates such as California where spring frosts do not occur. Low-chill selections made in this type of environment require testing in the subtropics to screen for problems associated with growing peaches in these locations (blind nodes, pointy fruit shape often accompanied by suture bulges, uneven ripening and bud drop). All

cultivars from this private breeding programme are protected by plant patent. USA, Florida, University of Florida Since its inception in 1953, the programme has released over 40 cultivars of peach and nectarine that are being tested in 76 countries and territories and grown commercially in 23 countries. As this programme has been active for the past 50 years, many of the cultivars have been replaced by newer ones. Advanced germplasm from the UF programme has been used as parental material in most low-chill peach breeding programmes. In addition, breeders from Australia, Mexico, Spain, Taiwan and the USA have studied at the UF programme and developed breeding philosophies and techniques from this association. Breeders from many other low-chill programmes have beneﬁted from close interaction with the UF programme. The original objectives at UF were to produce a series of peach and nectarine cultivars adapted to Florida and bearing high-quality, melting-ﬂesh fruit with short FDP of <100 days (Sherman and RodriquezAlcazar, 1987). The ‘Florda’ series of peaches and ‘Sun’ series of nectarines comprise this group of cultivars. More recently, the UF programme has changed to breeding non-melting peaches and nectarines in order to improve ﬂavour (Sherman et al., 1990). The idea is that with ﬁrmer, non-melting ﬂesh, growers can leave fruit on the tree closer to its physiological fullripe stage and still have sufﬁciently ﬁrm fruit to market. After incorporating the non-melting ﬂesh gene from Mexican, North Carolina and Brazilian germplasm, the breeders have selected heavily to remove undesirable traits of long FDP, high chill, lack of red skin, offﬂavours in over-ripe fruit (Karakurt et al., 2000) and low acidity. The non-melting ﬂesh series of peach and nectarine cultivars are preﬁxed with ‘UF’ (‘UFSun’, ‘UFQueen’, etc.). Main selection criteria are for either white or yellow non-melting ﬂesh, more than 11% TSS, higher red skin over-colour, higher aroma and ﬂavour, less twiggy (selecting for thicker and fewer fruiting laterals) tree structure with high ﬂower bud density, few blind nodes, low

Low-chill Cultivar Development

bud drop, and fruit set with night temperature above 14°C. Since 1992, UF has acquired plant breeding rights on all new cultivars. Additionally, UF, the University of Georgia and the US Department of Agriculture cooperate in a breeding programme at Attapulgus, Georgia to produce mid-chill cultivars requiring 400 to 650 CU but with some in the 250 to 400 CU range (Beckman et al., 1995; Krewer et al., 1998). Cultivars released from this programme are named with the preﬁx ‘Gulf’, for example ‘Gulfking’ and ‘Gulfprince’.

USA, Texas, Texas A&M University The TAMU stone fruit breeding programme commenced at College Station in 1939 and is selecting both medium- (350–650 CU) and low-chill (<350 CU) cultivars. In the 1980s, collaborative work with UF resulted in joint releases of ‘Flordagrande’, ‘TropicBeauty’, ‘TropicSnow’ and ‘TropicSweet’. Low-chill breeding continues with evaluation at the South Texas Research and Extension Center at Weslaco and at sites in Florida, California, Mexico, Thailand and Uruguay. An initial objective of this work was to develop peach cultivars ripening after ‘Flordaprince’ and before ‘TropicBeauty’. The ﬁrst release is ‘TropicPrince’, a yellow-ﬂeshed, melting peach, ripening after ‘Flordaprince’. During the 1990s, TAMU began to develop business collaborations with Burchell Nursery in the USA and several organizations in Spain, Australia and Uruguay to better utilize diverse genotypes in breeding and to generate funding. These collaborations have allowed the TAMU programme to expand the breeding objectives beyond yellow-ﬂeshed peaches to include work on non-melting, white-ﬂeshed, low-acid, high soluble solids nectarines and peento materials.

5.3 Common Objectives in Low-chill Peach Breeding Objectives of low-chill peach breeding overlap to a large extent with those for high-chill peach. Successful new cultivars must combine

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characteristics that make the trees well adapted and productive, and the fruit desired by consumers. Many of the selection traits that are common in both high- and low-chill breeding programmes have been described previously (Scorza and Okie, 1990; Scorza and Sherman, 1996; Byrne et al., 2000). The following discussion concentrates on those traits that require particular selection emphasis as a consequence of working with low-chill genotypes.

Low chilling requirement The effects of chilling in breaking leaf and ﬂower bud endo-dormancy are not well understood and this is reﬂected by the variety of methods used for measuring chilling requirement. Weinberger (1950) deﬁned 1 chill-hour as 1 h at or below 7.2°C (45°F); a peach cultivar with a chilling requirement of 800 chill-hours would need 800 h below 7.2°C to break dormancy. Richardson et al. (1974) presented the ‘Utah’ model which ascribes units of chill and allowed for negation of chilling by high temperatures. In this model, 1 chill unit is the maximum amount of chilling that can occur at the optimum temperature with partial chilling accumulated at less optimum temperatures. Erez et al. (1990) proposed a dynamic model that allows for negation of chilling but only by high temperatures occurring immediately after the chilling. In low-chill regions, where the daytime winter temperatures are often in the chill negation range, the dynamic model appears to be more effective than the Utah or chill-hour model (Allan et al., 1995). The Weinberger–Sharpe model (Sharpe et al., 1990) uses average monthly winter temperatures to predict how cold the winter was and thus the relative amount of winter chilling accumulated. This model is useful for predicting location chilling accumulation in order to choose cultivars with similar chilling requirements for cultivar testing. Breeders require a method of measuring the chilling requirement of genotypes. One method is to use controlled screening tests whereby whole trees, rooted cuttings, excised shoots or single nodes are forced to ﬂower in

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warm glasshouses after exposure to known amounts of chilling temperatures (Dennis, 2003). These tests are expensive and it is not feasible to incorporate them into a breeding programme that requires evaluation of thousands of genotypes. In practice, peach breeders use bloom date as an indicator of chilling requirement with the lowest-chill genotypes ﬂowering ﬁrst (Scorza and Sherman, 1996). Standard cultivars are used as comparators. In the UF programme the standards used are ‘Okinawa’ (150 CU), ‘Sunred’ (250 CU), ‘Early Amber’ (350 CU) and ‘Sunlite’ (450 CU) (Sherman and Lyrene, 1998). Several authors have reported on progenies in which the mean chilling requirement of the seedlings was statistically the same as the mid-parent mean (Lesley, 1944; Lammerts, 1945; Sharpe, 1961; Bassols, 1973). The conclusion is that chilling requirement is a quantitatively inherited character with genes having a cumulative, similar effect. However, there is some evidence for one or a few genes with major effects (Scorza and Sherman, 1996), skewing the distribution curve of the progeny towards the lower-chilling parent. In the Brazilian breeding programme it has been possible to produce seedlings with good adaptation to mild winters in the ﬁrst generation of crossing between low-chill Brazilian seed parents and high-chill Canadian and US pollen parents. The low-chill seed parents that have been efﬁcient in transferring lower chilling requirement to their progeny are ‘Maciel’, ‘Precocinho’ and ‘Diamante’, and particularly ‘Cerrito’ and ‘Sunred’ (M.C.B. Raseira, Brazil, 2004, personal communication).

Time of flowering Time of ﬂowering depends on two factors: the CU necessary to complete rest and the growing degree-hours (GDH) required after endodormancy to reach full bloom (Richardson et al., 1974; Citadin et al., 2001). Breeders may wish to select for late bloom to reduce the risk of spring frost damage. If there was variability for both CU and GDH in peach then it should be possible to produce late-ﬂowering cultivars by increasing the CU requirement or

the GDH requirement or both. In low-chill locations, the CU requirement cannot be increased a great deal without reduction in productivity that occurs with inadequate chilling and loss of adaptation. It is difﬁcult and expensive to measure the separate components of CU and GDH, and there is still much to understand in terms of the critical threshold temperatures that are needed for their accumulation (Felker and Robitaille, 1985). A pragmatic solution is to select for late bloom and productivity at the same time. In this way, the selected genotypes are not late blooming due to an increased CU requirement that makes them poorly adapted. Selection for late-blooming genotypes in a medium- to high-chill environment that reliably set high crop loads was examined by Souza et al. (2000) in a population of low- and medium-chill peaches. The cultivars ‘Sunland’ and ‘Gaschina Novembre’ had high breeding values for late bloom and high fruit density, indicating they would be suitable parents for making genetic progress for both traits. Working with 1311 low-chill genotypes belonging to 30 different progenies, Quezada et al. (2000) found extremely high values for both broad sense and narrow sense heritability in blossom date (close to 1), and concluded that predictable progress could be achieved based on parents’ behaviour. Souza et al. (1998a) also reported a high heritability of 0.78 for full bloom date in a medium-chill peach population at the TAMU programme. In this population, selection of the 5% of genotypes with earliest bloom and inter-mating for one generation would decrease the average bloom date of the population by 14 days. Most late-ﬂowering peach genotypes are not productive when grown in low-chill locations due in large part to inadequate chilling, but possibly also due to failure to set under high night temperatures (Edwards, 1987; Rouse and Sherman, 2002a). There are reports of low-chill genotypes that bloom late such as some Mexican germplasm from Aguascalienties (Scorza and Okie, 1990) and the cultivars ‘BR-1’, ‘Delicioso’ and ‘Della Nona’ from Brazil (Citadin et al., 2001). There also appear to be some cultivars, such as ‘Flordaprince’ and ‘TropicBeauty’, that are able to set crops under

Low-chill Cultivar Development

high (16–18°C) night temperatures (Rouse and Sherman, 2002a). There may be scope for selecting for late bloom using this type of germplasm that has high heat requirements to ﬂower and ability to set later in the ﬂowering season when nights are warmer.

Flower bud density Flower bud density is of importance in regions subject to spring frost damage. High ﬂower bud density can provide insurance against crop loss in that buds of different developmental stages have varying threshold mortality temperatures (Proebsting and Mills, 1978). Genotypes with high ﬂower bud density will have a range of undeveloped buds at a given date when frost occurs. The medium-chill peach ‘Texstar’ (450 CU) sets heavy crops under spring freeze conditions. It produces ten times the number of ﬂower buds necessary for a commercial crop and loses about 70% during bloom in years with and without freezes (Byrne, 1986). This loss was greater than other clones that failed to set commercial crops during the freeze, but was compensated by the very high ﬂower bud density of ‘Texstar’. Peach and nectarine cultivars from the UF breeding programme generally have high ﬂower bud density, which was inherited from ‘Okinawa’, one of the original low-chill parents (Sherman and Lyrene, 2003). The high ﬂower bud density is necessary to ensure regular crops after Florida’s frequent spring freezes. In locations such as coastal northern New South Wales and Queensland in Australia, spring freezes seldom occur and the high ﬂower bud density of UF cultivars is an expensive burden to orchardists because of the high cost of handthinning fruitlets. Flower density (0.41) and node density (0.48) were reported to have moderate heritability, which would allow manipulation of either trait (Souza et al., 1998a).

Blind nodes and bud drop Blind nodes are nodes that lack ﬂoral and vegetative buds and are therefore a cause of

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reduced productivity. Formation of blind nodes was observed to occur most frequently when temperatures were high and tree growth was low (Boonprakob and Byrne, 2003). There is great genotypic variability for this trait (Boonprakob et al., 1994; Richards et al., 1994) and several cultivars exist with low blind node propensity (Table 5.6). Bud drop in peaches has high genetic variability and is usually associated with highly ﬂuctuating winter temperatures or high mean minimum mid-winter temperatures. In a study of 13 peach cultivars over 10 years at Fresno, California, Weinberger (1967) concluded that a mid-winter mean minimum above 4.4°C was critical for appearance of bud drop in susceptible cultivars. Temperate peach cultivars bred in uniformly cool winter climates often transmit bud drop when hybridized into a low-chill programme, thus selection must be practised where winters are not uniformly cool.

Fruit development period Almost all low-chill breeding programmes have short FDP as a major objective in order to produce early-ripening cultivars. In many subtropical locations, early ripening is required to ensure the crop is harvested prior to the onset of the summer rainy season and the associated problems with disease and fruit decay. At Gainesville, Florida, the rainy season generally commences in the second week of June, which means that all the adapted 350 CU genotypes have FDP of <100 days (Sherman and Rodriguez-Alcazar, 1987). Independent of this reason, early ripening is of economic importance because of the high fruit prices for early-season fruit. Length of FDP and time of ripening are highly heritable traits in low-chill and mediumchill peach germplasm (Souza et al., 1998b) and are readily altered by selection. The occurrence of bud sports ripening 7–10 days earlier than the original clone and the presence of redleaf markers (Fig. 5.2/Plate 49) in early-ripening cultivars (Sherman et al., 1972) indicate there may be genes with a major effect on ripening time. The earliest-ripening

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Table 5.6. Blind node propensity of peach and nectarine clones tested at Gainesville, Floridaa and College Station, Texasb. Clonea

Blind nodes (%)

‘Fla.4-4’ ‘Rayon’ ‘TropicSweet’ ‘Sunred’ ‘Sunhome’ ‘Sunlite’ ‘Sundollar’ ‘Newbelle’ ‘Oro A’ ‘Fla.90-44C’

aFrom bFrom

10 28 31 32 41 46 50 64 69 84

Cloneb ‘Fla.1-8’ ‘Desertred’ ‘Flordaking’ ‘Gulfpride’ ‘Earligrande’ ‘Loring’ ‘Goldcrest’ ‘Sunhome’ ‘P51-2’ ‘Sentinel’ ‘BY3-1197’ ‘Junegold’ ‘Sunland’ ‘Elberta’ ‘Juneprince’ ‘BY4-7124’ ‘BY5-938’ ‘BY3-600’ ‘Springcrest’ ‘Cherrygold’

Blind nodes (%) 11 16 33 36 37 38 39 40 41 42 44 45 45 47 51 56 59 60 66 81

Richards et al. (1994). Boonprakob et al. (1994).

Fig. 5.2. Regular green leaf peach seedlings in foreground and peach seedling displaying redleaf character associated with short fruit development period (FDP) in centre at Nambour, Queensland, Australia. This trait can be used for early identification of short FDP seedlings in late summer. (From Sherman et al., 1972.)

Low-chill Cultivar Development

low-chill cultivars have FDP of the order of 60 to 70 days (Table 5.7) and so can still be decreased signiﬁcantly when compared with high-chill cultivars such as ‘Goldcrest’ that have FDP of 55 days (Ramming and Tanner, 1987).

Fruit shape Symmetrical and rounded fruit are desirable because they result in less damage during

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harvest and handling. Production of fruits with large stylar tips and/or suture bulges is a common problem in mild winter regions (Fig. 5.3/Plate 50). For a single cultivar, the tip size and suture bulge may vary across locations and years, with larger tips and bulges more frequent in warmer locations (Topp and Sherman, 1989). Some genotypes that are round in cool locations become pointed when grown in warmer regions (Fig. 5.4/Plate 51) but others such as ‘Sunlite’ nectarine remain relatively tip-free at all locations. Heritability estimates

Table 5.7. Low-chill peach and nectarine cultivars with short fruit development period (FDP)a. (From Okie, 1998.) Cultivar

Crop

‘Flordadawn’ ‘Sherman’s Early’ ‘Flordaglobe’ ‘Fla.85-1’ ‘Flordaking’ ‘Sundollar’ ‘Flordastar’

Peach Peach Peach Peach Peach Nectarine Peach

aDays

Chilling (CU)

FDP (days)

250 425 475 400 400 400 225

60 60 62 67 69 70 72

from flowering to harvest.

Fig. 5.3. Peach fruit with prominent stylar tips that are commonly observed in cultivars with poor adaptation to mild winter locations and are selected against in low-chill breeding.

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Fig. 5.4. Influence of location on fruit shape. This medium-chill (450 CU) peach selection produced: (a) round fruit at the high-chill (900 CU) location of Stanthorpe, Queensland, Australia and (b) pointed fruit at the low-chill (200 CU) location of Nambour, Queensland, Australia.

of 0.45 and 0.43 for fruit tip and fruit shape rating, respectively, indicate that genetic advance for these traits is possible (Souza et al., 1998b). Some recent cultivars from Florida, Texas and southern Brazil are examples of the achieved goal for round fruit shape.

Fruit firmness In traditional melting-ﬂesh genotypes, ﬁrmness is mostly a measure of evenness of ripening within a fruit at good red over-colour and yellow ground colour development. Thus, to

Low-chill Cultivar Development

increase ﬁrmness, especially in genotypes with short FDP (<100 days) where ﬁrmness is lacking compared with genotypes with FDP of 120–180 days, breeders have selected for advanced red skin and yellow ground colour while the fruit is physiologically immature, resulting in low-brix fruit with low ﬂavour or aroma. Two ﬂesh types, non-melting and stony-hard, offer potential to overcome this problem by allowing the fruit to mature (tree ripen) with higher brix and aroma while retaining ﬁrmness for shelf-life. Both the non-melting and stony-hard ﬂesh traits are controlled by single recessive genes (Scorza and Sherman, 1996). Non-melting ﬂesh is characterized by absence of the endopolygalacturonase enzyme that is responsible for ﬂesh softening in melting peaches (Lester et al., 1996). Mature fruit with non-melting ﬂesh soften at a slower rate than those with melting ﬂesh. Stony-hard ﬂesh fruit produce no ethylene and so stay ﬁrm unless exposed to exogenous ethylene (Haji et al., 2003). It will be important to study consumer reaction to both these ﬂesh types in developing ﬁrm peaches that are suited to particular markets (Brovelli et al., 1999; Williamson and Sargent, 1999). The non-melting ﬂesh trait is present in all the recent cultivar releases in the low-chill breeding programmes at Chapingo and Queretaro in Mexico and at UF in the USA. Since the 1980s, Brazil has released dual-purpose low-chill cultivars with non-melting yellow ﬂesh. The stony-hard ﬂesh trait is present in old low-chill peach cultivars in China and Taiwan which generally produce fruit that are white-ﬂeshed, small and with long FDP. Ou and Wen (2003) use one such Taiwanese peach cultivar, ‘In-ge-taur’, as a comparator in a release note for a new melting-ﬂesh cultivar. Several low-chill breeding programmes are experimenting with the use of stony-hard ﬂesh but no cultivars have been released.

Disease resistance Increased pressure from disease and insect pests is encountered in subtropical compared with temperate growing regions. There is

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often more active development and multiple generations of the pest due to higher spring and summer temperatures, increased rainfall, increased length of the growing season and warmer winters which allow carryover of pests from one season to the next. Breeding for resistance to these pests is therefore important in low-chill peach breeding (Topp and Sherman, 2000). Scorza and Okie (1990) list 22 fungal and bacterial pathogens, 11 viruses, four nematodes and 28 insects as problems in peach culture. Of these, only resistance to nematodes, bacterial spot, brown rot, powdery mildew, rust and gummosis are actively being selected for in low-chill breeding programmes (Table 5.8). Genetic resources available for Prunus resistance breeding are well documented by Scorza and Okie (1990) and Byrne et al. (2000). Brown rot is a major disease of peach, causing blossom blight and fruit infection (Ogawa et al., 1995). Many low-chill peachgrowing regions aim to ﬁnish production before the rainy season because of the difﬁculty and expense of controlling this disease. The Brazilian peach cultivar ‘Bolinha’ was reported to be resistant to brown rot as indicated by reduced rate of lesion development and sporulation and low incidence of infected fruit in the ﬁeld (Feliciano et al., 1987). This resistance occurs in the fruit epidermis and is associated with high levels of phenolic compounds in the fruit ﬂesh and epidermis (Gradziel et al., 1998). Unfortunately the phenolic compounds, chlorogenic acid and caffeic acid, which are associated with resistance are also associated with development of ﬂesh browning. ‘Bolinha’ has been used as a parent in the EMBRAPA breeding programme and brown rot resistance has been incorporated in the recently released peach ‘Jubileu’ (Raseira and Nakasu, 2000a). ‘Pepita’ also has low levels of brown rot but this is considered a result of early ripening and thus due to infection avoidance (Raseira and Nakasu, 2000b). Leaf rust (Tranzchelia discolor (Fuckel) Tranzchel & Litvinov) is a major disease in peaches grown in subtropical climates with high summer rainfall. The extent and onset of defoliation is related to the time of initial infection (Bertrand, 1995). In temperate regions, leaf rust seldom appears before late August

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Table 5.8. Pests and diseases being selected for in low-chill peach cultivar development. (Data from Scorza and Okie, 1990; Okie and Pusey, 1996; Brooks and Olmo, 1997; Byrne et al., 2000; W. Sherman, USA, 2004, personal communication.) Breeding programme

Genotypes with some level of resistance

Meloidogyne javanica Meloidogyne incognita Xanthomonas campestris pv. pruni (Smith) Dye

UF

Monilinia fructicola (Wint.) Honey Monilinia laxa (Aderh. & Ruhl.) Honey Sphaerotheca pannosa (Wallr.:Fr.) Lev.

EMBRAPA

‘Okinawa’ and ‘Flordaguard’ rootstocks ‘Flordahome’ ornamental ‘Flordastar’, ‘Flordacrest’, ‘Sunblaze’, ‘Suncoast’, ‘Sunhome’, ‘Sunraycer’, ‘FlordaMex 1’ ‘Bolinha’, ‘Pepita’, feral Mexican seedlings ‘Sungold’

Disease

Pathogen

Nematodes Bacterial spot

Brown rot

Powdery mildew

Rust

Gummosis

Tranzchelia discolor (Fuckel) Tranzchel & Litvinov Botrysphaeria dothidea (Moug.:Fr.) Ces. & De Not.

UF

UF UF Mexico Brazil UF

UF USDA (Byron, GA)

‘Flordagold’, ‘Flordagrande’, ‘Flordahome’, ‘Flordaking’, ‘Okinawa’ ‘Aztecgold’, ‘Hermosillo’, ‘Oro A’ ‘Diamante’ ‘UF2000’, ‘UFQueen’, ‘SunBest’

‘Sundowner’ PI65821

UF, University of Florida; EMBRAPA, Brazilian Agricultural Research Enterprise; USDA, US Department of Agriculture.

(northern hemisphere) and so does not cause signiﬁcant early defoliation. However, in the subtropics, rust appears in June (northern hemisphere) and the subsequent premature defoliation results in early leaﬁng and ﬂowering. Early defoliation was shown to affect depth of dormancy, growth ability of buds and bud development (Lloyd and Firth, 1990). In locations where winter freezes occur, the return bloom is killed and subsequent yield potential is reduced. Perez et al. (1993) reported that local Mexican seedling selections were more resistant to rust than introduced cultivars. Highest levels of resistance were found in the evergreen types, with resistance partially correlated with late ripening (r = 0.62). For the peach cultivar ‘UF2000’, it was reported that ‘leaves did not drop readily when infected with rust as on most varieties’ (Sherman and Lyrene, 2000). Following this observation it was found that 12 genotypes (including the cultivars ‘UFQueen’, ‘SunBest’ and ‘UF2000’) from the UF breeding

programme had resistance to rust-induced defoliation (Rouse and Sherman, 2002b). The 12 resistant genotypes averaged 5% defoliation compared with 90% defoliation for the remaining 181 susceptible genotypes. Resistant selections had less rust than susceptible selections at Imokalee in 2001, averaging two and 61 lesions per leaf, respectively. The authors speculated that the mode of inheritance involved recessive genes for resistance because the resistant genotypes had susceptible parents. Emphasis on breeding for resistance to disease and pests is likely to increase in the future. Currently, orchardists will plant susceptible cultivars and bear the cost of increased plant protection if the fruit quality (size, colour, ﬁrmness, shape and ﬂavour) is high enough. In the future, deregistration of fungicides and insecticides is likely to increase due to public pressure. Under these conditions, genetic resistance combined with alternative management techniques (bait spraying,

Low-chill Cultivar Development

pheromone disruption, protective canopies, improved sanitation, etc.) will become more important in subtropical peach culture.

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selection management this can be increased up to 15 years. Some of the problems in producing and managing breeding populations in the subtropics are discussed in the following section.

5.4 Management of Low-chill Breeding Populations Hybrid seed production Low-chill breeders use speciﬁc management techniques to take advantage of, and overcome problems associated with, the subtropical environment. Long growing seasons allow trees to reach large sizes; pests and diseases go through many breeding cycles; high and ﬂuctuating winter temperatures reduce effective chilling; genotypes ﬂowering in late winter and early spring are prone to frost damage; and ﬂowering and harvest periods are often prolonged. The shortest possible time for one cycle of a recurrent mass selection programme, from pollination to cultivar release, is 8 years (Table 5.9). With poor seedling and advanced

Table 5.9.

Hybrid seed in temperate fruit breeding programmes is harvested in early to late summer, stratiﬁed for 2–3 months and germinated in autumn. In the subtropics, the seed is harvested in late spring, stratiﬁed for 4–6 weeks and germinated in summer when maximum temperatures are often above 30°C. Rosetting of seedlings can be a major problem under these conditions (Fig. 5.5/Plate 52). At the UF breeding programme, germinating seed is placed close to evaporative coolers in the greenhouse for the ﬁrst 10–14 days after germination to reduce ambient temperatures and

Calendar of events in one cycle of low-chill breeding.

Year

Activity

Numbers

0

Identification, collection and propagation of parental material Hybridization of parents; harvest, stratify and germinate hybrid seed; grow-on seedlings and field plants 1st year of field growth for seedling population 50% of seedlings produce fruit in 2nd leaf; evaluate fruit and tree characteristics; select outstanding genotypes Propagate selected genotypes on to virus-tested rootstock and plant at test sites Propagated selections undergo first season of growth at test sites Evaluate remainder of seedling population; select outstanding genotypes Propagate selected genotypes on to virus-tested rootstock and plant at test sites Evaluate 1st crop of superior selections Evaluate 2nd crop of superior selections Screen promising selections for pollen-borne viruses Evaluate 3rd crop of superior selections Make decision to release Increase budwood supply Complete Plant Breeders Rights Name and release cultivar

20 to 50 parents

1 2 3

4

5 6 7

8

20,000 to 40,000 pollinations to produce 4000 seeds 2,000 to 3,000 seedlings 1,000 to 1,500 fruiting seedlings Propagate 20 selections Test all 20 selections at two sites Propagate 20 selections Test about five elite selections at six sites

Release cultivar for commercial planting

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Fig. 5.5. (a) Rosetting of peach seedling terminal bud can be a major source of seedling loss in the glasshouse or during transplanting to the field. (b) Normal shoots developing from below the rosetted terminal.

decrease rosetting. Rosetting is also cultivardependent and was found to be high in seedlings from genotypes with FDP of <110 days but dropped rapidly as FDP increased (Bacon and Byrne, 1995). Experience at UF with rootstock seed indicates that genotypes with FDP of >120 days can be successfully germinated with no rosetting by drying and then re-imbibing

the seed prior to stratiﬁcation. Seeley et al. (1998) used this method to germinate ‘Johnson Elberta’ seed and reported that rosetting decreased with increasing duration of stratiﬁcation over a range of stratiﬁcation temperatures. Byrne et al. (2000) noted that stratifying endocarpremoved seed at 3–5°C rather than at 7–10°C decreased rosetting. Thus, both stratiﬁcation

Low-chill Cultivar Development

temperature and duration inﬂuence rosetting. Pinching out the rosetted terminal bud of the rosetted seedling can force lower buds to sprout and so partly alleviates the problem (Barbosa et al., 1989). This is not 100% effective and is not possible in plants that have no basal buds. Application of giberellic acid to rosetted peach × almond rootstock plantlets derived from tissue culture was effective in forcing new shoots (Tsipouridis and Thomidis, 2003). Many low-chill breeding programmes have early ripening as an objective and so short FDP seed must be germinated. Seed from genotypes with FDP of <90 days is considered immature and generally requires embryo culture for adequate seed germination, while those with FDP of <70 days require in ovulo embryo culture to allow the embryo to develop inside the seedcoat prior to germination. There is an intermediate stage of FDP of 80–90 days when embryos can be germinated with standard stratiﬁcation, but with varying results depending on the genotype and environment during fruit development. Generally, trees with heavy crop loads will ripen fruit later and so give improved seed germination (W.B. Sherman, USA, 2004, personal communication). Low-chill peach breeders sometimes wish to combine high-chill and low-chill parents in order to introduce speciﬁc tree or fruit characteristics from temperate cultivars into their low-chill breeding populations. Usually, low-chill pollen is collected from the subtropical location and used the same season for pollinating the high-chill parent in a temperate location. Alternatively, the high-chill pollen can be collected the previous year, stored and then used in the subtropical location. It is difﬁcult to decide the best location for growing out these hybrid populations. Chilling requirement of these populations is skewed towards the low-chill parent, with the medium-chill seedlings the largest class, but there will be transgressive segregants (seedlings with chilling outside the range of the two parents). If the aim is solely to select low-chill genotypes in this ﬁrst generation then it is possible to grow the population in the subtropical environment. Selection for ﬂower bud chilling requirement on the basis of seed chilling requirement

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would be useful in allowing the separation of genotypes at the time of germination into different chill categories. Observations have frequently been made that seed from low-chill genotypes requires less time in stratiﬁcation to germinate than seed from high-chill genotypes. Rodriguez-Alcazar and Sherman (1985) studied peach germplasm with chilling requirements of 200 to 450 CU and found a signiﬁcant but low correlation (r = 0.21) between individual seed chilling requirement and the ﬂower bud chilling requirement of the resulting seedling tree. Perez-Gonzalez (1990) studied feral Mexican and introduced peach genotypes that had a wide range of chilling requirements, from ‘Okinawa’ (150 CU) to ‘Elegant Lady’ (750 CU). There was a strong correlation between the time of bloom of individual trees and time to germinate for the resulting selfed seed, for both the Mexican (r = 0.71) and the introduced (r = 0.87) germplasm. In hybrid combinations between early-, medium- and late-blooming genotypes, there was also a correlation between the chilling requirement of the parents and the stratiﬁcation period required to germinate the resulting seed. It seems that where the parents do not differ greatly in chilling requirement it is not practical to pre-select for chilling requirement on the basis of length of seed stratiﬁcation; however, it should be possible to use the relative mean stratiﬁcation time of seed lots from divergent chilling germplasm as an indicator of broad chilling requirement to allow selection of appropriate sites for evaluation of the resulting seedlings. An interesting side note of this work (Perez-Gonzalez, 1990) was the marked difference between the selfed populations of local Mexican feral selections and introduced selections in terms of ﬂowering time and seed germination. While there was a strong correlation between parental ﬂowering time and resulting seed germination time for both sets of material, it was noted that the Mexican peaches ﬂowered much later for the same relative seed germination time. Perez concluded that the feral Mexican germplasm, with natural selection occurring for generations in a spring frost environment, had a high heat requirement for ﬂowering or seed germination (Perez-Gonzalez, 1990).

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Seedling populations An ideal seedling management system will minimize the juvenile period to accelerate genetic gain, provide a uniform environment for all seedlings to minimize non-genetic variation, allow accurate prediction of the seedling’s worth as a potential cultivar and do all this at the lowest possible cost (Rodriguez-Alcazar et al., 1986). Techniques adopted in low-chill breeding programmes to facilitate these objectives include the use of high-density plantings, protective canopies, growth regulators and standard orchard practices to encourage rapid tree growth (i.e. irrigation, fertilization, pest control). High-density planting of seedlings increases breeding efﬁciency by reducing costs of land, soil fumigation, irrigation and weed control (Sherman and Lyrene, 1983). Sherman et al. (1973) described a high-density fruiting nursery where the trees were planted at propagation nursery densities (1.0 m × 0.2 m), but left until fruiting rather than transplanted after one season (Fig. 5.6/Plate 53). This system promotes rapid growth in height and so

enhances precocious fruiting by increasing the distance between roots and apical buds (Zimmerman, 1972). Rodriquez-Alcazar et al. (1986) studied the performance of seedlings in a high-density peach nursery at Gainesville, Florida and the subsequent performance of grafted selections from this nursery. They found a signiﬁcant correlation between the two sets of material for ratings of FDP, chilling requirement, fruit weight and fruit colour, but not for crop load, fruit shape or ﬁrmness. It was noted that poor correlations may indicate the limited range of variability in the selected population rather being than an indication that the selection procedure was not efﬁcient in discarding those with low expectations or in identifying superior genotypes. In forest tree breeding studies the heritability of various traits such as diameter at breast height has been estimated at differing tree ages to allow determination of the most efﬁcient stage of measurement. Similar studies using a full population of all stage 1 and stage 2 seedlings would be needed for an assessment in peach.

Fig. 5.6. High-density fruiting nursery at Gainesville, Florida, showing the size of second leaf peach seedlings grown in the subtropics.

Low-chill Cultivar Development

Reducing generation length is a major objective in seedling management because the rate of response to selection is inversely proportional to the length of the selection cycle (Hansche, 1983). Selection for precocity and implementation of high levels of management to encourage rapid seedling growth in high-density nurseries have reduced peach breeding cycles to 3 or 4 years (Scorza and Sherman, 1996). In current commercial lowchill breeding germplasm it is not uncommon to have 20–75% of the seedlings fruit 2 years from seed. Juvenility may be further reduced by increasing the proportion of the population that fruits in the second growing season or by inducing a proportion of the seedlings to fruit 1 year from seed. Repeated cycles of the fruiting nursery system have appeared to increase the precocity and the percentage of seedlings fruiting in 2 years. With the long growing seasons and warm temperatures in the subtropics it is common for seedlings to be 2–3 m tall in the ﬁrst year. In the second year almost all the seedlings will be at a height when they have reached the juvenile–adult phase change. Applications of growth regulators such as paclobutrazol have been reported to reduce the length of the juvenile period in citrus seedlings (Snowball et al., 1994) and similar methods should be tested in peach. Avoiding stratiﬁcation of spring-harvested low-chill seed by direct germination methods (Taylor, 1957) followed by early summer planting of resulting seedlings would allow production of trees that were 1–2 m in height by the end of that subtropical growing season. These seedlings may then be induced to ﬂower the following spring, thus reducing the generation time to 1 year. Testing advanced selections Methods for testing advanced selections vary across low-chill breeding programmes. They include the common elements of rapid, impartial testing over multiple sites and years, comparison with standard cultivars and use of commercial agronomic systems. At the UF breeding programme, the minimum amount of data required prior to release

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is three commercial crops obtained from two to ﬁve budded trees at one representative location. In practice, there is usually more data because advanced selections are concurrently tested at numerous sites. In other programmes, such as ARC Infruitec in South Africa, there is a phase of semi-commercial planting prior to release. Although most of the low-chill breeding programmes exist at public institutions, there has been increasing pressure to obtain external funding sources to assist in cultivar development. Funding partners are usually involved in the testing of advanced selections and provide valuable feedback to the breeder on the worth of the new selections and the direction of the breeding programme. These partners may be nurseries, fruit-growing companies, packinghouses, market agents, retailers, grower cooperatives or individual orchardists.

5.5 Conclusions The quality of low-chill peach cultivars has increased signiﬁcantly since the mid-1960s. Many industries started with cultivars such as ‘Flordasun’ and ‘Sunred’ that allowed production of peach and nectarine in new locations, and at harvest times that had previously not occurred. The long-running breeding programme at UF in the USA has had a signiﬁcant impact on world peach production with its cultivars planted extensively around the world, while the programmes at EMBRAPA and IAC in Brazil and ARC Infruitec in South Africa have been successful in supplying cultivars for their local industries. More recently, low-chill breeding has started in desert environments (California and southern Texas), tropical highlands (Mexico and Thailand) and in the humid subtropics (Australia, Taiwan). The driving force for developing lowchill peach cultivars is the production of early-ripening fruit to extend the peach season. In some countries such as Brazil and Thailand, where only low-chill peaches are produced, a full range of low-chill ripening times is required; but for most locations, low-chill peaches provide an early supplement to the high-chill

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season. If forecasts of global warming are correct, low-chill cultivars will be required in more locations. Low-chill peach breeding has received far less resources than high-chill breeding, in keeping with the smaller size of the low-chill peach industry. Combined with the suboptimal environmental conditions that exist in most low-chill production regions, this means that the quality of low-chill cultivars has often been secondary to high-chill cultivars. Most of the ideal peach-growing locations (Mediterranean environments) require medium- and high-chill cultivars and in these environments breeders have been able to select strongly for fruit quality characteristics without diluting selection intensity for environmental adaptation. All of the current low-chill peach breeding programmes are incorporating the signiﬁcant high-chill peach breeding gains

into their programmes by the introgression of high-chill germplasm. With increased pressure on public breeding programmes to obtain external funding, there has been a trend of increasing protection of new cultivars with Plant Breeders Rights and Plant Patents. This has resulted in less sharing of germplasm. With increased consumer demand for consistently high fruit quality, breeders have shifted emphasis in selection from productivity to eating quality. This has only been possible because of the earlier breeding work that provided germplasm with good adaptation to many of the problems encountered in low-chill peachgrowing locations. The emphasis in breeding for quality will continue, and there will be increased emphasis on novel fruit types for consumers and increased disease resistance and altered tree architecture for producers.

Contributors Bacon, Terry, Sun World International, Inc., PO Box 80298, Bakersfield, CA 93380-0298, USA. Barbosa, Wilson, Instituto Agronomico (IAC), Caixa Postal 28, 13001-970 Campinas, Sao Paulo, Brazil. Beppu, Kenji, Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan. Boonprakob, Unaroj, Department of Horticulture, Kasetsart University, Mampangsaen, Nakhonpathorn 73140, Thailand. Burger, Stella, Stargrow South Africa, PO Box 12536, Die Boord 7613, South Africa. Byrne, David, Texas A&M University, Department Horticultural Science, College Station, TX 77843-2133, USA. Darmody, Liz, Zee Sweet Pty Ltd, PO Box 21 Monbulk, VIC 3793, Australia. Kataoka, Ikuo, Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan. Perez, Salvador, Prol. Zaragoza 408, Jardines de la Hacienda, Queretaro, Qro 76180, Mexico. Porter, Gavin, ANFIC, George Street, Bathurst, NSW 2795, Australia. Richards, Graeme, University of Western Sydney, Richmond, NSW 2753, Australia. Rodriguez-Alcazar, Jorge, Centro de Fruitcultura, Colegio de Postgraduados, Chapingo 56230, Mexico. Russell, Dougal, Department of Primary Industries, PO Box 501, Stanthorpe, QLD 4380, Australia. Smith, Chris, ARC Infruitec–Nietvoorbij, Private Bag X5013, Stellenbosch 7599, South Africa. Wang, Lirong, Zhengzhou Fruit Research Institute, Chinese Academy of Science, Zhengzhou, Henan 450009, People’s Republic of China. Wen, Ien Chie, TARI, 189 Chungcheng Road, Wufeng, 413 Taichung, Taiwan, Republic of China.

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Souza, V.A.B., Byrne, D.H. and Taylor, J.F. (2000) Predicted breeding values for nine plant and fruit characteristics of 28 peach genotypes. Journal of the American Society for Horticultural Science 125, 460–465. Taylor, J.W. (1957) Growth of non-stratified peach embryos. Proceedings of the American Society for Horticultural Science 69, 148–151. Topp, B.L. and Sherman, W.B. (1989) Location influences on fruit traits of low-chill peaches in Australia. Proceedings of the Florida State Horticultural Society 102, 195–199. Topp, B.L. and Sherman, W.B. (2000) Breeding strategies for developing temperate fruits for the subtropics, with particular reference to Prunus. Acta Horticulturae 522, 235–240. Tsipouridis, C. and Thomidis, T. (2003) Methods to improve the in vitro culture of GF677 (peach × almond) peach rootstock. New Zealand Journal of Crop and Horticultural Science 31, 361–364. Wang, L., Zhu, G. and Fang, W. (2002) Peach germplasm and breeding programs at Zhengzhou in China. Acta Horticulturae 592, 177–182. Ward, K.M. (1952) The peach. Queensland Agricultural Journal 74, 323–334. Watson, T.D., Albritton, L., Barker, T. et al. (2001) Climate Change 2001: Synthesis Report. Summary for Policymakers. An Assessment of the Intergovernmental Panel on Climate Change. http://www.ipcc.ch/pdf/ climate-changes-2001/synthesis-spm/synthesis-spm-en.pdf (accessed January 2008). Wei, S. (2001) Singapore & Hong Kong market research for early season stone fruit. Australian Fresh Stone Fruit Quarterly 3, 8–12. Weinberger, J.H. (1950) Chilling requirement of peach varieties. Proceedings of the American Society for Horticultural Science 56, 122–128. Weinberger, J.H. (1967) Studies on bud drop in peaches. Proceedings of the American Society for Horticultural Science 91, 78–83. Wen, I.C. and Sherman, W.B. (2002) Evaluation and breeding of peaches and nectarines for subtropical Taiwan. Acta Horticulturae 592, 191–196. Williamson, J.G. and Sargent, S.A. (1999) Postharvest characteristics and consumer acceptance of non-melting peaches. Proceedings of the Florida State Horticultural Society 112, 241–242. Zimmerman, R.H. (1972) Juvenility and flowering in woody plants: a review. HortScience 7, 447–455.

6

Fresh Market Cultivar Development W.R. Okie,1 T. Bacon2 and D. Bassi3

1USDA-ARS

Southeastern Fruit and Tree Nut Research Laboratory, Byron, Georgia, USA 2Sun World International, Inc., Bakersfield, California, USA 3University of Milan, Milan, Italy

6.1 Introduction 6.2 Early Cultivation 6.3 Early US Breeding Programmes North-eastern USA and Canada South-eastern USA California 6.4 Modern US Breeding Programmes North-eastern USA and Canada South-eastern USA California 6.5 European Programmes Bulgaria France Greece Hungary Italy Poland Romania Serbia Spain Ukraine and former Soviet states 6.6 Paciﬁc and African Programmes China Japan Korea New Zealand South Africa 6.7 Conclusions

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6.1 Introduction

6.2 Early Cultivation

Successful peach production depends on suitable cultivars, regardless of where the industry is located. Peaches have a short shelf-life compared with many crops and each cultivar has a short production season. As a result, multiple cultivars are needed to provide fresh fruit from April to September (October to March in the southern hemisphere) across many regions and climates. Few consumers recognize speciﬁc peach cultivars in the market and few cultivars are marketed by name. Such anonymity allows the rapid acceptance of new cultivars, thus encouraging additional cultivars to be developed. In general, peaches for fresh market consumption must suit the intended market. In most cases preferred fruit are large (6–8 cm diameter), predominantly red with yellow ground colour and with short pubescence or glabrous (nectarine), ﬁrm enough to be transported (perhaps for several weeks for exporting industries), of regular round shape and of good eating quality (taste and texture). Flesh colour in the USA has traditionally been yellow, but white is acceptable or preferred in some markets. Most fresh market peaches are freestone, except for the early-season cultivars. Important exceptions are those sold in countries preferring non-melting or canning clingstones (often with minimal external red blush), such as southern Italy, Spain, Mexico and other countries with Spanish inﬂuence. Many of the later-season nectarines are also clingstone, apparently because of higher eating quality compared with freestone nectarines in that season. In recent years the market has diversiﬁed in terms of ﬂesh colour, acidity (normal or low), texture (melting, non-melting and stony-hard) and shape (round or ﬂat). Changes are also coming in tree architecture to provide cultivars ranging from dwarf through standard to pillar and weeping, although commercial adoption of non-standard trees remains to be seen. Most of the breeding for low-chill regions, as well as that for canning peaches, is discussed in other chapters in this book (see Chapters 5 and 7, respectively).

As peaches spread around the world, most orchards consisted of seedling trees. For centuries, farmers selected superior trees from those grown from seed. Over time distinct strains arose in the various regions where peaches were well adapted. In many areas these local strains are still grown, at least as a source for rootstock seed. Examples are the vineyard peaches of the former Yugoslavia, ‘Criollo’ in Argentina, ‘San Miguel’ in Spain and locally grown cling peaches in central America. Fruit growers later wished to preserve the trees that possessed useful or superior characteristics and began to vegetatively propagate these individuals. Early Spanish explorers and colonists brought the ﬁrst peaches to North America as seed. This new fruit was also spread across the south-eastern and south-western states by Native Americans to the extent that some later European explorers thought peaches were native to the USA. Descendants of these seedlings became known as ‘Indian’ peaches and live on in types such as ‘Tennessee Natural’ and ‘Indian Blood’. Later, mostly whiteﬂeshed cultivars from England and France were brought into the eastern USA. Beginning in the early 1800s, these European cultivars and the best local seedlings began to be propagated by budding. Hedrick’s (1917) classic work, The Peaches of New York, listed 2181 cultivars known at that time. A similar, briefer work from Europe which included nectarines included many more European cultivars (Jouin, 1913). Many of the cultivars in these books were of unknown seedling origin. For nearly all the rest only the seed parent was known. In most areas where peaches were adapted, the industries were based on local cultivars well into the 20th century. As late as 1937, a listing of important US cultivars was all seedling selections (Cullinan, 1937). Up until this time the nectarine was primarily a novelty crop grown in drier climates for the purpose of drying. The small size and a marked tendency for the skin to crack in rainy weather limited its commercial production elsewhere.

Fresh Market Cultivar Development

T. Rivers of Hertfordshire, England attempted to improve peaches and nectarines by systematically growing seedlings of betteradapted cultivars and selections beginning in the 1820s, making him perhaps the ﬁrst peach breeder. Without knowledge of modern genetics and control of the pollen parent, he had only limited success despite releasing over 30 peach cultivars (Rivers, 1866; Hoare, 1950). The rediscovery of Mendel’s work and the development of modern genetics impacted peach breeding as it was initiated by public institutions. Rivers’ grandson published one of the ﬁrst reports of intentional hybridization in 1906 (Rivers, 1906), in which he discussed inheritance of glabrous skin (nectarine), ﬂower type and gland type. His assessment of the task of peach breeding was prophetic (and a good pun): ‘It is a labor of Sisyphus, but the stone occasionally lodges on the top of the hill’. Although peaches have been improved in most areas in which they were grown by selection of adapted types, the dramatic improvement of the last century has taken place mostly in North America.

6.3. Early US Breeding Programmes In 1850 the ‘Chinese Cling’ (‘Shanghai Shui Mi’) was introduced into the USA as a potted tree. Seeds of this peach planted in Marshallville, Georgia by S.H. Rumph produced the cultivars ‘Georgia Belle’ and ‘Elberta’, which formed the basis of the early industries across the USA (Cullinan, 1937; Myers et al., 1989). At that time most peaches were white-ﬂeshed English and French cultivars or their descendants. ‘Elberta’ was found to be much ﬁrmer and widely adapted, such that it was grown from the south-east to the north-east, providing a continuous supply of fruit of this cultivar all season long. Yellow-ﬂeshed peaches showed bruising less than white-ﬂeshed peaches and gradually yellow came to predominate, as breeders released mostly yellow-ﬂeshed cultivars. ‘Elberta’ is now grown in only a few places, but the name remains one of the few that the public recognizes. ‘Elberta’ is found in the parentage of most commercial peaches

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developed in the USA. Today, peach cultivars are less celebrated and are viewed as one of many aspects of production. It is unlikely that any new cultivar will become as widely known among the general public as did ‘Elberta’. Several amateur breeders produced early selections in the USA (Cullinan, 1937; Okie, 1998). J.W. Kerr of Denton, Maryland crossed ‘Elberta’ with ‘Early Beauty’, ‘Rivers’ and ‘Mountain Rose’ in 1888, resulting in ‘Denton’, ‘Elriv’ and ‘Elrose’. It is not clear if these were hand pollinations, but they appear to be the ﬁrst recorded hybrids of peach. J.W. Steubenrauch of Mexia, Texas selected a number of popular cultivars from seedlings. In about 1900, he budded a tree with both ‘Elberta’ and ‘Belle October’ to obtain seedlings combining characters of both parents. ‘Frank’ was the most successful result of this crossing. Around 1900, the peach grower J.H. Hale found an off-type tree on his farm in Connecticut, which also performed well on his Georgia farm. Introduced in 1912 as ‘J.H. Hale’, this peach was widely planted, in part due to its superior ﬁrmness, and often used in breeding in later years. It was thought to have been a seedling of ‘Elberta’ as well. Over the next century, the cultivar picture changed from a time when most new cultivars were once chance seedlings found by peach growers (Table 6.1). During the 20th century, numerous state and federal breeding programmes were undertaken in the USA. Although peaches and nectarines were grown in many countries at that time, little breeding was done outside the USA, a result perhaps of the maturity of the industries elsewhere as well as the lack of structured research capabilities reﬂected in the land grant universities of the USA. In any case, peach breeding ﬂourished in the USA in the 20th century; progress was so dramatic that new, improved US cultivars spread around the world, often replacing existing local cultivars and selections. Breeding in the USA can be divided into four segments – north, south, deep south and west. In the northern tier of states, as one might expect, bud and tree hardiness are critical issues in breeding. Tolerance to rain and humid conditions and the resulting diseases is important, which is true across the entire eastern USA. Similar cultivars are used from

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Table 6.1. Historically important peach and nectarine (*) cultivars and their date and locale of origin. (From Cullinan, 1937.) Cultivar ‘Late Crawford’ ‘Early Crawford’ ‘Chinese Cling’ ‘St John’ ‘Georgia Belle’ ‘Elberta’ ‘Phillips’ ‘Champion’ ‘Lovell’ ‘Hiley’ ‘Admiral Dewey’ ‘Mayflower’ ‘J.H. Hale’ ‘Paloro’ ‘Fay Elberta’ ‘Golden Jubilee’ ‘Halehaven’ ‘Sunhigh’ ‘Redhaven’ ‘Quetta’* ‘Lippiatt’s’* ‘Le Grand’*

Year 1815 1820 1850 1860 1870 1870 1880 1880 1882 1886 1899 1909? 1912 1912 1915 1926 1932 1938 1940 Pre-1906 Pre-1916 1942

the north down to the uplands of the southern states. The main peach industry in the southern states runs across the region between the uplands and the coastal plain, and is subject to years when chilling is inadequate for some peaches. In this zone mid-winter temperatures are rarely an issue, but it is critical to have cultivars requiring 650–850 h of chilling below 7°C. As one moves towards the coast where the annual chilling is even less, a different set of cultivars is required (see Chapter 5). Generally, as a given peach cultivar is cultivated further south, its fruit tends to have more prominent tips and sutures, and to retain a green ground colour closer to softening time. Finally, in California, chilling and hardiness are less important due to the more moderate climate. However, high summer temperatures tend to reduce red skin colour in comparison to the same cultivar grown in the eastern states. California peaches often have fewer ﬂower buds, which reduces thinning costs and enhances fruit size, but which results in light crops when grown in colder climates.

Origin New Jersey, USA New Jersey, USA Shanghai, China ?, USA Georgia, USA Georgia, USA California, USA Illinois, USA California, USA Georgia, USA Georgia, USA North Carolina, USA Connecticut, USA California, USA California, USA New Jersey, USA Michigan, USA New Jersey, USA Michigan, USA Pakistan New Zealand California, USA

North-eastern USA and Canada New York The ﬁrst formal institutional breeding programme was established in 1895 in Geneva, New York. S.A. Beach planted open-pollinated seeds of ‘Elberta’. In 1910 U.P. Hedrick made the ﬁrst crosses there. Hedrick’s major contribution was to assemble The Peaches of New York, an excellent reference on peach cultivars and culture (Hedrick, 1917). As with most of these early programmes, populations were modest and progress was slow. Only one cultivar was released in the ﬁrst 50 years of the programme. In recent years breeding at Geneva has stopped and only testing of new cultivars and selections continues. Iowa and Illinois Programmes in Iowa and Illinois began in 1905 and 1907, respectively, to develop more coldhardy peaches for the mid-west USA. Iowa breeders S.A. Beach and T.J. Maney were

Fresh Market Cultivar Development

innovative in their use of cold-hardy germplasm such as ‘Bailey’ and Prunus davidiana, but the result was a step back in terms of fruit size and quality. The only release from this work in Iowa was ‘Polly’ in 1932. Breeding in Illinois produced no cultivars until the ‘Prairie’ series in 1946 (Mowry, 1960). J.E. Markham, a private breeder, in 1932 released ‘Hal-Berta Giant’, which was the ﬁrst patented peach (US Plant Patent 7). Breeding is hampered in climates where cropping is unreliable. As with most of the northern programmes, these are now closed. Ontario Canada represents the northern limits of commercial peach production (Layne, 1997). Protected sites along the Great Lakes in Ontario are suitable for cold-hardy cultivars. In 1911 peach breeding was begun by the Ontario Department of Agriculture at Vineland, with the goals of producing cultivars to extend the ‘Elberta’ season as well as to develop cultivars for canning. Fourteen cultivars had been released by 1964, the most important of which were ‘Veteran’, ‘Valiant’ and ‘Vedette’. Since then the emphasis has shifted to development of canning clings (see Chapter 7). Meanwhile a second programme was started at Harrow by Agriculture Canada. G.M. Weaver and later R.E.C. Layne developed cold-hardy peaches and nectarines that thrived in their climate and had suitable fruit characteristics. This programme pioneered testing selections methodically by use of controlled freezing chambers to gauge cold hardiness of wood and buds. Many of their cultivars were and still are widely planted in Ontario and the northern USA, especially ‘Canadian Harmony’, ‘Harbrite’, ‘Harson’, ‘Harrow Diamond’ and ‘Harrow Beauty’. Nectarines ‘Hardired’ and ‘Harblaze’ have also been important. New Jersey Breeding in New Jersey began at Rutgers University in 1914 with C.H. Connors and later M.A. Blake. At that time the main early cultivars were ‘Greensboro’, ‘Waddell’, ‘Connetts’, ‘Lola’ and ‘Carman’, followed in ripening by ‘Hiley’, ‘Belle’ and ‘Elberta’. The objectives of

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the programme were to study peach genetics and develop a replacement for ‘Carman’. The ﬁrst releases from this early breeding came in 1925 with the release of 15 new cultivars, which represent the ﬁrst cultivars released by an institutional breeding programme in the USA (Blake and Connors, 1936). By 1937 three of these ranked in the top ten cultivars grown in the state, with ‘Golden Jubilee’ the most successful of the group. This programme was perhaps the most diverse in the country, developing not only fresh market peaches, but also nectarines and canning clings. In later years ﬂat and low-acid types were also included. M.A. Blake, and then later L.F. Hough and C.H. Bailey, were the ﬁrst to extensively collect and utilize germplasm from around the world, in order to provide new characters useful to the industry (Blake and Edgerton, 1946). Over the 20th century New Jersey released more new cultivars than any other peach breeding programme. Virginia Despite an early start to breeding in Virginia (1914), little progress was made until midcentury, when G.D. Oberle released a series of peaches and nectarines. He selected strongly for climatic adaptation and his releases such as ‘Jefferson’, ‘Monroe’ and ‘Washington’ were quite cold-hardy and resistant or tolerant to bacterial spot and brown rot. Oberle also released nectarines, ‘Cavalier’, ‘Redbud’, ‘Cherokee’ and others, that were better able than most to tolerate the rainy climate of the eastern USA (Oberle, 1971). Oberle was not replaced and the programme ended in the 1970s. Massachusetts and New Hampshire Peach breeding in New England began in Massachusetts in 1918. Breeders J.K. Shaw, J.S. Bailey and A.P. French grew only a few thousand seedlings, none of which were deemed worthy of release. However, they made very close observations of their populations and were able to determine the inheritance of many characters. Their 1949 bulletin summarized the then current state of peach genetics and clariﬁed the inheritance of most important characters (Bailey and French, 1949).

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Breeding work there terminated shortly thereafter, but continued for 15 more years at New Hampshire under A.F. Yeager and E.M. Meader. In 1964 Meader released ‘Reliance’, which is one of the most cold-hardy peaches known, although the fruit quality is not up to commercial standards. Michigan Although a latecomer to the breeding business, Michigan stands out in impact on the industry. Stanley Johnston was the son of an agricultural extension agent in Michigan. He was hired as Superintendent of the South Haven Experiment Station in 1920, a position he held until his death in 1969. He recognized that the local peach industry grew too much ‘Elberta’, so there was potential for earlier, ﬁrm, red peaches. He saved the seeds from pollination studies done to prove ‘J.H. Hale’ needed a pollinator and from these made his ﬁrst selections, resulting in the release of ‘Halehaven’ (1932) and ‘Kalhaven’ (1938). Although he was not trained as a geneticist, he had a keen eye for what the farmer needed. A cross of ‘Halehaven’ by ‘Kalhaven’ resulted in ‘Redhaven’, released in 1940 (Iezzoni, 1987). When initially released it was the ﬁrst good freestone on the market. It quickly came to prominence for higher-chill regions because of its productivity, ﬁrmness and appearance, and at one time was the most widely grown peach in the world. Even now it is still widely grown, although it is being replaced in some areas. Later Michigan releases from a lifetime total of 21,000 seedlings included ‘Fairhaven’, ‘Sunhaven’, ‘Richhaven’, ‘Glohaven’ and ‘Cresthaven’ (Kessler, 1969).

(USDA) initiated a breeding programme in 1936 at its research facility in Beltsville, Maryland to develop high-quality, cold-resistant peaches (Havis et al., 1947; Okie et al., 1985). Breeder F.P. Cullinan (1937) wrote a classic chapter on stone fruit breeding up to that time for the 1937 USDA Yearbook of Agriculture. He was followed by breeders A.L. Havis and H.W. Fogle. Although the programme had only a limited number of releases, including ‘Ranger’ (1952) and ‘Redglobe’ (1954), important contributions were made to peach genetics. ‘Redglobe’ is the still widely grown in the south-eastern USA, making it one of the oldest cultivars still important there. In 1980 the programme was moved to a new facility in Kearneysville, West Virginia.

South-eastern USA Texas Texas has a wider range of chilling than most states, so it is difﬁcult for a single programme to cover the entire gamut. Although Texas had a long history of private breeding, public breeding at Texas A&M University in College Station only started in 1935. Chilling accumulation at College Station is moderate most years, so more effort went into developing low- to moderate-chill cultivars, a chill range which also had fewer breeders working to improve it. No cultivars were named until 30 years later, with the release of ‘Sam Houston’, followed by ‘TAMU Denman’ and ‘Milam’. As the programme under D.H. Byrne has shifted more towards low-chill development in recent years, it is discussed further in Chapter 5. Georgia

Maryland Breeders at University of Maryland began work in 1929, but the ﬁrst release was ‘Redskin’ in 1944. It is still grown in some areas but is declining in popularity. Breeding efforts soon ended, but advanced selections were carried on with the intent of developing late-ripening cultivars with better red colour and fruit quality. Later releases included ‘Marhigh’, ‘Marsun’ and ‘Marqueen’, which are littlegrown now. The US Department of Agriculture

USDA stone fruit breeding in Georgia began in 1937 at the Horticultural Fruit Laboratory in Fort Valley, in the centre of the main peach production area (Okie et al., 1985). J.H. Weinberger was the peach breeder until 1954, when he transferred to Fresno, California to begin the peach breeding there. Weinberger published seminal papers about the chilling requirements of peach cultivars in addition to naming several important peach cultivars. He developed cultivars such as ‘Cardinal’

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Plate 1. One-year-old fruiting shoots at bloom. Plate 2. Dwarf peaches in a commercial orchard. Plate 3. Relationship between crotch (α) and extension (β) angles. Plate 4. Leaf stipules at petiole base. Plate 5. Narrow leaves (left) compared to normal sized (right). Scale in centimetres.

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Plate 6. Leaf glands: (A) reniform; (B) globose; (C) eglandular (note close-up, below). Plate 7. Red leaf (left) and green leaf (right) peach trees. Plate 8. Fruit skin colour variability. From top centre going clockwise: a yellow nectarine (anthocyaninless), a white peach (anthocyaninless), a yellow peach (100% blush), a white peach, a non-melting peach, a yellow flat nectarine, a white flat peach, a white nectarine and a yellow nectarine. Plate 9. Hyper-sensitivity reaction on a resistant peach after a proof bite by a green aphid. Plate 10. Flower type: showy.

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Plate 14. Main fruit shapes in commercial cultivars: globose (left), flat (centre), oblong (right). Plate 15. Fruit size gain in F1 progeny from distant-size parents. Plate 16. Flesh colour variability. From left, top row: non-melting flesh, two yellows (greenish and bright yellow), a white; bottom row: red flesh (‘blood’), a yellow melting (anthocyaninless), a yellow and a white melting (flat shape), a white stony-hard (anthocyaninless). Plate 17. Red 'blood' flesh in peach (courtesy of A. Liverani, Forli, Italy). Plate 18. Red 'blood' flesh in nectarine (courtesy of A. Liverani, Forli, Italy). Plate 19. Genetic variation for red 'blood' flesh trait in peach (courtesy of W.R. Okie, Byron, Georgia, USA).

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Plate 20. Stony-hard fruit: white (anthocyaninless) flesh. Plate 21. Stony-hard fruit: yellow flesh. Plate 22. Comparison between mature (left) and immature (right) embryos taken from ‘Spring Crest’ peach at two different stages: the immature embryos fail to germinate under standard stratification procedures and need to be rescued in vitro as the very early ripening genotypes. Plate 24. Slow ripening nectarine trees after leaf fall (dormant season).

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Plate 23. Main phenological stages in peach (courtesy of E. Bellini, Florence University, Italy).

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Plate 25. A Chinese painting by Ma Tai (1885–1935), telling a story that an old man with white hair but a young, boyish face always steals peaches. People make fun of this long-lived man, but he explains ‘Peach is good for my health’. Plate 26. Chinese peach production regions: (I) north-west drought region; (II) northern China plain region; (III) Changjiang River humid region; (IV) Yunnan–Guizhou high plateau cold region; (V) Qinghai–Tibet plateau cold peach region; (VI) north-eastern China cold region; (VII) southern China subtropical region. Plate 27. Modern greenhouse production. Plate 28. Modern greenhouse production before postharvest canopy removal.

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Plate 29. Modern greenhouse production after postharvest canopy removal. Plate 30. Conventional orchard. Plate 31. Modern high density orchard. Plate 32. Modern high density orchard (dormant). Plate 33. Ornamental 'chrysanthemum' peach. Plate 34. Ornamental 'longevity' peach (from Wang and Zhuang, 2001).

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Plate 35. A monoploid peach with some fruits. Plate 36. A weeping tree trained in central axis. Plate 37. Flat nectarines (‘platerines’ in French). Plate 38. Scheme based on genotypic choice of parents to obtain pure lines. In each generation, parents giving progenies with low horticultural value are eliminated. Plate 39. Emasculated flower (on left) (courtesy of W.R. Okie, Byron, Georgia, USA). Plate 40. Pollination by honeybee (courtesy of D.R. Layne, Clemson, South Carolina, USA).

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Plate 41. Dehydrated stamens ready for artificial pollination: anthers and filaments render the pollen less sticky. Plate 42. Emasculated flower pollinated by finger, a fast way for cross-breeding. Plate 43. Self-pollination with waterproof paper bags. Plate 44. Young seedling at the end of embryo culture. Plate 45. Seedling orchard at first flowering. Plate 46. Initial physical map of linkage group 1 of peach depicted in the Prunus genome website (http://www.bioinfo.wsu.edu/gdr/).

47 48 Plate 47. General Prunus genetic map (Joobeur et al., 1998) and developing peach physical/EST map. Markers depicted in bold have been used to develop contigs of peach BACs, which are depicted as the light-coloured circles with the number of BACs detected by each marker inscribed in the circle. Green circles denote two adjacent markers detecting the same BACs. Black flags denote peach and tomato EST positions with the number of ESTs at this location posted above the flags. Plate 48. Numbers of new low-chill peach and nectarine cultivars released from four countries, 1980–1992. These countries accounted for 94% of low-chill cultivars released in this period (adapted from Della Strada et al., 1996).

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Plate 49. Regular green leaf peach seedlings in foreground and peach seedling displaying red leaf character associated with short fruit development period (FDP) in centre at Nambour, Queensland. This trait can be used for early identification of short FDP seedlings in late summer (Sherman et al., 1972). Plate 50. Peach fruit with prominent stylar tips that are commonly observed in cultivars with poor adaptation to mild winter locations and are selected against in low-chill breeding. Plate 51. Influence of location on fruit shape. This medium-chill (450 CU) peach selection produced: (A) round fruit at the high-chill (900 CU) location of Stanthorpe Queensland and (B) pointed fruit at the low-chill (200 CU) location of Nambour Queensland. Plate 52. (A) Rosetting of peach seedling terminal bud can be a major source of seedling loss in the glasshouse or during transplanting to the field. (B) Normal shoots developing from below the rosetted terminal. Plate 53. High density fruiting nursery at Gainesville, Florida showing size of second leaf peach seedlings grown in subtropics.

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Plate 54. Ripe fruit of ‘Rubyprince’ peach, a typical modern peach with extensive red blush and short pubescence. Plate 55. Processing clingstone peach showing the uniformly yellow, firm, non-melting flesh and associated clingstone type stone-to-flesh adhesion. Plate 56. Harvest sequence of California processing peach cultivars using the fresh market freestone ‘Fay Elberta’ as a reference cultivar (1 – grower selection; 2 – private breeder release; none – released by public breeding programme). Plate 57. History of processing clingstone cultivar release by public breeding programmes in California showing punctuated release at approximately 20-year intervals. Plate 58. Basic components of a processing peach breeding programme with estimated duration in years.

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Plate 59. Fruit ripe date for progeny from self-pollination of the cultivar ‘Carson’ showing unusual bi-modal distribution. (‘Carson’ normally ripens approximately 40 days after 1 June). Plate 60. Poor lye peeling of a clingstone genotype with unacceptably thick epidermis. Plate 61. Halved section of overripe clingstone peach demonstrating the common pattern of vascular strands radiating from endocarp to outer mesocarp. Plate 62. Rooted hardwood cuttings of peach. Plate 63. Mist propagation facility for rooting of semi-hardwood cuttings. Plate 64. Rooted semi-hardwood cuttings that were treated with auxins.

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Plate 65. Hundreds of micropropagated plantlets in commercial facility. Plate 66. The main steps of the micropropagation cycle. Plate 67. Acclimatization of young micropropagated plantlets. Plate 68. Excised embyros in aseptic culture.

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72

73

Plate 69. Plantlets generated from aseptic embryo culture. Plate 70. Traditional open vase tree form. Plate 71. Palmette tree form. Plate 72. Central leader tree form. Plate 73. Fusetto orchard.

Fresh Market Cultivar Development

and ‘Dixired’ that shifted the earliest ripening date 2 weeks earlier than before. V.E. Prince continued the breeding in 1954. In 1964, the programme moved 20 miles east to the newly opened South-eastern Fruit and Tree Nut Research Laboratory in Byron. Prince also developed many important peaches, in particular ‘Springcrest’, which became the most widely grown peach since ‘Redhaven’. ‘Springcrest’, along with ‘Springbrite’ and ‘Springold’, moved the earliest ripe date several weeks even earlier, albeit at the expense of fruit size and eating quality. Together Prince and Weinberger released 21 peaches, one nectarine and ‘Nemaguard’ rootstock. Only a few are still being heavily planted although ‘Nemaguard’ is still the major peach rootstock in California. One of Weinberger’s selections, FV89-14, spawned an amazing range of descendants although it was too susceptible to bacterial spot for release on its own. Its east and west coast progeny include ‘Springcrest’ (and

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all its descendants) and many others (Table 6.2). ‘Springcrest’ at one time dominated early peach production in California and Europe (Okie and Myers, 1991). North Carolina F.E. Correll Jr was hired to start a peach breeding programme at North Carolina State in 1955. About 10 years earlier C. Clayton had been hired as a fruit pathologist. Clayton had a good horticulture background and was very active in the efforts to help growers. It was apparent to him that the peach industry needed cultivars resistant to bacterial spot disease if it was going to thrive on the state’s sandy soils. After Correll was hired the two of them cooperated in one of the ﬁrst crossdiscipline team efforts to develop diseaseresistant tree fruits. Although their cultivars were not widely grown outside North Carolina, the project was successful and their close

Table 6.2. Peach and nectarine cultivars descended from US Department of Agriculture selection FV89-14, listed by most immediate parent. Parents are shown in bold and bud mutations in italics. First-generation offspring are underlined. (From Okie and Myers, 1991.) FV89-14

‘Springcrest’

‘Maycrest’

Other parenta

‘Autumn Red’ ‘Camden’ ‘Fayette’ ‘Flamecrest’ ‘Flavorcrest’ ‘Goldcrest’ ‘Goldprince’ ‘Gulfcrest’ ‘Gulfking’ ‘Spring Baby’ ‘Springcrest’ ‘Spring Gem’ ‘Springold’ ‘Starlite’ ‘Sunprince’ ‘TexKing’

‘Cristelle’ (=‘Primecrest’) ‘Earlicrest’ ‘Early Crest ’ (=‘San Isidoro’) ‘Early Maycrest ’ ‘Firecrest ’ ‘Maycrest’ ‘Morning Sun’ ‘Queencrest’ ‘Ray Crest ’ ‘Ruby May ’ ‘Starcrest ’ (=‘Chastar ’)

‘Early Maycrest ’ ‘Michaelian (Ra-2)’ ‘Queencrest ’

‘Crimson Lady’ —'Crimson Princess' —‘Snow Duchess’

‘Earlitreat’ ‘Gayla Rich’ ‘Kay Glo’ ‘Klondike White’ ‘May Sweet’ ‘Polar Light’ ‘Rich May’ ‘Siesta Gem’ ‘Spring Treat’ ‘Snow Dance’ ‘Snow Kist’ ‘Snow Peak’ ‘Sunlit Snow’ ‘Super Rich’ ‘Sweet Alice’ ‘Sweet Crest’ ‘Vista Snow’ ‘Zee Diamond’ ‘Zee Fire’

‘Crown Princess’ —'Golden Princess' —‘Candy Red’ —‘Ivory Queen’ —‘Ivory Princess’

aIndented

‘Ambercrest’ ‘Crimson Lady’ ‘Crown Princess’ ‘Golden Crest’ ‘Honey Bee’ ‘Snow Duchess’ ‘Springprince’ ‘Sugar Time’ ‘Supecheight’ ‘Supechnine’

cultivars are descended from parent immediately above.

‘Fayette’ —‘June Crest’ —‘PP16,179’ —‘Super Lady’ —‘Topcrest’ ‘Topcrest’ —‘Bev’s Red’ —‘Snow Prince’

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cooperation was a model for others coming after them. Correll also put great emphasis on low ﬂesh browning as a project goal. The peach breeding was successful in developing a series of bacterial spot-resistant cultivars, the most resistant of which were ‘Clayton’ and ‘Candor’. Other popular cultivars were ‘Norman’, ‘Winblo’ and ‘Biscoe’ (Werner and Ritchie, 1982). In recent years the programme under D.J. Werner emphasized late bloom and ability to crop despite spring frosts. ‘Contender’ has become popular for this reason, and the newest releases ‘Intrepid’ and ‘Challenger’ are also quite bud hardy. Werner also released a series of columnar (‘pillar’) shaped ornamentals with double ﬂowers: ‘Corinthian Pink’, ‘Corinthian Rose’ and ‘Corinthian White’, along with ‘White Glory’, a weeping whiteﬂowered nectarine. The North Carolina programme continues evaluations but is no longer making new crosses. Louisiana Louisiana began peach breeding in 1951 under P.L. Hawthorne and later J.C. Taylor, although the Calhoun Research Station had been involved in cultivar testing since 1889. The emphasis was on disease resistance, mainly to bacterial spot, reliable cropping and the fruit attributes of size, attractiveness, ﬂavour and shipping quality. Some of the most important cultivars released were ‘La Premiere’ (1965), ‘Surecrop’ (1973), ‘Harvester’ (1973) and ‘Majestic’ (1979). ‘Harvester’ has been one of the primary south-eastern US cultivars since its release (Graham, 1999). A secondary programme at Idlewild, Louisiana developed moderate-chill peaches for local markets, including low-acid types popular among certain local consumers.

California As early as 1860 there were already over a million peach trees in California. By 1886 California was shipping boxes of ‘Alexander’, ‘Early Crawford’, ‘Late Crawford’ and ‘Hales Early’ to the eastern USA. At about this same time the drying industry began to expand. ‘Lovell’ and ‘Muir’, discovered as chance seedlings, were found to be well suited to drying.

By 1910 dried production was over 20,000 t (Butterﬁeld, 1938). After ‘Elberta’ and ‘J.H. Hale’ were introduced, they dominated the shipping industry until about 1940. Burbank’s ‘July Elberta’ (probably no relation to ‘Elberta’), released in 1930, was the only cultivar of his to be commercially important and the second peach to be patented (US Plant Patent 15). Butterﬁeld (1938) lists 61 mostly chance seedling peach cultivars that had originated in California by that time along with this comment: ‘With all of the many California peach cultivars shown in the accompanying list, it would seem that nothing else would be desired’. University of California Public peach breeding in California had begun at University of California at Riverside in 1907 to develop low-chill peaches suited for southern California. A similar programme was begun in 1919 at Chaffee Junior College in Ontario, California. In the process of developing lower-chill peaches, W.E. Lammerts also did the most thorough study of inheritance of ornamental features such as multiple petals (double ﬂowers) (Lammerts, 1945). The most important release from the low-chill work was ‘Babcock’, a crisp (maybe it is a stony-hard ﬂesh?), low-acid, white-ﬂeshed peach that was the precursor to the low-acid peaches that are currently in vogue, and in fact was grown for many years as a niche market (Weldon and Lesley, 1933; Butterﬁeld, 1938). It was also apparently a source, through its offspring ‘Giant Babcock’, of the very ﬁrm texture of some modern low-acid whites such as ‘White Lady’. University breeders had little impact on freestone peach breeding, although University of California at Davis did release several cultivars in 1977 such as ‘Firered’ and ‘Calred’. P.E. Hansche also put substantial effort into developing dwarf peaches with commercial fruit quality, releasing several cultivars including ‘Valley Red’ in 1989 (Hansche and Beres, 1989). So far dwarf peaches have not had commercial impact due to management issues, but breeding continues in Italy. As the shipping industry developed, there was a need for new cultivars over a wider season that could be picked more ﬁrm, with better colour and shipped over greater

Fresh Market Cultivar Development

distances. Up to that time most freestone cultivar development was conducted by federal and state research programmes in the eastern USA. Two private breeders, G. Merrill and F.W. Anderson, initiated programmes in California to breed cultivars especially for the developing California industry. These two pioneers remained friends throughout their long careers and it is reported that, early in their work, they established a ‘gentleman’s agreement’ that Merrill would focus on peach breeding and Anderson would concentrate on nectarines (J. Slaughter, California, 2004, personal communication). Merrill G. Merrill (1899–1973) worked mainly with peaches, introducing important cultivars such as ‘O’Henry’, ‘Early O’Henry’, ‘Elegant Lady’, ‘Spring Lady’, ‘Angelus’, ‘Sparkle’, ‘Parade’,

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‘Gemfree’, ‘Merrill Gemfree’, ‘June Lady’, ‘Red Lady’, ‘Halloween’, ‘Franciscan’, ‘Forty Niner’, ‘Sundance’ and others, many of which are still being grown worldwide. During the 1970s and early 1980s, up to 40% of all peaches shipped in California were Merrill cultivars (Zaiger, 1988). Moreover, three Merrill peaches, ‘Elegant Lady’, ‘Angelus’ and ‘O’Henry’, are still among the top planted cultivars in California today (Tables 6.3 and 6.4). Merrill worked with various nurseries in California who assessed tree royalty charges to commercial growers. Merrill remained active in cultivar development until shortly before his death in 1973 and his work helped to establish the next generation of breeders (Stark, 1974). Anderson Nectarines were a novelty crop in California in the middle of the last century, as the fruit

Table 6.3. Leading California peach cultivars in order of production averaged over 2002–2003. (From CTFA, 2003.) Cultivar ‘O’Henry’ ‘Elegant Lady’ ‘Rich Lady’ ‘Autumn Flame’ ‘Summer Lady’ ‘Zee Lady’ ‘Ryan Sun’ ‘Crimson Lady’ ‘September Sun’ ‘Snow Giant’ ‘Summer Sweet’ ‘Crown Princess’ ‘Brittney Lane’ ‘Fancy Lady’ ‘Flavorcrest’ ‘Diamond Princess’ ‘September Snow’ ‘Queencrest’ ‘Spring Snow’ (40GH121) ‘Snow King’ ‘Autumn Snow’ (‘Yukon King’) ‘Sweet Scarlet’ ‘August Lady’ ‘Super Rich’ ‘Saturn’ ‘Ivory Princess’

Harvest starts: day/month/year

Production (t)

29/7/2003 4/7/2003 7/6/2003 11/8/2003 21/7/2003 15/7/2003 7/8/2003 23/5/2003 23/8/2003 31/7/2003 30/6/2003 27/5/2003 29/5/2003 13/6/2003 11/6/2003 30/6/2003 16/8/2003 13/5/2003 14/5/2003 23/7/2003 29/7/2003 30/5/2003 5/8/2003 6/5/2003 5/6/2003 3/6/2003

23,099 21,137 10,001 9,290 9,012 8,624 7,890 7,880 7,846 6,621 6,068 5,660 5,404 5,341 5,080 4,705 4,628 4,535 4,325 4,182 3,890 3,776 3,772 3,364 3,061 3,044

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Table 6.4. Peach tree sales reported by California nurseries, 1999–2002 (three planting years), arranged by season of ripening. (From CTFA, 2003.) Cultivar Early ‘Burpeachfourteen’ ‘Super Rich’ ‘Queencrest’ ‘Burpeachone’ ‘Spring Snow’ ‘Crimson Lady’ ‘Brittney Lane’ ‘Ivory Princess’ ‘Earlirich’ ‘Rich Lady’ Others Total Mid-season ‘Vista’ ‘Country Sweet’ ‘Burpeachfive’ ‘Summer Sweet’ ‘Elegant Lady’ ‘Sweet Dream’ ‘Burpeachsix’ ‘Angelus’ ‘Zee Lady’ ‘O’Henry’ Others Total Late ‘Autumn Snow’ ‘Ryan Sun’ ‘September Snow’ ‘Burpeachfour’ ‘Burpeachthree’ ‘September Sun’ ‘Fairtime’ ‘Autumn Flame’ ‘Snowfall’ ‘Sweet September’ Others Total

Flesha

Acidityb

Released

8 May 10 May 12 May 19 May 24 May 25 May 29 May 6 Jun 7 Jun 10 Jun

Y Y Y Y W Y Y W Y Y

M M M M L M M L M M

2003 1997 1987 2001 1997 1992 1998 2000 1994 1990

Mid Mid Mid Mid Mid Mid Mid Mid Mid Mid

15 Jun 18 Jun 1 Jul 7 Jul 19 Jul 20 Jul 21 Jul 25 Jul 31 Jul 5 Aug

Y Y Y W Y Y Y Y Y Y

M L M L M L M M M M

Late Late Late Late Late Late Late Late Late Late

15 Aug 20 Aug 28 Aug 31 Aug 1 Sep 2 Sep 5 Sep 7 Sep 8 Sep 14 Sep

W Y W Y Y Y Y Y W Y

L M L M M L M M L L

Season

Ripe

V. early V. early V. early Early Early Early Early Early Early Early

TOTAL PEACHES

Origin

Trees

Per cent

Burchell Zaiger L. Balakian Burchell Zaiger Bradford Zaiger Bradford Zaiger Zaiger

69,000 142,406 35,489 83,100 67,713 27,878 71,493 41,754 39,237 22,570 146,608 747,248

4.0 8.2 2.0 4.8 3.9 1.6 4.1 2.4 2.3 1.3 8.4 43.1

1996 1999 2002 1992 1979 1998 2002 1966 1986 1970

Zaiger Zaiger Burchell Zaiger Merrill Zaiger Burchell Merrill Zaiger Merrill

25,387 71,950 56,632 24,532 57,513 42,792 45,415 23,348 26,100 35,273 268,633 677,575

1.5 4.1 3.3 1.4 3.3 2.5 2.6 1.3 1.5 2.0 15.5 39.0

1997 1983 1992 2002 2002 1987 1968 1996 2000 1997

Zaiger Chamberlin Zaiger Burchell Burchell Chamberlin USDA J. Doyle Zaiger Zaiger

19,311 30,729 26,927 29,000 17,000 13,697 44,682 55,689 12,239 42,887 18,261 310,422

1.1 1.8 1.6 1.7 1.0 0.8 2.6 3.2 0.7 2.5 1.1 17.9

1,735,245

USDA, US Department of Agriculture. aFlesh colour: Y, yellow; W, white. bAcidity type: M, standard; L, sub-acid.

was small, with little red skin colour, unattractive green ground colour, and a tendency for the skin to crack (Ramming, 1988). ‘Stanwick’, ‘Gower’ and ‘Quetta’ (Werner and Okie, 1998) dominated California production.

F.W. Anderson, a private breeder in Merced, California, began intercrossing of nectarines such as ‘Quetta’ (from Pakistan) and ‘Lippiatt’s’ (from New Zealand) with large peaches. The release in 1942 of ‘Le Grand’ nectarine,

Fresh Market Cultivar Development

which was the ﬁrst large, attractive nectarine, was the basis of the nectarine industry worldwide. Most of our current nectarines can be traced back to ‘Le Grand’ or his other releases. As a result Anderson is widely known as the ‘father of the modern nectarine industry’. He introduced many other important cultivars including ‘Sun Grand’, ‘Red Grand’, ‘Grand Haven’, ‘May Grand’, ‘Early Sun Grand’, ‘Summer Grand’, ‘Spring Grand’, ‘Red June’, ‘June Grand’, ‘Aurelio Grand’, ‘Red Diamond’, ‘Summer Beaut’, ‘Spring Red’ and ‘Autumn Grand’. Anderson’s nectarines dominated markets throughout the world for many years, and during the 1970s over 90% of all nectarines shipped in California were his introductions (Zaiger, 1988). Currently only ‘Red Diamond’ remains a major cultivar (Table 6.5). Anderson worked with commercial nurseries who asses-

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sed a per-tree royalty to commercial growers and with Stark Brothers Nursery for sales of backyard trees (L.G. Bradford, California, 2004, personal communication). Not only was Anderson inﬂuential in the fruit industry, he had an important inﬂuence in establishing the next generation of California breeders as well. N.G. Bradford, who went on to establish Bradford Genetics, started working with Anderson as a farm hand in 1941, became general foreman in 1950, and continued until Anderson’s death in 1982. C.F. Zaiger also worked with Anderson during 1956–1957 and went on to establish Zaiger Genetics, one of the most important breeding programmes today. Anderson remained active in breeding late into his 80s and sold his programme to N.G. Bradford shortly before his death in 1982 (Bradford, 1988).

Table 6.5. Leading California nectarine cultivars in order of production averaged over 2002–2003. (From CTFA, 2003.)

Cultivar ‘Spring Bright’ ‘Summer Fire’ ‘Summer Bright’ ‘August Red’ ‘Rose Diamond’ ‘September Red’ ‘Ruby Diamond’ ‘Diamond Bright’ ‘Arctic Snow’/‘White Jewel’ ‘Red Jim’ ‘Fire Pearl’ ‘Bright Pearl’ ‘Arctic Pride’ ‘Diamond Ray’ ‘Honey Blaze’ ‘Grand Pearl’ ‘Red Diamond’ ‘Mayglo’ ‘Royal Glo’ ‘Arctic Sweet’ ‘Honey Kist’ ‘Arctic Mist’ ‘Fire Sweet’ ‘Arctic Star’ ‘Summer Blush’ ‘Mayfire’

Harvest starts: day/month/year

Production (t)

10/6/2003 19/7/2003 4/7/2003 12/8/2003 23/5/2003 22/8/2003 23/6/2003 2/6/2003 2/6/2003 7/8/2003 12/7/2003 5/7/2003 8/8/2003 30/6/2003 7/6/2003 30/6/2003 25/6/2003 13/5/2003 21/5/2003 6/6/2003 12/6/2003 6/9/2003 15/7/2003 24/5/2003 12/8/2003 8/5/2003

21,998 15,812 15,372 11,641 11,343 8,558 8,512 7,948 7,947 6,598 6,179 5,800 5,631 5,188 4,925 4,889 4,425 4,322 4,252 4,163 3,779 3,723 3,610 3,461 3,437 3,147

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US Department of Agriculture USDA began peach breeding in California in 1920 at Palo Alto and later Davis, primarily to develop better canning and drying peaches. Later the cling breeding was shifted to University of California at Davis and the fresh market breeding was expanded by J.H. Weinberger, who had worked in fruit breeding with the USDA in Fort Valley, Georgia from 1937 and moved to Fresno, California in 1954 to continue his breeding work (Okie et al., 1985). Although Weinberger grew relatively few seedlings (about 4000 total stone fruits per year in Fresno, which included plums and apricots), he had clear goals in mind and a discerning eye to ﬁnd the best in his material. His PhD training in plant physiology helped him to ‘know his organism’ and he published important papers on chilling and adaptation. Extensive on-farm testing ensured the named cultivars were likely to be successful. During a period in the 1980s Weinberger’s nectarines, including the leading cultivar at the time, ‘Fantasia’, were responsible for over 40% of total nectarine production in the USA. Other important Weinberger nectarines at the time included ‘Fairlane’, ‘Firebrite’, ‘Flamekist’, ‘Flavortop’ and ‘Independence’. Weinberger peach cultivars comprised over 25% of the peaches shipped in California at this time, including ‘Coronet’, ‘Desert Gold’, ‘Fairtime’, ‘Fayette’, ‘Flamecrest’, ‘Flavorcrest’, ‘Redtop’, ‘Regina’, ‘Summerset’ and ‘Suncrest’. ‘Flavorcrest’ and to a lesser extent ‘Springcrest’ are the only cultivars of his that are still signiﬁcant in production (Table 6.3). He also developed the leading nematode-resistant rootstocks, ‘Nemaguard’ and ‘Nemared’, on which over 90% of stone fruit are grown in California (Childers and Sherman, 1988). Weinberger’s proliﬁc success, and the fact that USDA cultivars are available worldwide with no royalty charge, caused uncertainty with private breeders during the 1970s and 1980s, and prompted C.F. Zaiger in 1988 to refer to the private breeder as ‘a dying breed’ (Zaiger, 1988). After his retirement from the USDA in 1973, Weinberger consulted with Superior Farming Company (now Sun World International, Inc.) to help establish their breeding programme near Bakersﬁeld, California and remained

active in the fruit industry until shortly before his death in 2000.

6.4. Modern US Breeding Programmes Most breeding for fresh market peaches follows similar protocols. Advanced selections and cultivars from in-house as well as other programmes are evaluated to ﬁnd superior parents. Parents with superior characteristics are crossed by hand with the objective of producing seedlings that combine the desirable qualities of the parents. Seed from the crossings (or open-pollinated seed of previous seedlings) is usually artiﬁcially stratiﬁed. Seedlings grown in a greenhouse can be planted the spring following harvest, saving time, or moved to a nursery for a year. Small seedlings are transplanted in the spring to seedling rows, usually with trees spaced 0.5–1 m apart. At this spacing trees become crowded after several years so must be evaluated and quickly rogued. Seedling trees usually bear fruit in the third summer from planting, at which time the best are selected for further testing or propagation and the rest removed. Seedling trees can be readily evaluated for most visual fruit characters, but fruit usually is smaller than on a commercially grown tree. Eating quality is the most difﬁcult aspect to judge, as a taste test of a single fruit is often not representative of the entire tree. In climates that are highly variable from year to year, more years of observations are needed to get a true picture of the selection’s adaptation because many characters such as crop, size, shape and quality can vary greatly from year to year. One means to reduce the time factor for such areas is to plant budded trees in several widespread locations. A few breeders do complete evaluations of every seedling, but most ﬁnd this too time-consuming except for selected populations. Most public breeders grow from 1000 to 5000 seedlings per year, which is all their resources of land and labour will allow. Some of the private programmes may grow ten times this quantity, which naturally allows for more rapid progress. The timeframe from cross to release is usually 10–15 years for a public programme,

Fresh Market Cultivar Development

but frequently private breeders do less testing and thus have a shorter turnover time. In the last several decades, public peach breeding in the USA has been reduced, particularly in marginal climates where peach production is more challenging; industries have shrunk and industry support has waned. State programmes have also been hurt by budget cuts (at both the state and local levels) since tree fruit breeding is expensive, long term and less dramatic than some other research areas. Many of the programmes never had much impact, a result of inadequate resources of time and money, as well as climatic problems. It is difﬁcult to make progress when crosses and seedling crops are often killed by frost. In contrast to the recent US situation, countries in Europe and Asia have recognized the value of developing cultivars speciﬁcally adapted for their climate and industry. These new programmes have a big advantage in having much better parents to choose from due to the last century of improvement in the USA. For example, obtaining selections with high red skin colour is facilitated if a breeder uses the newer full-red peaches such as ‘O’Henry’ and ‘Rich May’ as parents.

North-eastern USA and Canada Major cultivars grown in the north-eastern USA and Michigan are shown in Table 6.6. Most of these are from northern breeding programmes, or are mutations of northern cultivars. In general the cultivars are less recently released compared with what is grown in California, a reﬂection of the breeding effort that has been available to produce new improved cultivars. New Jersey The New Jersey breeding programme has continued under J.C. Goffreda and A. Voordeckers with a dual emphasis. Recent selections include standard yellow- and white-ﬂeshed peaches with resistance to bacterial spot and constriction canker (Fusicoccum or Phomposis canker). In addition they have emphasized niche markets, including ﬂat (peento or pantao) peaches, low-acid and stony-hard (crisp) ﬂesh, also

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with disease resistance. ‘Saturn’ (NJF-2), probably the ﬁrst bred ﬂat peach, was named by Starks Nursery in 1985 but languished until the late 1990s when California growers began marketing it as a specialty item (Table 6.3). The programme plans on releasing ten or so cultivars in the next couple of years, including a series of stony-hard peaches, at least three ﬂat peaches, one nectarine and several melting white- and yellow-ﬂeshed peaches. Rutgers also released a cold-hardy, lateblooming ornamental, ‘Jerseypink’. US Department of Agriculture–Agricultural Research Service The Beltsville breeding work (now USDA– Agricultural Research Service or USDA-ARS) has been continued at Kearneysville, West Virginia, by R. Scorza. Releases ‘Bounty’ and ‘Sentry’ have become important north-eastern USA cultivars (Table 6.6). ‘Earliscarlet’ provides a brightly coloured, adapted nectarine for eastern US growers. Non-standard tree growth habits have been a focus in recent years, and much has been done to understand the different forms and patterns of growth. Advanced selections include those with semidwarf and compact growth habits, which reduce tree size and pruning while maintaining a manageable size. Two new releases are the ﬁrst fruit type cultivars using the columnar (‘pillar’) gene. ‘Crimson Rocket’ is homozygous for the gene and is columnar in habit; ‘Sweet-N-Up’ is heterozygous, which gives it an intermediate upright architecture. These tree shapes are conducive to more dense plantings. Michigan The Michigan State University peach breeding programme since 1992 has been under the direction of W. Shane who has expanded work initiated by A.F. Iezzoni, now primarily a cherry breeder. The traditional breeding programme is developing yellow (mostly) and white, melting-ﬂesh cultivars in the post‘Redhaven’ season with better skin colour, size, ﬁrmness, productivity and disease resistance. Particular emphasis is placed on mid-winter cold hardiness and resistance to Leucostoma canker, which causes serious limb decline in

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Table 6.6. Major fresh market peach cultivars in the north-eastern and south-eastern USA, listed by ripening date, with source and release date. (In part from J. Frecon, USA, 2005, personal communication.) Cultivar North-eastern USA ‘Harrow Diamond’ ‘Harrow Dawn’ ‘Sentry’ ‘Garnet Beauty’ (=‘Redhaven’ mutation) ‘Redhaven’ ‘JohnBoy’ (=‘Loring’ mutation) ‘Harrow Beauty’ ‘Flamin Fury PF17’ ‘Bounty’ ‘Loring’ ‘Flamin Fury PF23’ ‘Blake’ ‘Harcrest’ ‘Cresthaven’ ‘Jerseyqueen’ ‘Encore’ ‘Laurol’ (=‘Jerseyqueen’ mutation) ‘Flamin Fury PF24-007’ ‘Redskin’ South-eastern USA ‘Springprince’ ‘Sunbrite’ ‘Goldprince’ ‘Rubyprince’ ‘Summerprince’ ‘Juneprince’ ‘GaLa’ ‘Harvester’ ‘Cary Mac’ (=‘Loring’ mutation) ‘Redglobe’ ‘Majestic’ ‘Summergold’ ‘Fireprince’ ‘Contender’ ‘Cresthaven’ ‘Sunprince’ ‘O’Henry’ ‘Flameprince’ ‘Big Red’ (unreleased) ‘Autumnprince’

Origin

Year

Ontario Ontario USDA-ARS, West Virginia Ontario Michigan AES New Jersey AES Ontario Michigan – Friday USDA-ARS, West Virginia Missouri AES Michigan – Friday New Jersey AES Ontario Michigan AES New Jersey AES New Jersey AES New Jersey Michigan – Friday Maryland AES

1984 1996 1980 1958 1940 1988 1983 1993 1988 1946 1993 1953 1983 1963 1964 1980 1992 1996 1944

USDA-ARS, Georgia USDA-ARS, Georgia USDA-ARS, Georgia USDA-ARS, Georgia USDA-ARS, Georgia USDA-ARS, Georgia USDA, Louisiana Louisiana AES South Carolina USDA-ARS, Maryland Louisiana AES USDA-ARS, Georgia USDA-ARS, Georgia North Carolina AES Michigan AES USDA-ARS, Georgia California – Merrill USDA-ARS, Georgia USDA-ARS, California USDA-ARS, Georgia

1998 1976 1989 1997 1992 1985 1992 1973 1976 1954 1979 1970 1985 1987 1963 1981 1970 1993 ~1980 1998

USDA-ARS, US Department of Agriculture–Agricultural Research Service; AES, Agricultural Experiment Station.

colder climates. In the early 1990s Iezzoni and others initiated a long-term project to develop canker-tolerant peaches. They identiﬁed peach selections with resistance to canker, which

were then used as parents to move the resistance into high-quality peaches. The programme has generated 2000 to 3000 seedlings per year, resulting in the naming of ‘Beaumont’ in 2004.

Fresh Market Cultivar Development

Fruit Acres The scarcity of new cultivars adapted to the north-east in the last 20 years prompted a resurgence in private breeding in Michigan, home to two breeding programmes started by growers, who run them in conjunction with commercial peach orchards. The ‘Fruit Acres’ programme was started by J.E. Friday and is now run by his daughter and son-in-law, A. and R. Bjorge, located in Coloma. They are marketing the ‘Stellar’ series of peaches. Popular releases in more northern states include ‘Coralstar’, ‘Glowingstar’ and ‘Redstar’. ‘Flamin Fury’ A second Michigan breeding programme was started by cousin P.J. Friday, also in Coloma. He has developed the ‘Flamin Fury’ or ‘PF-’ series of peaches. These cultivars have provided a needed set of redder, bacterial spot-resistant new peaches for the region. Some such as PF12A, PF23 and PF17 have been well accepted commercially, primarily in the northern USA. More recently PF24-007 has been widely planted due to its very large size. Ontario Breeding in Ontario has been consolidated into a single programme at Vineland, with the station now under the University of Guelph rather than the provincial government. With the retirement of N.W. Miles, breeding for lateseason canning peaches continues as an emphasis under J. Subramanian. Unfortunately the programme at Harrow was a victim of budget cutting and in 1996 it was closed. Advanced Harrow selections are at Vineland for ﬁnal testing. Subramanian will also be aiming to develop mid- and late-season whiteand yellow-ﬂeshed freestones with improved bacterial spot resistance. It is unclear if nectarine development will continue.

153

north-eastern USA, most are publicly bred cultivars from within the region. Arkansas The University of Arkansas peach breeding programme was begun in the mid-1960s by J.N. Moore with strong cooperation with R. Rom. The main focus of the programme was canning cling peach breeding, primarily for baby food use. The contribution from F. Hough and Rutgers University was very substantial in the early years (see Chapter 7). The programme focus shifted in the late 1990s under J.R. Clark to emphasize fresh market peaches and to continue the nectarine programme that had been ongoing for some years. ‘White River’ (2002) was the ﬁrst fresh market peach from the programme, and was followed in 2004 by low-acid types ‘White County’ and ‘White Rock’ (Clark et al., 2005). Nectarines released from the programme are ‘Westbrook’, ‘Arrington’ and ‘Bradley’ (all in 2000). The latter two nectarines are non-melting ﬂesh types. The programme objectives include the continued improvement of nectarines, with emphasis on white- and yellowﬂeshed types with melting and non-melting ﬂesh. Fresh market peach breeding focuses primarily on white-ﬂeshed peaches with nonmelting ﬂesh. Sub-acid and standard acidity types are included in the programme as are free- and clingstones. A small project to improve ﬂat peaches is also under way. Bacterial spot resistance is a major priority in the programme, as the programme is operated in an area with high selection pressure for this trait. The germplasm used in the programme has been largely US cultivars and breeding selections from other programmes. A series of four ornamentals with dwarf (‘Bonﬁre’, ‘Leprechaun’) or weeping (‘Crimson Cascade’, ‘Pink Cascade’) habits was released in 1994. Louisiana

South-eastern USA Major southern cultivars are listed in Table 6.6, excluding moderate- and low-chill cultivars which are discussed in Chapter 5. As with the

Peach breeding in Louisiana ebbed in the 1980s after a series of difﬁcult winters. Under C.E. Johnson and later C.J. Graham, the programme expanded to develop adapted peaches with high productivity and disease resistance. Unfortunately budget cuts resulted

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in the termination of the programme in 2004. Recent releases from the moderate-chill programme at Clinton now under C.E. Johnson include ‘LaBelle’, ‘LaRouge’ and ‘LaSweet’. North Carolina In recent years the programme under D.J. Werner emphasized late bloom and ability to crop despite spring frosts. ‘Contender’ has become popular for this reason and the newest releases ‘Intrepid’ and ‘Challenger’ are also quite bud hardy. ‘China Pearl’ was released to provide a late-blooming, white-ﬂeshed peach. Werner also released a series of pillar-shaped ornamentals with double ﬂowers: ‘Corinthian Pink’, ‘Corinthian Rose’ and ‘Corinthian White’, along with ‘White Glory’, a weeping whiteﬂowered nectarine. Other recent releases include ‘Carolina Gold’, a yellow, melting-ﬂesh, late-season cultivar, and ‘Galactica’, a large, low-acid, white peento. The North Carolina programme continues evaluations but is no longer making crosses. US Department of Agriculture–Agricultural Research Service The south-eastern US peach industry is plagued by variability in winter climate, which makes it difﬁcult to select cultivars that get adequate chill every year but do not bloom too early and suffer from frost damage. The USDAARS peach breeding programme at Byron, Georgia is now the primary source of new commercial cultivars for the south-eastern USA, given the reduction in programmes in adjacent states. Peach growers need a sequence of cultivars ripening from 60 days before, to 30 days after, ‘Elberta’ (mid-July at Byron). The cultivar must be consistently productive, giving large-sized, ﬁrm and wellblushed fruit. Critical time slots lacking suitable cultivars are the period before ‘Springcrest’ and the seasons 1–2 weeks before and after ‘Elberta’. New releases ‘Scarletprince’, ‘Julyprince’, ‘Early Augustprince’ and ‘Augustprince’ may ﬁll the late-season niche. Most of the 4000 seedlings planted annually in recent years have been aimed at developing midand late-season peaches, rather than very early. Since 1980 all yellow-ﬂeshed peaches

have used ‘-prince’ as part of the name, to honour V.E. Prince’s efforts in establishing the Byron facility and to provide a ‘brand’ name for growers. The most successful releases have been ‘Juneprince’, ‘Goldprince’, ‘Sunprince’, ‘Flameprince’, ‘Rubyprince’ (Fig. 6.1/Plate 54) and ‘Springprince’ (Okie, 1997). White-ﬂeshed peaches ‘Scarletpearl’ and ‘Southern Pearl’, as well as white-ﬂeshed nectarine ‘Roseprincess’, have been useful for local markets. Auxiliary interests are in chilling as it relates to the possibility of developing a low-chill but high-heat requirement peach, narrow-leaf trees, and novelty fruits including blood-ﬂesh and ﬂat shape.

California The California Tree Fruit Agreement (CTFA) reports shipments of over 170 different peach and nectarine cultivars that provide fresh fruit from April through October (Tables 6.3 and 6.5). Private breeders dominate the ﬁeld of cultivar development in California due to reduced funding of government breeding programmes and to improvements in their ability to work globally and enforce intellectual property (IP) rights. The main private California breeding programmes in terms of size are Zaiger Genetics, Inc., Bradford Genetics, Inc., Burchell Nursery, Inc. and Sun World International, Inc. In order to remain competitive, all these programmes have developed strong international programmes and may derive as much or more revenue from international sources as from domestic sources. Private breeders derive revenue from IP licensing, often in the form of per-tree royalty assessments collected by licensed nurseries. There has also been a recent trend to develop ‘variety clubs’ and other production royalty programmes with managed plantings and development of ‘branded’ stone fruit series. Many large growers and marketers worldwide are turning to managed programmes because of the perception that unmanaged plantings lead to unhealthy overproduction and reduced fruit quality. In the USA, the Zaiger, Bradford and Burchell programmes are linked closely to nursery companies that

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Fig. 6.1. Ripe fruit of ‘Rubyprince’ peach, a typical modern peach with extensive red blush and short pubescence.

work with the programmes to test and promote new cultivars, and have exclusive rights to tree sales of most of the programmes’ releases. The result of these relationships is evident in recent tree sales in California, where 76% of peach trees and 84% of nectarine trees sold during 1999–2002 were cultivars from these three programmes (Tables 6.4 and 6.7). US Department of Agriculture–Agricultural Research Service D.W. Ramming has continued peach breeding at USDA in Fresno (now at Parlier) from 1974, emphasizing the very early and very late seasons, as well as improved eating quality. His research on embryo culture as a means to produce seedlings of early × early seedlings,

which normally have low-viability seed, has enabled the programme to develop much improved ultra-early cultivars such as ‘Mayﬁre’ and ‘Crimson Baby’ nectarines as well as ‘Spring Baby’ and ‘Spring Gem’ peaches. ‘Spring Baby’ was one of the ﬁrst non-melting ﬂesh peaches for the shipping market. Since all early peaches are clingstone for physiological reasons, the clingstone character associated with the non-melting ﬂesh was not a problem, and it could hang on the tree longer without premature softening. The embryorescue technique has since been adopted on a larger scale by the private programmes, with impressive results. ‘Autumn Red’ was released to provide a high-quality, well-coloured, lateripening peach. ‘September Free’ is a highquality, freestone, late-ripening nectarine, as

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Table 6.7.

Nectarine tree sales reported by California nurseries, 1999–2002 (3 planting years), arranged by season of ripening. (From CTFA, 2003.)

Cultivar

Mid-season ‘June Pearl’ ‘Spring Bright’ ‘Kay Pearl’ ‘Ruby Sweet’ ‘Diamond Ray’ ‘Arctic Jay’ ‘Grand Pearl’ ‘Honey Kist’ ‘Fire Sweet’ ‘August Pearl’ Others Total

Acidityb

Released

7 May 7 May 23 May 27 May 30 May 1 Jun 1 Jun 9 Jun 11 Jun 14 Jun

Y Y Y Y Y Y W Y Y W

M M M M L M L M L L

1983 2003 1999 2001 1999 1993 1995 1996 1998 1996

16 Jun 24 Jun 27 Jun 28 Jun 4 Jul 9 Jul 10 Jul 19 Jul 27 Jul 13 Aug

W Y W Y Y W W Y Y W

L M L L M L L L L L

1995 1991 1999 1997 1994 1997 1997 1995 1997 1999

Ripe

V. early V. early Early Early Early Early Early Early Early Early

Mid Mid Mid Mid Mid Mid Mid Mid Mid Mid

Origin

Trees

Per cent

USDA Burchell USDA Zaiger Bradford Zaiger Zaiger Bradford Zaiger Zaiger

34,083 23,677 27,258 30,700 41,538 25,902 23,590 59,197 64,480 18,863 63,830 413,118

2.9 2.0 2.3 2.6 3.6 2.2 2.0 5.1 5.6 1.6 5.5 35.6

Bradford Bradford Bradford Bradford Bradford Zaiger Bradford Zaiger Bradford Bradford

21,193 30,449 29,065 30,806 29,315 22,159 32,227 23,118 27,049 35,095 174,300 454,776

1.8 2.6 2.5 2.7 2.5 1.9 2.8 2.0 2.3 3.0 15.0 39.2

W.R. Okie et al.

Early ‘Mayfire’ ‘Burnecten’ ‘Crimson Baby’ ‘Red Roy’ ‘Kay Sweet’ ‘Royal Glo’ ‘Arctic Star’ ‘Diamond Bright’ ‘Honey Blaze’ ‘Arctic Sweet’ Others Total

Flesha

Season

Late Late Late Late Late Late Late Late Late V. late

TOTAL NECTARINES aFlesh

colour: Y, yellow; W, white. type: M, standard; L, sub-acid.

bAcidity

19 Aug 20 Aug 27 Aug 31 Aug 3 Sep 3 Sep 5 Sep 11 Sep 13 Sep 19 Sep

W Y W Y W Y Y Y W Y

L M L M L M M M L L

2000 2000 1993 1988 1992 2003 1999 2003 1999 1986

Bradford N. Waldner Zaiger Bradford Zaiger Bradford USDA Burchell Zaiger Bradford

5,180 111,546 20,058 10,596 41,330 7,146 11,696 20,600 36,243 28,320 0 292,715 1,160,609

0.4 9.6 1.7 0.9 3.6 0.6 1.0 1.8 3.1 2.4 0.0 25.2

Fresh Market Cultivar Development

Late ‘Regal Pearl’ ‘August Fire’ ‘Arctic Pride’ ‘August Red’ ‘Arctic Snow’ ‘September Bright’ ‘September Free’ ‘Burnectfour’ ‘Arctic Mist’ ‘September Red’ Others Total

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an alternative to the many late clings on the market. ‘Mayﬁre’, ‘Crimson Baby’ and September Free’ have been widely planted in recent years (Table 6.7). Most recently, ‘Galaxy’ was released to provide a large ﬂat peach as an adjunct to ‘Saturn’. It is the largest ﬂat peach currently available. Although ARS cultivars had a reputation for high quality and success due to extensive on-farm testing, industry impatience with the pace of public breeding in comparison to the much larger private programmes and their many new cultivars is resulting in de-emphasizing of peach breeding relative to the past. Zaiger Genetics, Inc. Zaiger Genetics is a family-owned breeding organization that was founded in Modesto by C.F. (Floyd) Zaiger and his wife in 1958 after he had worked for two seasons as an apprentice with fruit breeding pioneer F.W. Anderson. Zaiger patented his ﬁrst cultivars, ‘Royal Gold’ peach and ‘Crimson Gold’ nectarine, in the 1960s, and today the company holds over 200 US plant patents. Floyd has been the principal breeder through much of the history of the programme, but today he works together with his children to direct the programme. The Zaigers have achieved global prominence for a robust and comprehensive breeding programme that includes peaches, nectarines, plums, apricots, cherries and Prunus rootstocks. Through the years Zaiger has been quick to recognize opportunities and respond to industry needs throughout the world. It started

Table 6.8.

relatively early with white-ﬂeshed peach development, beginning in the late 1960s to develop white-ﬂeshed cultivars for European growers. In the 1990s, when California growers became interested in white-ﬂeshed fruit for Asian markets, Zaiger was ahead of other programmes. Zaiger has also led other breeders in the development of low-acidity, yellowﬂeshed cultivars, and was an early developer of lower-chilling cultivars for California. In the USA, Zaiger works with Dave Wilson Nursery, which tests new cultivars in its own commercial test block and sponsors fruittasting panels. In order for growers to distinguish fruit types, Zaiger groups cultivars into general series names (Table 6.8). Selected lowacidity peaches and nectarines with premium ﬂavour are also denoted as members of the ‘Zee Sweet®’ managed production programme and are licensed with production royalties in certain parts of the world. With peaches, 50% of recent tree plantings in California have been Zaiger cultivars, including the most heavily planted peach, the early-season cultivar ‘Super Rich’, with 8.2% of peach tree sales (Table 6.4). Two other early peaches, ‘Brittney Lane’ (4.1%) and ‘Spring Snow’ (3.9%), were heavily planted, as well as the mid-season, low-acidity, yellow-ﬂeshed ‘Country Sweet’ (4.1%). Zaiger peaches are well distributed through the ripening season with ﬁve of the top ten planted early- and mid-season cultivars, and four of the top ten late-season cultivars. With nectarines, 32% of recent tree plantings in California have been Zaiger cultivars, led by the low-acidity,

Series names used by private breeders for different types of peaches and nectarines. Yellow

Fruit/breeder Peach Bradford Burchell Zaiger Nectarine Bradford Burchell Zaiger

Acid

Low-acid

‘Princess’ ‘Flame’

‘Candy’ ‘Sweet Flame’ ‘Sweet’

‘Bright’ ‘Flare’ ‘Glo’

‘Sweet’ ‘Sweet Flare’ ‘Honey’

White Acid

‘Pearl’ ‘Snow Flare’

Low-acid

High quality

‘Ivory’, ‘Ice’, ‘Snow’ ‘Snow Flame’ ‘Snow’

‘Candy’ ‘Snow Flame’

‘Pearl’ ‘Snow Flare’ ‘Arctic’

‘Candy’

Fresh Market Cultivar Development

yellow-ﬂeshed ‘Honey Blaze’ cultivar with 5.6% of nectarine tree sales (Table 6.7). Other important Zaiger nectarines include ‘Arctic Snow’ (3.6%), ‘Arctic Mist’ (3.1%) and ‘Red Roy’ (2.6%). Zaiger’s success in nectarines is most evident in early-season cultivars which account for ﬁve of the top ten cultivars planted recently. Zaiger’s success in early-ripening nectarines is largely due to its relatively advanced embryo-rescue facilities. Additionally, two of the top ten planted mid-season nectarines and three of the top ten late-season nectarines are Zaiger releases (Table 6.7). Bradford Genetics, Inc. Bradford Genetics is a division of Bradford Farms, a family-owned organization in Le Grand that was founded by N.G. Bradford, who worked for the fruit breeding pioneer F.W. Anderson from the early 1940s until 1981, when he purchased the Anderson programme and breeding materials about a year before Anderson’s death. N.G. Bradford was the principal breeder for much of the history of the Bradford programme and continues to work with his son, L.G. Bradford, who directs the programme today. The Bradford programme started with mostly mid-season, yellow-ﬂeshed nectarines with traditional acidity and a relatively high chilling requirement. For the ﬁrst 10 years, Bradford built on Anderson’s success, aided by superior breeding parents such as ‘Red Diamond’ nectarine, which established a new standard for ﬁrmness and colour when released in 1972. Bradford nectarines continued to dominate the industry throughout the 1990s; however, increased competition from other programmes and changes in the industry encouraged expansion into other areas. During the 1990s, Bradford made a major shift towards development of white-ﬂeshed peaches and nectarines. The initial emphasis was to develop acidic, white-ﬂeshed cultivars that were preferred by growers in France. However, many of the white-ﬂeshed selections turned out to be low-acidity types, which fortunately coincided with the sudden growth of export markets in Asia, where low-acidity types are preferred. The resulting ‘Pearl’ series of low-acid, white-ﬂeshed nectarines has been

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very popular with growers in California and in the southern hemisphere. The white-ﬂeshed peaches ‘Ivory Princess’, ‘Ice Princess’ and ‘Snow Princess’ have also been popular cultivars worldwide. Additionally, to remain competitive, Bradford has made a shift towards development of earlier-ripening cultivars and cultivars with lower chilling requirement, although a lack of high-capacity embryo-rescue facilities has slowed progress. Today Bradford works closely with Bright Brothers Nursery in California, which tests new cultivars in commercial orchards and has exclusive rights to most Bradford cultivar tree sales in California. Bradford also has a strong presence in most fruit-growing regions in the world and L.G. Bradford reports that today more Bradford trees are sold overseas than in the USA. In order for growers to distinguish fruit types, Bradford groups cultivars into general series names (Table 6.8). With nectarines, Bradford continues to be a strong competitor and 45% of recent nectarine tree sales were Bradford cultivars, led by the early-ripening ‘Diamond Bright’ nectarine with 5.1% of nectarine tree sales (Table 6.7). Other important Bradford nectarines include ‘Kay Sweet’ (3.6%), ‘August Pearl’ (3%), ‘Grand Pearl’ (2.8%) and ‘Ruby Sweet’ (2.7%). It is noteworthy that seven of the top ten Bradford nectarines planted recently are low-acidity types. Bradford continues to be strongest in mid-season nectarines, with eight of the top ten planted cultivars in California. It is also strong in late-season cultivars, with four of the top ten cultivars. However, with early-ripening nectarines, only two of the top ten planted cultivars are Bradford releases. In spite of considerable progress with peaches, only 6% of recent peach tree plantings in California were Bradford cultivars, including ‘Ivory Princess’ with 2.4% of tree sales and ‘Crimson Lady’ with 1.6% (Table 6.4). However, the new generation of premium-ﬂavour peaches in the ‘Candy’ series may increase Bradford’s share in the future as growers begin to plant the new cultivars. Burchell Nursery, Inc. Burchell Nursery is a family-owned nursery company in Oakdale and Fowler, founded in

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1942 by I. Burchell, and led today by his son, W.T. Burchell, and his grandson, T.W. Burchell. The breeding programme was established so that Burchell could remain competitive with other large nurseries that had exclusive arrangements with breeders. In 1985, Burchell enlisted the aid of J.F. Doyle from the University of California to help establish a breeding programme in Fowler, California. However, by 1989, Doyle needed to return to a full-time commitment with the University of California, and J. Slaughter along with T. Gerdts, both Burchell ﬁeld representatives, stepped in to continue the programme. The release of ‘Autumn Flame’ peach, one of the top ten planted peaches today, was a result of Doyle’s contribution to the Burchell programme (Tables 6.3 and 6.4). To date more than 40 plant patents have been ﬁled. Burchell also works cooperatively with D.H. Byrne at Texas A&M University, to develop cultivars with low chilling requirement. New cultivar patents are ﬁled with a varietal name that has a preﬁx, ‘Burpeach’ (peaches) or ‘Burnect’ (nectarines), and a sequential numerical sufﬁx, resulting in a name such as ‘Burpeachone’. In addition to a varietal name, Burchell groups cultivars into trade names so that growers and marketers can distinguish fruit types (Table 6.8). The Burchell programme is unique in being wholly owned by a nursery company, and breeders Slaughter and Gerdts also act as salesmen, ﬁeld representatives and international licensing agents. They work closely with growers to test new cultivars in commercial orchards and offer technical support for the cultivars they develop. With peaches, 20% of recent tree plantings in California have been Burchell cultivars, led by the early-season peaches ‘Burpeachone’ (4.8% of peach tree sales) and ‘Burpeachfourteen’ (4%), and the mid-season peach ‘Burpeachﬁve’ (3.3%). Burchell cultivars are well distributed throughout the ripening season, with two of the top ten planted cultivars in each of the early-, mid- and late-season categories (Table 6.4). Thus far all of the top-planted Burchell peaches are acidic, yellow-ﬂeshed types. With nectarines 7% of recent tree plantings in California have been Burchell cultivars, including the early-season ‘Burnecten’ (2% of nectarine

tree sales) and the late-season ‘Burnectfour’ (1.8%), both acidic, yellow-ﬂeshed types (Table 6.7). Sun World International, Inc. After fruit breeding pioneer J.W. Weinberger retired from the USDA-ARS in 1973, he consulted with Superior Farming Company to help establish a breeding programme near Bakersﬁeld, California to develop stone fruit and table grape cultivars for the company’s use. In the late 1980s, two fruit breeders joined Superior Farming to continue the programme, D.W. Cain for table grapes and C. Fear for stone fruit breeding. When Sun World International, Inc., a grower and marketer of fruits and vegetables, purchased Superior Farming in 1989, Fear left the company. Stone fruit breeding, however, continued, ﬁrst under B.D. Mowery and later D.W. Cain, until 2000 when T.A. Bacon joined Sun World. Today Bacon conducts a peach breeding programme entirely focused on early-ripening cultivars, primarily at Bakersﬁeld. Sun World has highcapacity embryo-rescue facilities and greenhouses required for breeding early-ripening stone fruit. It also has one of the most robust low-chill (200 chill units or less) breeding programmes in the world in California’s Coachella Valley. New Sun World cultivar patents are ﬁled with a name that has a preﬁx ‘Supech’ (peaches) or ‘Sunect’ (nectarines) and a sequential numerical sufﬁx, resulting in a varietal name such as ‘Supechsix’. Sun World groups cultivars as to fruit type and markets them under umbrella brand names such as AMBER CREST® brand peaches. Individual cultivars are selected for the brands to provide a continuous series through the season, and can be replaced with improved cultivars without affecting brand name consistency. Currently the AMBER CREST® brand peach series consists of six yellow-ﬂeshed, traditional-acidity cultivars, beginning with the low-chill cultivars ‘Supechthirteen’ and ‘Supechﬁfteen’, which are harvested in the Coachella Valley during the ﬁrst half of April. ‘Supechsix’ and other cultivars grown further north in the San Joaquin Valley follow on in May. With nectarines, Sun World is evaluating several

Fresh Market Cultivar Development

low-chill cultivars that ripen during April in the Coachella Valley, and promotes ‘Sunectwentyone’, which ripens in the ﬁrst week of May in the San Joaquin Valley. The Sun World stone fruit programme has until recently developed new cultivars exclusively for Sun World plantings in the USA, but now international licensing is also available.

6.5 European Programmes For most of the 20th century, peach breeding in countries outside the USA was limited. In many places, cultivars from US breeding programmes were imported to replace local cultivars that were no longer proﬁtable to grow. Through the latter half of the 20th century there was limited breeding in Italy (notably by A. Morettini in Florence), France (primarily by R. Monet at Bordeaux), Australia (at Tatura for canning peaches) and other countries. Many national breeding programmes have been initiated or expanded since the mid-1980s.

Bulgaria The modern fruit industry in Bulgaria dates back to the early 1950s. After 1960 it grew rapidly, particularly in terms of horticultural advancements and new cultivars introduced, thanks to the role played by breeding programmes. Peaches spread to vast areas of the District of Sliven, well known in Bulgaria as the ‘Valley of the Peaches’, because they were well adapted there. The ﬁrst introduced cultivars in modern orchards were ‘J.H. Hale’ and ‘Elberta’, which were grown along with the locally wellknown, late-ripening ‘Dupnishka’. The same cultivars were the starting point of breeding programmes from the mid-1950s that resulted in the introduction of ‘Zlatna Krichimka’ (bud mutation of ‘J.H. Hale’) and ‘Septemvriiska’ (‘Elberta’ × ‘Karman’). Later, V. Velkov, Director of the Fruit Growing Institute in Plovdiv from 1962 to 1972, introduced ‘Rumyana’, ‘Asenova Krepost’, ‘Nay-Ranna Zhalta’ and ‘Velkova’. The same institute became the leader of an intense effort on peach breeding carried

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out at the experimental stations in Sliven, Pomorie and Petrich. Peach breeder Y. Grigorov introduced for the fresh market ‘Bulgarska Ranna’, ‘Yulska Edra’ and ‘Petrichka’, later followed by ‘Tundzha 1’ and ‘Tundzha 2’ for canning. At the same time another breeder, A. Arangelov, carried out a number of genetic studies on peach while also developing ‘Zlatna Krichimka’, ‘Chervena Kurtovka’, ‘Elinpelinska’ and ‘Zlatka’. By artiﬁcial mutagenesis A. Angelov developed ‘Plovdiv 1’, ‘Plovdiv 2’, ‘Plovdiv 6’ and ‘Yoneta’. Particularly important was the work of S. D’bov (1974, 1975), who hybridized peach with Prunus ferganensis for three decades, introducing cultivars resistant to powdery mildew (Podosphaera pannosa (Wallr.:Fr.) Braun & Takamatsu): ‘Aheloy’ and ‘Remil’ for fresh market and ‘Malo Konare’ and ‘Stoyka’ for canning. Breeding programmes for peach were restarted at Plovdiv in 1989 by A. Zhivondov and his group. They are based on the progress made in Bulgaria and worldwide but are focused on the new horticultural and market requirements. The major breeding objectives are: developing cultivars resistant to powdery mildew (with P. ferganensis as the source of resistance) and leaf curl (Taphrina deformans (Berk.) Tul.); widening the ripening season by the introduction of early and late cultivars; and establishing cultivars that are easy to train with size-controlled trees (e.g. columnar, dwarf, weeping). France The introduction of the ﬁrst peach trees in France is ascribed to the Romans under the name of ‘malum persicum’ even though, according to early Latin writers, the Gallic people already knew a freestone fruit called ‘galicum’, larger than the ‘persicum’ introduced by the Romans. Peach was truly widespread in all of France during the Middle Ages. Charlemagne recommended that all his ofﬁcers plant peach trees in their gardens. Grafting of peaches has been practised since the 16th century. The adoption of the ‘espalier’ (tree training on trellis or hedgerow) between 1635 and 1650 contributed to the improvement and the expansion of its culture. The old

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peach cultivars were grown in the gardens close to the large cities (e.g. Paris, Lyon), where the fruits could be easily sold. Selections from open-pollinated seedlings in the 16th century gave rise to cultivars adapted to various environments, such as ‘Hasty Ferriere’ in the Paris area. In the orchard of the ‘Sun King’ in Versailles, there were at least 40 different cultivars, whose names often evoked the female charms: ‘Nipple of Venus’, ‘Beautiful of Chevreuse’, ‘Large Mignonne’, etc. By the 18th century peaches were mainly whiteﬂeshed, the yellow ones being called either ‘alberge’ or ‘peach-apricot’. An inventory with descriptions of peach cultivars was carried out in the 19th century. In 1856, the railway connecting Paris, Lyon and Marseilles allowed the rise of new areas of peach production in southern France, in particular in Ardèche and Drôme provinces. At the turn of the century, Jouin (1913) catalogued over 300 peaches and nectarines based on leaf, fruit and ﬂower characteristics. In the 1930s the intensiﬁcation of peach production was made possible by the ‘invasion’ of the US cultivars coming from controlled-hybridization programmes. Following the Second World War the peach industry was strongly reshaped and nowadays the major areas of production are located in southern France, with Rhône-Alpes, Languedoc-Roussillon, Midi-Pyrénées and Provence-Alpes-Côte d’Azur being the most important provinces. Modern peach breeding in France may be traced back to the early 1960s (R. Monet, France, 2004, personal communication). After an earlier release of a white peach series from Hugard and Saunier (known as ‘Genadix’), R. Monet at the Institut National pour la Réchèrche Agronomique (INRA) started a formal programme to address the lack of knowledge of heritability of important traits (Monet, 1967, 1977, 1983; Monet and Bastard, 1982). In addition to traditional crossing and selection, he made inbred lines, pursuing the obtaining of ‘hybrid’ progenies as in maize or other vegetable crops. Although he reached the sixth inbred generation, he never attained his ﬁnal goal. He also described some novel traits, among them weeping tree habit and the resistances to green aphid and leaf curl (Massonie et al., 1982; Monet, 1984; Monet

et al., 1988). Some of his selections may still be useful as breeding material, particularly for the weeping habit and aphid resistance. He also released a ﬂat peach ‘Platina’ as well as a ﬂat nectarine, ‘Mesembrine’. At the end of the 1990s the programme was moved from Bordeaux to the station in Avignon. The present programme aims to breed for improved fruit quality as well as resistance to powdery mildew, leaf curl, green peach aphid, Plum pox virus (PPV) and nematodes (Pascal et al., 1998; Moing et al., 2003). This programme is focused on the introgression of resistance genes by repeated backcrosses to cultivars of commercial value (Sauge et al., 1998). The breeding programme is based on ‘Malo Konare’ and ‘Pamirskij 5’ as resistance sources to powdery mildew, and on ‘Weeping Flower Peach’ and ‘Rubira®’ for green peach aphid resistance. Both traits are controlled by major dominant genes (Pascal et al., 2002b). Early selection procedures in order to reduce selection cycles and ﬁeld evaluations against powdery mildew were carried out (Dirlewanger et al., 1996). Introgression of quantitative resistance from the wild related species P. davidiana (clone P1908), as a donor of resistance to several pests and diseases including PPV, has been explored and could lead to the acquisition of durable resistances (Pascal et al., 2002a). Qualitative trait loci (QTLs) involving both resistance and fruit quality traits were identiﬁed, with the aim to develop marker-assisted selection as the ﬁrst step of the selection process (Foulongne et al., 2003). One of the major problems of the interspeciﬁc crossing is the poor fruit characteristics of the wild parent, since even two generations of backcrossing were not enough to regain the commercial appearance of the fruits (Kervella et al., 2002; Quilot et al., 2004b). To overcome this constraint, a new approach was undertaken in order to improve the fruit quality, to understand the genetic variability observed in the interspeciﬁc progeny by combining QTL analysis and ecophysiological models (Quilot et al., 2004a). Tree growth habit is also under study, with the aim to obtain easy-to-train trees with short and thick branches, in order to assure large and uniform size of fruits (Genard et al., 1994; Kervella et al., 1994, 1998).

Fresh Market Cultivar Development

Partnership with private breeders (Pascal and Monteux-Caillet, 1998) led to the development of white (‘Caprice’, ‘Surprise’ and ‘Elise’) and yellow (‘Conquise’) peaches. More recently, several private enterprises have been involved, e.g. Meynaud, Valla and especially Maillard, whose introductions like ‘Big Bang®’ and ‘Sweetcap®’ are beginning to be widely planted in France as well as Spain and Italy. Some private growers are also involved in breeding for new cultivars, e.g. Buffat, Dumont and Monteux-Caillet are working with INRA. ‘Zephir®’ (‘Zephyr’ in the USA), ‘Emeraude®’, ‘Jade®’ and ‘Topaze®’ are the most widely known introductions from this cooperative programme, and make up about 5% of the white nectarine orchards in France. Also, some white-ﬂeshed peaches like ‘Opale®’ and ‘Melina®’ are frequently planted in all districts of peach cultivation. The main goal of these private breeding programmes is to develop new outstanding cultivars to meet the needs of the modern industry (size, ﬁrmness, productivity), of good taste (high sugar content, diversity of ﬂavours), with some emphasis on unusual traits like ﬂat-shaped fruits (particularly for white peaches) and ‘red ﬂesh’ nectarines (Zambujo, 2004). Today French cultivars represent about 30% of the peach industry in France. New INRA releases are nationally distributed by the association of nurseries ‘CEP Innovations’.

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spring frost, calcareous soils, etc.). The main goals of the programme are disease resistance (PPV, brown rot, Pseudomonas spp.) of nonmelting peaches, both yellow and white, using local (white-ﬂeshed ‘Flagar’), US (‘Andross’, ‘Fortuna’, etc.) or Japanese (white, low-acid peach ‘Akatsuki’) parents. More recently, a clonal selection project for old local cultivars has been started.

Hungary Hungary is characterized by a strong continental climate, but there are opportunities for small-scale cultivation in some regions: close to Budapest, in southern Hungary (SzegedSzatymaz) and in the milder region of the large Balaton Lake. Although there is no formal breeding work in the country, amateurs and scholars have collected local germplasm or made occasional crosses. Worthy of mention are the works of P. Tóth (active from 1930 to 1965) and I. Tamássy (1950s–1960s). Among the more notable Hungarian cultivars are ‘Mariska’ (white ﬂesh), ‘Piroska’ (white ﬂesh), ‘Vérbarack’ (red ﬂesh), all of local origin; and ‘Aranycsillag’ (yellow ﬂesh) and ‘Remény’ (ﬂat fruit, white ﬂesh) from controlled crosses. Overall, the peach industry is still based on old US cultivars, e.g. ‘Redhaven’, ‘Suncrest’, ‘Champion’, etc. (Szabó, 2007).

Greece Italy Although the peach reached Greece some centuries before the Christian era, it was propagated by seed until the beginning of the 20th century. Currently the peach industry is based on foreign cultivars, mainly from the USA. A breeding programme aimed at improving the ﬁeld resistance to PPV by crossing virus-susceptible, high-quality local accessions to some ﬁeld-tolerant US cultivars, e.g. ‘Elegant Lady’, ‘July Lady’ and ‘May Crest’, was begun and then stopped because of limited results. A programme was recently started at the Naoussa Pomology Institute in order to obtain both scion cultivars and rootstocks well adapted to the Greek environments (occurrence of

Italy, with a long history of peach cultivation, is one of the ﬁrst peach industries in the world. Peach germplasm importation from Asia dates back to the ﬁrst centuries BC according to the earliest-known written records from Latin scholars. Because of its very early establishment in Italy, and given its easy propagation by seed, peach germplasm developed a wealth of variability in terms of fruit type and season of ripening. With the predominance of self-pollination (Hesse, 1975; Fogle, 1977), repeated seed propagation led to the establishment of rather uniform populations used as local cultivars and only the most outstanding were propagated by grafting. Local preferences

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and natural pressure were crucial in guiding the selection of non-melting, yellow-ﬂeshed types in central and southern Italy, and of freestone, white-ﬂeshed types at northern latitudes, that were more adapted to the continental-like climate (Gallesio, 2003). This pattern was the same for many centuries and as recently as the mid-1960s in northern Italy about 50% of the commercial production was of white-ﬂeshed, local cultivars (Branzanti and Sansavini, 1965). They were appreciated by growers for their hardiness and yield reliability and by consumers for their distinctive fruit ﬂavour and fragrance. Market pressures suddenly reduced white peach production to 6% at the beginning of the 1980s in EmiliaRomagna, the major peach-growing district in northern Italy (Bassi et al., 1980). Nectarines were ﬁrst reported in Italy between the 14th and 15th century, possibly imported into Spain and southern Italy by the Arabs. They were called ‘pesche-noci’ (walnut-peach) for their small, greenishskinned fruit and, owing to this very poor fruit appearance, were regarded only as a curiosity (Gallesio, 2003) until the massive introduction of improved cultivars from California in the mid-1970s. The ﬁrst commercial orchards were started around the end of the 19th century (Zago, 1923; Ghinassi, 1927; Rosi, 1965; Baldini, 2001) using local germplasm, mainly white-ﬂeshed cultivars. As the ﬁrst yellow-ﬂeshed cultivars were made available from the USA, they gradually replaced the local types. Modern breeding programmes began in the late 1920s, with several amateurs as well as scientists pioneering the work: C. Cappucci, P. Martinis, A. Pieri, A. Pirovano and A. Ragionieri, among others. It was A. Morettini at the University of Florence who started a true large-scale breeding programme, lasting for over 30 years, until the 1970s (Fideghelli and Sartori, 1998). Neglecting the Italian germplasm and resorting only to introductions from the USA for his breeding stock, particularly ‘J.H. Hale’ (the ideotype at that time), Morettini developed about 20 cultivars (Pirovano, 1953; Morettini, 1961). They were both white- and yellow-ﬂeshed, standard fresh market peaches, covering a ripening season from mid-June to August, a rather large span

for that time. Other scientists in Rome (Pirovano, 1936) and Bologna (Capucci, 1950) developed mainly white peaches from local germplasm. None of these early introductions have commercial importance at present. Near the end of the 1960s, three public programmes were started almost simultaneously at the Institute of Fruitculture of the Ministry of Agriculture (operated in Rome and Forlì, northern Italy) and at the universities of Bologna and Florence. Mostly these programmes are aimed at the introduction of cultivars better adapted to the Italian (northern) environments with improved hardiness and yield reliability, since most of the commercial cultivars imported from California showed poor crop reliability. However, the booming of the peach industry in southern districts has driven new breeding for lowerchilling requirements. Much effort is being devoted to pest and disease resistance, particularly to brown rot (Monilinia spp.), leaf curl (T. deformans (Berk.) Tul.), powdery mildew (P. pannosa (Wallr.:Fr.) Braun & Takamatsu) and green aphids (Myzus persicae Sulzer). For brown rot, promising selections showing good ﬁeld tolerance are under advanced evaluation in the Bologna and Forlì programmes. Parents for resistance come from foreign germplasm, e.g. ‘Contender’ peach from the eastern USA (Liverani et al., 1997; Bassi et al., 1998b). For powdery mildew, a disease affecting all of the cultivated accessions (Roselli and Bellini, 1976), foreign germplasm such as ‘Oro A’ (a seedling of ‘Diamante’, a non-melting Brazilian cultivar; Rodriguez and Sherman, 1990) is being used. Although this trait seems quantitatively inherited, there are reports of major dominant genes (D’bov, 1974, 1975) and it is possible to select for a good level of resistance in the F1 populations (Liverani et al., 2003). For leaf curl, an interesting hypersensitivity resistance has been found in Italian local white peaches, e.g. ‘Cesarini’ and chance seedling ‘Exoascus RM’ (Bellini et al., 1998; Liverani et al., 2003). Promising selections are under evaluation. Fruit quality improvement has been addressed by different approaches. Given the rather good level of size and external appearance, efforts are being concentrated towards

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inner components, e.g. ﬂesh texture and ﬂavour (Bassi et al., 1998a; Liverani and D’Alessandro, 1999; Giovannini et al., 2004). Traits like lowacid taste, stony-hard ﬂesh, canning nectarines (anthocyanin-free fruit) and increased ascorbic acid are also of interest (Yoshida, 1970, 1976; Bellini, 1994; Bellini et al., 1996; Liverani et al., 2002). Genetic modiﬁcation of tree architecture could lead to the development of an easy-totrain tree. The topic has been addressed since the end of the 1970s; so far, commercial quality genotypes have been achieved for the dwarf, columnar and upright phenotypes (Fideghelli et al., 1979, 1992; Bassi et al., 1994; Liverani et al., 2004). The weeping type (Monet et al., 1988) has also been investigated (Bassi and Rizzo, 2000). In the large Italian peach collections (about 2400 accessions), more than 20% are of Italian origin (Bellini et al., 1990). Nevertheless, the pedigrees of the more than 200 Italian cultivars released in the last 25 years show a predominance of US cultivars, particularly from California. The most interesting recent results exploiting the local white-ﬂeshed peach germplasm are ‘Aliblanca’ and ‘Alirosada’ (from Forlì), ‘Maria Bianca’ (from Florence) and ‘Rubia’ and ‘Rubisco’ (from Bologna). Although it was terminated at the end of the 1980s, the programme of the former Institute of Fruitculture in Verona (north-eastern Italy) had the foresight to exploit the locally grown white peaches with the aim of improving their ﬁrmness and shelf-life while keeping their hardiness and outstanding ﬂavour. ‘Atalanta’ and ‘Ione’ were the best achievements from this notable breeding programme. More recently, a programme was started at the University of Palermo in Sicily, with the goal to introduce cultivars with different chilling requirements adapted to the diverse environments of the island. Desired adaptations include either medium- to low-chill at sea level or medium- to high-chill in the inner valleys and hills. Desired traits are late and very late (October) ripening season, nonmelting ﬂesh for fresh market with improved ﬂavour (over 15°Brix) and shelf-life, and altered growth habit (either columnar or brachytic dwarf). Parents are chosen from the rich Sicilian germplasm (Marchese et al., 2005)

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for the late-ripening and non-melting, highquality fruits (e.g. ‘Imera’, ‘Xirbi’, ‘Tudia’, ‘Tardiva di Leonforte’, etc.) and from Florida cultivars for the low-chilling requirements (‘Flordastar’, ‘Flordacrest’, etc.). Private programmes Several amateurs were actively involved in developing new cultivars at the onset of the modern Italian peach industry, often starting with local germplasm crossed to introductions from the USA (Branzanti and Sansavini, 1965). Almost all of this early work is lost, with a few exceptions. The white-ﬂeshed peach ‘Iris Rosso’, bred in the early 1950s by amateur P. Martinis, is still grown today. The following active private programmes are noteworthy: Bubani, CIV nurseries, Minguzzi, Morsiani, Montanari and Ossani. They are all located in northern Italy (EmiliaRomagna region). Their goals are strictly commercial and based on the exploitation of US cultivars, particularly nectarines, either via open and self-pollination or crossing with other commercial introductions, e.g. ‘Elegant Lady’, ‘Fantasia’, ‘Big Top’, etc. Ossani (1987) ﬁrst introduced several white-ﬂeshed nectarines starting from ‘Snow Queen’ and ‘Redgold’, some of them being very popular today (‘Caldesi’ and ‘Silver’ series). The private breeders have contributed more than 50% of the Italian peach introductions in the last 25 years (Fideghelli and Sartori, 1998). Finally, credit should be given to (Stark) ‘Redgold’: it is not only still the most widely grown nectarine in Italy, but also the most popular parent used in nectarine breeding programmes in Italy. Among the most noteworthy of its offspring are ‘Ambra’, ‘Caldesi’ white-ﬂesh series, ‘Orion’, ‘Maria Aurelia’ and ‘Venus’ among the nectarines, and ‘Rome Star’ among the peaches. Leading cultivars in northern Italy are shown in Table 6.9.

Poland A limited breeding programme was established at the Pomology Research Institute at Skierniewice in the mid-1960s, aimed at the introduction of cold-resistant peaches for the

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Table 6.9. The most important peach and nectarine cultivars in Italian orchards from a survey conducted in main northern Italy peach districts, representing around 60% of the regional production. Percentages are relative to the total number of trees in that age bracket (column). Cultivars from Italian programmes are in italics. (Data from CSO, Ferrara, Italy.)

Peaches ‘Springbelle’a ‘Fayette’ ‘Elegant Lady’ ‘Springcrest’ ‘Royal Glory’ ‘Redhaven’ ‘Royal Gem’ ‘Glohaven’ ‘Rich Lady’ ‘May Crest’ ‘Flavorcrest’ ‘Maria Marta’ ‘Suncrest’ ‘Sinphonie’ ‘Rosa del West’b,c ‘Kaweah’ ‘Rome Star’

>4 years (%) 15 9 7 6 6 4 4 4 4 4 3 3 3 1 1 – 1

1–3 years (%) 8 – – 2 10 5 4 2 8 – – 7 4 8 4 4 4

Nectarines ‘Stark Redgold’ ‘Venus’ ‘Big Top’ ‘Sweet Lady’ ‘Sweet Red’ ‘Maria Carla’ ‘Nectaross’ ‘Maria Aurelia’ ‘Maria Laura’ ‘Caldesi 2000’c ‘Supercrimson Gold’ ‘Ambra’ ‘Guerriera’ ‘Amiga’ ‘Laura’ ‘Lady Erica’ ‘Morsiani 60’

>4 years (%)

1–3 years (%)

14 9 9 5 5 5 4 4 4 3 3 3 3 – 2 – –

8 3 10 9 8 7 2 2 – – – 4 – 3 3 3 3

aBud

sport from ‘Springcrest’. seedling. cWhite-fleshed. bChance

Polish continental environment (Jakubowski, 1998). US cultivars were crossed to Chinese germplasm (‘Winter Peach’, ‘Manchurian Peach’) from north-west China, known for its cold hardiness. The programme was extended to the F2 stage and two cultivars were released from the resulting progeny, showing a tree hardiness similar (‘Inka’) or superior (‘Iskra’) to ‘Redhaven’. The programme was then discontinued. Several of their Chinese accessions were later imported into Canada (by R.E.C. Layne) and later into the USA for use as coldhardy rootstocks, including ‘Tzim Pee Tao’, ‘Chui Lum Tao’, ‘Hui Hun Tao’ and ‘Siberian C’.

Romania Peach breeding in Romania dates back to the end of the 1950s (Ivascu and Balan, 1998). The breeding stock has been developed from foreign cultivars, mainly from the USA

(‘J.H. Hale’, ‘Elberta’ and others), Harrow, Canada (for cold tolerance), from western European countries (France, Italy) and, lately, from China. The ﬁrst wave of breeding effort was aimed at obtaining cultivars adapted to the harsh continental environment of the country (ﬂuctuating temperatures in mid-winter, dropping as low as −35°C), particularly for the late season, owing to the sporadic cropping of the early-ripening cultivars due to the cold temperatures in spring. After 1985, more attention was paid to disease resistance (brown rot, leaf curl, powdery mildew, stem canker and PPV) owing to the heavy rains common in the peach-growing areas and the scarcity of effective chemicals for spray programmes because of the limited ﬁnancial resources of the country (Ivascu, 2002). After 1990, more diversiﬁed goals were added, concerning fruit types and quality (non-melting for canning and nectarines), extension of the ripening season and tree architecture (particularly for the brachytic dwarf) (Stanica et al., 2002a,b).

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Progress has been made at the Research Stations for Fruit Tree Growing at Baneasa and Constanza in breeding for cold resistance (‘Splendid’, ‘Superba de Toamna’, ‘Triumf’ and ‘Victoria’ peaches), improved nectarines (‘Cora’, ‘Delta’, ‘Mihaela’, ‘Romamer 2’ and ‘Tina’), dwarf tree (‘Cecilia’ and ‘Puiu’ peaches, ‘Livia’ and ‘Melania’ nectarines), ornamental (‘Dan’ nectarine and ‘Paul’ peach) and disease resistance (‘Victoria’ peach, highly resistant to both powdery mildew and stem canker; ‘Flacara’ peach, resistant to powdery mildew; several selections tolerant to leaf curl, brown rot or Pseudomonas spp.). Presently, about two-thirds of the most widely grown cultivars are releases from the Romanian breeding programmes. Serbia Peach breeding in Serbia (former Yugoslavia) started in the early 1950s at the Fruit Research Institute in Cˇ acˇak (Ogasanovicˇ, 1998), followed by programmes at Beograd and Novi Sad. Breeders began with US germplasm in order to obtain cultivars adapted to the country’s continental environment. More recently, cultivars from European countries, mainly Italy, were added as parents. Several new cultivars have been released, all selected from progenies derived from foreign germplasm: ‘Maja’, ‘Vesna’ and ‘Grocˇanka’ (all from selfpollination of ‘Glohaven’), as well as ‘Dora’, ‘Cˇ acˇak’, ‘Goca’ and ‘Julija’, among others. One of the peculiarities of the region is the wealth of peach landraces called ‘vineyard peaches’, traditionally propagated by seed, and also the most common source of peach rootstocks in the country (Vujanic′-Varga and Ognjanov, 1992). These peaches show a wide range of fruit types and some valuable horticultural traits (cold resistance, drought tolerance, disease resistance e.g. to powdery mildew and leaf curl), but so far have been scarcely used in breeding programmes. Spain Spain is known worldwide for its wealth of local germplasm, particularly of non-melting,

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yellow-ﬂeshed local accessions. In the late Middle Ages they were introduced into Central and South America, where they became landraces (Badenes et al., 1998b). Non-melting ﬂesh peaches are the most valuable in the Spanish fresh market and much work has been done on evaluation and clonal selection of the best types (Badenes et al., 1998a). At present, there are several ongoing breeding programmes, three in public institutions (since 1993, at Saragoza and Valencia) and at least seven in private enterprises (M.L. Badenes, Spain, 2004, personal communication). Other than speciﬁcally improving yellow clingstone peaches, efforts are aimed at improving fruit quality, disease resistance and broadening the ripening season. A minor goal is to improve ﬂat-shaped peaches, a favourite fruit in some markets. Some of the private programmes are focused on improving very early-ripening, melting-ﬂesh nectarines and peaches, best suited for the southern regions of the country, often resorting to foreign breeding stocks in agreement with US breeders.

Ukraine and former Soviet states Ukraine has a climate favourable for peach production, more so than most of the former Soviet Union, which is too cold. Ivan N. Ryabov at the Nikita Botanical Garden near Yalta began the programme over 50 years ago by collecting a great deal of peach germplasm in Central Asia and the Trans-Caucasus. Over the years dozens of cultivars of peaches and nectarines have been released that are more disease-resistant (particularly powdery mildew and leaf curl), cold-hardy and productive in their climate (Yezhov et al., 2005). Important peaches include ‘Krymsky Feyerverk’, ‘Sagdiets’, ‘Startovy’, ‘Dostoyny’, ‘Otlichnik’ and ‘Posol Mira’. Top nectarine releases include ‘Ametist’, ‘Evpatoriysky’, ‘Ishunsky’ and ‘Rubinovy 8’. The Uzbek Research Institute of Plant Industry, located in Tashkent Province of the Republic of Uzbekistan, was established in 1924 by the well-known Russian plant explorer and breeder Nikolai I. Vavilov. A modest peach breeding programme there released these adapted fresh market cultivars: peaches ‘Rannii

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Belii VIRa’, ‘Gulnoz’, ‘Zolotoi Ubilei’, ‘Chimgan’ and ‘Lyuchak’; and nectarine ‘Uchkun’ (Mavlyanova et al., 2005). The latter two peaches have been used for drying and canning as well. Breeding in Latvia traces back to before 1950 at the Horticultural Plant Breeding Experimental Station in Dobele and 1938 at the Botanical Gardens of the University of Latvia (Kaufmane and Lacis, 2004). To be grown successfully, peach cultivars need to be extremely cold-hardy and have good spring bud hardiness. Releases include ‘Ziemelu persiks’, ‘Zelda’, ‘Rita’, ‘Maira’ and ‘Viktors’. All are whiteﬂeshed except ‘Rita’; the latter two were released in 2004.

6.6 Pacific and African Programmes China Although China is the ancestral home of the peach, and the introduction of ‘Chinese Cling’ led to the development of improved peaches in the USA, breeding programmes are relatively new there. From the late 1950s until the 1990s there were canning cling programmes in several places. Fresh market breeding ﬂourished in the 1970s and 1980s but the 20 or so original programmes have been reduced to only six currently, mostly developing lowacid, white-ﬂeshed freestone peaches (L. Wang, Zhengzhou, 2007, personal communication). In general, the programmes have intercrossed Chinese and Japanese cultivars with US cultivars. There are no traditional nectarine cultivars in China and available Japanese germplasm was relatively poor in quality, so mostly US cultivars have been used for breeding. Breeding at Dalian Institute of Agricultural Sciences began with yellow canning clings, and releases ‘Fenghuang’ and ‘Lianhuang’ formed the basis of the Chinese canning industry. More recently focus has been on nectarines as well as late-ripening, freestone peaches. Beijing Academy of Agriculture and Forest Sciences has one of the older programmes, which began in the 1960s. ‘Qingfeng’ and ‘Maixiang’ are important releases. Flat peach cultivars include ‘Ruipan 1’ and ‘Ruipan 4’. Current efforts are directed at nectarines and late-ripening ﬂat

peaches. At the Beijing Forest Institute, there is a programme to develop low-chilling ornamental peaches. The programme at the Department of Horticulture, Jiangshu Academy of Agricultural Sciences in Nanjing, released the prominent early peach ‘Yuhualu’ in 1972 as well as other early peaches. Current efforts are aimed at late-ripening, freestone peaches with resistance to fungal gummosis. Nectarines tolerant of rainy climates are also being developed. Zhengzhou Fruit Institute in Henan is developing low- to medium-chill peaches and nectarines, as well as ﬂat nectarines. It also maintains a peach germplasm repository and has an interest in ornamental peaches. The Department of Horticulture of Shanghai Academy of Agricultural Sciences is developing early-ripening peaches and nectarines primarily; releases include ‘Chunlei’ and ‘Chunhua’ (Li, 1984; Wang and Lu, 1992). For more information on China, see Chapter 2.

Japan Many of the peaches grown in Japan originated as grower selections and mutations of traditional cultivars like ‘Hakuto’ and ‘Hakuho’ (Kozaki et al., 1996). ‘Hakuto’ is apparently descended from ‘Shanhai Suimitsuto’ (Yamamoto et al., 2003), which is thought to be synonymous with ‘Chinese Cling’. Consumers prefer high-quality, low-acid fruit with red blush. Nearly all peaches currently grown are white-ﬂeshed clings, but recently yellow-ﬂeshed peaches, such as ‘Ogonto’ and ‘Golden Peach’, have been increasingly grown for fresh consumption. Early-season production once declined due to problems producing consistently high-quality fruit, but the market is now recovering because of new early cultivars with relatively high quality (such as ‘Hikawa Hakuho’ from Yamanashi, and ‘Chiyohime’). The most important breeding programme has been carried on by the National Institute of Fruit Tree Science in Tsukuba. Under the direction of M. Yoshida and more recently M. Yamaguchi, it has released a series of peaches including ‘Chiyohime’, ‘Akatsuki’, ‘Natsuotome’, ‘Yuzora’ and ‘Akizora’. Local research stations located in the

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major production area of peach are also active in breeding, including Yamanashi (released ‘Yumeshizuku’, a very large peach), Nagano (released ‘Natsuki’), Fukushima (released ‘Fukuotome’ and ‘Hatsuotome’, very early peaches) and Okayama. Nectarine is not very popular because of the high acidity of available cultivars and the tendency for fruit cracking, but that may change with the release of low-acid nectarine cultivars from the breeding programme at the Yamanashi Prefectural Fruit Tree Experimental Station. ‘Sweet Nectarine Reimei’ and ‘Sweet Nectarine Reiou’ are yellow-ﬂeshed, while ‘Sweet Nectarine Shoku’ and ‘Sweet Nectarine Shogyoku’ are white-ﬂeshed. Ornamental peaches have been traditional favourites in Japan and many ﬂower types and tree growth habits are available.

Korea Peach culture in Korea dates back nearly 2000 years, but modern commercial production began 100 years ago with the introduction of better Japanese cultivars by scientists at what is now the National Horticultural Research Institute in Suwon. Although minimal breeding started in 1957, the emphasis was increased in the mid-1980s. Goals are to develop ﬁrmer, white-ﬂeshed, low-acid peaches that retain the high quality consumers prefer, but also have resistance to bacterial spot and other diseases. The most successful releases have been ‘Cheonhong’ nectarine and ‘Yumyeong’, a large, white, stony-hard cling peach consumed fresh (Chung et al., 1998). ‘Yumyeong’, a selection from Japanese parentage, has been used as a parent in other countries such as Italy and New Zealand because of its size and ﬁrmness.

New Zealand Peach breeding by HortResearch in Havelock North, New Zealand began as an effort to improve canning clings. In the mid-1980s work was expanded to develop fruit suitable for export, particularly for the Asian market,

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which prefers low-acid, white-ﬂeshed peaches. Cultivars must be adapted to the maritime climate with disease resistance and frost tolerance, along with having high-quality, shippable fruit. P.G. Glucina and currently M.T. Malone have released ‘Coconut Ice’ and ‘Scarlet O’Hara’ derived from ‘Yumyeong’ from Korea as well as ‘Havelock Pearl’ derived from ‘Hakuto’ from Japan. Breeding is also under way to develop adapted low-acid, white nectarines.

South Africa Early efforts in peach breeding in South Africa were for canning clingstones and lower-chill peaches. In recent years efforts have been made to develop highly blushed, adapted, yellow-ﬂeshed peaches and nectarines that will retain good quality after several weeks in transit. An Agricultural Research Council Infruitec–Nietvoorbij early dessert nectarine, ‘Alpine’ (released in 1997), has performed exceptionally well on European markets. Numerous other nectarine (‘Nectar’, ‘Royal Gem’, ‘Sunburst’, ‘Crimson Giant’) and peach (‘Excellence’, ‘Witzenberg’) cultivars have been named and other selections are still under evaluation for commercial use in the export market. Most are low-chilling except for ‘Royal Gem’, which is medium-chill. For more information see Chapter 5.

6.7 Conclusions Great progress has been made by peach breeders in the last century. Many modern cultivars are large-fruited and highly productive, with extensive red skin colour, little pubescence, round shape, and very ﬁrm, slow-softening, yellow or white ﬂesh. Unfortunately some of these gains have come at the expense of eating quality, for both genetic and cultural reasons. As a result, most programmes, and particularly the private breeders, are now putting increased emphasis on this aspect. In more difﬁcult climates, meaning outside California, the process has been slower to incorporate these advances into peaches that also

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have tolerance to problems associated with cold, rain and disease. In some cases industries have declined faster than breeders were able to develop suitable cultivars, thus taking the breeding programmes out as well. The trend towards patenting most new cultivars is changing the industries as well as the breeding programmes. Traditionally, public breeders shared and cross-tested breeding stock and advanced selections. Now that most public breeders are patenting new releases, less testing is done across sites in order to protect the selections. At the time of release growers may have less information available on which to base a decision to plant the cultivar. Private breeders are able to grow larger numbers of seedlings than public breeders and hence make bigger gains in improvement. Over time these improvements tend to be incorporated into other programmes. In some industries public breeders are focusing on germplasm screening and enhancement for characters such as disease resistance, while their private counterparts focus on cultivar development. In California, private breeders provide the bulk of freestone peach cultivars. This has not occurred in the eastern USA with the exception of the private programmes in Michigan. The success of the private Michigan programmes may relate to a void in new cultivars developed for the northern climates, but it is not clear if they will be self-sustaining. It seems unlikely that private programmes will be as successful in the fragmented eastern industries, which have more challenging climatic and disease situations relative to California. The increase in breeding programmes outside the USA is a welcome trend given the decline of public breeding programmes in the USA. It may reduce the overseas market for privately bred US cultivars, but in the long run will likely be of greater beneﬁt to the local industries. Few countries have a climate as ideal as that of California for growing peaches and nectarines. Locally selected cultivars can

be better adapted and reduce the risk of crop loss in years of high disease pressure.

Acknowledgements Thanks are due to the following scholars for providing information related to their countries: A. Zhivondov (Bulgaria); R. Monet and T. Pascal (France); C. Tsipouridis (Greece); Z. Szabó (Hungary); G. Baroni, E. Bellini, T. Caruso, A. Liverani, A. Martinelli (CIV), V. Mazzotti (CSO) and V. Ossani (Italy); A. Ivascu (Romania); V. Ognjanov (Serbia); M.L. Badenes (Spain); L. Wang (China); and M. Yamaguchi (Japan).

A note about references The American Pomological Society published brief descriptive lists of peaches and other fruit from 1920 to 1950. In 1942, R.M. Brooks and H.P. Olmo began a Register of New Fruit and Nut Varieties. The new register consisted of many lists published in the Proceedings of the American Society for Horticultural Science from 1944 to 1970 and later in HortScience. Periodically it was consolidated into book form (Anon., 1997). The most comprehensive single listing of cultivars is USDA Agricultural Handbook 714, which has descriptions of over 700 cultivars from the USA as well as a similar number from other countries, plus an index of 6000 names and synonyms (Okie, 1998). Unfortunately there is no single listing of the newest US patented cultivars other than the patents themselves, which can be viewed at http://www.uspto.gov/patft/index. html. Several excellent books with complete descriptions and photographs have been published in Europe, particularly France (most recently by Hilaire and Giauque, 1994) and Italy (most recently by Della Strada et al., 1984, 1986; Conte et al., 1994).

References Anon. (1997) The Brooks and Olmo Register of Fruit and Nut Varieties, 3rd edn. ASHS Press, Alexandria, Virginia.

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Layne, R.E.C. (1997) Peach and nectarine breeding in Canada: 1911 to 1995. Fruit Varieties Journal 51, 218–228. Li, Z.-L. (1984) Peach germplasm and breeding in China. HortScience 19, 348–351. Liverani, A. and D’Alessandro, D. (1999). La qualità gustative dei frutti nell’attività di miglioramento genetico del pesco presso l’ISF di Forlì. Rivista di Frutticoltura e di Ortofloricoltura 2, 30–37. Liverani, A., Calisesi, F. and Bendandi, C. (1997) Il miglioramento genetico del pesco per la resistenza a Monilia. In: Proceedings of ‘XXII Convegno Peschicolo’. Società Orticola Italiana, Cesena, Italy, pp. 103–106. Liverani, A., Giovannini, D. and Brandi, F. (2002) Increasing fruit quality of peaches and nectarines: the main goals of ISF-FO (Italy). Acta Horticulturae 592, 507–514. Liverani, A., Giovannini, D., Brandi, F. and Merli, M. (2003) Miglioramento genetico del pesco per la resistenza alle principali malattie crittogamiche. In: Proceedings of ‘Presentazione dei risultati ottenuti dal progetto finalizzato Mipaf-Frutticoltura’, Vol. 1. MiPAF (Ministero delle Politiche Agricole e Forestali), Cesena, Italy, pp. 33–35. Liverani, A., Giovannini, D., Brandi, F. and Merli, M. (2004) Development of new peach varieties with columnar and upright growth habit. Acta Horticulturae 663, 381–386. Marchese, A., Tobutt, K.R. and Caruso, T. (2005) Molecular characterisation of Sicilian Prunus persica cultivars using microsatellites. Journal of Horticultural Science and Biotechnology 80, 121–129. Massonie, G., Maison, P., Monet, R. and Grasselly, C. (1982) Résistance au puceron vert du pêcher, Myzus persicae Sulzer (Homoptera Aphididae) chez Prunus persica (L.) Batsch et d’autres espèces de Prunus. Agronomie 2, 63–70. Mavlyanova, R.F., Abdullaev, F.K., Khodjiev, P., Zaurov, D.E., Molnar, T.J., Goffreda, J.C., Orton, T.J. and Funk, C.R. (2005) Plant genetic resources and scientific activities of the Uzbek Research Institute of Plant Industry. HortScience 40, 10–14. Moing, A., Pöessel, J.L., Svanella-Dumas, L., Loonis, M. and Kervella, J. (2003) Biochemical basis of low fruit quality of Prunus davidiana, a pest and disease donor for peach breeding. Journal of the American Society for Horticultural Science 128, 55–62. Monet, R. (1967) Contribution à l’étude génètique du pêcher. Annales de l’Amélioration des Plantes 17, 5–11. Monet, R. (1977) Amélioration du pêcher par voie sexuée, exposé d’une méthode. Annales de l’Amélioration des Plantes 27, 223–234. Monet, R. (1983) Le pecher, génétique et physiologie. Masson, Paris. Monet, R. (1984) Heredity of the resistance to leaf curl (Taphrina deformans) and green aphid (Myzus persicae) in the peach. Acta Horticulturae 173, 21–23. Monet, R. and Bastard, Y. (1982) Estimation du coefficient de régression enfant/parent de quelques caractéres du pecher dans le cas de familles issues d’autofécondations. Agronomie 2, 347–358. Monet, R., Bastard, Y. and Gibault, B. (1988) Etude génétique du caractère ‘port pleureur’ chez le pêcher. Agronomie 8, 127–132. Morettini, A. (1961) Le nuove cultivar Morettini. Consiglio Nazionale delle Ricerche, Florence, Italy. Mowry, J.B. (1960) Selecting peach varieties for new plantings. Transactions of the Illinois State Horticulture Society and Illinois Fruit Council 94, 97–109. Myers, S.C., Okie, W.R. and Lightner, G. (1989) The Elberta peach. Fruit Varieties Journal 43, 130–138. Oberle, G.D. (1971) What’s new in peach varieties at VPI and the mid-Atlantic states. In: Proceedings of the 30th Annual Convention. National Peach Council, Atlanta, Georgia, pp. 116–119. Ogasanovicˇ, D. (1998) Dora, a medium late, good quality, peach cultivar. Acta Horticulturae 465, 193–196. Okie, W.R. (1997) USDA stone fruit breeding in the southeastern United States. Fruit Varieties Journal 51, 211–217. Okie, W.R. (1998) Handbook of Peach and Nectarine Varieties. US Department of Agriculture Handbook No. 714. US Government Printing Office, Washington, DC. Okie, W.R. and Myers, S.C. (1991) Springcrest peach. Fruit Varieties Journal 45, 190–192. Okie, W.R., Ramming, D.W. and Scorza, R. (1985) Peach, nectarine and other stone fruit breeding by the USDA in the last two decades. HortScience 20, 633–641. Ossani, V. (1987) Tre nuove nettarine bianche: Caldesi 2000, Caldesi 2010, Caldesi 2020. L’Informatore Agrario 22, 52–56. Pascal, T. and Monteux-Caillet, R. (1998) Peach breeding in France. Acta Horticulturae 465, 117–123. Pascal, T., Kervella, J., Pfeiffer, F.G., Sauge, M.H. and Esmenjaud, D. (1998) Evaluation of the interspecific progeny Prunus persica cv. Summergrand × Prunus davidiana for disease resistance and some agronomic features. Acta Horticulturae 465, 185–191.

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7

Processing Peach Cultivar Development T.M. Gradziel1 and J.P. McCaa2

1Department

of Plant Sciences, University of California, Davis, California, USA Monte Corporation, Stockton, California, USA

2Del

7.1 Introduction 7.2 Harvest 7.3 Raw Product Supply, Transport and Storage 7.4 Grading 7.5 Fruit Halving and Pitting 7.6 Peeling and Blanching 7.7 Sorting and Canning 7.8 Pasteurization 7.9 Marketing

7.1 Introduction The production of peaches for processing is an important industry in many temperate growing regions of the world (Table 7.1). In Europe, Spain and Greece are major producers with combined production often exceeding 500,000 t (canned net weight). Approximately 400,000 t of peaches are canned in North America, with most occurring in California (CCPA, 2003). In South America, Argentina and Chile are major canned peach exporters with combined production of approximately 112,500 t. Other important southern hemisphere producers include South Africa with approximately 100,000 t and Australia with 44,000 t. In California, the total 2002 processed peach (canned, purée, juice, frozen and dried) production of 587,506 t (USDA, 2004) surpassed the total fresh market production of

175 176 181 182 184 186 187 188 188

504,486 t for the USA as a whole (Tables 7.2 and 7.3). Total US production of processed peach was 617,021 t in 2002 or 55% of total fresh market and processed utilized peach production. In the major processing peach production regions, cultivars are developed within or alongside breeding programmes for fresh market fruit since the genetics and breeding methodologies are identical (Nakasu et al., 1981; Bellini, 1985; Moore, 1985; Fideghelli, 1987; Zhang et al., 1996; Layne, 1997; Todorovic et al., 1998; Mishich et al., 1998; Etienne et al., 2002). Information on peach genetics and genetic recombination strategies presented in Chapter 3 are thus applicable to the breeding of processing peach cultivars. The cultivar improvement programmes differ primarily in the breeding objectives and consequently the selection criteria, as fresh market and

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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Table 7.1. Estimated 2003/4 world production of canned peaches and change in production from the previous year. Southern hemisphere figures are for 2002/3 marketing year. (From CCPA, 2003.) Country USA Spain South Africa Argentina Greecea Chile Australia All other Total

Production (t) 380,270 154,000 98,000 67,000 52,000 45,500 44,000 17,500 858,270

Change (%) −5 −8 +27 +43 −82 +17 +8 N/A −24

aGreek productivity is down from a typical production of 400,000 t following two consecutive years of severe frost damage.

Table 7.2. Total 2002 utilized processing peach production in the USA. (From USDA, 2004.) Use and type Canned Clingstone Frozen Freestone Dried Freestone Purée, juice, etc. Clingstone Freestone Total

State

Production (t)

California Others

464,025 17,418

California Others

82,645 9,570

California

12,882

California All California USA

27,954 2,527 590,033 617,021

Table 7.3. Comparison of 2002 utilized fresh market and processing peach production for the USA. (From USDA, 2004.) Utilization Total fresh market Total processing freestone Total processing clingstone Total processing Total fresh market and processing

processing cultivar ideotypes differ in important and sometimes dramatic ways. A major difference between processing and fresh market cultivars is that processing peaches are largely handled as a bulk commodity, requiring greater fruit durability and uniformity for bulk handling and processing and greater yields to compensate for the generally lower price for the raw product. In addition, since most ﬂavour volatiles are lost during processing, processing peach breeding programmes must emphasize other components of peach ﬂavour (Sistrunk et al., 1979; Gonzalez et al., 1992; Mishich et al., 1998; Blanc and Arregui, 1999). While some fresh market freestone cultivars are processed (Tables 7.2 and 7.3), their soft melting ﬂesh and typical high levels of water-soluble anthocyanin pigments result in poor processed quality unless processing is by rapid freezing or drying. Approximately 83% of all processed peach cultivars utilize the clingstone, non-melting ﬂesh trait (Table 7.3) since the ﬁrm ﬂesh of such fruit (Fig. 7.1/Plate 55) is more resistant to physical damage during bulk fruit harvest, transport, processing and fruit slicing (Carles, 1984). Canning (including purée and juice) accounts for approximately 83% of all processed peach tonnage in the USA with other products being frozen slices and diced products, dried peaches and baby food (Table 7.2). Common processed forms include peach halves, sliced or diced peach, purée and juice. While the ﬁnal product and even the method of preparation may vary, most processing involves a common sequence of basic events as generalized in Fig. 7.2 (Dauthy, 1995; Burrows, 2001). To be successful, a cultivar must be compatible with the nuances of every component of the processing pathway. For this reason it is wise to consider cultivar selection criteria within the framework of this pathway.

Production (t) 504,486 107,624 509,397 617,021 1,121,507

7.2 Harvest Peaches for processing are generally harvested near the tree-ripe stage to maximize fruit size, yield and quality (Souty, 1972; Elkins, 1979;

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Fig. 7.1. Processing clingstone peach showing the uniformly yellow, firm, non-melting flesh and associated clingstone type stone-to-flesh adhesion.

Sistrunk et al., 1979; Carles, 1984; Delwiche et al., 1987; Brooks et al., 1993; Wang et al., 1993; Mishich et al., 1998; Blanc and Arregui, 1999). Most freestone peaches, because of their characteristic soft, melting ﬂesh at maturity, are harvested at an earlier ripening stage prior to ﬁnal ﬂesh softening (see Chapter 5). The non-melting clingstone peach (Fig. 7.1/ Plate 55) not only allows harvest at full maturity, but also the more rapid, bulk harvest required to compensate for the generally lower farm-gate value of processing clingstone peaches (Bourne, 1974; Pressey and Avants, 1978; Sistrunk et al., 1979). Machine harvest is sometimes used but can result in considerable fruit damage if tree, fruit and equipment attributes are not optimized (Ray and Morris, 1974; Zocca, 1975; Zocca and Fridley, 1977). Besides the non-melting clingstone fruit type, other traits which optimize harvest efﬁciency include open and accessible tree architecture, ease of fruit removal from peduncle and uniform ripening (Sistrunk et al., 1979; Egea et al., 1989; Grossman and DeJong, 1998). A wide range of tree architectures is possible in peach because of the genetic variations

available (Fideghelli et al., 1979; Scorza and Lightner, 1989; Gradziel and Beres, 1993; see also Chapters 3 and 6) and the common use of training and pruning practices to modify tree growth (Scorza and Sherman, 1996; Grossman and DeJong, 1998; DeJong et al., 1999). The open vase and, under higher densities, the perpendicular V system presently enjoy a wide popularity due to their efﬁcient light interception and easier maintenance (Grossman and DeJong, 1998; Mishich et al., 1998; DeJong et al., 1999). Differences in time to fruit maturity occur even within the more open tree architectures because of differences in fruit position within the scaffold and within the tree (Ray and Morris, 1974; Zocca, 1975; Zocca and Fridley, 1977; DeJong et al., 1999). Less fruit thinning is applied to processing peach, resulting in yields that can be up to 5 t/ha higher than fresh market freestone varieties (USDA, 2004), but which acts to further prolong the ripening period. Uneven ripening results in the need for inefﬁcient multiple hand pickings or a high percentage of lowgrade fruit if once-over or mechanical harvesting is employed (Ray and Morris, 1974; Zocca, 1975; Zocca and Fridley, 1977). Peach cultivars

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Harvest

Transport

Grading

Fruit halving and pitting

Peeling and blanching

Sorting and canning

Pasteurization

Marketing

Fig. 7.2.

A flow diagram for processing peach.

differ in the duration of both the ﬂowering period and the fruit ripening period (Sistrunk et al., 1979; Monastra et al., 1984; Fideghelli, 1987; Egea et al., 1989; Lopez-Rivares and Suarez-Garcia, 1994; Paunovic et al., 1996; Layne, 1997; Berman et al., 1998; Okie, 1998; Todorovic et al., 1998; Etienne et al., 2002). Flower and fruit ripening period both

contribute to uneven ripening and respond favourably to selection (Hansche et al., 1972; see also Chapter 3). Even the most uniformﬂowering cultivars will show differences in ripening time resulting from differences in sunlight exposure due to fruit position within the canopy. Within these physiological limitations, multiple harvest can still be minimized through selection for precocious fruit ﬂesh ripening (Gradziel, 1994) or through the selection of genotypes which resist rapid fruit quality deterioration and fruit abscission once full fruit maturity has been achieved, thus allowing delayed harvests (Sistrunk et al., 1979). The complete and rapid formation of a fruit abscission zone is also required for efﬁcient harvest but the cultivar should not be prone to preharvest fruit drop. Harvest yield remains the single most important determinant of cultivar success and one of the most difﬁcult for developing efﬁcient selection indices. Yield performance must be considered both within season and over the productive life of the orchard (DeJong et al., 1999). A typical processing peach orchard in California is expected to be productive for 20–30 years. Similarly, cultivar turnover is lower in processing peach compared with fresh market cultivars, which are more frequently replaced due to changing market preference (Scorza and Sherman, 1996). Many of the major processing peaches in world production, including ‘Loadel’, ‘Carson’, ‘Andross’ and ‘Halford’, were discovered over 50 years ago, with others such as ‘Sullivan #4’ released in 1929 (Anon., 1997; Okie, 1998) (Figs 7.3 and 7.4/Plates 56 and 57). Processing cultivars also need to be adaptable to a greater range in growing locations and environmental conditions. Extensive ﬁeld-testing is currently the only dependable indicator of ultimate cultivar performance (Monastra et al., 1984; Egea et al., 1989; Lopez-Rivares and Suarez-Garcia, 1994; Layne, 1997). While controlled hybridizations and the subsequent selection among resultant seedlings may consume 4–10 years of a breeding cycle, replicated regional trials of resulting selections typically consume an additional 10–16 years (Fig. 7.5/Plate 58). Breeding cycles exceeding 20 years from the initial hybridization to cultivar release are not unusual in processing cultivar development

Processing Peach Cultivar Development

Loadel(1)

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0

Stanislaus(2)

3

Carson(3)

5

Dee-Six (3)

5

Goodwin(3)

14

Bowen(1)

16

Fay Elberta(1)

17

Andross(3)

18

Arakelian(1)

19

Peak(1)

21

Klamp(3)

21

Tuolume(2)

22

Andora(1)

23

Ross(3)

23

Rizzi(3)

28

Dr. Davis(3)

30

Carolyn(3)

31

Monaco(1)

33

Lilleland(3)

35

Halford(1)

36 37

Everts(1) Wiser(1)

38

Riegels(3)

38

Stam(1)

39

Hesse(3)

40

Sullivan #4(1)

41

Corona(3)

44 0

5

10

15

20

25

30

35

40

45

50

Fig. 7.3. Harvest sequence days of California processing peach cultivars using the fresh market freestone ‘Fay Elberta’ as a reference cultivar (1, grower selection; 2, private breeder release; 3, released by public breeding programme).

programmes (Fig. 7.4/Plate 57). This need for more extensive testing has made processing peach breeding less proﬁtable for private breeding programmes, with most processing peach cultivars being released by public breeding programmes or as chance seedlings selected by growers (Fig. 7.3/Plate 56). Estimates of yield heritability based on current selection indices are typically less than 10% (Hansche et al., 1972). Emerging strategies of marker-assisted selection provide opportunities for more efﬁcient genetic selection for factors controlling yield (Bliss et al., 2002; Etienne et al., 2002; Aranzana et al.,

2003; see also Chapter 4). The effective interpretation of molecular marker data, however, will require an improved understanding of the developmental/physiological determinants of crop yield. At the most basic level, peach yield is a function of crop load and fruit size (Berman et al., 1998). Despite the high costs of subsequent fruit thinning (DeJong et al., 1999), initial high ﬂower/fruit densities are desirable as a buffer against subsequent detrimental environments such as insufﬁcient winter chilling, frost or storm damage, which can greatly reduced crop potential. Recent progress in characterizing fruit sizing potential has

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Hesse

Corona

Ripe period

4

Everts 3

Late Ross

Dr.Davis

Carolyn

Rizzi Lilleland

Andora Ross

Klamt

Riegels

Bowen 2

Fortuna

Carson

Andross Jungerman

Goodwin Tufts

Dee-Six

1 1940 1946 1952 1958 1964 1970 1976 1982 1988 1994 2000 1943 1949 1955 1961 1967 1973 1979 1985 1991 1997 Year Fig. 7.4. History of processing clingstone cultivar release by public breeding programmes in California showing punctuated release at approximately 20-year intervals (ripe period: 1, extra early; to 4, extra late).

Cultivar release

Select parents for desired traits

Crosses for genetic recombination (1 year)

(1–5 years)

Evaluate performance at multiple sites and years

Select among progeny (2–5 years)

(8–16 years)

Fig. 7.5. years.

Basic components of a processing peach breeding programme with estimated duration in

Processing Peach Cultivar Development

been made with the development of increasingly accurate models of vegetative and reproductive growth in clingstone peach (Berman et al., 1998; DeJong et al., 1999) and the use of these models in characterizing the relationships between cultivar yield and accumulated heat units (Berman et al., 1998). Theoretical maximum yields predicted by these models approach 70 t/ha, approximately 20 t/ha above the current industry average, but this is comparable to yields obtained in controlled ﬁeld studies (Berman et al., 1998).

7.3 Raw Product Supply, Transport and Storage Efﬁcient fruit processing is typically a ‘supply-on-demand’ enterprise, as postharvest storage is generally too expensive to be used routinely. Due to the high ﬁnancial investment in equipment, however, fruit processing facilities need to run at high capacity over the entire duration of the harvest season in order to maximize ﬁnancial return. To ensure a uniform supply of raw product for such ‘just-in-time’ delivery, processing plant ﬁeldsmen utilize fruit from different locations and, when necessary, from cold storage (Ray and Morris, 1974; Brecht et al., 1982; Kader et al., 1982; Kader, 1997). The preferred method of securing a constant supply of raw product, however, is through the planting of cultivars with sequential ripening times (Fig. 7.3/Plate 56). Ripening time in peach, while apparently controlled by many genes, has heritability as high as 0.84 (Hansche et al., 1972; Hansche and Boynton, 1986a). Such high response to selection has been conﬁrmed in many breeding programmes where targeted maturity time has generally been achieved by selecting parents having ripe dates which bracket the desired maturity time. While such breeding strategies often result in a large proportion of progeny ripening within the desired harvest period, occasionally the targeted harvest time will defy this parental averaging approach. The consequent gap in raw product supply can become a serious impediment to processing efﬁciency as shown by the 10-day production gap between the cultivars ‘Carson’ and

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‘Bowen’ (Fig. 7.3/Plate 56). The genetic nature of such aberrant maturity gaps is demonstrated in the distribution of progeny obtained by selﬁng the ‘Carson’ cultivar (Fig. 7.6/Plate 59). Rather than the expected normal distribution of ripening times centred near that of the selfed parent (or the parental mean in cross-pollinations), a bimodal distribution is observed where the ripening gap is similar to that observed in Fig. 7.3/Plate 56. The nature of such production gaps suggests the presence of inherent fruit developmental thresholds. For example, if the threshold event is achieved within the required time (perhaps relative to vegetative or endocarp growth), normal development will continue. For genotypes that have not yet achieved the developmental threshold, however, further development will be delayed. This problem is often overcome by bringing in outside, unrelated germplasm for hybridization with locally adapted breeding lines. Raw product availability will also limit the duration of the processing season. Midseason cultivars tend to show the highest per hectare yields, while yields in later-maturing cultivars decline. With increasingly earliermaturing cultivars, the reduction of available solar heat/light units becomes a major limitation to potential yield. Berman et al. (1998) have estimated yield penalties as high as 1.8 t/ha per day for genotypes ripening earlier than the ‘Loadel’ ripening period as charted in Fig. 7.3/Plate 56. Yield reductions from postharvest losses occur primarily as physical and disease damage during transport. O’Brien et al. (1978) found that only 56% of harvested fruit remained unbruised following typical transport to the processing plant. Physical protuberances, including peduncles remaining attached to the fruit and excessive ‘beaking’ of the fruit stylar end, will damage adjacent fruit in the bulk bins and so should be avoided. Damaged fruit is subsequently much more susceptible to disease. While processing peach cultivars are generally susceptible to the same diseases as fresh market peaches, the greater physical contact between fruit during harvest, transport and storage makes processing peach much more vulnerable to postharvest losses from fungal pathogens

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20

Number of seedings

15

10

5

0 5

15

25

35 45 55 Days after 1 June

such as Monilinia, Alternaria and Botrytis spp., which spread rapidly when fruit are in contact (Chapter 15). Losses during postharvest storage are primarily from such rapidly spreading fungal diseases and from the deterioration in fruit quality (Brecht et al., 1982). Selection for resistance to postharvest disease (Nakasu et al., 1981; Gradziel and Wang, 1993; Gradziel, 1994) and physiological deterioration (Kader et al., 1982; Robertson et al., 1992; Gradziel et al., 1993a,b; Kader, 1997) has been successful, although the underlying mechanisms are only now being characterized (Crisosto and Labavitch, 2002). The use of modiﬁed atmospheres to prolong fruit quality has shown only limited success for processing peach (Brecht et al., 1982; Kader, 1997) although cold storage in commercial facilities capable of manipulating storage atmospheres is routinely practised in California.

7.4 Grading Prior to processing, fruit is typically evaluated either at grading stations near the orchard or at the processing plant. The grading process, which often determines the price paid for the

65

75

85

Fig. 7.6. Fruit ripe date for progeny from self-pollination of the cultivar ‘Carson’ showing unusual bimodal distribution (‘Carson’ normally ripens approximately 40 days after 1 June).

shipment, evaluates fruit size, maturity, ﬁrmness and defects. Fruits smaller than 6 cm in diameter are often not purchased because they are difﬁcult to process and result in an inferior product. Fruits larger than approximately 9 cm are similarly difﬁcult to process in equipment adjusted for more standard sizes, and the higher levels of fruit thinning needed to achieve the larger size contributes to reduced yields. For this reason, the highestyielding cultivars produce large numbers of uniform size fruit of approximately 6–9 cm in diameter with undersized fruit typically representing less than 5% of total production. Fruit maturity is characterized primarily by ﬂesh colour after removing approximately 1 cm of the epidermis and underlying mesocarp tissue (Delwiche et al., 1987). Internal colour is compared against a colour standard, with fruit failing to achieve minimum colour levels being considered ‘green’ fruit and often not purchased. Flesh colour is determined primarily by the carotenoid pigments b-carotene and b-cryptoxanthin (Tourjee et al., 1998). Although the carotenoid biosynthesis pathway appears to be inﬂuenced by several genes (Chapter 3), selection for fruit ﬂesh colours ranging from golden-yellow to yellow-orange is readily achieved. Selection for high levels

Processing Peach Cultivar Development

of b-carotene may result in fruit with an undesirable dull orange ﬂesh colour and a ‘melonlike’ aftertaste. Higher b-cryptoxanthin levels result in a more desirable yellow-gold ﬂesh colour without aftertaste or loss of provitamin A carotenoid content (Tourjee et al., 1998). Red pigmentation of fruit ﬂesh is strongly selected against in processing peach cultivars because, unlike the water-insoluble and heatstable carotenoid pigments, the water-soluble red anthocyanin pigments break down during the cooking process, resulting in an undesirable brown staining of fruit ﬂesh and syrup. Since the fruit skin or epidermis is removed during processing, some red pigmentation or ‘blush’ is tolerated in processing cultivars (Fig. 7.1/Plate 55). Excessive red skin pigmentation, however, can lead to staining of the underlying tissue with associated fruit peeling problems (Fig. 7.7/Plate 60). Areas of red skin pigmentation are also associated with higher levels of bird damage in the ﬁeld (T.M. Gradziel, personal observation). Some recent processing peach cultivars, such as ‘Maria Serena’ (Bellini, 1983) and ‘Maria Dorata’ (Bellini, 2000) from Italy, show an apparent complete suppression of red anthocyanin pigmentation in the fruit. Chapparo

Fig. 7.7.

183

et al. (1995) have characterized the inheritance, genetic interaction and biochemistry of known anthocyanin phenotypes in peach, and studies have evaluated the genetic control of the anthocyanin-free trait (see Chapter 1) as well as its consequence on fruit sensory quality (T. Beckman, USA, 2004, personal communication). Peach ﬂesh ﬁrmness is commonly measured with hand-held penetrometer-type pressure testers because of their portability and ease of operation (Kader et al., 1982; Kader, 1997). Clingstone fruit ﬂesh tends to be heterogeneous, often being more ﬁbrous near the endocarp and more homogeneous near the epidermis (Fig. 7.8/Plate 61). Although more sophisticated instruments exist to measure the change in texture throughout the tissue, providing more precise information, they are more cumbersome to use for routine sampling (Bourne, 1974). Peaches with ﬂesh puncture pressures of less than 3 kg (after skin removal, measured with an 8 mm ﬂat probe) are often damaged during processing. Flesh pressures greater than 6 kg, however, are associated with excessive adhesion between the stony endocarp and ﬂeshy mesocarp, leading to problems in pit removal and, more seriously,

Poor lye peeling of a clingstone genotype with unacceptably thick epidermis.

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Fig. 7.8. Halved section of an overripe clingstone peach demonstrating the common pattern of vascular strands radiating from endocarp to outer mesocarp.

the retention of broken pit shards in processed fruit, making it hazardous to consumers. Endocarp cracking early in fruit development can also lead to large shards of the fractured pit being embedded in the ﬂeshy mesocarp. These early-split pits may lead to later splitting of the mesocarp or ﬂesh along the suture line, encouraging disease and insect contamination. Invisible split pits, in which the mesocarp remains intact, can often be identiﬁed by abnormally large fruit size and greater fruit asymmetry resulting from internal endocarp splitting and wound tissue development. Although such fruit can be salvaged by hand pitting, the extra cost of this special treatment makes split pits and genotypes prone to this problem undesirable. Even in high-quality processing cultivars, the ﬂesh colour and ﬁrmness can vary considerably with maturation from unripe to overripe fruit (Kader et al., 1982; Gradziel, 1994; Kader, 1997). Precise indices of fruit maturity are thus essential for accurate fruit grading. Despite a general selection for uniform fruit ﬂesh colour, commercial processing

cultivars can also vary considerably in their ﬁnal ﬂesh colour, which can confound fruit grading (Delwiche et al., 1987). For this reason, it is common to use separate colour standards to grade fruit maturity of different cultivar groups and/or maturity periods.

7.5 Fruit Halving and Pitting Fruit halving and pitting can be done by hand or by machine. Hand cutting, while more expensive, can utilize a range of different fruit sizes, textures and pit qualities, including split and broken pits. Hand pitting is typically achieved by sliding a sharp, concaveshaped knife under the pit to remove it from the ﬂesh. This cutting action results in an undesirable ‘scooped-out’ appearance of the fruit and most hand-pitted or irregularly cut fruit are diverted to sliced and diced products, where the irregularities are less apparent, or, if unsuitable for this, used in purées and pie ﬁllings (Burrows, 2001). High-quality fruit

Processing Peach Cultivar Development

may also be puréed directly to produce premium processed products such as baby foods. The common method of mechanical pitting uses a rotary torque pitter, where the individual fruit and pit is clasped by sharp knives from opposite sides at the suture line while counter-rotating rubber cups on either side of the fruit torque the cut halves away from the partially immobilized pit. The proper alignment of the peach suture with the pitting machine cutting knives is done mechanically by using the asymmetry of the peduncle cavity to determine the suture orientation (Delwiche, 1989). Consequently, peach cultivars developed for mechanical pitting need to have a well-deﬁned peduncle asymmetry, need to harvest free from peduncle and need to have a sufﬁciently long peduncle. Very short peduncle attaching the fruit to the tree branch will result in depressions at the peduncle area where the fruit grows around the branch. The resulting branch imprint can mimic the peduncle cavity, resulting in misalignment of fruit going into the mechanical pitter. Pitting machines are very efﬁcient but need to be adjusted for speciﬁc fruit shapes, textures and fruit and pit sizes. Different fruit sizes are handled by ﬁrst sorting incoming fruit and directing them to the appropriately adjusted mechanical pitter. Variations in fruit shape and ﬁrmness and pit size and integrity (split, fragmented, etc.) are more difﬁcult to manage and are common causes for mechanical pitter failures and consequent shut-down of associated processing lines. Uniformity for these characteristics is thus a prerequisite for processing cultivars. The genetic control of these traits is still poorly understood (Hansche et al., 1972; Scorza and Lightner, 1989; see also Chapter 1). While it is thus initially difﬁcult to predict progeny performance from parental genotypes, experience with different crossing combinations will identify genotypes more frequently associated with inferior progeny in one or more of these traits, and such genotypes should be avoided. Genotypes which normally develop good fruit symmetry can occasionally develop excessive fruit elongation with ‘beaking’ at the stylar end, particularly following warm winter/early spring conditions. While often associated with low winter-chill conditions, this elongated fruit

185

growth may be a consequence of the warmer temperatures during early spring growth. For this reason, breeding selections showing erratic performance under growing conditions likely to be encountered during commercial production should be rouged-out. A serious problem with mechanical pitting is the breakage of fragments from the ridged pit that then become embedded in the processed product. While certain genotypes are more prone to this problem, the non-melting ﬂesh canning clingstone peach is inherently predisposed to embedded fragments due to the clingstone or high stone-to-ﬂesh adhesion associated with the non-melting ﬂesh trait. Although recent genetic studies suggest that the two traits may be controlled by separate genes which are highly linked, over 50 years of intense breeding efforts have failed to develop non-melting ﬂesh freestone peach types suitable for canning. The combination of melting ﬂesh with clingstone pit adhesion is common in very early-ripening fresh market peaches, but here the clingstone nature is a consequence of rapid fruit development and the true freestone genotype can be readily determined by crossing to later-maturing tester lines. Gradziel (2002) has reported the recovery of good-quality, ﬁrm-ﬂesh freestone peaches in backcrosses from peach × almond (Prunus dulcis) interspeciﬁc hybrids. While the controlling genes appear distinct from both freestone and clingstone, the trait appears unstable in certain environments, resulting in rapid ﬂesh softening in overripe fruit. A second strategy to breeding ﬁrm-ﬂesh, freestone peach involves the incorporation of the ‘stonyhard’ trait into high-quality freestone types. Stony hard also appears to be genetically distinct from the freestone/clingstone trait and acts by suppressing the normal ethylene-induced fruit softening at ripening (Haji et al., 2003). Breeding lines combining the stonyhard and freestone trait have demonstrated greater ﬂesh ﬁrmness in ripe fruit, but the level of ﬁrmness (typically about 3 kg) was insufﬁcient to avoid extensive damage during processing and was also associated with undesirable textural changes in processed samples. Beckman and Sherman (1996) and Van Der Heyden et al. (1997) have described a non-melting, semi-freestone trait which, while

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not yet fully genetically characterized, appears to be readily recovered in certain crossing combinations (T.M. Gradziel, personal observation). Unfortunately, the ripe fruit remains softer than clingstone fruit and the semi-freestone trait appears to be strongly associated with a pronounced red anthocyanin pigmentation of the fruit pit cavity, making it unacceptable for canning (see also earlier evaluation of this trait by Robertson et al., 1992). Unless the association between melting ﬂesh and freestone habit can be altered, freestone cultivars will remain unsuitable for most processing uses. Breaking this undesirable association might be achieved through breakage of the putative genetic linkage between these traits or, alternatively, the incorporation of independent genes promoting a more freestone tendency in non-melting genetic backgrounds. Pressey and Avants (1978) have reported that, unlike melting-ﬂesh freestones, non-melting clingstone fruit lack endopolygalacturonase activity. Callahan et al. (2004) demonstrated a correlation with the non-melting ﬂesh texture and observed deletions in the endopolygalacturonase gene cluster. These ﬁndings suggest that opportunities for genetically engineering a suppression of the putative ﬂesh-softening endopolygalacturonase gene in freestone genotypes though pleiotrophic effects such as unstable mesocarp integrity may ultimately confound this approach. The incorporation of the clingstone trait into fresh market varieties, however, is common in many parts of the world, particularly Europe and South America, because the associated non-melting ﬁrm ﬂesh facilitates shipping and handling, allowing higher-quality fruit to be harvested closer to the tree-ripe stage (see Chapter 5). This greater versatility of the clingstone/non-melting trait has encouraged the development of dual-purpose peaches for both processing and fresh market (Wilson and Boudreaux, 1986; Raseira et al., 1998; Bellini, 2000), thus allowing greater marketing ﬂexibility. The ﬂavour of fresh clingstone peaches is distinct from freestone peaches with their more pronounced aromatic components. Shortly after the full-ripe stage of maturity, clingstone peaches often also develop a characteristic off-ﬂavour which appears to be associated with alcohol metabolism.

7.6 Peeling and Blanching While clingstone are usually distinguished from freestone peaches by their ﬁrmer, non-melting ﬂesh and continued adhesion between the endocarp and inner mesocarp in ripe fruit, they also show greater adhesion between the exocarp (skin) and outer mesocarp tissue (Rotaru, 1994). In full-ripe, melting-ﬂesh, freestone cultivars, a breakdown in the adhesion between the skin and underlying ﬂesh often allows the skin to be readily peeled from the fruit, particularly after blanching. The more pronounced attachment in clingstone cultivars necessitates more rigorous methods for peeling. In bulk processing, clingstone peach halves are frequently peeled by immersion in or spraying with hot caustic solutions such as 1–2.5% lye for 30–60 s (Dauthy, 1995; Burrows, 2001). The loosened skin is then physically removed by passing the peach halves under powerful water sprays which also wash off remnants of the caustic solution. Although caustic solutions are recycled, their eventual disposal is becoming increasingly costly and other methods of skin removal are being evaluated. Steaming fruit to loosen the skin followed by skin removal by rotating rubber or abrasive rollers can be effective if the cultivar has a thinner epidermis or less pronounced epidermis-to-mesocarp adhesion. Both epidermis thickness and adhesion are strongly affected by environmental conditions, making this approach less dependable. Poor peeling can occur in either approach for excessively thick epidermis tissue, which should be avoided in new cultivars (Fig. 7.7/ Plate 60). Intense red blushing of the skin should also be avoided as it can lead to staining and peeling problems of the underlying ﬂesh tissue. Carroad et al. (1980) have determined that steam generation for use in peeling, blanching and cooking accounts for 98% of all energy consumed in a clingstone peach cannery. Because the peel is removed in processing, greater variations for epidermis characteristics are tolerated in processing cultivars, which can be exploited for improved disease and pest resistance. More compact epidermal cell layers, and higher levels of phenolics, pectin and cutin, have been incorporated in processing varieties to improve fungal resistance. Similarly, high trichome densities with their

Processing Peach Cultivar Development

associated pest resistance (Massonié et al., 1982; Monet and Massonié, 1994) and peach ‘fuzziness’ are acceptable in processing cultivars since they are removed during processing. Removal of the epidermis and underlying tissue during processing also acts to remove most residues from pre- and postharvest pesticide treatments (Lentza, 1995; Lentza and Chitzanidis, 1995, 1996). The range of breeding options allowed by the removal of the epidermis at processing is demonstrated by the development of processing peach selections in which the epidermis retains its immature green colour and associated high levels of fungal resistance at full maturity as determined by ﬂesh colour (Gradziel, 1994). Following peeling, peaches are blanched for 1–2 min in steam or water at 80°C to inactivate the oxidizing enzymes which otherwise turn exposed ﬂesh brown. Blanching also suppresses the oxidation and associated degeneration of fruit phytonutrients, thus preserving their availability to the consumer (Elkins, 1979). Canning results in signiﬁcant initial phytonutrient losses from the heat treatment but the remaining phytonutrients are more stable during later storage, whereas freezing will show less initial loss but increasing loss with storage time (Chang et al., 2000). Previous bruising of ﬂesh that occurred during harvest and transport is not controlled by blanching. Control is primarily by selecting against high levels of phenolics and polyphenyloxidases which catalyse the ﬂesh-browning reactions. Sizeable genetic differences in both phenolic and polyphenyloxidase levels have been demonstrated in processing peach genotypes (Gradziel and Wang, 1993; Chang et al., 2000). Hansche and Boynton (1986b) have estimated the heritability for fruit enzymatic browning at 0.35 for freestone selections. A high vulnerability to ﬂesh bruising is also a major limitation to the processing of white-ﬂeshed clingstone peaches, though white-ﬂeshed processing cultivars have been released (Lu et al., 1995).

7.7 Sorting and Canning Following peeling, the halved peaches are sorted and graded. The best-quality halves

187

are canned as Fancy USDA grade. The smaller, less perfect fruit are designated, in diminishing order, as Choice, Standard, Second and Pie grades (Burrows, 2001). Sliced and diced peaches can be prepared from damaged or otherwise irregular halves. After cutting, the fruit is inspected to remove any damaged or blemished sections. Fruit is typically placed into cans, then hot syrup is added and the can is closed using steam-ﬂow closure (Dauthy, 1995; Burrows, 2001). Container size can range from multi-litre to single-serving tinned metal and plastic containers or to glass packs of generally intermediate volumes. The tin in the metal cans act as a catalyst to preserve fruit colour brightness (Blanc and Arregui, 1999; Burrows, 2001). The mixing of cultivars having different ﬂesh colours or colour brightness is avoided because such differences in fruit colour give the consumer the impression that some of the fruit from an individual container is either immature or over-mature. Differences in individual fruit ﬂavour and sweetness tend to be masked when canned in the traditional 30°Brix syrup or natural fruit juice. Raw fruit ﬂavour and sugar level become more important when fruit is packed in lighter syrup or water. Kader et al. (1982) and Kader (1997) have reported that fresh fruit ﬂavour is positively correlated to processed ﬂavour when established cultivars are evaluated. However, the fruit volatiles normally associated with ﬂavour in fresh peaches are lost in processing and cultivar ﬂavour is largely determined by sugar content and still poorly understood non-volatile ﬂavour components such as organic acids (Gonzalez et al., 1992). Genetic variability in both fruit sugar and organic acid content has been characterized in processing peach (Gonzalez et al., 1992; Brooks et al., 1993; Wang et al., 1993; Etienne et al., 2002) though it remains largely unexploited, partly due to low heritability (Etienne et al., 2002). Hansche et al. (1972) and Hansche and Boynton (1986a) estimated heritability of 0.17 and 0.35, respectively, for freestone selections. While reporting low heritability for the individual processing clingstone sugars sucrose, glucose, fructose and sorbitol, Brooks et al. (1993) reported heritability of 0.72 or higher for total soluble solids, acidity and sugar:acid ratios.

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In the preliminary evaluations of breeding selections, fresh ﬂavour, with the exception of soluble solids content, is generally not a good indicator of processed product ﬂavour since signiﬁcant changes can occur with processing. The nectarine cultivars, for example, with their typical high levels of acids, sugars and aromatic volatiles, can develop ‘off-ﬂavours’ when processed. Consequently, while clingstone nectarines exist (see Bellini, 2000), they are typically not used for processing. The processing of samples under commercial conditions remains the only effective way to evaluate processed quality of new selections. Fruit texture, phytonutrient content and colour can also change with processing, sometimes in unanticipated ways (Tourjee et al., 1998; Chang et al., 2000). Poor fruit quality, including damaged, blemished and undersized fruit, reduces case yield efﬁciency (the proportion of the initial raw product that can be successfully processed). Large pit size and poor pit quality leading to split and/or fragmented pits are major causes of case yield reductions. A red anthocyanin staining and/or brown, corky, imprinting of the fruit pit cavity is often associated with greater pit fragmentation and may be related to modiﬁed lignin synthesis since the development pathways are physiologically related. Because anthocyanins are heat-labile and water-soluble, cultivars expressing this trait are undesirable as the red anthocyanins tend to oxidize to a red-brown colour when processed, leading to staining of the syrup in addition to the peach ﬂesh.

7.8 Pasteurization In the ﬁnal stage of processing, the sealed and canned fruit are pasteurized in hot water or atmospheric steam followed by rapid cooling. The cooking time will depend on the container volume, the type of fruit product and fruit pH. At a pH of 4.6 or higher, Clostridium spp. and related bacteria can become a contamination problem if not cooked for longer periods. Increased cooking time, however, results in decreased ﬁrmness of the processed product. Ca additives may be added to pre-

serve textural ﬁrmness but are not commonly utilized (Dauthy, 1995; Burrows, 2001). Lower fruit pH levels reduce the required cooking time and so the associated fruit softening, but also alter the sugar:acid ratio, which is often associated with improved ﬂavour perception (Sistrunk et al., 1979; Gonzalez et al., 1992; Wang et al., 1993). The raw fruit pH of processing cultivars typically ranges from 3.5 to 4.5 and while lower pH selections are possible, they are not widely utilized in processing. Citric acid may also be added to acidify the fruit. At pH values of less than 4, bacteria will not multiply and shorter pasteurization treatment is allowed (Burrows, 2001). Aseptic processing, using rapid sterilization techniques which are less damaging to fruit quality, are routinely used for purées and juices (Bettison, 2001; Burrows, 2001). Technological advances to allow aseptic processing of whole or sectioned fruit offer the promise of better preservation of fruit ﬂavour, texture and phytonutrient content (Leonard et al., 1983).

7.9 Marketing Market globalization of the processing food industries is imposing greater uniformity and standardization on the ﬁnal processed product. Greater market ﬂexibility, including singleserving packaging size, greater phytonutrient content and new fruit mixtures (cocktails), are moving the processed peach ideotype to more compact sizes and more yellow-gold ﬂesh colour. Both processors and consumers are demanding reduced pesticide residues in the product. Global competition among both processed and fresh fruits has promoted the processing of a premium product, competitive with fresh market ﬂavour and eating quality, yet with the convenience and versatility of convenient packaging, storability and phytonutrient enhancement. This continuing emphasis on processed product quality is shifting the measure of industry productivity from orchard or production yield to case yield (the proportion of the initial raw product that can be processed to ﬁnal products meeting the raised quality standards). To achieve these higher case yields, new cultivars will be required

Processing Peach Cultivar Development

to produce a higher-quality product with reduced agrochemical inputs yet without loss in orchard productivity. While genetic options within the traditional peach germplasm appear too limited to achieve these larger breeding goals, a rich source of new germplasm has recently been characterized within wild peach (Pascal et al., 1997) and almond relatives (Martínez-Gómez et al., 2003a,b). Successfully introgressed traits include improved fruit ﬂavour and textural quality, pest resistance and ripening habits allowing once-over harvesting (Gradziel, 2002). Unlike seedpropagated annual crops, processing peach enjoys several advantages for such novel gene introgression. Progeny combining the best traits from both parents, while rare, are propagated vegetatively, effectively capturing the elite genotype. The extensive cultural management typical for peach allows considerable ﬂexibility in adapting to atypical tree characteristics,

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which can often be managed by modiﬁed cultural practices. Technologies utilized within the processing stream (Fig. 7.2) can also be adapted to handle novel fruit types as long as case yield efﬁciencies are maintained. For example, the use of high-speed colour sorters allows the concurrent processing of standard peach types along with newer orange-gold ﬂesh types with their higher provitamin A contents. Similarly, modiﬁcations of the standard mechanical pitter used for freestone peaches allow their use with ﬁrm, non-melting ﬂesh, freestone types. Concurrently, the development of new technologies for rapid pasteurization and aseptic packaging will make available minimally processed, tree-ripe fruit in consumer-convenient packaging allowing extended storage at ambient temperatures. In effect, processed fruit will become less an alternative to fresh fruit and more an augmented or ‘value-added’ form of fresh fruit.

References Anon. (1997) The Brooks and Olmo Register of New Fruit and Nut Varieties. ASHS Press, Alexandria, Virginia. Aranzana, M.J., Pineda, A., Cosson, P., Dirlewanger, E., Ascasibar, J., Cipriani, G., Ryder, C.D., Testolin, R., Abbott, A., King, G.J., Iezzoni, A.F. and Arús, P. (2003) A set of simple-sequence repeat (SSR) markers covering the Prunus genome. Theoretical & Applied Genetics 106, 819–825. Beckman, T.G. and Sherman, W.B. (1996) The non melting semi-freestone peach. Fruit Varieties Journal 50, 189–193. Bellini, E. (1983) Maria Serena, a new early maturing peach for processing. Rivista di Frutticoltura e di Ortofloricoltura 45, 9–10. Bellini, E. (1985) Recent changes in peach growing in Italy. Ponte del Concordato Italiano Grandine 52, 52–70. Bellini, E. (2000) Maria Dorata, an anthocyanin free nectarine for processing and fresh consumption. L’Informatore Agrario 56, 63–64. Berman, M.E., Rosati, A., Pace, L., Grossman, Y.L. and DeJong, T.M. (1998) Using simulation modeling to estimate the relationship between date of fruit maturity and yield potential in peach. Fruit Varieties Journal 52, 229–235. Bettison, J. (2001) Packaging for fruit products. In: Arthey, D. and Ashurst, P.R. (eds) Fruit Processing, Nutrition, Products, and Quality Management, 2nd edn. Aspen Publishers, Gaithersburg, Maryland, pp. 205–224. Blanc, P. and Arregui, M. (1999) Tinned peaches: the clingstone peach reviewed for today’s taste. Arboriculture Fruitière 533, 33–36. Bliss, F.A., Arulsekar, S., Foolad, M.R., Becerra, V., Gillen, A.M., Warburton, M.L., Dandekar, A.M., Kocsisne, G.M. and Mydin, K.K. (2002) An expanded genetic linkage map of Prunus based on an interspecific cross between almond and peach. Genome 45, 520–529. Bourne, M.C. (1974) Textural changes in ripening peaches. Canadian Institute of Food Science and Technology Journal 7, 11–15. Brecht, J.K., Kader, A.A., Heintz, C.M. and Norona, R.C. (1982) Controlled atmosphere and ethylene effects on quality of California canning apricots and clingstone peaches. Journal of Food Science 47, 432–436. Brooks, S.J., Moore, J.N. and Murphy, J.B. (1993) Quantitative and qualitative changes in sugar content of peach genotypes (Prunus persica (L.) Batsch.). Journal of the American Society for Horticultural Science 118, 97–100.

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Burrows, G. (2001) Production of thermally processed and frozen fruit. In: Arthey, D. and Ashurst, P.R. (eds) Fruit Processing, Nutrition, Products, and Quality Management, 2nd edn. Aspen Publishers, Gaithersburg, Maryland, pp. 149–176. Callahan, A.M., Scorza, R.M., Bassett, C., Nickerson, M. and Abeles, F.B. (2004) Deletions in an endopolygalacuronase gene cluster correlate with non-melting flesh texture in peach. Functional Plant Biology 31, 159–168. Carles, L. (1984) Clingstone peaches, fruits specially adapted for the manufacture of fruits in syrup. Arboriculture Fruitière 31, 47–48. Carroad, P.A., Singh, R.P., Chinnan, M.S., Jacob, N.L. and Rose, W.W. (1980) Peach processing. Journal of Food Science 45, 723–725. CCPA (2003) USDA: world canned peach supply falls. Cling Peach Review 39, 8. Chang, S., Tan, C., Frankel, E.N. and Barrett, D.M. (2000) Low density lipoprotein antioxidant activity of phenolic compounds and polyphenol oxidase activity in selected clingstone peach cultivars. Journal of Agricultural and Food Chemistry 48, 147–151. Chapparo, J.X., Werner, D.J., Whetten, R.W. and O’Malley, D.M. (1995) Inheritance, genetic interaction, and biochemical characterisation of anthocyanin phenotypes in peach. Journal of Heredity 86, 32–38. Crisosto, C.H. and Labavitch, J.M. (2002) Developing a quantitative method to evaluate peach (Prunus persica) flesh mealiness. Postharvest Biology and Technology 25, 151–158. Dauthy, M.E. (1995) Fruit and Vegetable Processing. FAO Agricultural Services Bulletin No. 119. Food and Agriculture Organization of the United Nations, Rome. DeJong, T.M., Tsuji, W., Doyle, J.F. and Grossman, Y.L. (1999) Comparative economic efficiency of four peach production systems in California. HortScience 34, 73–78. Delwiche, M.J. (1989) Alignment detection of clingstone peaches during pitting. American Society of Agricultural Engineers No. 89-6021. Delwiche, M.J., Tang, S. and Rumsey, J.W. (1987) Maturity evaluation of clingstone peaches by optical measurement. American Society of Agricultural Engineers No. 87-6018. Egea, L., Egea, J., Garcia, J.E. and Berenguer, T. (1989) A comparative trial of clingstone peach cultivars. ITEA Produccion Vegetal 20, 35–43. Elkins, E.R. (1979) Nutrient content of raw and canned green beans, peaches, and sweet potatoes. Food Technology 33, 66–70. Etienne, C., Rothan, C., Moing, A., Plomion, C., Bodenes, C., Dumas, L.S., Cosson, P., Pronier, V., Monet, R. and Dirlewanger, E. (2002) Candidate genes and QTLs for sugar and organic acid content in peach (Prunus persica (L.) Batsch). Theoretical & Applied Genetics 105, 145–159. Fideghelli, C. (1987) Recent fruit cultivars from Fruit Culture Institute, Rome. Genetica Agraria 41, 201–213. Fideghelli, C., Della Strada, G., Quarta, R. and Rosati, P. (1979) Genetic semi-dwarf peach selections. In: Proceedings of Eucarpia Fruit Section Symposium, Tree Fruit Breeding. INRA, Angers, France, pp. 3–7. Gonzalez, A.R., Mauromoustakos, A., Prokakis, G. and Aselage, J. (1992) Sugars and acidity of processing peaches in Arkansas. Arkansas Farm Research 41, 11–12. Gradziel, T.M. (1994) Changes in susceptibility to brown rot with ripening in three clingstone peach genotypes. Journal of the American Society for Horticultural Science 119, 101–105. Gradziel, T.M. (2002) Almond species as a source of new genes for peach improvement. Acta Horticulturae 592, 81–88. Gradziel, T.M. and Beres, W. (1993) Semidwarf growth habit in clingstone peach with desirable tree and fruit qualities. HortScience 28, 1045–1047. Gradziel, T.M. and Wang, D. (1993) Evaluation of brown rot resistance and its relation to enzymatic browning in clingstone peach germplasm. Journal of the American Society for Horticultural Science 118, 675–679. Gradziel, T.M., Beres, W., Doyle, J. and Weeks, C. (1993a) ‘Rizzi’: a processing clingstone peach with extended postharvest storage potential. HortScience 28, 230. Gradziel, T.M., Beres, W. and Pelletreau, K. (1993b) Inbreeding in California canning clingstone peach cultivars. Fruit Varieties Journal 47, 160–168. Grossman, Y.L. and DeJong, T.M. (1998) Training and pruning system effects on vegetative growth potential, light interception, and cropping efficiency in peach trees. Journal of the American Society for Horticultural Science 123, 1058–1064. Haji, T., Yaegaki, H. and Yamaguchi, M. (2003) Softening in stony hard peach by ethylene and induction of endogenous ethylene by 1-aminocyclopropane-1-carboxylic acid (ACC). Journal of the Japanese Society of Horticultural Science 72, 212–217. Hansche, P.E. and Boynton, B. (1986a) Heritability of juvenility in peach. HortScience 21, 1195–1197.

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Hansche, P.E. and Boynton, B. (1986b) Heritability of enzymatic browning in peaches. HortScience 21, 1197– 1198. Hansche, P.E., Hesse, C.O. and Beres, V. (1972) Estimate of genetic and environmental effects on several traits in peach. Journal of American Society for Horticultural Science 97, 9–12. Kader, A.A. (1997) A summary of CA requirements and recommendations for fruits other than apples and pears. In: Proceedings of the Seventh International Controlled Atmosphere Research Conference (CA 1997). Vol. 3. Fruits other than Apples and Pears. UC Davis Press, Davis, California, pp. 217–221. Kader, A.A., Heintz, C.M. and Chordas, A. (1982) Postharvest quality of fresh and canned clingstone peaches as influenced by genotypes and maturity at harvest. Journal of the American Society for Horticultural Science 107, 947–951. Layne, R.E.C. (1997) Peach and nectarine breeding in Canada: 1911 to 1995. Fruit Varieties Journal 51, 218–228 Lentza, R.C. (1995) Residues of iprodione in fresh and canned peaches after pre- and postharvest treatment. Journal of Agricultural and Food Chemistry 43, 1357–1360. Lentza, R.C. and Chitzanidis, A. (1995) Residues of benomyl on and in fresh and canned peaches following treatments to control storage decay. Annales de l’Institut Phytopathologique Benaki 2, 121–130. Lentza, R.C. and Chitzanidis, A. (1996) Residues of dicloran in clingstone peaches after pre- and postharvest application. Bulletin of Environmental Contamination and Toxicology 56, 231–239. Leonard, S.J., Heil, J.R., Carroad, P.A., Merson, R.L. and Wolcott, T.K. (1983) High vacuum flame sterilized fruits storage study on sliced clingstone peaches, sliced Bartlett pears and diced fruit. Journal of Food Science 48, 1484–1491. Lopez-Rivares, E.P. and Suarez-Garcia, M.P. (1994) Agronomic performance of 19 clingstone peach cultivars in the Middle Valley of Guadalquivir. ITEA Produccion Vegetal 90, 6–17. Lu, G.L., Su, J.Y., Chen, Z.F., Wang, J.W. and Li, J. (1995) A promising, canning, white-fleshed peach variety Yubai. Journal of Fruit Science 12, 51–53. Martínez-Gómez, P., Arulsekar, S., Potter, D. and Gradziel, T.M. (2003a) An extended interspecific gene pool available to peach and almond breeding as characterized using simple sequence repeat (SSR) markers. Euphytica 131, 313–322. Martínez-Gómez, P., Arulsekar, S., Potter, D. and Gradziel, T.M. (2003b). Relationships among peach, almond and related species as detected by SSR markers. Journal of American Society for Horticultural Science 128, 667–671. Massonié, G., Maison, P., Monet, R. and Grasselly, G. (1982) Resistance au puceron vert du pêcher Myzus persicae Sulzer (Homoptera aphididae) chez Prunus persicae (L.) Batsch et d’autres espèces de Prunus. Agronomie 2, 63–70. Mishich, P., Todorovich, R., Zec, G., Misic, P. and Todorovic, R. (1998) Breeding peach cultivars for fresh use and canning. Rasteniev dni Nauki 35, 575–577. Monastra, F., Proto, D., Fideghelli, C., Grassi, G., Della Strada, G., Magliano, V. and Pennone, F. (1984) Cultivars for processing: agronomic and technological data sheets. Clingstone peaches. L’Informatore Agrario 40, 51–86. Monet, R. and Massonié, G. (1994) Déterminisme génétique de la résistance au puceron vert (Myzus persicae) chez le pêcher. Résultats complémentaires. Agronomie 2, 177–182. Moore, J.N. (1985) Four new fruit cultivars for the South. HortScience 20, 651. Nakasu, B., Bassols, M. and Feliciano, A. (1981) Temperate fruit breeding in Brazil. Fruit Varieties Journal 35, 114–122. O’Brien, M., Fridley, R.B. and Claypool, L.L. (1978) Food losses in harvest and handling systems for fruits and vegetables. Transactions of the ASAE 21, 386–390. Okie, W.R. (1998) Handbook of Peach and Nectarine Varieties. US Department of Agriculture Agricultural Handbook No. 714. US Government Printing Office, Washington, DC. Pascal, T., Kervella, J., Pfeiffer, F.G., Sauge, M.H. and Esmenjaud, D. (1997) Evaluation of the interspecific progeny Prunus persica cv. Summergrand × Prunus davidiana for disease resistance and some agronomic features. Acta Horticulturae 465, 185–191. Paunovic, S.A., Paunovic, A.S. and Fideghelli, C. (1996) Investigation of peach germplasm (Prunus persica sp. vulgaris = vineyard peach) in situ in Yugoslavia. Acta Horticulturae 374, 201–207. Pressey, R. and Avants, J.K. (1978) Difference in polygalacturonase composition of clingstone and freestone peaches. Journal of Food Science 43, 1415–1417. Raseira, M.C.B., Nakasu, B.H., Fortes, J. and Martins, O.M. (1998) ‘Leonense’, a dual purpose peach cultivar, adapted to southern Brazil. Fruit Varieties Journal 52, 89–91.

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Ray, L. and Morris, J.R. (1974) Post-harvest behavior of once-over harvested peaches. Arkansas Farm Research 23, 2. Robertson, J.A., Meredith, F.I., Lyon, B.G., Chapman, G.W. and Sherman, W.B. (1992) Ripening and cold storage changes in the quality characteristics of nonmelting clingstone peaches (FLA 9-20C). Journal of Food Science 57, 462–465. Rotaru, G. (1994) Comparative anatomy of the pericarp in the fruit of plum, apricot and peach. Buletinul Academiei de Stiinte a Republicii Moldova. Stiinte Biologice si Chimice 3, 11–18. Scorza, R. and Lightner, G.W. (1989) The pillar peach tree and growth habit, analysis of compact × pillar progeny. Journal of American Society for Horticultural Science 114, 33–38. Scorza, R. and Sherman, W.B. (1996) Peaches. In: Janick, J. and Moore, J.N. (eds) Fruit Breeding. Vol. 1. Tree and Tropical Fruits. Wiley, New York, pp. 325–440. Sistrunk, W.A., Rom, R.C., Moore, J.N., Junek, J. and Brown, S.A. (1979) Quality parameters for evaluating clingstone peach selections. Arkansas Farm Research 28, 2. Souty, M. (1972) Vitamin C in peaches for canning. Qualitas Plantarum et Materiae Vegetabiles 21, 223–228. Todorovic, R.R., Misic, P.D., Zec, G.N. and Monet, R. (1998) Twenty five years of peach breeding in the research institute INI ‘PKB Agroekonomik’, Beograd. Acta Horticulturae 465, 137–140. Tourjee, K.R., Barrett, D.M., Romero, M.V. and Gradziel, T.M. (1998) Measuring flesh color variability among processing clingstone peach genotypes differing in carotenoid composition. Journal of the American Society for Horticultural Science 123, 433–437. USDA (2004) USDA – National Agricultural Statistics Service, Noncitrus Fruits and Nuts. http://ffas.usda.gov/ htp/Hort_Circular/2006/01-6/canned%20peach%20feature%20Nov%202005.pdf (accessed November 2004). Van Der Heyden, C.R., Holford, P. and Richards, G.D. (1997) A new source of peach germplasm containing semi-freestone nonmelting flesh types. HortScience 32, 288–289. Wang, T., Gonzalez, A.R., Gbur, E.E. and Aselage, J.M. (1993) Organic acid changes during ripening of processing peaches. Journal of Food Science 58, 631–632. Wilson, P.W. and Boudreaux, J.E. (1986) Developing a dual purpose peach in Louisiana. Fruit Varieties Journal 40, 93–96. Zhang, G.R., Zong, X.P., Shen, Y.S., Wang, Z.Q., Zuo, Q.Y. and Zhu, G.R. (1996) Zhenghuang 5, a new late canning peach cultivar. Journal of Fruit Science 13, 130–131. Zocca, A. (1975) Further trials on the mechanical harvesting of clingstone peaches. In: Atti Incontro Frutticolo su Raccolta Meccanica e Sistemi di Allevamento per la Frutticoltura da Industria. Società Orticola Italiana, Bologna, Italy, pp. 53–56. Zocca, A. and Fridley, R.B. (1977) Mechanical harvesting of clingstone peaches. Journal of Agricultural Engineering Research 22, 247–257.

8

Rootstock Development

Gregory L. Reighard1 and Filiberto Loreti2 1Department

of Horticulture, Clemson University, Clemson, South Carolina, USA of Fruit Science and Crop Protection, University of Pisa, Pisa, Italy

2Department

8.1 Introduction 8.2 Selection Criteria for Peach Rootstocks Graft compatibility Ease of sexual or asexual propagation Resistance to abiotic stresses Resistance to soil pests and diseases Increased yield and fruit quality Tree size control and anchorage 8.3 Characteristics of Peach Rootstocks Section Euamygdalus species cultivars Sections Euprunus and Microcerasus species cultivars Interspeciﬁc hybrid cultivars 8.4 Peach Rootstock Breeding Programmes Research institutions and objectives Rootstocks in development 8.5 Outlook

8.1 Introduction New rootstock cultivars possessing diverse horticultural traits for stone fruit crops including peach (Prunus persica (L) Batsch) are being developed by both public and private programmes for testing and release to fruit growers worldwide (Renaud et al., 1988; Felipe et al., 1997; Loreti, 1997; Loreti and Massai, 2002a; Reighard, 2002; Moreno, 2004). Rootstocks provide a cultural tool for peach growers to increase productivity and improve efﬁciency via better tree survival, controlled tree vigour

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and increased fruit size, yield and quality. Thus, the choice of rootstock becomes as economically important as the scion cultivar whenever peach trees must be grown on soils having high bulk density, coarse texture (sand), parasitic nematodes, root rot fungal pathogens, high pH or other orchard replant problems. If one or more of these conditions are present, peach tree survival and growth can be improved signiﬁcantly by selecting the appropriate rootstock for each soil or site situation. Historically, peach cultivars that were grown in Australia, Brazil, Canada, Chile,

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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China, France, Greece, Italy, Mexico, New Zealand, South Africa, Spain and the USA had been grafted to peach seedling rootstocks that inherently lacked traits such as scion dwarﬁng and tolerance to soil waterlogging, drought, calcareous soils, ectoparasitic nematodes, crown gall (Agrobacterium tumefaciens), soil-borne fungal pathogens and orchard replant problems (Layne, 1987). However, as production costs increased and chemical control practices became cost-prohibitive or unavailable, new interspeciﬁc Prunus L. rootstocks were developed to overcome these biotic and abiotic soil obstacles, which had been simply circumvented in years past by orchard relocation, tile drainage or chemical fumigation (Loreti, 1984, 1997). This chapter discusses traditional and new rootstock cultivars for peach and their potential for solving some of the speciﬁc soil and site problems that peach growers are experiencing worldwide. In addition, selection criteria, horticultural characteristics and breeding programmes for these rootstocks are discussed.

8.2 Selection Criteria for Peach Rootstocks Graft compatibility Peach is partially to completely graft-compatible with several species within its taxonomic Section Euamygdalus Schneid, which includes P. persica, Prunus dulcis (Mill.) D.A. Webb and Prunus davidiana (Carr.) Franch. Peach and especially nectarine are much less graft-compatible with other Prunus spp. from Sections Euprunus, Prunocerasus and Microcerasus. Breeding new rootstocks for peach from intra- and interspeciﬁc crosses requires extensive nursery- and ﬁeld-testing of numerous budded peach and nectarine scion cultivars to ascertain good graft compatibility for tree health and survival under normal orchard conditions (Yamaguchi et al., 2004; Zarrouk et al., 2006). Thus, breeders must understand the types and potential causes of incompatibility between different rootstock and scion genotypes. Peach is compatible with itself and peach × almond hybrids. Compatibility is

much less with almond (P. dulcis), but some almond genotypes have been selected for compatibility with peach for use as peach rootstocks in Hungary, Moldova, Egypt and Algeria (J. Anderson, Utah, 2005, personal communication; F. Loreti, unpublished results; Z. Szabo, Hungary, 2005, personal communication). Peach is also compatible with P. davidiana and its hybrids with peach. Other peach-like species such as Prunus mira Koehne, Prunus ferganensis (Kostov & Rjabov) Kovalev & Kostov and Prunus kansuensis Rehder have been successfully used as rootstocks for peach in China (Wang et al., 2002). Peach has been budded with many species from Section Euprunus. Compatibility has been good with some rootstock selections and cultivars from Prunus insititia L. (damson plums), Prunus spinosa L. (sloe plums), Prunus domestica L. (European plums), Prunus salicina Lindl. (Japanese plums) and Prunus cerasifera Ehrh. (Myrobalan or cherry plums). Myrobalan plums are often more compatible when they are ﬁrst hybridized with other plums. Salesses and Bonnet (1992) reported the existence of two types of genetic incompatibility of the Myrobalan and sloe plums with peach. In the case of ‘Damas GF 1869’ (a pentaploid rootstock, probably P. domestica × P. spinosa), at least two dominant alleles are responsible for the incompatibility of peach cultivars grafted on this rootstock (Salesses and Alkai, 1985). However, this is not the case for Myrobalan, which may have another type of genetic control. Incompatibility between Myrobalan and peach appeared to be a translocated type, which is evident by abnormal scion behaviour such as leaf yellowing and reduction in vigour. Translocated incompatibility appeared to result from impaired phloem transport from the shoots to the roots due to the degeneration and/or decrease in the number of sieve tubes at the graft union, which reduced carbohydrate transport to the roots and eventually starved them after 1 or 2 years (Moing and Gaudillere, 1992; Moreno et al., 1994a). McClintock (1948) also observed this for peach cultivars budded to ‘Marianna 2624’, a P. cerasifera hybrid. However, incompatibility between sloes and peach appeared to be localized by having weak graft unions characterized by necrosis and absence of

Rootstock Development

ligniﬁed tissues in the graft union (Salesses et al., 1988). Peach has been propagated on several species from Sections Prunocerasus and Microcerasus with limited success. The best examples are some commercially available selections of Prunus americana Marshall (e.g. Bailey Nurseries, Newport, Minnesota) and Prunus pumila L. (‘Pumiselect®’) that appear to be somewhat to very compatible with many peach cultivars. Some other species of these sections that have been tried as peach rootstocks or interstocks are Prunus subcordata Benth. (Roberts and Westwood, 1981), Prunus angustifolia Marshall and Prunus hortulana L.H. Bailey (Johnson, 1938; Graham, 2002), Prunus besseyi L.H. Bailey (Funt and Goulart, 1981; Indreias et al., 2004), Prunus japonica Thunb. and Prunus tomentosa Thunb. (Funt and Goulart, 1981; Wang et al., 2002). All of these species tend to dwarf peach scion cultivars.

Ease of sexual or asexual propagation All rootstocks developed for commercial release should be nursery- or micropropagationfriendly to allow for adequate production of trees to sell at a market-driven price. The past use of peach seedling rootstocks for peach by the nursery industry was partially driven by the availability of inexpensive seed from cannery cultivars, the ease of seedling propagation and budding, and the lack of proven substitute cultivars, both seedling and clonal. The last half of the 20th century brought an increase in rootstock breeding and selection, resulting in nematode-resistant peach seedling rootstocks and Prunus L. hybrids resistant to nematodes in addition to tolerance to different soil textures and chemistries (Pinochet et al., 1999, 2002). New clonal hybrid rootstocks necessitated technological innovations before propagators could generate sufﬁcient liners for tree fruit nurseries. Propagation methods for hardwood and softwood cuttings were reﬁned and then replaced by tissue culture and micropropagation systems to mass-produce thousands of select single genotypes of P. insititia and P. domestica as well as hybrid Prunus L. rootstocks

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for peach (Zuccherelli, 1979; Martinelli, 1985; Fiorino and Loreti, 1987; Andreu and Marin, 2004). One of the ﬁrst examples was ‘GF 677’, which progressed from propagation by rooting softwood cuttings under mist to tissue culture of explants for the micropropagation of millions of transplants annually (Loreti and Morini, 1983). Therefore, fruit tree rootstocks should be screened ﬁrst for ease of propagation by either seed or asexual propagation, before they are released to commercial fruit nurseries and the growers.

Resistance to abiotic stresses Calcareous and high bulk density soils Peach seedling rootstocks are not adapted to poorly drained, heavy clay soil or to calcareous soil where pH is above 7.5. When peach cultivars budded to peach rootstocks are planted in high pH or alkaline soil, trees become weak, unproductive and iron-deﬁcient. A number of new hybrid rootstocks developed in Europe were selected for these calcareous conditions. These include: (i) the French rootstocks ‘Jaspi®’ ((P. domestica × P. salicina) × P. spinosa L.), ‘Julior®’ (P. insititia × P. domestica), ‘GF 677’ (a natural peach–almond hybrid) and ‘Cadaman’ (P. persica × P. davidiana); (ii) the Italian rootstocks ‘Barrier 1’ (P. persica × P. davidiana), ‘Mr.S. 2/5’ (P. cerasifera × P. spinosa?), ‘Mr.S. 2/8’ (P. cerasifera) and ‘Sirio’ (P. persica × P. dulcis); and (iii) the Spanish rootstocks ‘Adesoto 101’ (P. insititia), ‘Montizo’ (P. insititia) and the peach–almond hybrids ‘Adafuel’, ‘Adarcias’, ‘Garnem’, ‘Felinem’ and ‘Monegro’ (Cambra, 1990; Moreno et al., 1994b, 1995a; Felipe et al., 1997; Loreti, 1997). Compatibility with peach is fair to excellent with these rootstocks except for ‘Jaspi’ (Loreti and Massai, 2002a), and high pH problems are lessened when these rootstocks are used instead of peach seedlings for many peach and some nectarine cultivars. Waterlogging Peach grown on peach seedling rootstocks and planted in poorly drained or seasonally waterlogged soils eventually declines or dies.

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Many European Prunus L. rootstocks developed in the past 20 years are listed as tolerant of waterlogging. Rootstocks labelled as tolerant to waterlogged soils and ‘compatible’ with peach include ‘Jaspi®’, ‘Julior®’, ‘Penta’ (P. domestica), ‘Tetra’ (P. domestica), ‘Mr.S. 2/5’, ‘Barrier 1’, ‘Adesoto 101’, ‘Montizo’ and ‘Krymsk® 1’ (P. tomentosa × P. cerasifera). In South Africa, ‘SAPO 778’, which is ‘Siberian C’ peach crossed with a plum–almond hybrid by Zaiger Genetics, Inc. (Modesto, California), is also moderately tolerant of wet soils (Lötze, 1997). Many of these rootstocks were developed in Mediterranean climates that receive their rainfall in the winter. However, in other peach-growing areas of the world such as eastern North America, waterlogging can occur during the growing season. Therefore, in regions outside where these rootstocks were developed, it is uncertain whether these rootstocks are tolerant of wet soil conditions in both the dormant season and the growing season. Only future testing will answer these questions.

86’ (P. cerasifera × P. persica), may offer more cold hardiness than the Canadian peach rootstocks since they were developed from Prunus species from colder regions that are marginal for peach production due to very cold winters and spring freezes. Another option may be selected clones of P. americana, which is coldhardy. Currently, open-pollinated seedlings from P. americana genotypes selected for compatibility with peach are being used as peach rootstocks by several mail order nurseries for the fruit hobbyist market in the northern USA. Cool soil temperatures up to 60 days after peach bloom in low-chill areas of Australia are thought to be responsible for ‘spring shock syndrome’, which signiﬁcantly reduces yields and is inﬂuenced by rootstock (Malcolm et al., 1999). Low-chill adapted rootstocks such as ‘Okinawa’ and ‘Flordaguard’ as well as other cultivars and selections are being tested in low-chill production areas of Australia to ameliorate this syndrome.

Resistance to soil pests and diseases Winter temperatures Winter cold hardiness of peach root systems varies considerably among rootstock cultivars. The absence of snow cover and some orchard ﬂoor management practices can increase the susceptibility of peach seedling rootstocks to cold injury. Rootstocks that are inherently cold-hardy or de-acclimatize at a slower rate after warm temperatures are necessary to grow peaches in cold regions. Many of the available cold-tolerant peach rootstocks originated from a now defunct Canadian breeding programme (Layne, 1987) and more recently from the Vavilov Research Institute of Plant Industry (VRI) near Krymsk, Russia. Releases of the cold-hardy peach seedling rootstocks ‘Siberian C’, ‘Harrow Blood’, ‘Tzim Pee Tao’ and ‘Chui Lum Tao’ have improved cold hardiness of peach scion cultivars (Weaver, 1967a,b; Layne and Jui, 1994) but have had some other deﬁciencies such as susceptibility to nematodes or fungal root rots. Therefore, their commercial utility is limited. The recent introduction of three Russian rootstocks, ‘Krymsk® 1’, ‘Krymsk® 2’ (P. incana (Pall.) Batsch × P. tomentosa) and ‘Krymsk®

Parasitic nematodes Many nematode species successfully parasitize peach roots and reduce peach tree growth and productivity. Four kinds of nematodes are recognized as harmful to peach tree roots (Nyczepir and Becker, 1998). They are the ring (Mesocriconema xenoplax (Raski) Loof & de Grisse), root-knot (Meloidogyne incognita (Kofoid & White) Chitwood, Meloidogyne javanica (Treub) Chitwood, Meloidogyne arenaria (Neal) Chitwood, Meloidogyne floridensis Handoo et al. and Meloidogyne hapla Chitwood), root-lesion (Pratylenchus vulnus Allen & Jensen and Pratylenchus penetrans (Cobb) Chitwood & Oteifa) and dagger (Xiphinema americanum Cobb) nematodes. Rootstocks often are categorized as immune, resistant, tolerant or susceptible to nematodes. Tolerant rootstocks are fair to good hosts for a speciﬁc nematode, but nematode reproduction and feeding does not signiﬁcantly alter the rootstock’s ability to supply the scion’s mineral, hormonal and water requirements to survive, grow and bear fruit. Rootstocks susceptible to a speciﬁc nematode are good hosts for

Rootstock Development

nematode reproduction and are negatively affected by nematode feeding in terms of tree survival, growth and fruiting (Nyczepir and Becker, 1998). Ring nematode, an ectoparasitic nematode, has been linked directly to both the onset of peach tree short life syndrome (PTSL) in the south-eastern USA (Zehr et al., 1976; Nyczepir et al., 1983) and the bacterial canker complex in California (Davis and English, 1969; McKenry, 1989). Many different peach rootstocks including the new hybrid releases have been tested for reaction to ring nematode. However, most were good hosts for ring nematode (Westcott et al., 1994) and were susceptible to PTSL (Okie et al., 1994a). Only one rootstock, the peach seedling ‘Guardian®’, has had acceptable survival in ﬁeld tests in South Carolina and Georgia (Okie et al., 1994b; Beckman et al., 1997a; Reighard et al., 1997) even though it is a good host for ring nematode (Nyczepir et al., 1992). In California, ‘Lovell’ peach seedlings that are sold as clones from Duarte Nursery (Hughson, California) have shown a level of ring protection that is similar or slightly superior to ‘Guardian®’, although ‘Guardian®’ provides superior rootknot nematode protection over ‘Lovell’ (M. McHenry, California, 2006, personal communication). However, ﬁnding resistance to ring nematode in a Prunus L. rootstock that is also compatible with peach has been unsuccessful thus far. Root-knot nematodes signiﬁcantly reduce peach tree growth. There are ﬁve known species of root-knot nematode (M. arenaria, M. incognita, M. javanica, M. floridensis, M. hapla) as well as a number of races within each species that feed on peach. M. incognita and M. javanica are the most common on peach in the USA. Many peach rootstocks were introduced to the USA in the 20th century because of their root-knot nematode resistance (Day, 1953). These included ‘Shalil’, ‘Yunnan’ and ‘Okinawa’. These rootstocks either were not resistant to M. javanica or had other problems and were eventually replaced via selective breeding, which led to the root-knot resistant rootstocks ‘Nemaguard’, ‘Nemared’, ‘Flordaguard’ and ‘Guardian®’ (Brooks and Olmo, 1961; Ramming and Tanner, 1983; Sherman et al., 1991; Okie et al., 1994b).

197

During this same time, in other peachgrowing countries, breeders also selected for root-knot resistance. Plum rootstocks tended to be immune to Meloidogyne spp., while other rootstocks tended to have different levels of resistance. Root-knot resistant rootstocks released include the Italian rootstocks ‘Barrier 1’, ‘Penta’ and ‘Tetra’; the Spanish rootstocks ‘Adesoto 101’, ‘Garnem’, ‘Felinem’ and ‘Monegro’; and the French rootstocks ‘Myran®’ (a cross of ‘Belsiana’ (P. cerasifera × P. salicina) and ‘Yunnan’ peach) and ‘Ishtara®’ (a cross of ‘Belsiana’ and a (P. persica × P. cerasifera) hybrid) (Fernández et al., 1994; Moreno et al., 1995a; Esmenjaud et al., 1997; Felipe et al., 1997, Nicotra and Moser, 1997; Gomez-Aparisi et al., 2001). Root-lesion (P. vulnus and P. penetrans) and dagger (X. americanum) nematodes are two other ectoparasitic nematodes that feed on and damage peach roots. Root-lesion nematodes can reduce tree growth and fruit production if not controlled. P. vulnus is a problem in the southern USA and California, while P. penetrans occurs in northern areas. Peach rootstocks listed as tolerant to P. vulnus in Europe are ‘Rubira®’, ‘GF 305’, ‘Penta’, ‘Tetra’ and ‘P.S.B2’ (P. persica) (Alcañiz et al., 1996). Some new rootstocks showing P. vulnus tolerance in greenhouse studies in Spain are ‘Krymsk® 86’ and to a lesser extent ‘Krymsk® 1’ and ‘Krymsk® 2’ (Pinochet et al., 2000). These same three rootstocks in California have shown some resistance to root-lesion nematode in the greenhouse and/or 2-year-old ﬁeld studies, but they have been susceptible to root-knot nematodes (M. McKenry, California, 2006, personal communication). In Canada, testing of ‘GF 305’ by McFadden-Smith et al. (1998) showed that this rootstock was quite susceptible to P. penetrans and that the Canadian peach seedling rootstock ‘Chui Lum Tao’ was more tolerant in greenhouse studies. In addition, ‘Bailey’, ‘Higama®’ and ‘Guardian®’ were less susceptible to P. penetrans than many of the European rootstocks tested, while in California the level of susceptibility in ‘Guardian®’ to P. vulnus was similar to ‘Nemaguard’ (M. McKenry, California, 2006, personal communication). However, multiple nematode species and races create a signiﬁcant obstacle to ﬁnding a broadly adapted, nematoderesistant rootstock.

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Dagger nematodes damage peach trees by serving as the vector for Tomato ringspot virus, which causes stem pitting. Since many weed species such as dandelions (Taraxacum officinale Weber) are hosts for this virus, dagger nematode resistance or virus tolerance in rootstocks is probably the best way to prevent infection and/or tree injury. Dagger nematode species are vectors for other nepoviruses throughout the world. Peach seedling rootstocks are not resistant to dagger nematodes, and therefore, non-P. persica rootstocks need to be evaluated for resistance to the nematode or the virus. Some cherry plum P. cerasifera genotypes are less sensitive to Tomato ringspot virus (Hoy and Mircetich, 1984; Halbrendt et al., 1994). Therefore, rootstocks such as the clonal rootstocks ‘Mr.S. 2/5’ and ‘Mr.S. 2/8’ from Italy, ‘Krymsk® 1’ from Russia and ‘Adara’ (P. cerasifera) from Spain may offer some resistance, but they still remain untested for these viruses, and ‘Adara’ has limited compatibility with peach (Moreno et al., 1995b). Pathogenic soil fungi On ﬁne-textured, high bulk density or poorly drained soils, peach seedling rootstocks are at risk of becoming infected with Phytophthora spp. de Bary, which causes crown rot (Elena and Tsipouridis, 2000). Similarly, all rootstocks of P. persica are susceptible to the oak root rot fungus (Armillaria mellea (Vahl:Fr.) P. Kumm. and Armillaria tabescens (Scop.) Dennis et al.) regardless of soil texture or drainage. Both fungi are difﬁcult to control or eradicate; therefore, genetic resistance to them is highly desirable in rootstocks. Many hybrid rootstocks released by European breeders are listed as tolerant to replant sites and soil diseases. However, speciﬁc soil diseases usually are not identiﬁed. ‘Ishtara®’ and ‘Myran®’ were reported by Renaud et al. (1988) to be resistant or tolerant to oak root rot (A. mellea) in France, but Beckman and Pusey (2001) in the south-eastern USA found these rootstocks were susceptible to A. tabescens. This suggests that after these exported rootstocks emerge from quarantine facilities in regions outside Europe, they will still require additional ﬁeld-testing to evaluate traits such as ‘disease resistance’ before

they are commercially produced in large numbers for local growers. Increased yield and fruit quality Numerous studies have found that some peach rootstocks increase yield, fruit size and fruit quality of commercial peach cultivars (Layne, 1994; Moreno et al., 1994b; Guidoni et al., 1998; Loreti and Massai, 2002b; Massai and Loreti, 2004; Reighard et al., 2004). Under conventional training systems, yield increases reported for selected rootstocks have been primarily due either to increased tree vigour and precocity or to increased tree survival and longevity. Fruit quality improvements such as size, skin colour and soluble solids content (SSC) have largely been observed from peach cultivars on plum and interspeciﬁc hybrid rootstocks (De Salvador et al., 2002; G. Reighard, unpublished results). On typical peach orchard sites (i.e. welldrained soils), peach seedling rootstocks have performed as well as any peach-compatible rootstocks composed of other Prunus L. species or interspeciﬁc hybrids. Long-term testing (i.e. NC-140 project) of primarily peach seedling rootstocks throughout North America (Perry et al., 2000; Reighard et al., 2004) showed that rootstocks that induced the highest scion productivity were those that induced the best scion growth or survival at individual locations. In a former NC-140 test, ‘Redhaven’ on all ﬁve of the peach seedling rootstocks plus ‘GF 677’, a peach–almond hybrid, grew the largest and had the highest yields compared with several interspeciﬁc plum hybrid rootstocks (Perry et al., 2000). Although ‘GF 677’ was the most vigorous rootstock, it also had the lowest yield efﬁciency compared with the peach seedling rootstocks. In another 20-location NC-140 test, ‘Redhaven’ on peach seedling rootstocks ‘Lovell’, ‘GF 305’, ‘Montclar®’ and ‘Guardian®’ had tree heights and crown widths that were signiﬁcantly greater than on 15 other rootstocks (Reighard et al., 2004). ‘Redhaven’ cumulative fruit yields were also highest on these four rootstocks. Fruit production appeared to be directly affected by the number of bearing shoots supported by the canopy.

Rootstock Development

However, cumulative yield efﬁciency (kg/cm2 TCSA) was highest on the lower-yielding but slightly less vigorous peach rootstocks ‘Bailey’ and ‘Tennessee Natural 281-1’. On problem orchard sites, rootstocks that impart a survival advantage to peach cultivars generally will out-yield precocious and vigorous rootstocks that do not survive or grow well due to negative biotic or abiotic factors. Examples of these problems are calcareous soils, ﬁne-textured soils, drought, pathogenic fungi, bacteria and nematodes, cold climates and replant sites. In many of these situations, peach seedling rootstocks are often not the best option. Thus, testing and selection of appropriate rootstocks for peach growth and survival are necessary for each production area. Data from the NC-140 peach trials suggested that rootstock cultivar productivity, in relation to all rootstocks tested, tended to be consistent across time. Therefore, since relative rankings of the rootstock cultivar yields changed little during the prime bearing years, the yield potential for a rootstock compared with other rootstocks at each test location could be determined as soon as the trees reached full production at approximately 4 or 5 years. Fruit weight can sometimes be signiﬁcantly inﬂuenced by rootstock, but cultural (pruning and thinning) and environmental factors (water and sunlight) often obscure or negate these rootstock-imparted differences, especially on peach seedling rootstocks. Hybrid rootstocks such as ‘Ishtara®’ (semi-dwarf) and ‘Myran®’ (vigorous) have typically produced larger and smaller fruit, respectively, in the NC-140 trials in the USA (G. Reighard, personal observation). However, these differences have been very small (<10 g). Other rootstock trials ongoing and in progress have reported increased fruit size with semi-dwarf and dwarﬁng hybrid rootstocks (R.S. Johnson, California, 2006, personal communication). Dwarf-type rootstocks require high-density planting systems; and therefore different parameters (i.e. spacing, canopy volume) are used to measure yield and production efﬁciency. Besides fruit size, data documenting other effects induced by the rootstock on fruit quality such as SSC and skin colour are limited (Albás et al., 2004). Smaller canopy size due to size-controlling rootstocks may increase

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sunlight penetration and thus indirectly improve fruit skin coloration and SSC. Dwarfing rootstocks such as ‘Krymsk® 1’, ‘Krymsk® 2’ and ‘Mr.S. 2/5’ have increased fruit SSC in some peach cultivars in South Carolina (G. Reighard, unpublished results). In Italy, ‘Ishtara®’, ‘Mr.S. 2/5’ and ‘Barrier 1’ increased fruit size and SSC (De Salvador and Monastra, 1996; Remorini et al., 2005). Tree size control and anchorage Peach seedling rootstocks including brachytic dwarfs rarely reduce scion vigour by more than 10–15%. Until the past 10–20 years, size control in peaches through the use of rootstocks of other Prunus species has not been achieved satisfactorily owing to incompatibility or poor tree vigour. Without graft-compatible, size-controlling rootstocks such as in apple, increases in peach orchard productivity via intensive training systems are probably unattainable. Fortunately, new dwarﬁng rootstocks for peaches are being selected for reduced vigour, graft compatibility and sustained fruit production without reductions in fruit size and quality. European rootstocks considered mildly dwarﬁng (approximate percentage of peach standard) include ‘Ishtara®’ (70%), ‘Julior®’ (70%), ‘Rubira®’ (90%), ‘Tetra’ (90%), ‘Mr.S. 2/5’ (90%), ‘Adara’ (80%), ‘Adarcias’ (70%) and the Italian peach seedlings ‘P.S.A5’ (80%) and ‘P.S.B2’ (90%). Semi-dwarﬁng rootstocks are ‘Pumiselect®’ (60%), a P. pumila L. selection developed in Germany (Jacob, 1992), ‘Sirio’ (60%) (Loreti and Massai, 1998), ‘Adesoto 101’ (60–80%) and ‘Krymsk® 1’ (formerly ‘VVA-1’) (50%) and ‘Krymsk® 2’ (formerly ‘VSV-1’) (40%) (Devyatov, 1996). In addition, in California a new release ‘Controller 5’ (formerly ‘K-146-43’) for peach (DeJong et al., 2004a, 2005) is now in advanced testing and has reportedly maintained yield efﬁciency and fruit size despite signiﬁcant tree dwarﬁng. Other dwarﬁng rootstocks for peach include the use of P. japonica and P. tomentosa in Japan (Mizutani et al., 1985; Murase et al., 1986), although they may be too dwarﬁng, and new selections coming from the breeding programmes in Italy (e.g. ‘I.S.’ series, Pisa) and Spain (CSIC, Zaragoza). The degree of

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dwarﬁng of these rootstocks will vary with the climate, soil type and site history. Therefore, until there is extensive geographic testing, it is unknown how these rootstocks will perform as size-controlling rootstocks in other peach production areas.

8.3 Characteristics of Peach Rootstocks Several factors have recently prompted international research work to focus on the development of new rootstocks suitable for the needs of modern peach growing. These factors can be summarized as: (i) expansion of peach growing into non-optimal and lowchill areas; (ii) the need for rootstocks that can reduce canopy vigour and increase planting densities; (iii) the search for greater resistance to diseases and soil or environmental problems; and (iv) as alternatives to use of soil fumigants. Thus, the range of rootstocks now available for peach worldwide has increased dramatically over the last few years. Traditionally, three groups can be identiﬁed, based on their genetic origin. 1. Euamygdalus species cultivars (P. persica, Persica vulgaris). 2. Euprunus species cultivars (P. domestica, P. insititia, P. cerasifera). 3. Interspeciﬁc hybrid cultivars (from controlled or natural hybridization of a combination of Prunus species including P. persica, P. dulcis, P. domestica, P. cerasifera, P. insititia, P. davidiana, P. spinosa, P. salicina). Until the last decade or so, only a few rootstocks were commonly used in peach orchards. Among those recently developed, some have been found to perform well in some peachgrowing areas, while for other rootstocks the results are still inconclusive (Table 8.1). Below we summarize the most commonly known rootstocks and those offering more interesting prospects for the future. Section Euamygdalus species cultivars Open-pollinated peach seedlings are still the most widely used rootstock for peach worldwide. Nursery peach seed usually originates

from one of three sources: (i) local feral peach trees or naturalized populations; (ii) commercial processing or drying cultivars; or (iii) peach rootstock cultivars planted in virusindexed seed orchards. Naturalized or wildtype peaches continue to be used in many countries, where in some cases they represent the most frequently used rootstock for peach. Seeds from P. persica are still used in some countries of the Mediterranean basin, giving rise to what is called the ‘Slavic seedling’, which is often referred to as P. vulgaris P. Mill. This rootstock, originating from the Balkan peninsula, has small stones (pits) which produce a high yield of nursery seedlings. However, the problem with seeds from wild-type peaches is their genetic variability and lack of uniformity in the nursery and the orchard. In addition, these peach seedlings can have viral infection rates ranging between 5 and 10%. Overall, feral peach seedlings – and the ‘Slavic seedling’ in particular – can be considered good rootstocks, but their primary disadvantage compared with peach rootstock cultivars is the tendency to produce very heterogeneous plants, due to the fact that commercial nursery seeds are often derived from different genetic sources (Loreti, 1984). In the important peach-growing countries, peach seedling rootstocks are now almost exclusively cloned peach cultivars that are maintained in virus-indexed orchards. A survey recently conducted in these countries indicated that peach seedling rootstocks are still the most commonly used rootstocks for peach, especially those obtained from commercial cultivars (Loreti and Massai, 2006a). Some of the more commonly used peach rootstock cultivars are ‘Halford’, ‘Lovell’, ‘Bailey’, ‘Siberian C’, ‘Guardian®’, ‘Nemared’ and ‘Nemaguard’ in the USA and Canada; ‘Jerez’, ‘Jalacingo’ and ‘Tetela’ in Mexico; ‘Cuaresmillo’ in Argentina; ‘Chucho Picudo’ in Chile; ‘Aldrighi’ and ‘Capdeboscq’ in Brazil; ‘Elberta’ and ‘Golden Queen’ in Australia and New Zealand; ‘Ohatsu’ (‘Ohatsumomo’), ‘Tsukuba#1’ and ‘Tsukuba#4’ in Japan; ‘Baladi’ in Israel; ‘Mit Gharmr’ in Egypt; ‘Missour’ in Algeria; ‘Halge’ in Iran; ‘Kakamas’ in South Africa; ‘I.D. 20/Ag1’ in Greece; ‘De Balc’ in Romania; ‘B-VA-2’ and ‘Lesiberian’ in the Czech Republic; ‘CEPE’ and ‘C.2630’ in Hungary; and ‘Mandzurska’

Table 8.1.

Commercial peach rootstock cultivars and their reported horticultural characteristics. Nematode resistance Origin (country)b

Species codec

Vigour ratingd

‘GF 305’ ‘Montclar®’ ‘Rubira®’ ‘P.S.B2’ ‘Lovell’, ‘Halford’ ‘Nemaguard’ ‘Guardian®’ ‘Bailey’ ‘Siberian C’ ‘GF 677’ ‘Adafuel’ ‘Garnem’ ‘Felinem’ ‘Adarcias’ ‘Sirio’ ‘Castore’, ‘Polluce’ ‘Hansen 2168’, ‘Hansen 536’ ‘Nickels’ ‘Penta’ ‘Tetra’ ‘Mr.S. 2/5’ ‘Krymsk® 86’

France France France Italy USA USA USA USA Canada France Spain Spain Spain Spain Italy Italy USA

1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2

2 2 3 2 2 1 1 3 3 1 1 1 1 2 3 2 1

USA Italy Italy Italy Russia

2 3 3 4 5

1 1 2 3 2

Cold hardinesse

Mi/Mjf

Ppvg

Mxh

Tolerance to wet soilsi

Alkaline soil tolerance

No No No No No No No Yes Yes No No No No No No No No

3 3 3 1 3 1 1 3 3 3 3 1 1 3 3 ? 1

3 3 2 2 2 2 2 2 3 3 3 3 2 3 3 ? 2

3 3 2 ? 2 3 2 3 3 3 ? 3 ? ? ? ? 3

2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3

No Some Maybe No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes

No No No No Yes

1 1 1 1 3/1

1 2 3 3 1

3 2 3 3 ?

3 1 1 1 1

Yes Yes Yes Yes Yes

Rootstock Development

Rootstock cultivara

(Continued) 201

202

Table 8.1.

continued Nematode resistance Origin (country)b

Species codec

Vigour ratingd

‘Krymsk® 1’ ‘Krymsk® 2’ ‘Adesoto 101’ ‘Montizo’ ‘Julior®’ ‘Pumiselect®’ ‘Barrier 1’ ‘Cadaman®’ ‘Ishtara®’ ‘Myran®’ ‘Controller 5’ ‘Viking’

Russia Russia Spain Spain France Germany Italy France France France USA USA

6 7 8 8 9 10 11 11 12 12 13 14

3 4 3 3 3 3 1 2 3 1 4 1

Cold hardinesse Yes Yes No No No Yes No No No No No No

Mi/Mjf

Ppvg

Mxh

Tolerance to wet soilsi

3 3 1 1 1 1 1 1 1 1 3 1

2 2 3 3 3 3 2 3 3 ? 3 1

3 ? 3 3 3 2 3 3 3 3 3 2

1 2 1 1 1 3 1 1 2 1 3 1

Alkaline soil tolerance Yes Some Yes Yes Some No Yes Yes No No No Yes

aAdditional testing of compatibility with peach cultivars is advised for ‘Ishtara®’, ‘Krymsk® 1’ and ‘Krymsk® 2’. Excessive suckering may occur with ‘Adesoto 101’ and ‘Julior®’. bCountry of origin and/or initial testing. cSpecies type: 1, Prunus persica; 2, Prunus dulcis × P. persica; 3, Prunus domestica; 4, Prunus cerasifera; 5, P. cerasifera × P. persica; 6, Prunus tomentosa × P. cerasifera; 7, Prunus incana × P. tomentosa; 8, Prunus insititia; 9, P. insititia × P. domestica; 10, Prunus pumila; 11, P. persica × Prunus davidiana; 12, (P. cerasifera × Prunus salicina) × P. persica; 13, P. salicina × P. persica; 14, unknown interspecific cross. d1, vigour similar to ‘GF 677’ or ‘Nemaguard’; 2, vigour similar to ‘Lovell’; 3, vigour 5–25% less than ‘Lovell’; 4. vigour at least 30% less than ‘Lovell’. eRootstock is considered to have better cold hardiness than ‘Lovell’. fResistance to root-knot nematodes (Meloidogyne incognita, Meloidogyne javanica): 1, immune or resistant; 2, moderately resistant or some tolerance; 3, susceptible; ?, unknown. gResistance to root-lesion nematode (Pratylenchus penetrans or Pratylenchus vulnus): 1, immune or resistant; 2, moderately resistant or some tolerance; 3, susceptible; ?, unknown. hResistance to ring nematode (Mesocriconema xenoplax): 1, immune or resistant; 2, moderately resistant or some tolerance; 3, susceptible; ?, unknown. iTolerance of fine-textured soils when waterlogged: 1, good; 2, fair; 3, poor.

G.L. Reighard and F. Loreti

Rootstock cultivara

Rootstock Development

and ‘Rakoniewicha’ in Poland. The seedlings obtained from these cultivars are preferable because they are largely virus-free and more genetically uniform than those from feral or naturalized peach trees. Among peach seedling rootstocks, cultivars showing certain distinct bioagronomic characteristics and different degrees of susceptibility to biotic and abiotic stresses have been selected in recent decades. Some of these selections are now seldom used, such as ‘GF 305’, while others are gaining in popularity. For instance, the ‘P.S.’ series from the University of Pisa, namely ‘P.S.A5’, ‘P.S.A7’ and ‘P.S.B2’ (Loreti and Massai, 2002a), and the selections developed in France, such as ‘Montclar®’ and to a much lesser extent ‘Rubira®’ and ‘Higama®’, are being planted where peach seedling rootstocks grow well. Peach rootstocks in the USA have almost exclusively been and still are open-pollinated seedlings of P. persica. Currently these peach seedlings, derived primarily from the rootstock cultivars ‘Lovell’, ‘Halford’, ‘Nemaguard’, ‘Nemared’, ‘Bailey’ and ‘Guardian®’, constitute greater than 95% of the peach rootstocks used in the USA. Of these six rootstocks, ‘Lovell’ and ‘Halford’ are thought to be siblings, and ‘Nemared’ and ‘Guardian®’ have ‘Nemaguard’ in their pedigree. ‘Bailey’ is not related by parentage to the other ﬁve seedling rootstocks. In ﬁeld-testing, these rootstocks differ in vigour, root-knot nematode resistance and bacterial canker (i.e. PTSL) tolerance, but have similar effects on many other horticultural traits including economically important ones such as fruit size and yield of scion cultivars. All of these peach seedling rootstocks are susceptible to the same soil diseases and conditions, which limit their productivity and longevity in many otherwise good production sites. ‘GF 305’ ‘GF 305’ was selected at the National Institute of Agronomic Research (INRA) in Pont-de-laMaye, France in 1945 for its vigorous growth and uniformity in the nursery (Grasselly, 1983). This rootstock is compatible with all peach and nectarine cultivars and has good growth and productivity in the ﬁeld.

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However, ‘GF 305’ is very susceptible to Agrobacterium, Phythophtora, root-knot and root-lesion nematodes and some viruses, and now is being planted less. It is still used by virologists as a virus indicator in peach. ‘P.S.’ series The ‘P.S.’ series originated at the Department of Fruit Science and Crop Protection of Pisa University (Scaramuzzi et al., 1976). The most interesting selections were ‘P.S.A5’, ‘P.S.A6’, ‘P.S.A7’ and ‘P.S.B2’, which were selected for their uniform growth and the different degree of vigour induced in the scion. ‘P.S.A6’ is the most vigorous (similar to Balkan peach seedlings) while ‘P.S.B2’, ‘P.S.A7’ and ‘P.S.A5’ are 10–15%, 15–20% and 20–25% less vigorous, respectively, than ‘P.S.A6’ (Loreti and Massai, 1995; Pellegrino et al., 1997). ‘P.S.A5’ is a peach seedling rootstock that induces less vigour in the scion than do other peach seedlings and encourages uniform growth, precocity, good crop efﬁciency and improved fruit quality in scion cultivars (Loreti and Massai, 1988). Furthermore, it has a slightly higher resistance to waterlogging than most other peach seedlings, while its alkalinity tolerance is similar to other seedling rootstocks. It is resistant to Verticillium wilt (Cirulli et al., 2001). ‘P.S.A5’ is particularly suitable for the free spindle or delayed vase training system and is excellent for fertile soils, vigorous or early-ripening cultivars, and medium–high density planting systems. ‘P.S.A6’ is uniform and rapid growing in the nursery and can be propagated via hardwood cuttings. It induces high vigour in grafted trees, though slightly less than ‘GF 677’, and performs well in poor soils. Under these conditions and without irrigation, it still is highly productive by virtue of its welldeveloped root system. ‘P.S.A7’ also induces very uniform vigour and rapid growth of seedlings in the nursery. Like other peach seedlings, it is not well adapted to wet, heavy and poorly drained soils, but appears better adapted to loam soils with medium or high fertility. Furthermore, while maintaining good productivity and fruit quality, it induces 15–20% less vigour in the scion than does a standard seedling. This allows for

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slightly narrower tree spacing in fertile soils and with vigorous cultivars. ‘P.S.B2’ is characterized by uniform and rapid growth of seedlings in the nursery and can be propagated by hardwood cuttings, but has some susceptibility to powdery mildew. Resistance of ‘P.S.B2’ to root waterlogging and calcareous soils is similar to that observed in other peach seedlings. This rootstock is less sensitive to replant problems, probably on account of its greater resistance to P. vulnus. It also performs well even in heavy soils, provided that waterlogging does not occur. ‘P.S.B2’ induces medium–high vigour in grafted trees, but at least 10–15% less than Slavic seedlings, as well as high productivity, early ripening and good fruit quality. ‘Rubira®’ ‘Rubira®’ was selected from peach seedlings grown at INRA from a Californian seedlot imported in 1960 and owes its name to its redcoloured leaves. ‘Rubira®’ seedlings have uniform and vigorous growth in the nursery, but are slightly susceptible to powdery mildew (Loreti, 1984) and resistant to the green peach aphid, Myzus persicae (Sulzer) (Massonie and Paison, 1979). ‘Rubira®’ induces 15–20% lower vigour than ‘GF 677’ and is more precocious with good productivity. It is therefore recommended for vigorous cultivars that are slow to enter into production and for higher planting densities. It is also less susceptible to crown gall (A. tumefaciens) and P. vulnus than other peach seedlings, but is susceptible to M. incognita and M. arenaria nematodes (Loreti, 1984). ‘Higama®’ ‘Higama®’ was selected from peach seedlings grown from another seedlot imported in 1960 from Japan at INRA (Grasselly, 1983). This rootstock induces high vigour in the scion and is suitable for early-season cultivars. In addition, ‘Higama®’ has a higher sensitivity to iron chlorosis (J.-L. Poëssel, France, 2001, personal communication) and crown gall than other peach seedling rootstocks, but has a fair degree of resistance to M. javanica and M. incognita nematodes. However, it had relatively

low yields and survival in several trials (De Salvador and Monastra, 1996; Reighard et al., 2004). ‘Montclar® Chanturgue’ ‘Montclar®’ was selected at INRA in 1960 and has similar characteristics to ‘Higama®’ with regard to high seed production, uniform seedling growth and vigour in the nursery, and increased vigour in scion cultivars (Grasselly, 1983). It differs from the other French seedling rootstocks in exhibiting greater resistance to iron-induced chlorosis and better uptake of iron and magnesium from the soil. It is a popular peach rootstock in Europe. ‘Nemaguard’ ‘Nemaguard’ rootstock was selected from seedlings from a seedlot received in 1949 by the US Department of Agriculture (USDA), which was labelled P. davidiana and was eventually released as ‘FV 234-1’ in 1959 (Brooks and Olmo, 1961). Thought to be a putative hybrid of P. persica × P. davidiana, ﬁeld observations (Okie, 1998) and molecular studies (Lu et al., 1996) indicate that it is primarily P. persica. ‘Nemaguard’ seedlings are uniform and vigorous, compatible with peach and nectarine cultivars, and impart excellent scion vigour and productivity. It has good resistance to M. incognita, M. javanica and M. arenaria, but recent research has conﬁrmed that a new root-knot species (M. floridensis) (Handoo et al., 2004) can reproduce in the roots of ‘Nemaguard’ (Nyczepir and Beckman, 2000). ‘Nemaguard’ is fairly tolerant of crown gall, but is sensitive to P. vulnus, fungal root rots, Verticillium, iron chlorosis and root waterlogging and may reduce winter hardiness of scion cultivars in cold climates. ‘Nemaguard’ suckers extensively and is very sensitive to ring nematode (M. xenoplax) feeding, which leads to tree injury and death from bacterial canker (Pseudomonas syringae pv. syringae van Hall) and PTSL (Zehr et al., 1976; Nyczepir et al., 1983). Despite these limitations, ‘Nemaguard’ is one of the most widely planted stone fruit rootstocks in California and South America. For peach production, however, it performs best on fumigated ring nematode-infested

Rootstock Development

soils, virgin peach sites, and soils that have root-knot nematode problems. ‘Nemared’ ‘Nemared’ is a redleaf selection released in 1983 by the USDA that has ‘Nemaguard’ in its lineage (Ramming and Tanner, 1983). ‘Nemared’ in the nursery is similar to ‘Nemaguard’ but produces seedlings with less lateral branches thus facilitating budding. Field characteristics of ‘Nemared’ are also similar to ‘Nemaguard’, except ‘Nemared’ produces a slightly more vigorous tree with equal or better root-knot resistance, but has increased susceptibility to bacterial canker (M. McKenry, California, 2006, personal communication). ‘Guardian® BY520-9’ ‘Guardian®’ rootstock traces its lineage back four generations to a ‘Nemaguard’ cross in 1954 and was released in 1993 jointly by USDA and Clemson University (Okie et al., 1994b). ‘Guardian®’ has many traits similar to ‘Nemaguard’. The primary differences are that ‘Guardian®’ has lower seed germination, slightly less root-knot nematode resistance (Nyczepir et al., 1999, 2006), supports fewer M. xenoplax, and exhibits signiﬁcantly higher tolerance to ring nematode, bacterial canker and PTSL (Beckman et al., 1997a; Reighard et al., 1997). The latter trait has made it the most popular rootstock, especially for nematode-infested replant sites in the south-eastern USA, even though it is susceptible to Armillaria root rot. ‘Lovell’ and ‘Halford’ ‘Lovell’ and ‘Halford’ are old drying and processing peach cultivars that were selected as seedlings from California orchards around 1882 and 1921, respectively (Okie, 1998). ‘Lovell’ has high seed germination of uniform seedlings that are compatible with all peach and nectarine cultivars. Scion vigour is slightly less than on ‘Nemaguard’. ‘Lovell’ does not sucker and is susceptible to root-knot and root-lesion nematodes, but has better tolerance to ring nematodes, bacterial canker and PTSL than ‘Nemaguard’. ‘Lovell’ is susceptible to waterlogging, crown gall, Phytophthora spp. and Armillaria spp. ‘Halford’ is similar to

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‘Lovell’ in nursery and ﬁeld characteristics and is even thought to be a ‘Lovell’ seedling. Since ‘Lovell’ is no longer used as a drying cultivar, seed can only be obtained from nursery seed orchards. Thus, ‘Halford’ has gradually supplanted ‘Lovell’ in the nursery trade. However, since ‘Halford’ is usually sold in bulk as cannery pits, questions about whether it is true to type occasionally arise. ‘Bailey’ ‘Bailey’ is a naturalized peach selection from Iowa, circa 1836, that produces uniform seedlings with good vigour (Okie, 1998). It has good cold hardiness for a peach and is rated only slightly less cold-hardy than ‘Siberian C’. It has fair tolerance to root-lesion nematode and is a popular rootstock on sandy soils in more northern climates. It will usually produce a slightly smaller tree than ‘Lovell’, but is very productive. It is susceptible to rootknot nematodes, waterlogging, fungal root rots and PTSL in the southern USA. ‘Siberian C’ ‘Siberian C’ was selected by the Agriculture Canada Research Station at Harrow, Ontario (Canada) in 1967 (Weaver, 1967b; Layne, 1980; Okie, 1998). The seedlings are uniform with good cold hardiness. Cultivars grafted to this rootstock show medium or medium–low vigour and good precocity. Productivity and crop efﬁciency are satisfactory. ‘Siberian C’ has the additional advantage of inducing slightly earlier ripening time, as well as having a lower susceptibility to Leucostoma or Valsa canker (Leucostoma cincta (Sacc.) Hohn.), but it is not tolerant of root waterlogging, nematodes, bacterial canker or crown gall. ‘Siberian C’ tends to de-harden the scion cultivar before spring in moderate climates, and therefore is mostly planted in colder regions.

Sections Euprunus and Microcerasus species cultivars Species of Section Euprunus cover a wide range of rootstocks, but only a few have become widely used for peach. Rootstocks from these

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species are more resistant to waterlogging, calcareous soil, replant problems and speciﬁc soil pathogens than Section Euamygdalus species. However, these rootstocks have other problems with peach such as nutritional deﬁciencies, non-uniform growth, excessive suckering and frequent graft incompatibility (Loreti, 1984). These negative characteristics were present to various degrees in ‘historical’ rootstocks such as ‘Akerman’, ‘Brussel’, ‘Common Plum’, ‘Common Mussel’, ‘Pershore’ and others, which now have mostly disappeared by virtue of genetic improvements by breeders within these species. Therefore, only commonly known rootstocks that have promising traits are described. Prunus insititia cultivars ‘St. Julien A’ is a selection from a plum population derived from P. insititia, which includes genotypes that have morphological and likely genetic characteristics (Casas et al., 1999) similar to P. domestica. Seedlings from this genetically complex population exhibit extreme morphological variability, which also leads to heterogeneous size control in budded scions. Therefore, a number of clones (e.g. A, B, C, G, J, K) were selected at East Malling, UK, among which ‘St. Julien A’ was the most interesting and widely used (Fiorino, 1967). This clone is propagated fairly easily by layering, and also by hardwood cuttings. ‘St. Julien A’ is compatible with commercial peach cultivars and is considered cold-hardy. However, it now is used infrequently because of its sensitivity to calcareous soil and pathogens such as P. syringae (Reighard, 1994). ‘St. Julien GF 655/2’ was selected by INRA from open-pollinated seedlings of ‘St. Julien d’Orleans’ and is propagated by layering, hardwood cuttings and micropropagation (Loreti, 1984; Zacchini and Morini, 1995). ‘GF 655/2’ has a rather shallow root system that does not adapt well to droughty soils, but it is fairly tolerant of calcareous, heavy, waterlogged soils and replant sickness, albeit to a lesser degree than ‘Damas GF 1869’ (P. domestica × P. spinosa) (Salesses, 1977). It also induces medium–low vigour, precocity and satisfactory scion productivity. Consequently, this rootstock is suitable for medium- to high-density planting systems even in highly fertile soils. ‘GF 655/2’

suckers profusely (even more so if propagated in vitro) but less than ‘GF 1869’ and has good resistance to crown gall (Bliss et al., 1999) and the silver leaf fungus (Stereum purpureum). ‘Adesoto 101’ (‘Empyrean® 101’ in the USA) was selected by the Experimental Station of Aula Dei (ESAD-CSIC) in Zaragoza (Spain) from a population of open-pollinated seedlings of ‘Pollizo de Murcia’ (Moreno et al., 1995a). This clonal rootstock can be used for peach, apricot, plum and almond and has good compatibility with all peach and nectarine cultivars tested in Spain (M. Moreno, Spain, 2006, personal communication). However, poor scion growth and/or survival on ‘Adesoto 101’ have been observed in two peach cultivars at several test locations in the USA (G. Reighard, unpublished results). It propagates easily by both hardwood cuttings and in vitro techniques (preferred nursery method) and also adapts satisfactorily to calcareous (up to 10–11% limestone), ﬁnetextured and waterlogged soils. Peach cultivars budded on this rootstock show lower vigour than trees budded on peach seedling or ‘Damas GF 1869’ and the fruits ripen about 3–7 days earlier. ‘Adesoto 101’ is resistant or immune to M. arenaria, M. incognita and M. javanica and is moderately tolerant of P. vulnus (Pinochet et al., 1999) but has been highly susceptible to bacterial canker and PTSL in South Carolina (Reighard et al., 2006). Prunus domestica cultivars ‘Damas C’, derived from P. domestica, was extensively used in the past as a peach rootstock. ‘Damas C’ was selected from ‘Black Damas’ (P. domestica) at the former East Malling Research Station, UK (Hatton, 1921; Taylor, 1949; Tydeman, 1956). This rootstock is easily propagated by layering, but not by hardwood cuttings. ‘Damas C’ induces good vigour in budded trees, but its shallow root system leads to weak anchorage. It is suitable for wet, cold soils that are not very deep. However, it suckers profusely, which is why it has fallen out of favour with commercial producers. ‘GF 43’ rootstock was selected in 1950 by INRA from a ‘Prune d’Ente’ seedling. It is readily propagated by micropropagation,

Rootstock Development

though propagation by stooling and hardwood cuttings has been unsatisfactory. Having a deep and well-developed root system, this rootstock exhibits good tolerance of slightly calcareous, wet and heavy soils and is intermediately resistant to root waterlogging (Grasselly, 1987). It induces vigour in budded trees similar to peach seedlings and has good graft compatibility with all cultivars tested. However, trees on ‘GF 43’ are non-precocious with low production efﬁciency. ‘GF 43’ produces few or no suckers and is somewhat sensitive to replant sickness and susceptible to Chlorotic leaf spot virus, which can cause graft incompatibility. ‘Tetra’ (‘Empyrean® 3’ in the USA) rootstock originated from open-pollinated seedlings of ‘Regina Claudia Verde’ at the Experimental Institute of Fruit Growing, Rome, Italy. It readily propagates by either micropropagation or hardwood cuttings. Trees are vigorous and uniform in the nursery and easily budded or grafted. ‘Tetra’ has a uniformly developed root system, which has good anchorage. In addition, it adapts to many soil types and has resistance to calcareous soils comparable to that of ‘GF 677’ but with good tolerance of root waterlogging. ‘Tetra’ has excellent compatibility with peach, nectarine, apricot and plums and rarely suckers. Flowering can be delayed 5–6 days compared with ‘GF 677’. Tree vigour is 15–20% less on ‘Tetra’ than on ‘GF 677’, and fruit ripens 3–4 days earlier. ‘Tetra’ is mostly resistant to root-knot nematodes (Meloidogyne spp.), highly susceptible to P. vulnus, and preliminary trials show resistance to Phytophthora cinnamomi and tolerance to A. mellea (Nicotra and Moser, 1997; M. McKenry, California, 2006, personal communication). ‘Penta’ (‘Empyrean® 2’ in the USA) rootstock originated from open-pollinated seedlings of ‘Imperial Epineuse’ at the Experimental Institute of Fruit Growing, Rome, Italy. Its characteristics are similar to ‘Tetra’, except it differs in its ability to induce higher vigour, similar to ‘GF 677’, and it does not induce early fruit ripening (Nicotra and Moser, 1997). In California ﬁeld trials, it was a very good host for M. xenoplax and was similar to ‘Nemaguard’ in its host status to P. vulnus (M. McKenry, California, 2006, personal communication).

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Prunus pumila cultivars ‘Pumiselect®’ (‘Rhenus 2’), a P. pumila selection from Germany (Jacob, 1992), is compatible with many peach cultivars. It is resistant to M. javanica and tolerant of sandy soils and drought but is susceptible to waterlogging, A. tabescens and iron chlorosis, and sometimes exhibits uneven anchorage, leading to leaning. Peach fruit size on ‘Pumiselect®’ rootstocks was reported to be smaller than on peach rootstocks (Reighard et al., 2007). Selections of P. pumila such as ‘Mando’ have been poor hosts for ring nematodes (M. xenoplax) (Westcott et al., 1994). However, in Californian trials, ring nematode host status for ‘Pumiselect®’ was less than ‘Nemaguard’ but higher than ‘Lovell’ seedlings (M. McKenry, California, 2006, personal communication).

Interspecific hybrid cultivars The most interesting hybrids of this group are derived from peach × almond and peach × P. davidiana, which have helped remedy serious problems caused by nematodes and iron chlorosis, the latter being extremely common in many European peach-growing areas. Furthermore, since interspeciﬁc hybrids are less susceptible to certain pathogens, they are a useful tool for overcoming abnormalities of the soil environment such as root waterlogging, droughty soils, salinity or replant problems. Among these rootstocks, the peach–almond ‘GF 677’ has become the most widespread rootstock in the European peach-growing areas. Research in the last few years has reported several similar new hybrids possessing superior horticulture traits that are still under ﬁeld trials (Salesses et al., 1998; Moreno, 2004; Massai and Loreti, 2004). New peach rootstock cultivars have been imported into the USA during the past 10–15 years with the majority of them being complex Prunus L. hybrids that must be propagated vegetatively. The pedigrees of these hybrids contain several different Prunus L. species which confer traits that P. persica lacks, such as adaptation or tolerance to heavy soils, waterlogging, alkalinity, drought, vigour control and soil fungal diseases (Reighard, 2000).

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Within the USA, a few clonal rootstocks are being used in commercial peach production on a limited scale. ‘Atlas’ and ‘Viking’ from Zaiger Genetics, Inc. in California are interspeciﬁc Prunus L. hybrids used on replant sites due to their replant tolerance, root-knot resistance, protection against ring nematode and tree vigour (www.davewilson.com), although ‘Viking’ grows off much better the ﬁrst year if grown as a container tree rather than as a bare-root seedling. An old (i.e. 1957) USDA-released cultivar, ‘Hiawatha’ (P. besseyi × P. salicina), is now being evaluated for vigour control as a rootstock. Several other promising size-controlling clonal rootstocks were released in 2004 from California. These rootstocks are P. salicina × P. persica hybrids and are named ‘Controller 5’ (formerly ‘K146-43’) and ‘Controller 9’ (formerly ‘P30-135’) (DeJong et al., 2005). Both these rootstocks are good hosts to M. incognita and P. vulnus nematodes (M. McKenry, California, 2006, personal communication). Peach × almond hybrids ‘GF 677’ (‘Paramount®’ in the USA) is a natural hybrid selected by INRA. It may be propagated by softwood and hardwood cuttings, but now is exclusively propagated in vitro (micropropagation). It is a very vigorous rootstock (10–15% more vigorous than peach seedlings) with a well-developed root system that ensures good anchorage. It is adapted to infertile and droughty soils as long as they are permeable and well-drained. Its resistance to iron chlorosis is high, having good productivity even in soils with 10–12% limestone. In addition, replant problems are ameliorated because of its vigour. These characteristics, along with good graft compatibility with commercial peach and nectarine cultivars, have made this rootstock extremely popular in Italy and other Mediterranean basin countries, where it is almost as widespread as the standard seedling rootstocks (Loreti and Massai, 1995). Despite these favourable traits, ‘GF 677’ often induces excessive scion vigour, resulting in delayed precocity, low yields in the ﬁrst few years, smaller fruit size and poor fruit colour. However, these defects disappear when the trees achieve a vegetative–reproductive

balance and enter into full production. Still, this rootstock is not recommended for very fertile soils or high planting densities. ‘GF 677’ also adapts poorly to heavy and waterlogged soils since it is sensitive to root waterlogging. Furthermore, it is susceptible to A. mellea, M. incognita, A. tumefaciens, Phytophthora cactorum and S. purpureum (Loreti and Massai, 1995), and has a lesser degree of susceptibility to Verticillium albo-atrum, somewhere between that of almond and peach (Loreti and Massai, 2006a). The ‘I.S.’ series of clones were derived from seedlings obtained by open pollination of the peach–almond hybrid ‘GF 557’, which was selected by the Department of Fruit Science and Crop Protection at the University of Pisa (Loreti and Massai, 1998). This series has many characteristics in common with ‘GF 677’, but they differ by the different degrees of vigour induced in scion cultivars. The most interesting clones are, in increasing order of vigour, ‘Sirio’, ‘Castore’ and ‘Polluce’ (Loreti and Massai, 1998, 2006b). ‘Sirio’ (formerly ‘I.S. 5/22’) has poor root induction ability and is difﬁcult to propagate by stoolbeds and layering, but can be propagated by cuttings and even more efﬁciently with in vitro micropropagation (Loreti and Massai, 1994). ‘Sirio’ produces a good root system and is adapted to fertile and permeable soils, but still exerts control over vegetative growth. Its resistance to iron chlorosis is good, though slightly less than that of ‘GF 677’. Compared with trees grafted on to ‘GF 677’, trees budded on ‘Sirio’ are about 40% smaller, yield earlier and have better crop efﬁciency, larger fruit size and improved fruit colour. It is compatible with the main commercial cultivars. ‘Sirio’ is suitable for highdensity planting systems on fertile and chlorosis-inducing soils where ‘GF 677’ cannot be used, due to its vigour. It is unknown if ‘Sirio’ is suitable for replant sickness sites (Loreti and Massai, 1998). ‘Castore’ (formerly ‘I.S. 5/19’) also has poor root induction ability, but can be micropropagated in vitro. ‘Castore’ prefers fertile and permeable soils, whereas it is unsuitable for non-tiled heavy and waterlogged soils. It is a semi-dwarﬁng rootstock, reducing

‘I.S.’ SERIES.

Rootstock Development

vegetative growth to about 30% less than ‘GF 677’. Production is good, and ‘Castore’ achieves high crop efﬁciency based on fruit yield versus vegetative growth parameters. Fruit quality is improved with higher SSC, favourable sugar:acid ratio and intense fruit colour. Moreover, this stock also is adapted to infertile soil. ‘Castore’ is very suitable for fertile soils and high-density planting systems (Loreti and Massai, 2006b). ‘Polluce’ (formerly ‘I.S. 5/8’) is similar to ‘Castore’ in difﬁculty to propagate, but it can be micropropagated. Like other peach– almond hybrids, it is not suitable for wet, heavy and inadequately drained soils, but is adapted to permeable soils with medium or high fertility. It induces about 20% less vigour to the scion than ‘GF 677’, and produces good yields with high yield efﬁciency and improved fruit quality. ‘Polluce’ offers an alternative to ‘GF 677’ in medium- to high-fertility soils, where it allows closer tree spacing in orchards and easier tree maintenance. In poor soils, it can be semi-dwarﬁng but still achieves good production (Loreti and Massai, 2006b). The Hansen clones were selected by the University of California (USA) from a seedling population obtained by a peach × almond cross (Kester and Asay, 1986). They are propagated by hardwood cuttings, but also can be micropropagated. Both of these rootstocks induce greater vigour than peach seedlings, but have productivity similar to peach and ‘GF 677’. In addition, both have tolerance to calcareous soils and resistance to root-knot nematodes (M. incognita, M. javanica) and have tolerance to drought and saline soils. ‘Hansen 2168’ (= ‘Hansen 2’) is moderately tolerant of Phytophthora but both clones are very sensitive to crown gall, with ‘Hansen 536’ (= ‘Hansen 5’) slightly more susceptible. They also are more susceptible than peach to Verticillium wilt, waterlogging, and perhaps bacterial canker. Since these rootstocks have only recently been introduced in Europe, they still need time to be evaluated; although preliminary observations are not promising because they have not been as tolerant to calcareous soils as ‘GF 677’ or other new European rootstocks (M. Moreno, Spain, 2006, personal communication).

‘HANSEN 2168’ AND ‘HANSEN 536’.

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‘ADAFUEL’. ‘Adafuel’, an almond–peach hybrid, was selected at ESAD-CSIC (Zaragoza, Spain) from a seedling population obtained by open pollination of the ‘Marcona’ almond cultivar (Cambra, 1990). It propagates easily by hardwood cuttings, giving a better rooting percentage than ‘GF 677’. ‘Adafuel’ is extremely vigorous and is suitable for calcareous and loam soils provided they are well-drained. It is graft-compatible with most commercial peach and almond cultivars and is similar to ‘GF 677’ in its growth and yield characteristics as a rootstock (Moreno et al., 1994b). ‘Adafuel’ is resistant to powdery mildew (Sphaerotheca pannosa), plum rust (Tranzschelia pruni-spinosae) and shot hole (Corineum beijerinckii), but is very susceptible to Meloidoigyne spp., which limits its commercial utility. ‘ADARCIAS’. ‘Adarcias’, like ‘Adafuel’, is an almond–peach hybrid selected from an openpollinated seedling population at ESADCSIC. It readily propagates by hardwood cuttings, but can be micropropagated in vitro (Moreno and Cambra, 1994). It is a rootstock that performs well in calcareous and loam soils if they are well-drained. ‘Adarcias’ induces lower vigour than ‘Adafuel’ and ‘GF 677’, but has greater crop efﬁciency and higher fruit SSC (Albás et al., 2004). Therefore it reduces excessive tree growth, and thus limits management costs. It is graft-compatible with the several peach and nectarine cultivars tested thus far. Nursery trials indicate that ‘Adarcias’ is resistant to C. beijerinckii Oud. and T. pruni-spinosae (Pers.) Diet.

Peach × Prunus davidiana hybrids ‘Cadaman® Avimag’ rootstock was selected in Hungary from an interspeciﬁc hybrid of P. persica × P. davidiana, and then introduced in France by INRA (Edin and Garcin, 1996). ‘Cadaman®’ can be propagated by softwood or semi-hardwood cuttings. The vigour induced in the scion is initially comparable to that of ‘GF 677’, but vigour tends to decrease 4 or 5 years after orchard establishment. Furthermore, ‘Cadaman®’ induces earlier precocity, comparable productivity and larger fruit size compared with ‘GF 677’. ‘Cadaman®’ shows good resistance to waterlogging, unlike peach–almond

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hybrids, and is tolerant to iron chlorosis and replant sickness. It is also resistant to M. incognita and M. javanica, but is as good a host to M. xenoplax as ‘Nemaguard’. Owing to its high vigour, ‘Cadaman®’ is not an appropriate rootstock for high-density planting systems. ‘Barrier 1’ (‘Primo’ or ‘Empyrean® 1’ in the USA) is another peach × P. davidiana hybrid selected at the former Institute for the Propagation of Woody Species, Florence, Italy. The vigour induced by ‘Barrier 1’ is similar to or greater than that by ‘GF 677’, and ‘Barrier 1’ has an extensive, deep root system that ensures good anchorage. It propagates easily by hardwood cuttings or micropropagation. It is well adapted to different pedologic environments such as calcareous soil, waterlogging or replant sickness, and has good resistance to root-knot nematodes (Roselli, 1998; Loreti and Massai, 2002a). Furthermore, it induces higher productivity and larger fruit size than does ‘GF 677’. Therefore, this rootstock is adapted to replant soils that have waterlogging problems where peach–almond hybrids cannot be used. Prunus cerasifera hybrids The rootstocks ‘Mr.S. 2/5’ and ‘Mr.S. 2/8’ were selected by the Department of Fruit Science and Crop Protection of the University of Pisa, Italy from an open-pollinated Myrobalan (P. cerasifera) population. The origin of ‘Mr.S. 2/5’ is uncertain, but since it is a pentaploid hybrid (2n = 40) it probably is a spontaneous P. cerasifera × P. spinosa hybrid (Loreti et al., 1988). It also could be a P. domestica × P. spinosa hybrid like ‘Damas GF 1869’ (also 2n = 40), since its morphological characteristics are similar to those of P. domestica. The two ‘Mr.S.’ clones have many characteristics in common, such as easy propagation by layering, hardwood cuttings and micropropagation. For commercial propagation, the in vitro micropropagation method is used. Budding operations must begin a few days earlier than in other rootstocks, because the vegetative growth in the nursery ceases rather early (Loreti and Massai, 1995). In addition, ‘Mr.S. 2/5’ is sensitive to rust (T. pruni-spinosae (Pers.:Pers.) Diet.), but less so to Phytophthora spp. and Armillaria spp. Graft compatibility has been good with all tested

peach and nectarine cultivars, and scion vigour is reduced by 10–15% compared with that of peach seedlings and by 25–30% compared with ‘GF 677’. Both rootstocks are tolerant of replant disease. Suckering has been limited in Italy but excessive suckering in ‘Mr.S. 2/5’ has been observed in the USA (G. Reighard, personal observation). Peach production on these rootstocks has been good with good fruit size, increased SSC and good fruit colour compared with ‘GF 677’ (De Salvador and Monastra, 1996; Loreti and Massai, 1999). Fruit also ripen a few days earlier on ‘Mr.S. 2/5’. Differences between the two ‘Mr.S.’ clones are that ‘Mr.S. 2/5’ has greater resistance to crown gall (Zoina and Raio, 1999), calcareous soil and root waterlogging, and can survive extended periods of low soil oxygen content. ‘Myran® Yumir’ or ‘Myran®’ is an interspeciﬁc hybrid of ‘Belsiana’ plum (probably P. cerasifera × P. salicina) and ‘Yunnan’ peach selected by INRA in 1950 and propagates by hardwood and semi-hardwood cuttings (Renaud et al., 1988). ‘Myran®’ induces medium–high vigour in grafted peach cultivars and has good graft compatibility. Scion vigour of mature trees has been less than ‘GF 305’ peach in Europe, but in the USA scion vigour is 10–15% greater than for peach rootstocks (Reighard et al., 2004). Fruit ripening, fruit size and colour are similar to trees grafted on to the peach seedling, but yield efﬁciency has been low in the USA. ‘Myran®’ is free from suckering, tolerant of root waterlogging, tolerant to A. mellea (i.e. France not USA) and Meloidogyne spp. nematodes, but it is sensitive to calcareous soil and susceptible to bacterial canker and PTSL (Grasselley, 1987; Renaud et al., 1988; Reighard et al., 1997). ‘Ishtara® Ferciana’ or ‘Ishtara®’ is a complex interspeciﬁc hybrid of ‘Belsiana’ plum (probably P. cerasifera × P. salicina) and a natural hybrid of P. cerasifera × P. persica selected by INRA (Grasselly, 1987; Renaud et al., 1988). It is a multiple species-compatible rootstock, which induces medium vigour and can be used for peach, apricot and plum cultivars. ‘Ishtara®’ has good graft compatibility with peach, rarely suckers, and has shown good resistance to the peach tree borer (Synanthedon exitiosa (Say)) in the USA (Reighard et al., 2004). It adapts well to different soil and climatic

Rootstock Development

conditions, although sensitivity to waterlogged and calcareous soils has been observed in Europe. In Italy, ‘Ishtara®’ has induced earlier fruit maturity by several days in ‘Suncrest’ (Loreti and Massai, 2002b), but no phenology differences in peach have been observed in the USA (Reighard et al., 2004). Productivity is good on loams and fertile soils, where it reduces peach tree growth by up to 30% and improves fruit size. However, fruit yields have been low in the USA, and peach cultivars on ‘Ishtara®’ are extremely susceptible to bacterial canker and PTSL (Reighard et al., 1997). European plum hybrids ‘Julior® Ferdor’ or ‘Julior®’ is an interspeciﬁc hybrid of P. insititia × P. domestica selected in 1965 by INRA. It is graft-compatible with peach, plum and apricot cultivars and is propagated by hardwood cuttings and micropropagation. ‘Julior®’ induces low to medium vigour, albeit greater than ‘GF 655/2’, and is a dwarﬁng rootstock for peach cultivars even in very fertile soils (Loreti and Massai, 2002a). It has good resistance to root waterlogging, but is sensitive to calcareous soil above pH 8.2 (Grasselly, 1988). It is quite variable in growth in different pedoclimatic environments, lacks precocity and suckers profusely soon after orchard establishment. ‘Redtop’ peach on ‘Julior®’ rootstock in South Carolina has had poor yields, low yield efﬁciency, early fruit maturity, improved fruit quality and high mortality from bacterial canker (G. Reighard, unpublished results). In California, ‘Julior®’ supports four times the ring nematode numbers of that for ‘Nemaguard’ (M. McKenry, California, 2006, personal communication). ‘Jaspi® Fereley’ or ‘Jaspi®’ rootstock was selected by INRA from a cross of P. salicina × P. spinosa (Renaud and Salesses, 1990). It is a multiple species-compatible rootstock, but is more suitable for apricot and plum than peach as compatibility with peach is limited. ‘Jaspi®’ induces 20% less vigour than peach seedlings in Europe, but is very dwarﬁng (~60% of standard) in trials in the USA. It is adapted to difﬁcult soil environments due to its tolerance to waterlogging, calcareous soil and replant sickness, but peach cultivars on

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‘Jaspi®’ are extremely susceptible to bacterial canker (Reighard et al., 2006). Unfortunately, ‘Jaspi®’ is not recommended in the USA because it is probably incompatible with many peach cultivars.

8.4 Peach Rootstock Breeding Programmes The adoption of rootstocks more suited to the requirements of technologically advanced fruit growing began in Europe in the 1950s, but it was not until the development of intensive fruit growing that it assumed greater importance. For pome fruits such as apple and pear, the introduction of new rootstocks occurred rapidly, so that in recent years there is almost exclusive use of clonal rootstocks. However, for stone fruits like peach, the demand for non-traditional rootstocks emerged somewhat later, when peach began to be planted extensively into areas having soil and climatic conditions that were not fully suited to this species such as waterlogged, compacted, subcalcareous or alkaline soils, and environments subject to frequent low temperatures in winter and, in particular, spring frosts (Loreti, 1988). It is now generally accepted that considerable technical and economic advantages can be achieved by using rootstocks selected for their genetic characteristics and environmental adaptation. Such rootstocks have become widely available in the nursery trade, the demand is increasing and the market is insisting on new rootstocks with enhanced qualities. This has prompted a number of scientiﬁc institutions, public organizations and private breeders to develop new rootstocks that more closely match the requirements of modern fruit growing. In Europe, research has been particularly active in countries such as France, Spain and Italy, where extensive work on genetic improvement of fruit tree rootstocks has been undertaken for several decades with special attention now being focused on new rootstocks for peach. Table 8.1 lists many standard and recently released rootstocks being used for commercial peach production throughout the world.

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Research institutions and objectives

testing, but they hold tremendous promise for ‘designer’ rootstocks in the future.

France In France, genetic improvement and evaluation of peach rootstocks by INRA began in the 1940s and has focused over the last 30 years on both the selection of new lines and clones from common rootstocks and on the development of multiple species-compatible, interspeciﬁc hybrids. In addition to evaluation of the main bioagronomic parameters, attention has focused on determination of sensitivity to the main biotic and abiotic sources of stress in order to select the most tolerant or resistant rootstocks. To that end, numerous trials were conducted to assess seed germination, chilling requirements, seedling morphology and uniformity of progeny from selected mother tree genotypes or ‘cultivars’. Signiﬁcant genotypes were obtained by virtue of the selection programme designed ﬁrst by J. Souty at Pont-de-la-Maye and then subsequently by R. Bernhard, C. Grasselly and G. Salesses. The programme was based primarily on the interspeciﬁc peach–almond cross, with more recent experiments focusing on developing new peach × P. davidiana hybrids. Concurrently, an interspeciﬁc hybridization programme using different Prunus L. species was initiated. The objectives were to create genotypes with greater resistance to root waterlogging, nematodes, Phytophthora and Armillaria, and to improve graft compatibility and scion dwarﬁng traits (Salesses et al., 1998). The vast and complex genetic improvement work carried out by INRA for over half a century has resulted in the development of numerous peach rootstocks, some of which are already widely adopted in Mediterranean basin countries. Currently a new genetic improvement programme is under way using P. cerasifera and almond hybrids with the aim of selecting new rootstocks resistant to root waterlogging, drought, iron chlorosis and Meloidogyne spp. nematodes (Dirlewanger et al., 2002). This programme has successfully used biotechnology via marker-assisted selection to pyramid resistance genes from three species into one rootstock. Progeny from this programme are still under development and

Italy In Italy, rootstock genetic improvement was begun in the late 1950s by Professor F. Scaramuzzi. Attention focused on assessment of the bioagronomic characteristics of a very extensive range of rootstocks belonging to different species obtained either by crosses or by selection of seedlings and wild types collected in different areas of Italy or other Mediterranean countries (Scaramuzzi et al., 1976). This work was continued in more depth by F. Loreti, R. Guerriero and R. Massai, ﬁrst at the former Istituto di Coltivazioni Arboree in Pisa and then, since 1986, at the Department of Fruit Science and Crop Protection of the University of Pisa. Research carried out since the late 1950s has mainly involved genetic improvement programmes for pear, plum, apricot and particularly peach rootstocks. The programme objectives for the development of peach rootstocks were: (i) uniform growth in the nursery; (ii) use of seed propagation; (iii) graft compatibility with most peach and nectarine cultivars; (iv) different degrees of dwarﬁng of the scion to facilitate adaptation to different soil fertility and orchard systems; (v) increased production efﬁciency and improvement of fruit quality; and (vi) resistance or reduced susceptibility to biotic and abiotic stresses, with special attention to root waterlogging, salinity, drought, calcareous iron chlorosis and replant problems. This programme has successfully produced tolerant peach seedling and interspeciﬁc hybrid rootstocks with differing levels of scion dwarﬁng. Another Italian institution that devoted considerable resources to genetic improvement of peach rootstocks is the Experimental Institute of Fruit Growing in Rome. Research began in the late 1970s, and primarily focused on rootstocks tolerant to waterlogging and calcareous soil. Trials were conducted on seedlings obtained by open pollination from about 100 plum cultivars. At the same time, a programme for selection of rootstocks resistant to M. incognita, M. javanica and P. vulnus nematodes was undertaken, using P. persica

Rootstock Development

and peach–almond hybrids (Nicotra and Moser, 1997, 1998). Since 1995, work in Italy on genetic improvement and bioagronomic evaluation of peach rootstocks has been coordinated and funded by the Ministry of Agricultural and Forestry Policies through two national projects. The ﬁrst of these, ‘Genetic Improvement of Rootstocks’, focuses on development of rootstocks through crossing and selection programmes, and more recently through biotechnology methods. The second project, ‘Evaluation of Rootstocks’, evaluates the most widely used rootstocks available in the Italian nursery market. Fourteen ‘Operative Units’, composed of members of university institutes, experimental stations and producer associations, are involved in work on this project and have established experimental ﬁeld trials in the most important Italian peach-growing areas (Loreti, 1997). This project observes the bioagronomic behaviour of proposed peach rootstocks prior to their release for commercial use. Information is then made available to fruit growers through the publication of periodic lists in which rootstocks are classiﬁed into one of three categories: recommended, promising or non-recommended (Fideghelli and Nicotra, 2002). Spain In Spain, selection of peach rootstocks was initiated in the 1960s with the identiﬁcation of P. insititia clones that could be easily propagated by hardwood cuttings. The ﬁrst studies were performed at EEAD-CSIC in Zaragoza using ‘Pollizo de Murcia’ germplasm, which is a P. insititia population that was widely used in local nurseries due to its ease of propagation by suckers and tolerance to iron chlorosis, root asphyxia and salinity (Cambra, 1970). Attention focused initially on graft compatibility of the test material with peach, apricot, plum and almond cultivars and its adaptation to compacted and calcareous soils. Efforts were subsequently directed towards identifying clones with naturally high rooting potential, in order to limit commercial propagation by suckers to avoid virus diseases. Additional ‘Pollizo’ clone selection

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programmes were undertaken in the following years by EEAD-CSIC and Unidad de Fruticultura del Centro de Investigación y Tecnologia Agroalimentaria de Aragón (CITA, formerly SIA-DGA) of Zaragoza and the Centro Regional de Investigaciones Agrarias of La Alberca, Murcia. On the other hand, at the EEAD-CSIC, selection of peach × almond hybrids began in 1970 with the identiﬁcation and collection of spontaneous hybrids or open-pollinated seedling populations from throughout Spain. Work basically focused on ease of vegetative propagation, graft compatibility with peach and almond, and tolerance to iron chlorosis. Later, the best clones were evaluated for vigour and production characteristics in grafted scion cultivars (Cambra, 1990; Moreno and Cambra, 1994). Recently, these research institutes and the private nursery Agromillora Catalana SA have moved towards developing rootstocks with greater tolerance to soils with high active limestone content, prolonged summer drought and poor soil fertility – all of which represent characteristics found in the most important peach-growing areas in Spain (Aragón, Catalonia and Murcia) – as well as resistance to root-knot and root-lesion nematodes (Pinochet et al., 2002). Therefore, controlled interspeciﬁc crosses have been made with the purpose of bringing together the desirable traits of plum species (P. cerasifera, P. insititia), P. davidiana, almond and peach into new rootstocks (Moreno, 2004). USA and Canada Peach rootstock development in the USA evolved in the early 20th century and was carried out by scientists from the USDA and public universities. This work has now shifted during the past 20 years to mostly private nurseries and breeders. Initially, much of the ﬁrst rootstock research for peach occurred in the 1930s and 1940s to ﬁnd cultivars or selections that were tolerant to the known biotic and abiotic stresses on peaches (Tufts, 1929; Hutchins, 1936; Long and Whitehouse, 1943; Weinberger et al., 1943; Havis et al., 1946; Day, 1953). This work largely screened new germplasm and existing cultivars from P. persica

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and other Prunus L. species for desired traits. Later, the ﬁrst breeding work was initiated to incorporate root-knot nematode resistance from sources such as ‘Shalil’, ‘Yunnan’, ‘S-37’, ‘Okinawa’ and ‘Nemaguard’. This work progressed from the 1950s and 1960s (Hansen et al., 1956; Sharpe, 1957; Sharpe et al., 1969) to the 1980s and 1990s (Sherman et al., 1981, 1991; Ramming and Tanner, 1983; Okie et al., 1994b), where a number of selections were released (e.g. ‘Nemared’, ‘Flordaguard’ and ‘Guardian®’). Since at least the mid-1980s, peach– almond rootstocks for calcareous soil have been developed at the University of California (UC) at Davis by D. Kester (e.g. ‘Hansen 2168’ and ‘Hansen 536’, ‘Nickels’), Burchell Nursery, Inc. (Oakdale, California) (e.g. ‘SLAP’ = ‘Cornerstone’) and Bright’s Nursery, Inc. (Reedley, California) (e.g. ‘Bright’s Hybrid®’), and dwarﬁng rootstocks by USDA and UCDavis (DeJong et al., 2004a,b). Widely adapted, interspeciﬁc rootstocks (e.g. ‘Citation’, ‘Viking’ and ‘Atlas’) have been released by Zaiger Genetics, Inc. for multiple types of soil and replant problems. In the southern USA, rootstocks that are resistant to bacterial canker and Armillaria spp. are currently under evaluation at USDA in Byron, Georgia (Beckman et al., 1997b) and for tolerance to salinity and calcareous soils in Texas (Ottman and Byrne, 1988; Shi and Byrne, 1995). Most all other peach rootstock development and evaluation in the USA are of imported rootstocks licensed by commercial nurseries. Many of the above rootstocks are tested in North America in the NC-140 national rootstock trials (www.nc140. org) prior to or shortly after being available to fruit growers. In Canada, ‘Harrow Blood’ and ‘Siberian C’ rootstocks were released in 1967 by Agriculture Canada at Harrow, Ontario (Layne, 1980; Okie, 1998). Later, the Harrow breeding programme under R.E.C. Layne selected several genotypes from ‘Bailey’ × ‘Siberian C’ crosses. These selections plus two cultivars, ‘Chui Lum Tao’ and ‘Tzim Pee Tao’, from northern China are being evaluated for cold hardiness, P. penetrans tolerance and L. cinta resistance. Selections ‘H7338013’ and ‘H7338019’ have yielded as well as standard peach rootstocks but have not been named or

released (Layne and Jui, 1994; Reighard et al., 2004). Rootstocks in development Work on genetic improvement of stone fruit rootstocks continues to produce innovations that expand the range of rootstocks available on the world market (Beckman and Lang, 2003). Research on high-vigour almond– peach hybrids conducted in Spain has recently led to the selection of several clones of particular interest: ‘Monegro’, ‘Garnem’ and ‘Felinem’, all obtained by the Unidad de Fruticultura SIA-DGA of Zaragoza from the almond ‘Garﬁ’ × ‘Nemared’ cross. These root well with high vigour (greater than ‘GF 677’), have red-coloured leaves, and are tolerant to calcareous soil and resistant to root-knot nematodes (Felipe et al., 1997; Gomez-Aparisi et al., 2001; Iglesias et al., 2004; Moreno, 2004). The Centro de Investigación y Desarrollo Agroalimentario from Murcia has also recently developed an almond–peach rootstock, ‘Mayor®’, which has high vigour and performs satisfactorily on poor, calcareous and droughty soils, but is highly susceptible to root-knot nematode (Pinochet et al., 2002). A large group of new rootstocks has been developed over the past few years in Eastern Europe. In particular, genetic improvement work conducted in Romania (Indreias et al., 2004) has led to the development of a number of rootstocks derived from peach seedling selections (e.g. ‘Tomis 1’, ‘Tomis 79’, ‘T16’, ‘P1s’, ‘Oradea 1’, ‘De Balc’) or from selections of interspeciﬁc crosses of Prunus spp. (e.g. ‘Adaptabil’, ‘Miroper’). In Hungary, a number of peach– almond selections are being investigated. These include ‘O.R.T. (XXXI) 50’, ‘O.R.T. (XXXI) 51’, ‘C 410’ and ‘PeMa’ (Z. Szabo, Hungary, 2004, personal communication). In Serbia, vineyard peach and Myrobalan seedling selections are being tested as peach rootstocks (Ognjanov et al., 2004). In addition, cold-hardy rootstocks have been developed for peach in Russia by G. Eremin from interspeciﬁc crosses of Prunus spp. The selections ‘VVA-1’, ‘VSV-1’ and ‘Kuban 86’ have been licensed for testing and trademarked as ‘Krymsk® 1’, ‘Krymsk® 2’ and ‘Krymsk® 86’, respectively.

Rootstock Development

In Asia, China has begun to select for rootstocks for its diverse geography and endemic soil and pest problems (Wang et al., 2002). However, no selections have yet been released outside China. In Japan, the ‘Tsukuba’ series (P. persica), the ‘Yusuraume’ series (P. tomentosa) and P. japonica selections have been developed (Yoshida and Seike, 1981; F. Loreti, unpublished results). All are root-knot resistant and semi-dwarﬁng except for the ‘Tsukuba’ series, which has a wide range of tree vigour.

8.5 Outlook New and better peach rootstocks from France, Italy, Spain and other countries will soon be available to replace older commercial rootstocks. Almost all of these rootstocks are species hybrids that must be propagated vegetatively, such that in vitro micropropagation is being

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or will be used to mass-produce these unique hybrid rootstocks. As new technology permits efﬁcient mass propagation of these valuable genotypes, proprietary issues (i.e. ownership, patent royalties) abound. This is due, in part, to the decrease in public research funding and the considerable resources and time invested to develop and test fruit tree rootstocks. Other factors also may complicate the commercial release of new rootstocks within and outside their country of origin, such as patent laws and licensing agreements that must be negotiated between government agencies, nurseries and grower groups. Despite these potential roadblocks, new rootstocks are gradually ﬁltering through to fruit growers. These improved cultivars together with the continued advances in biotechnology and the genome mapping of the Rosaceae family (www.rosaceae. org; Arús et al., 2006) will lead to even more dynamic rootstocks for peach within the next 20 years.

References Albás, E.S., Jiménez, S., Aparicio, J., Betrán, J.A. and Moreno, M.A. (2004) Effect of several peach × almond hybrid rootstocks on fruit quality of peaches. Acta Horticulturae 658, 321–326. Alcañiz, E., Pinochet, J., Fernández, C., Esmenjaud, D. and Felipe, A. (1996) Evaluation of Prunus rootstocks for root-lesion nematode resistance. HortScience 31, 1013–1016. Andreu, P. and Marin, J.A. (2004) Micropropagation enhances in vitro establishment and multiplication of new cultivars from field grown plants of Adesoto 101 (Prunus insititia) rootstock. Acta Horticulturae 658, 605–609. Arús, P., Yamamoto, T., Dirlewanger, E. and Abbott, A.G. (2006) Synteny in the Rosaceae. Plant Breeding Reviews 27, 175–211. Beckman, T.G. and Lang, G.A. (2003) Rootstock breeding for stonefruits. Acta Horticulturae 622, 531–551. Beckman, T.G. and Pusey, P.L. (2001) Field testing peach rootstocks for resistance to Armillaria root rot. HortScience 36, 101–103. Beckman, T.G., Reighard, G.L., Okie, W.R., Nyczepir, A.P., Zehr, E.I. and Newall, W.C. (1997a) History, current status and future potential of Guardian™ peach rootstock. Acta Horticulturae 451, 251–258. Beckman, T.G., Nyczepir, A.P. and Okie, W.R. (1997b) The USDA-ARS stone fruit rootstock development program at Byron, Georgia. Acta Horticulturae 451, 237–241. Bliss, F.A., Almehdi, A.A., Dandekar, A.M., Schuerman, P.L. and Bellaloui, N. (1999) Crown gall resistance in accessions of 20 Prunus species. HortScience 34, 326–330. Brooks, R.M. and Olmo, H.P. (1961) Register of new fruit and nut varieties: Nemaguard peach. Proceedings of the American Society of Horticultural Science 78, 634–635. Cambra, R. (1970) Selección de ‘Pollizos de Murcia’ y otros ciruelos locales españoles. ITEA Producción Vegetal 1, 115–126. Cambra, R. (1990) ‘Adafuel’, an almond × peach hybrid rootstock. HortScience 25, 584. Casas, A.M., Igartua, E., Balaguer, G. and Moreno, M.A. (1999) Genetic diversity of Prunus rootstocks analyzed by RAPD markers. Euphytica 110, 139–149. Cirulli, M., Amenduni, M., Colella, C., El-Shaer, E. and D’Amico, M. (2001) Ricerca di portinnesti resistenti alla tracheoverticilliosi. Italus Hortus 8, 50–52. Davis, J.R. and English, H. (1969) Factors related to the development of bacterial canker in peach. Phytopathology 59, 588–595.

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Okie, W.R., Beckman, T.G., Nyczepir, A.P., Reighard, G.L., Newall, W.C. Jr and Zehr, E.I. (1994b) BY520-9, a peach rootstock for the southeastern United States that increases scion longevity. HortScience 29, 705–706. Ottman, Y. and Byrne, D.H. (1988) Screening rootstocks of Prunus for relative salt tolerance. HortScience 23, 375–378. Pellegrino, S., Massai, R., Loreti, F. and Strocco, S. (1997) Comportamento bio-agronomico di alcune selezioni di pesco Franco innestate con la cv. ‘Maria Bianca’. Frutticoltura 11, 47–50. Perry, R., Reighard, G., Ferree, D., Barden, J., Beckman, T., Brown, G., Cummins, J., Durner, E., Greene, G., Johnson, S., Layne, R., Morrison, F., Myers, S., Okie, W., Rom, C., Rom, R., Taylor, B., Walker, D., Warmund, M. and Yu, K. (2000) Performance of the 1984 NC-140 cooperative peach rootstock planting. Journal of the American Pomological Society 54, 6–10. Pinochet, J., Calvet, C., Herenandez-Dorrego, A., Bonet, A., Felipe, A. and Moreno, M. (1999) Resistance of peach and plum rootstocks from Spain, France, and Italy to root-knot nematode Meloidogyne javanica. HortScience 34, 1259–1262. Pinochet, J., Fernandez, C., Calvet, C., Hernandez-Dorrego, A. and Felipe, A. (2000) Selection against Pratylenchus vulnus populations attacking Prunus rootstocks. HortScience 35, 1333–1337. Pinochet, J., Fernandez, C., Cunill, M., Torrents, J., Felipe, A., Lopez, M.M., Lastra, B. and Penyalver, R. (2002) Response of new interspecific hybrids for peach to root-knot and lesion nematodes, and crown gall. Acta Horticulturae 592, 707–716. Ramming, D.W. and Tanner, O. (1983) ‘Nemared’ peach rootstock. HortScience 18, 376. Reighard, G.L. (1994) Field performance of 28 Prunus rootstocks and interstems in South Carolina. HortScience 29, 476. Reighard, G.L. (2000) Peach rootstocks for the United States: are foreign rootstocks the answer? HortTechnology 10, 714–718. Reighard, G.L. (2002) Current directions of peach rootstock programs worldwide. Acta Horticulturae 592, 421–428. Reighard, G.L., Newall, W.C., Beckman, T.G., Okie, W.R., Zehr, E.I. and Nyczepir, A.P. (1997) Field performance of Prunus rootstock cultivars and selections on replant soils in South Carolina. Acta Horticulturae 451, 243–250. Reighard, G., Andersen, R., Anderson, J., Autio, W., Beckman, T., Baker, T., Belding, R., Brown, G., Byers, R., Cowgill, W., Deyton, D., Durner, E., Erb, A., Ferree, D., Gaus, A., Godin, R., Hayden, R., Hirst, P., Kadir, S., Kaps, M., Larsen, H., Lindstrom, T., Miles, N., Morrison, F., Myers, S., Ouellette, D., Rom, C., Shane, W., Taylor, B., Taylor, K., Walsh, C. and Warmund, M. (2004) Growth and yield of Redhaven peach on 19 rootstocks at 20 North American locations. Journal of the American Pomological Society 58, 174–202. Reighard, G.L., Ouellette, D.R. and Brock, K.H. (2006) Growth and survival of 20 peach rootstocks and selections in South Carolina. Acta Horticulturae 713, 269–274. Reighard, G.L., Ouellette, D.R. and Brock, K.H. (2007) Survival, growth and yield for Carogem peach on an interstem and two dwarfing rootstocks. Acta Horticulturae 732, 303–306. Remorini, D., Massai, R. and Loreti, F. (2005) Effetto del portinnesto e della gestione della chioma sulla qualità dei frutti di pesco. Frutticoltura 12, 43–48. Renaud, R. and Salesses, G. (1990) Prunier/pecher: deux nouveaux port-greffes. Fruits et Legumes 73, 22–23. Renaud, R., Bernhard, R., Grasselly, C. and Dosba, F. (1988) Diploid plum × peach hybrid rootstocks for stone fruit trees. HortScience 23, 115–117. Roberts, A.N. and Westwood, M.N. (1981) Rootstock studies with peach and Prunus subcordata Benth. Fruit Varieties Journal 35, 12–20. Roselli, G. (1998) Miglioramento genetico dei portinnesti presso il CNR di Firenze. Frutticoltura 4, 20–22. Salesses, G. (1977) Research about the origin of two Prunus rootstocks, natural interspecific hybrids: an illustration of a cytological study carried out in order to create new Prunus rootstocks. Annales de L’Amelioration des Plantes 27, 235–243. Salesses, G. and Alkai, N. (1985) Simply inherited grafting incompatibility in peach. Acta Horticulturae 173, 57–62. Salesses, G. and Bonnet, A. (1992) Some physiological and genetic aspects of peach/plum graft incompatibility. Acta Horticulturae 315, 177–186. Salesses, G., Renaud, R. and Bonnet, A. (1988) Creation de port-greffe par hybridation interspecifique au sein des pruniers. In: Proceedings of 8th Colloque sur les Recherches Frutieres. INRA-CTIFL, Bordeaux, France, pp. 151–159. Salesses, G., Dirlewanger, E., Bonnet, A., Lecouls, A.C. and Esmenjaud, D. (1998) Interspecific hybridization and rootstock breeding for peach. Acta Horticulturae 465, 209–217.

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9

Propagation Techniques F. Loreti and S. Morini

Department of Fruit Science and Crop Protection, University of Pisa, Pisa, Italy

9.1 Introduction 9.2 Nursery Seedling Propagation Nursery site and soil Propagation from seed 9.3 Nursery Hardwood Cutting 9.4 Greenhouse Semi-hardwood Cutting 9.5 Micropropagation Preparation of the propagation material Explant disinfection and setting up aseptic culture Shoot proliferation Rooting and preparation for in vivo growth Transfer and acclimatization of young plants Culture medium Problems connected to in vitro propagation 9.6 Embryo Culture 9.7 Stoolbeds and Layering 9.8 Scion Propagation Budding and grafting Micrografting Herbaceous grafting 9.9 Outlook

9.1 Introduction Crop efﬁciency of a peach orchard during its commercial life is inﬂuenced by several factors such as planting system, cultural practices, environmental and soil conditions. The nursery quality of the maiden trees used to plant the orchard also plays a prominent role because, if

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its quality is poor, it can invalidate the other factors. Tree quality is represented by a number of bioagronomic, genetic and sanitary characters, which collectively make the orchard capable of reaching its higher cropping potential. Tree quality depends on the right choice of plant material, propagating techniques and cultural management in the nursery.

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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Peach cultivars, like the majority of fruit tree species, are genetically heterozygous and therefore propagated exclusively by asexual methods. This is considered necessary because reproduction from seed produces individuals that differ appreciably from one another and from the parent tree. Thus, although current propagation techniques make it possible to obtain selfrooted varieties, grafting desirable scions on to suitable rootstocks still represents the most common propagation technique for peach. Grafting is also favoured by the recent development of a wide range of rootstocks capable of overcoming the problems related to biotic and abiotic stress that could not be satisfactorily addressed with self-rooted cultivars. In addition, scion vigour can more easily be controlled by the use of appropriate rootstocks, which limit canopy growth and consequently also reduce management costs. Further advantages of medium–low vigour rootstocks are their ability to induce early cropping of the scion and enhance its production efﬁciency; they also adapt well to the current trend towards increased planting density even in highly fertile soils. Budding and grafting represent the worldwide method for scion cultivar propagation. For rootstocks, on the other hand, both sexual and asexual propagation methods can be adopted.

9.2 Nursery Seedling Propagation Nursery site and soil For establishment of nursery activities, there are several general principles that must be observed. Of particular importance is the choice of nursery site and soil. Both of these aspects are fundamental for economically sound nursery management. In choosing an appropriate site, the nursery should be established on a topographically level site to facilitate the various cultural operations, with easy access to irrigation water and in full sun. Ideally, areas that may be affected by late spring frost should be avoided, as young growing shoots could suffer freezing injury during the growth phase, resulting in

stunted maiden trees that are too small for commercial sale. This is of particular importance if the June budding technique is to be adopted. Grafting operations can be conducted in June only if the rootstock has achieved a sufﬁcient diameter by the end of spring. Windy sites should be avoided because they require the additional cost of protection by an artiﬁcial or living windbreak. Proximity to the ocean coast should likewise be avoided because winds carrying salt can cause foliar damage leading to fairly extensive necrosis especially of young leaves and shoot tips. Choice of soil type is important. Soil textures that are too heavy, too light or poorly drained should be avoided. To obtain goodquality rootstocks it is necessary to choose medium-texture, well-drained soils with access to irrigation water. A further requirement is that soils previously used for peach growing should be avoided in order to preclude the risk of replant disorders. Nurserymen who do not have sufﬁcient land available to ensure proper rotation of the nursery plants are obliged to treat the soil with fumigants. Methyl bromide is the most commonly used fumigant, especially for the control of nematodes. However, it should not be overlooked that this fumigant not only creates problems of a microbiological nature, but also its use throughout the European Union was prohibited after 2005. As an alternative, good results have been obtained by soil solarization (Katan and DeVay, 1991), which has been adopted for replant problems in peach nurseries (Di Vaio et al., 2001). In addition, it is essential to acquire information on soil nutritional status and pH prior to nursery establishment. A deﬁciency of macro- or microelements could be corrected by suitable fertilization. It is more difﬁcult, on the other hand, to correct pH when active limestone results in a pH of 8–10, causing severe symptoms of leaf chlorosis. Finally, soils contaminated with crown gall (Agrobacterium tumefaciens) should never be used for nursery production. Propagation from seed Propagation from seed still represents the most widely adopted method for nursery

Propagation Techniques

production of peach seedling rootstocks. Although the availability of clonal rootstocks for peach has over the last few years led to progressively decreasing use of seedlings, there are a number of reasons why seedlings are still the preferred propagation method today. The ﬁrst reason is economic given the lower cost of obtaining pits (stones) and producing seedlings in the nursery as compared with clonal rootstocks, the latter requiring royalty fees. Another reason consists of the easy availability of seedlings to the nursery market, as the material utilized is obtained from the seed of commercial varieties extracted during industrial processing, from Prunus sylvestris (Slavic seedling) produced at low cost in the Balkan countries or, in some cases, from wildtype peaches, although the latter are now used only in countries with less advanced fruit-growing practices. A wide selection of interesting peach seedlings is now available, carefully selected for speciﬁc genetically homogeneous characters transmitted to the progenies by sexual reproduction. If selected seedlings are to be used, the pits are produced by setting up special ﬁelds of seed-bearing mother trees. Care is taken to isolate them from any peach orchards in the vicinity, to prevent unwanted cross-pollination. Examples of such seedling lines are ‘Rubirà’, ‘Higamà’ and ‘Montclar’ from France; ‘P.S.A5’, ‘P.S.A6’ and ‘P.S.A7’ from Italy; ‘Siberian C’, ‘Bailey’ and ‘Harrow Blood’ from Canada; and ‘Nemaguard’, ‘Nemared’ and ‘Guardian’ from the USA. Not only are these seedlings homogeneous within their line, but they have also been selected for their different degrees of vigour, frost resistance induction of the scion, or reduced susceptibility or resistance to nematodes. Seed provenance and characteristics are important considerations for seed propagation. Seeds should be obtained from areas having a climate similar to the planned growing area, in order to avoid any difﬁculty of climatic adaptation that could result in stunted growth. This danger is particularly likely to arise if seedlings are grown in a colder climate than the area of seed provenance (Hartmann et al., 2002). When pits are supplied by the processing industry, it is preferable to make use of varieties

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that have already been tested as rootstocks. Many commercial varieties commonly used for processing are important seed sources for rootstocks. Such is the case of ‘Lovell’, ‘Halford’, ‘Bailey’ and ‘Suncling’ in the USA, Canada and Mexico; ‘Polara’ and ‘Sims’ in Argentina; ‘Algrighi’ and ‘Capdeboscq’ in Brazil; and ‘Golden Queen’ and ‘Elberta’ in Australia, etc. It is clear that such varieties produce rootstocks whose characteristics are less uniform than in genetically selected lines of peach, but they are still more satisfactory than wild-type peach. A useful precaution is to avoid collecting seeds from very early-ripening varieties, as these have poor germination ability due to the presence of aborted or immature embryos. It is also important to separate the pits promptly from the fruit ﬂesh, preferably as soon as the fruit has been picked, after which they should be washed and dried and placed in storage rooms until needed for stratiﬁcation. Knowledge of seed dormancy constitutes another crucial factor in nursery practice. Dormancy is due partly to the presence of the stony endocarp, which prevents moisture penetration, with the result that seed imbibition and embryo development cannot take place. But it is also caused by the presence of inhibiting substances such as abscisic acid, which is considered to be an important factor preventing seed germination and inducing embryo dormancy in other stone fruits as well (Lang, 1996). Dormancy breaking can be achieved by stratifying pits in sand or other material that is kept moist and well aerated. Stratiﬁcation is maintained at a temperature of 3–5°C for 10–12 weeks of vernalization but with the possibility of varying both the temperature and the duration as a function of the rootstock’s speciﬁc chilling requirements. It is generally observed that by stratifying the pits at 5°C, the highest germination percentage is obtained after 60 days for ‘P.S.A6’ and after 74 days for ‘P.S.B2’. Higher temperatures or insufﬁcient chilling could lead to development of seedlings with normal roots but rosetted epicotyls. Excessive duration of cold stratiﬁcation could induce a portion of seeds to enter secondary dormancy (Guerriero and Scalabrelli, 1984).

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Other methods are also available for breaking dormancy, such as pit scariﬁcation or hormone treatment of seeds. In the former case, the aim is to crack the woody endocarp in order to make it permeable to moisture and oxygen, but without damaging the seed. For hormone treatment, gibberellic acid (GA3) may be used to overcome physiological dormancy and stimulate germination in seeds with dormant embryos (Koornneef et al., 2002). It may also be possible to allow chilling to occur directly in the ﬁeld in the autumn (direct seedbed sowing or even row sowing in mounds), although a brief period of stratiﬁcation may still be beneﬁcial. While this technique may be advantageous in order to perform budding in June (on account of more rapid seedling growth), it may cause a poorly branched root system and consequently be more affected by transplantation once the rootstock liners are planted out. The row spacing adopted in the nursery is important. While inter-row spacing may to some extent depend on the implements utilized for normal cultural techniques, it is advisable not to adopt excessively close spacing within the row, in contrast to the tendency often observed in common nursery practice. Adequate spacing within the row is particularly important when it is necessary to obtain maiden trees that are abundantly feathered between 40 and 60 cm from the ground. It is likewise crucial for certain training systems, such as the sprint palmette, free spindle and delayed open centre, in which these feathers are used to build the framework of the ﬁrst branches.

9.3 Nursery Hardwood Cutting Propagation from cuttings is based on the ability of plant cells to resume meristematic activity and produce adventitious roots in tissues that have reached a fairly advanced stage of differentiation. Since the cutting is represented by a portion of an organ (growing shoot, dormant shoot, leaf or root) that is separated from the mother plant, it may suffer from the inﬂuence of environmental conditions. Thus in order to promote rooting, metabolic activity

must be shielded from the adverse effects of stress that could impair rhizogenesis. Only species characterized by a naturally high rooting potential or endowed with burr knots can be propagated by setting the cuttings to root directly in the nursery. Numerous studies on the behaviour of self-rooted peach cultivars have shown that the results are poor. However, this propagation method is adopted exclusively for some clonal rootstocks. Among the various types of cuttings (softwood, semi-hardwood and hardwood), hardwood and to a lesser extent semi-hardwood cuttings are the only ones used for commercial peach propagation. Hardwood cuttings collected from the mother trees during the autumn– winter period are generally 25–30 cm long and are taken from the median or apical portion of 1-year-old shoots. Since they are composed of a number of distinct tissues, hardwood cuttings generally possess nutritional, energy and hormone substances capable of inducing root initiation and the consequent development of adventitious roots. But when such substances are present in insufﬁcient quantity to promote rhizogenesis, appropriate treatment or propagation techniques must be undertaken to enhance the rooting process. It should also be noted that the rhizogenic potential of a given peach rootstock or cultivar is dependent upon a number of factors, including the characteristics of the mother tree, the time of harvesting of the cuttings, rhizogenic treatment and the propagation technique adopted. It has been extensively documented for many species that there are distinct advantages in taking cuttings from trees reared exclusively for the production of propagation material. This not only guarantees that the cuttings will be genetically true to type and of suitable health status, but it also allows better control over the factors inﬂuencing their rooting potential. Thus it is well known in nursery practice that the management techniques applied to mother trees can exert positive effects on the rooting potential of cuttings, although no documented studies on this aspect in peach are available. For example, the type of training can inﬂuence rooting by modifying the vigour of branches from which cuttings are taken: if trees are severely pruned to encourage the formation of more vigorous

Propagation Techniques

branches, a favourable effect on rooting is generally observed (Bartolini and Fiorino, 1978). It was also found that the application of speciﬁc fertilizer dressings may modify the tissue nutritional balance, leading to more effective induction and growth of adventitious roots. In this regard, some minerals such as P, K, Ca and N have been shown to be signiﬁcantly involved in the rooting process (Blazich, 1988). Furthermore, the use of stock hedges maintained for harvesting cuttings not only allows implementation of management techniques speciﬁcally designed to ensure good-quality cuttings (fungal and hormone treatment to enhance the rooting potential of cuttings), but also facilitates the planning and harvesting of propagation material at times most suitable for rhizogenesis (Bartolini and Fiorino, 1978). In this context, one important observation is that the time of harvesting of cuttings has a noticeable effect on adventitious root formation, which shows marked variation in response during the autumn–winter period. Some studies (Loreti et al., 1985) have reported that peach cuttings taken between October and January generally exhibit a more satisfactory rooting response in the northern hemisphere. Some plum rootstocks used for peach, which either are now very infrequent or have been completely abandoned, such as ‘Brompton’, ‘S. Giuliano A’, ‘GF 1869’, ‘GF 43’ and ‘GF 655/2’, were long propagated from cuttings harvested during this period. More recently, other rootstocks have shown fairly high rooting percentages when cuttings are harvested during the autumn period. Among the different genotypes, a certain variability of response in relation to different time periods is observed. Consequently, the outcome of rooting may not always be fully satisfactory. A number of physiological markers of rooting competence (e.g. content of auxins and phenolic compounds, enzymes, etc.) appeared to be related to the rooting of cuttings (Fadl and Hartmann, 1967; Bassuk and Howard, 1981; Bhattacharya, 1988), but they were not always reliable among the several species to predict rooting response. Recently, another physiological parameter not directly involved in the rooting process (i.e. redox status), has provided interesting results as a

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rooting marker (Sorce et al., 2004). Moreover, only for a few species (Lorenzi and Ceccarelli, 1978) are reliable and easily recognizable morphological rooting markers known to identify the most suitable moment for taking cuttings. In most cases to date, the time for harvesting cuttings is established empirically on the basis of the operator’s experience regarding the behaviour of a given genotype. The duration of the period in which cuttings have the greatest rooting potential is another highly important factor for the success or failure of the rooting process. Some rootstocks, such as the peach–almond hybrid ‘GF 677’, have only a limited period during which cuttings can be taken, namely from December to January. Other peach genotypes, such as ‘P.S.B2’, have a much longer period, ranging from September to January (Loreti et al., 1985). However, if cuttings of this rootstock are harvested towards the end of winter, rooting shows no appreciable difference whereas bud take in the ﬁeld is often drastically reduced. This highlights the crucial role of the time of harvesting on successful propagation. Despite this awareness, the phenomena that cause rhizogenesis to vary with variations in time of harvesting remain to be determined. While considerable importance is attributed to tissue physiological conditions and to the balance between different hormones that act as inhibitors or promoters of rooting, a multiplicity of factors can directly or indirectly inﬂuence the rooting process and some of these are yet to be deﬁned (Loreti and Pisani, 1982). In general, with hardwood cuttings, a substantial improvement in rooting has been obtained by applying auxins. Auxin applied to cuttings from rootstocks with good natural rooting potential was able to further enhance rooting performance when the cuttings were allowed to root directly in the nursery. But the most widespread and increasingly popular utilization of auxins in nursery practice concerns rootstocks that show poor rhizogenic activity, which in the past suffered from a very low success rate for propagation from cuttings. Many auxin compounds are available, among which IBA (indole-3-butyric acid) is the most frequently used. It can be applied at

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concentrations ranging from 10–20 ppm (dilute solutions) up to 1000–3000 ppm (concentrated solutions). In the former case, treatment consists of dipping the base of the cuttings into the solution for 12–24 h, while a quick dip of just a few seconds is sufﬁcient with concentrated solutions. An alternative method uses a powder preparation, which is more practical to handle but has proved to be less effective. The solutions generally used for peach hardwood rootstock cutting propagation are water–alcohol solutions with IBA concentrations ranging from 1000 ppm, to promote rooting of ‘P.S.A5’ or ‘P.S.B2’, to up to 2000 ppm, for the rootstocks ‘Tetra’ and ‘Penta’ (Nicotra and Moser, 1996). Additional procedures are sometimes adopted to further enhance rooting. In certain cases the cutting material is etiolated prior to IBA treatment, while at other times the cuttings may be subjected to washing for 24 h in running water before auxin is supplied. Rooting of cuttings treated with auxin can be enhanced by bottom heating. In fact, an appreciable improvement in both rooting and transplant take of November–January-harvested cuttings was observed with this technique (Erez and Yablowitz, 1981; Scalabrelli and Couvillon, 1986). This method exploits the positive effect of temperature in promoting tissue metabolic activity, whereby heat applied in conjunction with auxin treatment enhances the root induction process of cuttings harvested during the winter rest period (Fiorino and Loreti, 1965). Generally, in order to trigger formation of root initials, it may be sufﬁcient to maintain a temperature of 18–20°C for a few days around the basal portion of the cuttings, taking care to ensure that the upper part remains exposed to the cooler ambient temperature so that buds remain in the state of rest. The equipment required to set up bottom heating is simple and inexpensive: all that is needed is a heated bin supplied with a heat source at the base and a thermostat to set and maintain a constant temperature. Cuttings are planted in an inert medium, generally composed of perlite or perlite plus peat (3:1), which allows good aeration and suitable humidity. Cuttings rooted by this method usually exhibit a good root system with buds that are still quiescent, favouring successful transplant

take in the nursery (Fig. 9.1/Plate 62). Best results are obtained when a hardening phase is included prior to transplanting the rooted cuttings. This involves gradually decreasing the bin temperature until ambient temperature is reached, enabling root tissues to achieve a higher degree of differentiation and greater stability, with the twofold advantage of reducing the risk of transplantation injury and encouraging more rapid resumption of water and nutrient uptake from soil. However, in peach one important feature that should not be overlooked is that even if the rooting and transplanting stages are carried out with the utmost attention in order to preclude any damage to the roots, not all cuttings will survive in the nursery. Also, a certain degree of cutting mortality is noted during the rooting stage as well, regardless of whether rooting took place in the heated bin or directly in the nursery. Research into the underlying causes of this problem has shown that cuttings undergo a collapse that starts from the basal tissues, leading to the formation of large lysigenous areas which in turn cause the detachment of cortical tissue from the xylem (Fabbri, 1977; Biricolti et al., 1990). The cutting collapse seems to be independent of propagation techniques or the various treatments, while it is probably related to prunasin, a cyanogenic glycoside that decreases during rooting (Fiorino and Mattii, 1992). An increase, albeit still somewhat limited, in the cutting survival rate could possibly be obtained by subjecting the basal tissues of the cutting to washing for 24 h, both before auxin treatment and before transplanting rooted cuttings to the open ﬁeld (Bartolini and Fabbri, 1982). Washing would appear to have the effect of favouring removal of the above-mentioned cyanogenic glycosides or of some intermediate decomposition products such as cyanidric acid. Overall, bottom heating continues to offer a useful method for propagation of peach rootstocks, hardwood cuttings being taken from the end of autumn to the beginning of winter and then treated with IBA. As noted in the ‘Nursery Seedling Propagation’ section above, numerous rootstocks are propagated using this method including ‘Penta’, ‘Tetra’, ‘Adesoto 101’, ‘GF 677’, ‘Adafuel’, ‘Adarcia’, ‘Myran Yumir’, ‘Citation’, ‘Hansen 2168’, ‘Hansen 536’

Propagation Techniques

227

Fig. 9.1. Rooted hardwood cuttings of peach.

and ‘Yulior’, giving results that can vary from satisfactory to very good. But it should be kept in mind that these are now almost exclusively propagated in vitro.

9.4 Greenhouse Semi-hardwood Cutting As an alternative to propagation by hardwood cutting, semi-hardwood cuttings are

sometimes collected to propagate peach cultivars and rootstocks. Characterized by tissues that are still undergoing differentiation, semi-hardwood cuttings are harvested in the northern hemisphere during mid-July to mid-August, from non-ligniﬁed shoots. Since shoots have a partially woody consistency and generally have two leaves, semi-hardwood cuttings can only be used in conjunction with mist propagation

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(Fig. 9.2/Plate 63). This technique enables elevated relative humidity to be maintained inside the rooting environment (glasshouse, tunnel or special open-air facility) by means of a ﬁne mist spray. This leaves a thin ﬁlm of water on the leaves, thereby reducing evapotranspiration and the overall temperature of the cutting, with the latter continuing to exercise its metabolic activity. However, even with the most sophisticated devices for delivery of carefully measured quantities of water, total control of leaf evapotranspiration cannot easily be achieved on account of the variations in temperature and light intensity at different times of the day. Therefore the risk that cuttings may suffer water stress can never be excluded. If results are unsatisfactory when only a mist spray is applied, a cooling system and shade cover may provide a means of decreasing the temperature and light intensity within the glasshouse. In addition to the need for a suitable environment to avert the risk of water stress, semi-hardwood cuttings, like hardwood cuttings, show a better rooting performance when treated with auxins (Fig. 9.3/Plate 64). IBA is the most extensively used, but in some cases

Fig. 9.2.

good results have also been achieved with NAA (naphthalene acetic acid) or mixtures of the two hormones. Ideally concentrations should be low, and whenever possible it is preferable to use the water-soluble IBA potassium salt, rather than requiring a water–alcohol solution. Total auxin concentrations range between 100 and 500 ppm up to a maximum of 1000–3000 ppm. The base of the cutting is dipped in the solution for just a few seconds. Higher concentrations can lead to tissue dehydration due to the elevated alcohol content. This could lead to disintegration of cortical tissues at the base of the cuttings which may be predisposed to fungal and bacterial attack. Potential damage can be averted by using porous media, such as perlite, which allows good aeration and facilitates water drainage. Interesting rooting results have also been obtained by spraying cutting leaves with auxin (IBA or NAA at 25–50 ppm) in addition to, or instead of, the basal treatment (Fiorino and Vitagliano, 1968). Thus basal applications of 1000 ppm IBA combined with leaf spraying of 50 ppm IBA on ‘Okinawa’ cuttings resulted in 90% rooting, with more roots per cutting. Other promising treatments that enhanced

Mist propagation facility for rooting of semi-hardwood cuttings.

Propagation Techniques

229

Fig. 9.3. Rooted semi-hardwood cuttings that were treated with auxins.

rooting include spraying leaves with nutrient solutions at the end of each daily water-misting cycle. Treatment with boron, potassium and manganese was likewise found to increase the rooting percentage of ‘Okinawa’ cuttings, while manganese and iron were observed to be particularly active, achieving a noticeable increase in rooting by preventing early leaf senescence (Fiorino and Vitagliano, 1968). Although the rooting treatment clearly plays a crucial role in the rhizogenic process, it is by no means the only factor. The particular shoot portion from which the cutting is taken also has major importance, with apical cuttings giving a better rooting response than basal cuttings in some genotypes, while the opposite appears to be true in other genotypes (Marini, 1983). Many other aspects must also be taken into consideration, and nurserymen may often be guided by their own experience acquired in nursery practice. One vital aspect, however, common to all semi-hardwood cuttings, is the need for

extreme care through acclimatization prior to transfer to the open ﬁeld. This is because the leaf stomatal closure mechanism on new shoots developed during the rooting stage is slowed down because of the elevated relative humidity in the misting glasshouse. Thus, water loss from tissues can be severe once the cutting is transferred to the external environment. Therefore the cuttings must undergo a period of gradual reduction of relative humidity by progressively increasing the time intervals between misting operations. Alternatively, cuttings can be placed under shading facilities equipped with irrigation, until the delicate tissues have become accustomed to external environmental conditions and developed a sufﬁcient cuticle. A further consideration is that a considerably longer period of time is required to obtain a rootstock that can be budded with the scion. Since the cuttings are harvested during the summer and time must be allowed for root formation and acclimatization, trees will not

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be ready for grafting until the end of summer the following year. This means an extra burden of management costs in addition to the expense incurred in setting up the misting glasshouse, so that overall costs for semihardwood cuttings are likely to be noticeably higher than for hardwood cuttings. Assessment of the costs and beneﬁts of the different techniques must be conducted by the individual nurseryman based on speciﬁc nursery requirements. Economics aside, it can be stated that propagation by semihardwood cutting with the aid of the misting technique can be performed for a fairly wide range of clonal peach rootstocks, as described in the previous section.

9.5 Micropropagation Micropropagation is a method of vegetative propagation performed in the laboratory by means of in vitro tissue culturing. It is based on the concept of cell totipotency, ﬁrst hypothesized by Wichow in 1858 (Vasil and Vasil, 1972). Many studies with in-depth research were undertaken before it became possible to propose this technique as a commercial propagation method. A fundamental step in this developmental process was made by Morel (1964), who was the ﬁrst to succeed in clonal propagation of orchids from shoot tips. Since then notable progress has been achieved with horticultural species. Research on fruit trees began somewhat later, but intense experimental work has made it possible to move within just a few years from laboratory studies to commercial nursery production (Fiorino and Loreti, 1987). At present, micropropagation is adopted for a considerable number of fruit tree species, including varieties – but above all rootstocks – which have displayed severe limitations with conventional propagation methods. Micropropagation represents the most widely adopted method for propagation of numerous peach clonal rootstocks. With micropropagation many plants can be obtained with a small amount of starting material, within a very short period of time and in an extremely small space (Fig. 9.4/ Plate 65). As numerous new plantlets can be

obtained from a starting single bud or shoot tip, even one mother tree can be a sufﬁcient explant source. In addition, this technique makes it possible to propagate species (cultivars and rootstocks) characterized by poor rooting ability and therefore difﬁcult to multiply with traditional techniques. As the entire propagation cycle takes place in the laboratory, greater ﬂexibility is achieved in planning the production, which is no longer dependent on environmental and cultural conditions. It is also worth noting that in vitro-propagated plants not only are easily transportable, but are also subjected to less rigorous controls by customs, health authorities and quarantine services since the plantlets are free from pathogenic microorganisms at the end of the production cycle. In comparison with traditional propagation techniques, however, micropropagation presents several disadvantages. High costs are incurred in setting up the laboratories and purchasing the necessary consumables. Specialized scientiﬁc personnel as well as highly skilled operators are needed. Furthermore, somaclonal variation may arise in new adventitious shoots when the material is maintained in vitro too long. Plants with juvenile characteristics may also appear. Most of these negative aspects can be overcome by adopting suitable remedies at speciﬁc stages of micropropagation. Overall, the process leading from preparation of the mother trees to acclimatization of the new plantlets has been subdivided into ﬁve stages, representing the main steps of the micropropagation cycle (Fig. 9.5/Plate 66).

Preparation of the propagation material This step involves preparing the mother trees (or portions of these) from which explants will be collected for later culturing. The mother trees must not only possess the genetic characteristics of the cultivars and rootstocks to be obtained, but must also satisfy speciﬁc health requirements. In particular, they must be virusfree and have the lowest possible microbial load on external tissues, in order to ensure effective explant sterilization. Subjecting the

Propagation Techniques

231

Fig. 9.4. Hundreds of micropropagated plantlets in a commercial facility.

mother trees to one or two fungicide applications some days prior to explant harvesting has been found to facilitate achievement of the appropriate health status. A highly effective technique to sterilize the starting material consists of rearing the plants after having satisﬁed their chilling requirement. This is performed in a controlled environment with strict monitoring of light, temperature and hygiene conditions, where the buds will be induced to open and form new shoots. Given their low microbial load, such shoots can easily be sterilized in large quantities. Similar results can be obtained using robust and well-ligniﬁed 1-year-old branches. It is worth pointing out that the operations noted below and those carried out in the

following rooting stage should be conducted in a sterile environment, using a laminar ﬂow hood and taking care to sterilize working tools each time.

Explant disinfection and setting up aseptic culture This step consists of decontaminating the explants from any infectious agents that may be present. The success of this operation depends on the products utilized, as well as explant type and size. For peach, a single-node cutting is taken from actively growing shoots. The axillary bud is left intact but the axillary leaf is removed. Alternatively, after removing

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Culture establishment

Acclimatized plants

Shoot tip collection

Shoot proliferation

Plantlet acclimatization

Shoot rooting

Fig. 9.5.

The main steps of the micropropagation cycle.

larger leaves, a shoot tip explant no longer than about 1 cm may be used. Explants are washed under running water for 30 min and then sterilized with 20% sodium hypochlorite for 20 min or 0.15% mercury chloride for 8 min. These treatments have proved to be effective without causing appreciable tissue damage. Following sterilization, explants are rinsed three or four times in sterile distilled water and after renewing the explant basal cut they are transferred to proliferation medium.

Shoot proliferation The aim of this stage is to promote shoot formation from the axillary buds of each growing

explant. To induce this process, growth regulators (cytokinins) are added to the culture medium in order to reduce apical dominance. For peach, the most frequently used growth regulators are benzylaminopurine (BAP) and kinetin, varying from a minimum of 0.5–0.6 mg/1 to a maximum of 1–1.2 mg/1 in relation to the genotype and type of explant. Thus while it has been found sufﬁcient to add BAP 0.6 mg/1 to MS basal medium (Murashige and Skoog, 1962) in order to induce proliferation of ‘Hansen 2168’ and ‘Hansen 536’ rootstocks (Martinelli, 1985), for ‘P.S.B2’ the best results are obtained by adding BAP 1.2 mg/1 to WPM medium (Lloyd and McCown, 1980). N has also been shown to improve both initial growth and the number of axillary buds (Loreti et al., 1988).

Propagation Techniques

Proliferation can also be favourably inﬂuenced by the growth cabinet light conditions. A 4 h light/2 h dark cycle stimulates in vitro shoot formation and growth more successfully than a 16 h/8 h cycle (Morini et al., 1990). Other factors found to inﬂuence growth of cultures include the photoperiod, light quality (Loreti et al., 1991), agar type and concentration (Debergh, 1983) and culture vessel relative humidity (Sciutti and Morini, 1993). Once the optimal conditions for proliferation have been identiﬁed, the axillary buds are separated from each propagule. These are then transferred to fresh medium (subculture) every 15–20 days. The proliferation rate may at times be fairly low during the ﬁrst subcultures, but increases noticeably in subsequent subcultures. In peach rootstocks the rate is fairly high, ranging from a minimum of 10–15 shoots in some peach × almond clones (Loreti et al., 1985) to a maximum of 30–35, as in the case of ‘GF 677’ and plum ‘Mr.S. 2/5’. Rooting and preparation for in vivo growth Shoots obtained from the proliferation stage are separated and allowed to root on an auxin-enriched medium. Prior to rooting, it may be necessary to transfer poorly developed shoots to a medium containing cytokinin at low concentration in order to stimulate shoot extension. This operation results in more robust, homogeneous shoots that root better and are easier to handle. The auxins most widely utilized to promote rooting are IBA, IAA (3-indoleacetic acid) and NAA, supplied singly or in combination with one another. Concentration varies from 0.5 to 1–1.5 mg/1. It should be noted that rooting shoots may sometimes suffer pronounced stress due to a sudden change in the type of hormone used. During root induction in peach, an increased auxin concentration frequently causes leaf yellowing although rooting is not affected. Supplementing the substrate with polyamines leads to a marked improvement in quality of the rooted shoots, which thus develop good roots and normal leaves. The auxin concentration is of crucial importance. With excessive auxin, growth of the shoot tip may be slowed or arrested. This would have a

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negative effect during the acclimatization stage, in which the plantlets would no longer be capable of resuming rapid growth. Many other factors can inﬂuence the rooting stage, such as donor plant age and physiological status, juvenile status acquired through the various subcultures, temperature, light intensity and light/dark cycles in the growth chamber, in addition to the various components that make up the culture media (Debergh and Read, 1991). For most microcuttings, root induction takes place in vitro. However, after rhizogenic treatment the microcuttings could be allowed to root directly in vivo in a protected environment supplied with fogging or misting equipment. Generally initiation occurs in the presence of auxins, but some times they do not appear to be effective on rooting. Other substances, such as phenols and gibberellins, would seem to improve rooting ability. Some authors (Mosella Chancel et al., 1980) have suggested adopting a threephase procedure for in vitro rooting of a peach rootstock, modifying the hormone composition of the culture medium. In such an approach, induction occurs in the presence of auxins (IAA or NAA) and phenolic substances (phlorizin); initiation then takes place in the presence of the same auxins, phenolic substances (quercetin, rutin) and gibberellin (GA3), while root elongation is achieved in the absence of auxins and cytokinins but with gibberellin (GA3). In day-to-day practice, most micropropagation laboratories have developed their own experimental protocols. Their procedures are based on the fundamental principles of micropropagation and the most recent acquisitions of scientiﬁc research, but are designed also to reﬂect the laboratory’s speciﬁc experience in working on propagation of the different species, cultivars or clones. Transfer and acclimatization of young plants Young plantlets are next transferred from the culture vessel to the external environment. The transfer stage is an extremely delicate part of the micropropagation technique, as in vitrogrown plantlets frequently exhibit profound changes in the structure and functioning of their organs, potentially leading to stress during

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acclimatization. The extent of stress varies as a function of the species, cultivar or clone and also the methodology adopted. After the plantlets have been removed from the culture vessel, the root system is carefully washed and the plantlets are transplanted to the new medium. They will generally take more successfully if placed in a greenhouse equipped with a double tunnel, in similar temperature and humidity conditions as in the culture vessel. Once vegetative activity has resumed, temperature and humidity are gradually reduced until external environmental conditions are reached (Fig. 9.6/Plate 67). While duration of the acclimatization phase may vary depending on the genotype, it is normally around 20–30 days, after which the plantlets have grown to a height of 15–20 cm and achieved a sufﬁciently elevated degree of differentiation to allow transfer to the open ﬁeld (Morini and Barbieri, 1986). Planting out in the ﬁeld should be conducted in suitable climatic conditions, to avoid exposing the plantlets to excessive stress. Culture medium The success of micropropagation depends to a large extent on the type of culture medium

Fig. 9.6.

utilized. The medium is composed of macroand microelements, vitamins, growth regulators such as cytokinins, gibberellin and auxins, and a gelling agent (agar) to ensure that it is sufﬁciently compact to maintain the cultures in a vertical position. Furthermore, since in vitro cultures have only limited photosynthetic ability on account of the scant available carbon dioxide and low light intensity, the medium is also enriched with sucrose as an energy source. It is difﬁcult to state exactly what the best substrate for each rootstock is, as the response of a culture depends on a multiplicity of factors that may differ from one laboratory to another. This means that a given medium may need to be adjusted in various ways in relation to the response obtained from a given rootstock. In general, however, MS medium is the most widely used and has been extensively modiﬁed to adapt it to the various species. This medium has given excellent results with plum ‘Mr.S. 2/5’, ‘GF 677’, ‘GF 43’, ‘Damasco 1869’, ‘San Giuliano 655/2’ (Zuccherelli, 1979), ‘Nemaguard’ (Miller et al., 1982) and with some peach cultivars (Hammerschlag, 1982). Some clones of the ‘I.S.’ series (peach × almond hybrids) have given a better response with DKW medium (Driver and Kuniyuki, 1984).

Acclimatization of young micropropagated plantlets.

Propagation Techniques

Problems connected to in vitro propagation A number of problems arising while the explants are undergoing in vitro culturing or during the acclimatization stage may affect the outcome of this technique. Some of these difﬁculties are fairly easy to solve, while others are more complex and at times inseparable at the current state of scientiﬁc knowledge. Problems arising during in vitro culturing It is not unusual, especially during the spring, for culture vessels to be contaminated by fungi and/or bacteria. The cause of contamination frequently resides in inappropriate handling by the operator within the laminar ﬂow hood or inadequate sterilization of tweezers and scalpels. Such aspects are easily identiﬁed and can be solved simply by greater care in execution of the manoeuvres. Insufﬁcient sterilization of the culture substrate may constitute another possible cause. Other contaminations of a bacterial nature may appear at the base of the explant in cultures that have undergone prolonged in vitro culturing. In such cases, contamination may conceivably have arisen from bacteria that are endogenous to the tissue itself and happen to have found ideal growth conditions in the particular medium, although it can be difﬁcult to make a deﬁnite diagnosis. In seeking to attenuate the damage and restore explant viability, it is important to ascertain the intensity of contamination and the culturing stage during which it is manifested. During the shoot proliferation stage, if contamination is not severe, a successful remedy is to adopt PPM™ (Plant Preservative Medium), a heat-stable preservative/biocide which can be used to effectively prevent or reduce microbial contamination in plant tissue culture. This compound can slow down or halt bacterial development and enable a certain number of subcultures to be performed without appreciable effect on growth. Alternatively, rooting may be induced early in an attempt to salvage the greatest possible number of plantlets. Tissue vitriﬁcation can also represent a troublesome problem, appearing with variable incidence in relation to the genotype.

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Vitriﬁcation results from excessive water uptake by tissues and the symptoms are unmistakeable. If a culture has a predisposition to this condition, the symptoms will become more prominent with increasing culture growth. Attempts to alleviate or eliminate this problem should therefore focus on reducing the cytokinin concentration, or using a less biologically active cytokinin, increased agar and/or sucrose concentration, or lower culture vessel relative humidity. Since some peach rootstocks have notable susceptibility to vitriﬁcation, this phenomenon must be carefully monitored and kept under control to avoid excessive loss of cultures. Finally, explant tissues respond to the stimulus of the basal cut by producing parenchyma cells which appear as small or medium-sized masses of callus. However, the extent of the response varies with the genotype. Explant callus tissue is also stimulated by the presence of auxin in the proliferation substrate, even when the auxin concentration is very low. In general, the presence of callus at the explant base is undesirable, especially if a considerably large mass is produced. Under the stimulation of cytokinin, such callus could give rise to the differentiation of adventitious shoots of uncertain genetic characterization. The presence of callus during the shoot rooting stage likewise represents an undesirable phenomenon, because it may adversely affect subsequent plantlet acclimatization by favouring the development of microorganisms present in the transplantation substrate. In addition, it may undergo laceration, allowing the onset of rotting at the rupture site. Problems arising during plantlet acclimatization Shoot cultures may undergo pronounced changes in tissue structure and growth mechanisms as a result of elevated and constant relative humidity in the culture vessel and low light intensity in the growth cabinet. Thus, when rooted shoots are to be removed from the culture vessel and transferred to the external environment, it is essential to allow tissues to adapt gradually in order to avert stress during the acclimatization stage. First, it is

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vital that the roots are placed on a medium capable of promoting rapid and effective resumption of growth. This involves careful choice of the type of peat (Montalti, 1979), nutrient concentration and environmental conditions. Relative humidity is the most important factor that can inﬂuence plantlet acclimatization and it is maintained at high values by the means of double tunnels, where relative humidity is better controlled. Resumption of shoot tip activity indicates that the root system is viable. Shoot acclimatization can then be initiated by opening the tunnel for progressively longer periods of time. Great care should be taken in this operation as the plantlets are particularly susceptible to water loss through the leaves, whose anatomic structure presents incomplete palisade tissue, larger spaces in the spongiform tissue, lesser formation of cuticular wax on the leaf blade and completely open stomata that take a long time to restore the closure mechanism. But the greatest danger of all is the onset of severe water stress that would compromise plantlet growth or even survival. For species very susceptible to water stress, it would be advisable to submit the shoots to an acclimatization pretreatment a few days before the end of rooting. At this time, the partial opening of the in vitro culture vessel enables the plantlets to become accustomed earlier to the lower relative humidity of the external environment. With this procedure, possible leaf water stresses could be counteracted by water absorption from the roots, which still are in the rooting medium. Other potential problems should not be overlooked. For example, the plantlets could be susceptible to microorganisms for which the warm steamy conditions of the acclimatization glasshouse could represent an ideal incubator. Therefore, it is essential to ensure constant monitoring of plantlet health, so that any preventive treatment that may be required can be promptly undertaken with the aim of attenuating or preferably precluding the onset of such problems. Over the past few years a procedure has been developed which has been found highly effective during the plantlet acclimatization stage. It consists of the use of mycorrhizae at the moment of transfer from the culture

vessel to transplantation medium, as mycorrhizal symbiosis not only acts as a biofertilizer but also induces morphological, physiological and biochemical modiﬁcations in the plant. Mycorrhizal fungi generally have positive effects on root system growth, in terms of better water and nutrient uptake, greater resistance to various types of stress and sometimes also protection of roots against soil pathogens. The application of mycorrhizae to micropropagation has recently been reviewed (Morini and Giovannetti, 2004) and suitable nursery procedures should be devised as soon as possible.

9.6 Embryo Culture Embryo culture is a technique by which an immature embryo is excised from a seed and cultured in aseptic culture (Kester and Hesse, 1955, Hartmann et al., 2002) (Fig. 9.7/Plate 68). This technique is very useful to improve breeding programmes of early-maturing peach cultivars. In these cultivars, fruit mature before the embryo has completed its development. In natural conditions the embryo can abort, but it can be collected before fruit ripening and aseptically cultivated on an artiﬁcial growth medium to permit it to germinate and grow into a plant (Fig. 9.8/Plate 69). The success of the procedure depends upon the size of the embryo at collecting time and on the ripening time of the mother cultivar. Embryos of about 10 mm can be easily cultured on SBH medium (Smith et al., 1969) and the smaller embryos (5–10 mm) on MS medium (Ramming, 1990). Embryos in the globular stage and smaller are more difﬁcult to culture successfully. For embryos of 1–5 mm, the sucrose concentration in the growth medium was found to be more critical to embryo development than the hormone content (Ramming, 1990). Ovule culture, ﬁrst used in 1981, helped to better overcome the difﬁculty encountered with very small embryos. It is a procedure by which the ovules are cultured in Stewart and Hsu medium (Stewart and Hsu, 1977), in the presence of charcoal and a sucrose and fructose sugar source, for 4 weeks in the dark, at 25°C. At the end of this period, the embryos are excised and cultivated on WPM medium

Propagation Techniques

Fig. 9.7.

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Excised embryos in aseptic culture.

and 2% sucrose. After a cold treatment at 4°C for 10 weeks, the embryos are moved to light and 18°C to induce embryo growth (Anderson et al., 2006). Fruit storage before ovule culture is detrimental to both embryo growth and survival.

9.7 Stoolbeds and Layering Stoolbeds and layering are infrequent methods of vegetative propagation for clonal peach rootstock multiplication. Although not identical, both methods are based on the same principle: promoting vigorous juvenile shoots that are then partially covered with soil, sawdust or other material so that the basal zone is allowed to develop in the absence of light. Shoot rejuvenation and etiolation, together with the special humidity and aeration conditions that occur around the base of the shoots, favour root induction and development of adventitious roots. Etiolation may cause starch and phenolic compounds to accumulate in shoots and exert a positive inﬂuence on rhizogenesis (Maynard, 1991; Biricolti et al., 1994). The two techniques, described in detail by Hartmann et al. (2002), are widely used for propagation of clonal rootstocks of apple and pear, but have been only sporadically adopted for peach rootstocks. These techniques are used for the propagation of some rootstocks such as ‘St. Julian A’, ‘Damas C’ and ‘GF 655/2’, rootstocks that are no longer used for peach.

In addition to the poor results obtained so far with peach rootstocks (Fiorino, 1968, 1972), these two propagation methods suffer from a further severe limitation. In an extremely dynamic nursery market in which the demand for trees varies from year to year, neither the stoolbed nor the layering technique allows production to be planned in relation to market requirements. A nursery establishment designed for production of rooted shoots obtained with these methods has an average duration of 12–15 years, which inevitably implies that there will be years of insufﬁcient or excess production, depending on the ﬂuctuation of market demand.

9.8 Scion Propagation Budding and grafting It can be stated that grafting still constitutes virtually the only technique adopted for propagation of peach cultivars. A number of attempts have been made in recent years to utilize ‘self-rooted’ varieties of peach and nectarine, but the use of selected rootstocks is, in most cases, crucial. While many different grafting techniques are available, ‘budding’ is the one most widely adopted for peach. Wedge, splice-side and saddle grafts, frequent in the past for regrafting of adult trees, have now been largely abandoned. Chip budding, on the other hand,

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Fig. 9.8. Plantlets generated from aseptic embryo culture.

which is already widely utilized in the USA, is attracting growing interest among European nurserymen as well. But regardless of the type of graft, successful take of the graft depends fundamentally on three conditions. 1. Graft compatibility of scion and rootstock, ensuring a solid, durable and efﬁcient union.

2. Correspondence and intimate contact between scion and rootstock cambial zones. 3. Resumption of cambial activity of both rootstock (slightly earlier) and scion and beginning of the fusion process immediately after grafting operations have been performed. In addition, success of the graft and subsequent development of the maiden tree also

Propagation Techniques

depends on proper choice of the grafting period and care of the young trees in the nursery. Moreover, grafting can be used not merely for normal propagation of the cultivars but also to promote the recovery of trees affected by virus infection or mycoplasmas (micrografting). Budding is the technique that has become most popular in common nursery practice, on account of its simplicity and low cost. The technique consists of the insertion of a vegetative scion bud into the T-cut stem of the rootstock. It can be carried out at the end of the summer (‘dormant bud’), in spring (‘vegetative bud’) or in mid-June (‘June budding’) in the northern hemisphere. The dormant bud graft is performed starting from the last 10-day period of July up to mid-September on clonal seedlings or rootstocks that have reached a stem diameter of roughly 8–10 mm, when the young trees are in active growth. It has been noted that some rootstocks, such as ‘Mr.S. 2/5’, suffer early cessation of growth. In such cases, in order to ensure good bud take it is advisable to bring the budding operations forward by about 10–15 days compared to the seedling, as the crucial period of cambial activity and thus of lifting of the bark from the central stem is shorter (Loreti and Massai, 1995). The buds to be used for budding must be taken from virus-free mother tree shoots. Care must be taken to use those situated in the central part of the shoot, which are usually better shaped and riper. Budding is carried out at 10–15 cm from the ground, after removing the feathers. The scion should be shortened above the graft union, in spring, immediately before bud break. While they remain in the nursery, the budded trees should be managed according to normal cultural practices (removal of basal feathers, fertilization, irrigation and pesticide application) in order to obtain maiden trees about 1.2–1.4 m tall. The vegetative bud graft is less widely used than budding. It is mainly adopted in cases when the dormant bud inserted in the rootstock during the summer failed to take. When this occurs, the vegetative bud graft is performed in the following spring. In this case the buds used for budding should be taken from portions of shoots

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removed from the mother trees during the winter and stored in a moist cool environment (2–4°C) until required for budding. The graft is then performed according to the same technique as the dormant bud graft. The third type of budding, June budding, can be adopted only in areas characterized by a very mild spring, allowing early growth of the nursery trees. The technique described by Hartmann et al. (2002) consists of grafting peach seedlings which, due to appropriate management practices, have achieved a suitable size for grafting by mid-June. The buds, taken from actively growing shoots, open immediately after the grafting operation, giving rise to maiden trees that reach a height of 60–80 cm by October. One of the main advantages of June budding is that it allows peach maiden trees to be obtained within a single year, giving considerable savings on cost compared with the other two types of bud graft. Furthermore, the trees possess a more fasciculate root system, making them less susceptible to failure at transplanting. Another type of graft that is attracting increasing attention is chip budding. Although known for many years, it has only recently been adopted by European nurserymen. In addition to allowing greater ﬂexibility in time of execution, in many cases it is preferred to the dormant bud graft (T-budding) in order to supply trees characterized by both a stronger union at the point of the graft and also a more balanced and uniform development of the maiden trees. Finally, wedge, splice-side and saddle grafts that were widely used in the past are seldom used today. Previously they were performed to repeat grafts in cases when the tree did not correspond to the desired variety, or to rapidly convert an existing orchard to one with newer scion cultivars. Although this operation is technically valid, it is justiﬁable only if the cost of converting the orchard is lower than that of purchasing and establishing new trees. Micrografting This is a grafting technique performed in vitro, which has recently been introduced to

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favour the recovery of certain fruit tree species from virus infection without causing any impairment of genetic and varietal characteristics. Adopted for the ﬁrst time to restore virus-affected citrus trees to health, it was subsequently applied to some peach (Barba et al., 1995), almond and cherry cultivars sensitive to prolonged heat treatment. In peach, satisfactory recovery percentages have been obtained for some viral diseases such as Chlorotic leaf spot virus and Prunus necrotic ring spot virus, while in the case of Prune dwarf virus results varied according to the viral strain (Navarro et al., 1982). The technique consists of decapitating an in vitro-grown plantlet, after which a 0.2–0.3 mm portion of the tip of the cultivar to be grafted is placed on it. The micrografted plant is maintained in culture for 5–6 weeks prior to transplantation. The success of this technique depends on numerous important factors including the phenological status of the tip donor mother plant, the rootstock and substrate utilized, the micrograft growth conditions, and plantlet acclimatization to the external environment.

Herbaceous grafting This is a technique in which a shoot tip collected from in vitro culture is grafted on to a very young seedling rootstock (only a few millimetres in diameter). Cuttings may be produced by traditional techniques or from micropropagation and are raised in plastic containers (Preka and Cherubini, 2001). This type of grafting is performed ex vitro and is much simpler to execute than micrografting. Thus it is a technique that has higher propagation efﬁciency and in Italy some micropropagation laboratories have found it suitable for mass propagation. The rootstock is cut back at about 10 cm from the soil, incised longitudinally, and top-grafted with a scion that has the basal end cut to a V-shaped wedge. The scion is then inserted in the stock and tied with Parafìlm. Grafting establishment will occur in a greenhouse, at high relative humidity and controlled temperature. The major advantage of this type of grafting is that the new plant can be obtained in 1 year.

9.9 Outlook As reported above, the evolution of peach propagation techniques has produced signiﬁcant changes over time. Today, plants of high genetic, sanitary and agronomic quality are available. Nevertheless, a dynamic nursery industry exists that is aimed particularly at advanced propagation systems to improve the economic and production efﬁciency and to provide plants with superior characters. At present, it is very difﬁcult to predict further advancements in nursery techniques. Micropropagation was certainly the greatest innovation of the last few decades but it also showed some limitations with a number of genotypes that even today are propagated by traditional techniques. Better application of micropropagation for peach rootstocks is strictly related to the possibility of setting up more efﬁcient, less expensive and more functional procedures. A new stimulus to peach rootstock propagation could occur by somatic embryogenesis. This technology is based on the capacity of differentiated cells to resume meristematic activity under speciﬁc growth conditions controlled by bioreactors and to produce somatic embryos with structures similar to zygotic embryos. Some species propagated by this technique have shown the ability to produce large numbers of new plants, in less time and space than can be attained by micropropagation. The major problems currently are: the scarce response to somatic embryoinducing treatments shown by most woody fruit species; the difﬁculty of somatic embryos to convert into plants; and the rarity of somatic embryo-producing plants that are true to type. In the case of peach rootstocks, somatic embryogenesis could develop into a valid alternative to traditional techniques, but it is not possible to evaluate its applicability until the above-mentioned aspects are clearly deﬁned. Thanks to the uninterrupted advances of molecular biology, research on genes controlling root induction may facilitate the development of transgenic plants by genetic engineering or transformation by A. tumefaciens (Radchuk and Korkhovoy, 2005).

Propagation Techniques

Future research on mechanisms of adventitious rooting may enable the use of cuttings for propagating woody species as a suitable alternative to other techniques. Cutting propagation is actually easy to apply and needs relatively simple facilities and equipment that most nursery operations already have. Today an intense research activity is progressing to determine the underlying

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physiological, genetic and molecular aspects involved. Thus, we may expect that deeper knowledge on rooting mechanisms will be acquired in a reasonably short time. This should allow further improvements of the vegetative propagation techniques currently applied, producing new and more advanced propagation systems.

References Anderson, N., Byrne, D. and Ramming, D. (2006) In ovule culture success as affected by sugar source and fruit storage duration in nectarine. Acta Horticulturae 713, 89–92. Barba, M., Cupidi, A., Loreti, S., Faggioli, F. and Martino, L. (1995) In vitro micrografting: a technique to eliminate peach latent mosaic viroid from peach. Acta Horticulturae 386, 531–535. Bartolini, G. and Fabbri, A. (1982) Una doppia bagnatura per aumentare la sopravvivenza delle barbatelle di pesco. Rivista Ortoflorofrutticoltura Italiana 4, 323–329. Bartolini, G. and Fiorino, P. (1978) Gli interventi sulle piante madri per migliorare la radicazione delle talee. In: Seminario sul vivaismo e controllo della rizogenesi mediante fitoregolatori. Editrice Tecnico Scientifica, Pisa, Italy, pp. 9–25. Bassuk, N.L. and Howard, B.H. (1981) A positive correlation between endogenous root-inducing cofactor activity in vacuum-extracted sap and seasonal changes in rooting of M 26 winter apple cuttings. Journal of Horticultural Science 56, 301–312. Bhattacharya, N.C. (1988) Enzyme activity during adventitious rooting. In: Davis, T.D., Haissig, B.E. and Sankhla, N. (eds) Adventitious Root Formation in Cuttings. Dioscorides Press, Portland, Oregon, pp. 88–97. Biricolti, S., Mariotti, P. and Mattii, G.B. (1990) Anatomical studies on the collapse of rooted cuttings and grafts in peach. Advances in Horticultural Science 3, 159–162. Biricolti, S., Fabbri, A., Ferrini, F. and Pisani, P.L. (1994) Adventitious rooting in chestnut: an anatomical investigation. Scientia Horticulturae 59, 197–205. Blazich, F.A. (1988) Mineral nutrition and adventitious rooting. In: Davis, T.D., Haissig, B.E. and Sankhla, N. (eds) Adventitious Root Formation in Cuttings. Dioscorides Press, Portland, Oregon, pp. 61–69. Debergh, P.C. (1983) Effect of agar brand and concentration on the tissue culture medium. Physiologia Plantarum 59, 270–276. Debergh, P.C. and Read, P.E. (1991) Micropropagation. In: Debergh, P.C. and Zimmermann, R.H. (eds) Micropropagation: Technology and Application. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 1–14. Di Vaio, C., Buccheri, M. and Cirillo, C. (2001) Impiego della solarizzazione e della bromurazione del terreno nel reimpianto del pesco: effetto sullo sviluppo vegetativo di astoni in vivaio. Italus Hortus 8, 39–40. Driver, J.A. and Kuniyuki, A.H. (1984) In vitro propagation of Paradox walnut rootstock. HortScience 19, 507–509. Erez, A. and Yablowitz, Z. (1981) Rooting of peach hardwood cuttings for the meadow orchard. Scientia Horticulturae 15, 137–144. Fabbri, A. (1977) La propagazione del pesco per talea di ramo. Rivista Ortoflorofrutticoltura Italiana 1, 126–136. Fadl, M.S. and Hartmann, H.T. (1967) Relationship between seasonal changes in endogenous promoters and inhibitors in pear buds and cutting bases and the rooting of pear hardwood cuttings. Proceedings of the American Society for Horticultural Science 91, 96–112. Fiorino, P. (1968) Nuove tecniche per ottenere barbatelle di pesco. II – Ricerche sulla ‘propaggine per trincea’. Rivista Ortoflorofrutticoltura Italiana 52, 205–212. Fiorino, P. (1972) Nuove tecniche per ottenere barbatelle di pesco. IV – Ricerche sulla ‘margotta di ceppaia’. Rivista Ortoflorofrutticoltura Italiana 56, 100–104. Fiorino, P. and Loreti, F. (1965) La propagazione del pesco per talea legnosa. In: Atti del Congresso del Pesco. Tipo-lito degli Stimmatini, Verona, Italy, pp. 483–495.

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Fiorino, P. and Loreti, F. (1987) Propagation of fruit trees by tissue culture in Italy. HortScience 22, 353–358. Fiorino, P. and Mattii, G.B. (1992) The role of prunasin in ‘collapse’ of rooted peach cutting. Advances in Horticultural Science 1, 11–14. Fiorino, P. and Vitagliano, C. (1968) Nuove tecniche per ottenere barbatelle di pesco: III ‘Ulteriori ricerche sulla nebulizzazione’. Rivista Ortoflorofrutticoltura Italiana 6, 779–795. Guerriero, R. and Scalabrelli, G. (1984) Effect of stratification duration on seed germination of several peach line rootstocks. Acta Horticulturae 173, 185–190. Hammerschlag, F. (1982) Factors affecting establishment and growth of peach shoots in vitro. HortScience 17, 85–86. Hartmann, H.T., Kester, D.E., Davies, F.T. Jr and Geneve, R.L. (2002) Plant Propagation. Principles and Practices, 7th edn. Prentice-Hall, Upper Saddle River, New Jersey. Katan, J. and DeVay, J.E. (1991) Soil solarization: historical perspectives, principles, and uses. In: Katan, J. and DeVay, J.E. (eds) Soil Solarization. CRC Press Inc., Boca Raton, Florida, pp. 23–39. Kester, D.E. and Hesse, C.O. (1955) Embryo culture of peach varieties in relation to season of ripening. Proceedings of the American Society for Horticultural Science 65, 265–273. Koornneef, M., Bentsinka, L. and Hilhorstb, H. (2002) Seed dormancy and germination. Current Opinion in Plant Biology 51, 33–36. Lang, G.A. (1996) Plant Dormancy: Physiology, Biochemistry, and Molecular Biology. CAB International, Wallingford, UK. Lloyd, G.B. and McCown, B.H. (1980) Commercially feasible micropropagation of mountain laurel, Kalmia latifoglia, by use of shoot tip culture. Combined Proceedings of the International Plant Propagators Society 30, 421–427. Lorenzi, R. and Ceccarelli, N. (1978) Variazioni stagionali del potenziale rizogenp delle talee e sue modificazioni con fitoregolatori. In: Seminario sul vivaismo e controllo della rizogenesi mediante fitoregolatori. Editrice Tecnico Scientifica, Pisa, Italy, pp. 27–36. Loreti, F. and Massai, R. (1995) Orientamenti per la scelta dei portinnesti del pesco. L’Informatore Agrario 32, 37–42. Loreti, F. and Pisani, P.L. (1982) Physiological and technical factors affecting rooting in woody species. In: Proceedings of the XXIst International Horticultural Congress. International Society for Horticultural Science, Wageningen, The Netherlands, pp. 295–309. Loreti, F., Morini, S. and Grilli, A. (1985) Rooting response of BS B2 and G.F. 677 rootstocks cutting. Acta Horticulturae 173, 261–269. Loreti, F., Morini, S. and Concetti, S. (1988) Effect of potassium and nitrogen concentration on growth of peach shoots cultured in vitro. Acta Horticulturae 227, 311–317. Loreti, F., Muleo, R. and Morini, S. (1991) Effect of light quality on growth of in vitro cultured organs and tissues. The International Plant Propagation Society Combined Proceedings 40, 615–623. Marini, R.P. (1983) Rooting of semihardwood peach cuttings as affected by shoot position and thickness. HortScience 18, 718–719. Martinelli, A. (1985) Factors affecting in vitro propagation of the peach–almond hybrids ‘Hansen 2128’ and ‘Hansen 536’. Acta Horticulturae 173, 237–244. Maynard, B.K. (1991) Stock plant etiolation and stem banding effect on the auxin dose–response of rooting in stem cuttings of Carpinus betulus L. ‘Fastigiata’. Journal Plant Growth Regulation 10, 305–311. Miller, G.A., Coston, D.C., Denny, E.G. and Romeo, M.E. (1982) In vitro propagation of Nemaguard peach rootstock. HortScience 17, 194. Montalti, G. (1979) Influenza del substrato nell’ambientamento di alcune piante da frutto derivate da coltura in vitro. In: Atti dell’Incontro su: Tecniche di Colture in vitro per la propagazione su vasta scala delle specie ortoflorofrutticole. F&F Parretti Grafiche, Florence, Italy, pp. 119–126. Morel, G.M. (1964) Tissue culture. A new means for clonal propagation of orchids. American Orchid Society Bullettin 33. Morini, S. and Barbieri, C. (1986) La propagazione in vitro: fattori che condizionano l’acclimatazione delle piantine. L’Informatore Agrario 2, 67–72. Morini, S., Fortuna, P., Sciutti, R. and Muleo, R. (1990) Effect of different light–dark cycles on growth of fruit tree shoots cultured in vitro. Advances in Horticultural Science 4, 163–166. Morini, S. and Giovannetti, M. (2004) La micorrizazione, una biotecnologia per la produzione in vivaio di piante arboree da frutto di elevata qualita. Frutticoltura 12, 43–46.

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Mosella Chancel, L., Macheix, J.J. and Jonard, R. (1980) Les conditions du microbuturage in vitro su pecher (Prunus persica Batsch): influences combinées des substances de croissance et de divers compose phénolique. Physiologie Vegetal 18, 597–608. Murashige, T. and Skoog, F. (1962) A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiologia Plantarum 15, 473–497. Navarro, L., Llacer, G., Cambra, M., Arregui, J.M. and Juarez, J. (1982) Shoot-tip grafting in vitro for elimination of viruses in peach plants (Prunus persica Batsch). Acta Horticulturae 130, 185–192. Nicotra, A. and Moser, L. (1996) Two new plum rootstocks for peach and nectarines: penta and tetra. Acta Horticulturae 451, 269–271. Preka, P. and Cherubini, S. (2001) Tecniche di innesto erbaceo per la propagazione di piante arboree da frutto. Frutticoltura 5, 39–41. Radchuk, V.V. and Korkhovoy, V.I. (2005) The rolB gene promotes rooting in vitro and increases fresh root weight in vivo of transformed apple scion cultivar ‘Florina’. Plant Cell Tissue and Organ Culture 81, 203–212. Ramming, D.W. (1990) The use of embryo culture in fruit breeding. HortScience 25, 393–398. Scalabrelli, G. and Couvillon, G.A. (1986) The interaction between IBA treatment and other factors in rooting and establishment of peach hardwood cuttings. Acta Horticulturae 179, 855–862. Sciutti, R. and Morini, S. (1993) Effect of relative humidity in in vitro culture on some growth characteristics of a plum rootstock during shoot proliferation and on plantlet survival. Advances in Horticultural Science 4, 153–156. Smith, C.A., Bailey, C.H. and Hough, L.F. (1969) Methods for germinating seeds of some fruit species with special reference to growing seedlings from immature embryos. New Jersey Agricultural Experiment Station Bulletin 823. Sorce, C., Paolicchi, F., Ceccarelli, N., Lorenzi, R. and Picciarelli, P. (2004) Relation between cell redox status and adventitious rooting in cuttings of Cupressus sempervirens. In: SIFV-SIGA Joint Congress, Lecce, Italy, 15–18 September, vol. XLIII Annual Congress, p. 34. Stewart, J.M. and Hsu, C.L. (1977) In-ovulo embryo culture and seedling development of cotton (Gossypium hirsutum L.). Planta 137, 113–117. Vasil, I.K. and Vasil, V. (1972) Totipotency and embryogenesis in plant cell and tissue cultures. In vitro Cellular and Developmental Biology – Plant 8, 117–125. Zuccherelli, G. (1979) Moltiplicazione in vitro dei portinnesti clonali di pesco. Rivista di Frutticoltura 41, 15–20.

10

Carbon Assimilation, Partitioning and Budget Modelling T.M. DeJong1 and A. Moing2

1Department

of Plant Sciences, University of California, Davis, California, USA de Physiologia Vegetable, INRA, Bordeaux, France

2Unite

10.1 Introduction 10.2 Carbon Assimilation Leaf photosynthetic characteristics Fruit photosynthesis Canopy carbon assimilation 10.3 Carbon Partitioning Carbon partitioning within source leaves Carbon transport from the leaves Carbon partitioning within fruit Carbon partitioning within vegetative growing sink organs Carbon partitioning and mobilization in perennial parts Carbohydrate partitioning at the whole-plant level Effect of biotic stress 10.4 Modelling the Carbon Economy of Peach Models of fruit growth and carbon economy Modelling tree growth and carbon economy 10.5 Future Directions

10.1 Introduction Virtually all of the energy and nearly all of the dry matter that a plant obtains to support growth and development comes from solar energy and the process of photosynthesis. Ultimately, crop productivity is dependent on plant photosynthetic efﬁciency and the efﬁciency with which photosynthates are partitioned. Peach production is no exception, and peach tree growth and productivity are strongly dependent on the efﬁciency of carbon 244

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assimilation and the efﬁciency and effectiveness of the distribution and use of carbohydrates for tree growth maintenance and the production of quality fruit. In fact, most of the cultural operations that a fruit grower does are in some way connected to inﬂuencing either the assimilation of carbon or the distribution and use of carbohydrates in the plant. Therefore, it is important to have a basic understanding of the processes involved in carbon assimilation and the distribution and use of carbohydrates in peach trees.

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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Research speciﬁc to the leaf photosynthetic processes in peach is not as plentiful as for many other crops. However, there is adequate information to know the general behaviour of peach leaves with respect to most of the environmental and cultural factors that are known to inﬂuence leaf and canopy photosynthesis of crop plants. Interestingly, while research on peach leaf photosynthesis is not as plentiful as for some other crops, there is probably more research reported on the details of carbohydrate partitioning/distribution than for any other fruit tree species. Carbon partitioning and utilization by the various organs (sinks) of the plant has been extensively studied at several levels. There have been numerous studies concerned with the import and metabolism of speciﬁc carbohydrates in various sink tissues while others have focused on the total amounts of carbon that get distributed to the various parts and/ or functions of the plant and the factors that control that distribution. In this review we consider the uptake and metabolism of carbon of speciﬁc sink tissues and then look at the broader aspects of carbon partitioning and utilization at the whole-plant level.

10.2 Carbon Assimilation Leaf photosynthetic characteristics Like virtually all other temperate deciduous tree fruit species, peach leaves exhibit the classic characteristics of leaves having the C3 biosynthetic pathway of photosynthesis (Brown, 1994). Maximal reported rates of leaf CO2 assimilation are around 20–22 µmol/ m2/s (DeJong et al., 1989) while many researchers have reported lower values (Flore and Lakso, 1989). Leaf carboxylation efﬁciency appears to saturate well beyond intercellular CO2 concentrations of 300 ml/l (DeJong, 1983; Rosati et al., 1999) and estimated intercellular CO2 concentrations under normal conditions have been reported to be between 180 and 250 ml/l (DeJong, 1983, 1986a). Individual leaf CO2 assimilation appears to approach light saturation at 700–1000 mmol/m2/s depending on the leaf position in the canopy

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(DeJong, 1983; Kappel and Flore, 1983; Rosati et al., 1999). Walcroft et al. (2002) reported effects of changes in absorbed photosynthetically active radiation (PAR) on peach leaf morphological and physiological properties. Leaf mass per unit area and leaf N concentration were non-linearly related to absorbed PAR, and there was a weak linear relationship between leaf N concentration per unit mass and absorbed PAR. The leaf ribulose bisphosphate carboxylase (RUBISCO) content increases with the amount of N applied to young trees (Nii et al., 1997). In the canopy, spatial variability in photosynthetic capacity results from acclimatization to varying absorbed PAR as the crown develops, acclimatization being driven principally by changes in leaf mass per unit area rather than the amount or partitioning of leaf N (Rosati et al., 2000; Walcroft et al., 2002). At the molecular level, the RNA abundance of a light-harvesting type II chlorophyll a/b-binding protein is lower in mature shaded leaves compared with sunexposed leaves (Bassett and Callahan, 2003). The leaf photosynthesis apparatus of peach appears to be fairly insensitive to changes in temperature between 20°C and 32°C but can be substantially inhibited by temperatures above and below this range (Crews et al., 1975; Reyes-Lopez, 1984; Girona et al., 1993). Leaf stomatal conductance has been reported to be fairly closely coupled to leaf photosynthesis in peach and the coupling increases with exposure to water stress (Reyes-Lopez, 1984; Girona et al., 1993). Although peach is a mesophytic species, leaf CO2 assimilation appears to be fairly tolerant of water stress in the ﬁeld and leaves can maintain more than 50% of their photosynthetic capacity down to leaf water potentials as low as –2.0 MPa (Girona et al., 1993). However, there have been reports of sensitivity to drought treatments in pottedplant experiments (Rieger and Duemmel, 1992) and this sensitivity is not always related to leaf water potential, suggesting the involvement of non-hydraulic signalling (Rieger et al., 2003). Peach leaves also appear to be relatively tolerant to ozone air pollution in comparison with several other temperate deciduous fruit tree species (Retzlaff et al., 1991). Although it is widely accepted that leaf age strongly affects the photosynthetic capacity

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of individual leaves of most species (Flore and Lakso, 1989), there is very little data available speciﬁcally for peach. Peach tree canopies grow quite rapidly and peach leaf CO2 assimilation capacity is strongly inﬂuenced by internal canopy shading (Marini and Marini, 1983; DeJong and Doyle, 1985; DeJong et al., 1989; Rosati et al., 1999; LeRoux et al., 2001). Therefore it is difﬁcult to separate leaf age effects from changes in leaf light exposure in naturally growing ﬁeld canopies. It is apparent that leaves in the most exposed parts of the tree canopies tend to maintain relatively constant photosynthetic capacities in the absence of major stress during the middle part of the growing season from May to September (in the northern hemisphere) (DeJong, 1986a). Probably the most controversial reported inﬂuence on leaf CO2 assimilation rate in peach is the factor of crop load or proximity of fruit to leaves. Early work by Crews et al. (1975) reported approximately 20% higher rates of photosynthesis in leaves in close proximity to fruits compared with leaves measured further down the same branch and that leaf photosynthesis peaked during the period of peak fruit growth (i.e. maximum fruit sink strength). CO2 exchange measurements in these experiments used cut branches brought in from the ﬁeld. It is unclear what inﬂuence cutting a branch might have on sink effects on photosynthesis with this experimental set-up. At about the same time, Chalmers et al. (1975) reported that peach leaf photosynthesis can vary by as much as 50% due to sink demand corresponding to fruit development patterns in the ﬁeld. However, their conclusions are questionable because it is likely that their measurements were lightlimited and inﬂuenced by spreading of the tree due to crop load (Westwood and Gerber, 1958). Subsequent research has reported 11–15% higher leaf CO2 assimilation rates in fruited versus defruited mature peach trees during the peak period of fruit growth (DeJong, 1986a). The higher CO2 assimilation rates were attributed to increases in leaf stomatal conductance rather than mesophyll conductance or other leaf photosynthetic properties. Other research reported similar crop load effects on leaf stomatal conductance

with nectarines (DeJong, 1986b). Leaf photosynthesis can be strongly reduced within 48 h of fruit removal, indicating that sudden loss of fruit sink strength has a greater effect on CO2 assimilation than long-term presence of the fruit (Mandre et al., 1995). The relatively modest fruit effects on photosynthesis reported in these studies on peach in comparison with apple (Hansen, 1970; Avery, 1975) are probably due to the fact that peach is grown on vigorous rootstocks and there are many alternative vegetative sinks for carbohydrates in most situations (Flore and Lakso, 1989). There have been dramatic changes in peach genetic characteristics through domestication and breeding over the past couple of centuries. However, crop improvement efforts in peach have primarily focused on fruit quality traits and timing of fruit maturity. The resulting changes have apparently had little effect on leaf photosynthetic characteristics of peach (Quilot et al., 2004a), although there appears to be substantial variability in the related Prunus species, which are primarily related to tree canopy density and distribution of leaf N (DeJong, 1983; Rieger and Duemmel, 1992). Fruit photosynthesis In other rosaceous species such as apple, Vemmos and Goldwin (1994) suggested that ﬂower photosynthesis might play an important role in ﬂower growth and fruit set. However, no data are available for peach ﬂowers. Green peach fruit are capable of photosynthesis but the majority of CO2 assimilation that occurs in fruit even when they are small merely serves to offset a portion of the CO2 produced by respiration (Pavel and DeJong, 1993b). However, peach fruit photosynthesis is not insigniﬁcant and has been estimated to account for between 5% and 9% of the total carbohydrate budget of developing peach fruit, depending on the position of the fruit in the canopy (Pavel and DeJong, 1993b). Although these estimates of the photosynthetic contribution of peach fruits are lower than has been estimated for other species (Bazzaz et al., 1979; Kappes, 1985; Birkhold et al., 1992), the contribution of fruit photosynthesis to the overall carbon economy of peach fruit production

Carbon Assimilation, Partitioning and Budget Modelling

should not be ignored. Phosphoenolpyruvate carboxylase, involved in C4 and CAM (crassulacean acid metabolism) plant photosynthesis, is also involved in non-photosynthetic processes in all plant species and may contribute to re-assimilation of respired CO2 in peach fruit tissues as in apple (Blanke and Lenz, 1989).

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above the canopy. These relationships should make estimates of canopy photosynthesis of peach trees under non-stressed ﬁeld conditions much easier than they were previously thought to be.

10.3 Carbon Partitioning Canopy carbon assimilation Carbon partitioning within source leaves Like with all crops (Charles-Edwards, 1982), canopy photosynthesis depends on the amount of light intercepted by the plant as well as individual leaf photosynthetic capacity. Light interception can be strongly inﬂuenced by training system (Giuliani et al., 1998, Grossman and DeJong, 1998). Whole-canopy CO2 assimilation in peach has been measured directly (Giuliani et al., 1998) and calculated through modelling techniques (Grossman and DeJong, 1994b; Giuliani and Magnanini, 2002). Whole-canopy assimilation rates of peach trees can be more than 25 g CHO/m2/day during peak periods of the growing season. This is similar to values reported for herbaceous species (Ng and Loomis, 1984). These rates are possible, in spite of the relatively modest maximum leaf photosynthetic potential of peach (20–22 mmol/m2/s) compared with other C3 crop species (Brown, 1994), because of the high leaf area index of peach trees (Chalmers and van den Ende, 1975; Grossman and DeJong, 1998). Peach canopies generally have a high leaf area index after the initial spring growth ﬂush (6–8 m2 of leaf area per square metre of ground area) and individual leaf photosynthetic capacity varies greatly within the canopy. This variation has been shown to correspond to leaf N content per unit leaf area, leaf speciﬁc weight and leaf light exposure (DeJong, 1982; Kappel and Flore, 1983; Rosati et al., 2000; LeRoux et al., 2001). Rosati et al. (2002) have shown that there is also a linear relationship between calculated daily net CO2 assimilation and daily leaf light interception of individual peach leaves. Furthermore they demonstrated that daily canopy photosynthetic radiation use efﬁciency of crop canopies can be estimated from measurements of the photosynthetic light response of leaves at the top of the canopy and the incident PAR

Like most tree species in the Rosaceae, the primary products of photosynthesis in mature peach leaves are sorbitol, sucrose and starch with generally lesser amounts of glucose and fructose (Bieleski, 1982; Moing et al., 1992). Although there is signiﬁcant variation in the ratio of sorbitol to sucrose content in leaves of different peach cultivars, the leaf sorbitol content of all cultivars is higher than sucrose. The sorbitol:sucrose ratio of most cultivars examined is about 2–3:1 (Escobar-Gutiérrez and Gaudillère, 1994). In mature leaves sorbitol biosynthesis is accomplished by an NADPHdependent aldose-6-phosphate reductase that catalyses the conversion of the photosynthetic product glucose-6-phosphate to sorbitol-6phosphate (Hirai, 1981). A cDNA clone encoding this enzyme was ﬁrst isolated from apple (Kanayama et al., 1992). The sorbitol-6-phosphate is converted into sorbitol by a speciﬁc sorbitol6-phosphate phosphatase (Grant and ap Rees, 1981). The expression of aldose-6-phosphate reductase was studied in terms of protein and RNA in developing peach leaves, conﬁrming its association with the source function (Sakanishi et al., 1998). Aldose-6-phosphate reductase activity and protein level in leaves also varies seasonally. In apple, aldose-6phosphate reductase activity appears to be regulated by inorganic phosphate and divalent cations (Zhou et al., 2003a). Since sorbitol6-phosphate phosphatase activity is inhibited by inorganic phosphate and sorbitol (Zhou et al., 2003b), it may be a regulatory step in sorbitol biosynthesis. It appears that the relative concentrations of sorbitol, sucrose, glucose and fructose are fairly closely regulated in leaves photosynthesizing under constant steady-state laboratory conditions while starch increases steadily during the photoperiod

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(Moing et al., 1992). In leaf discs, the sorbitol content and the level of mRNA encoding putative aldose-6-phosphate reductase were higher under low temperature (Deguchi et al., 2002). The control mechanisms of cellular carbon partitioning into sorbitol versus sucrose in rosaceous species are unknown. However, there is some evidence that sucrose content is more tightly regulated than sorbitol in peach leaves (Moing et al., 1994) and that sucrose can be used for conversion into sorbitol within the leaf (Moing et al., 1992). Recently, in apple, the relationship between sucrose synthesis and sorbitol metabolism has begun to be unravelled. It has been shown that leaf sucrose phosphate synthase, catalysing one of the ﬁnal steps of sucrose synthesis in the cytosol of photosynthetic cells, is inhibited by sorbitol6-phosphate (Zhou et al., 2002). Early studies in apple showed that source leaves have minimal capacity for sorbitol degradation (Grant and ap Rees, 1981; Loescher et al., 1982). Therefore, the fate of sorbitol in source leaves is storage or export through phloem. However, this conclusion should be re-examined since one isoform of NADdependent sorbitol dehydrogenase involved in sorbitol breakdown was recently shown to be expressed in source leaves of apple (Park et al., 2002). As with other sugar alcohols, sorbitol can be stored temporarily in cell vacuoles of source leaves or in sinks, suggesting the presence of a tonoplast-bound alditol carrier as noted for mannitol-synthesizing species (Greutert et al., 1998). Environmental factors can inﬂuence the relative amounts of the various carbohydrates in the leaves. Factors that favour higher rates of photosynthesis, such as increasing light exposure, tend to enhance the ﬂux of all three major carbohydrates in peach leaves, with starch increasing the most at the highest light levels (Escobar-Gutiérrez and Gaudillère, 1997). Studies with apple and peach indicate that factors causing sudden increases in photosynthate supply relative to demand, such as lengthening photoperiod, CO2 enrichment or fruit removal, increase leaf sorbitol and starch content while sucrose is less affected (Wang et al., 1998, 1999; Ali and Nii, 1999). Drought stress has been reported to enhance the production of sorbitol relative to sucrose and starch in

both apple (Wang et al., 1996) and peach (Escobar-Gutiérrez et al., 1998; Rieger et al., 2003). However, this behaviour does not appear to contribute to increased osmotic adjustment in peach (Escobar-Gutiérrez et al., 1998). Carbon transport from the leaves The rate of carbohydrate turnover in peach leaves appears to be substantially less than reported for herbaceous species and this appears to correspond with a lower carbon export rate (Moing et al., 1992). Although minor concentrations of sorbitol, glucose, sucrose and fructose can be extracted from xylem of petioles of mature leaves and subtending shoots, the majority of carbohydrate export from leaves occurs in the phloem as sorbitol and sucrose (Moing et al., 1997). The sorbitol: sucrose ratio in the phloem sap generally corresponds to the ratio found in leaf tissue, i.e. about 2–3:1. Although the possibility of symplastic phloem loading of sorbitol has not been ruled out, it is likely that apoplastic phloem loading through an active transport pathway is the most important means of exporting carbohydrates from mature leaves in peach (Moing et al., 1997). H+-sucrose symporters, which are involved in active uptake of sucrose across the plasma membrane, have an essential role in phloem loading of sucrosetransporting species (Lemoine, 2000). H+polyol symporters certainly play an additional role in phloem loading in sorbitol-transporting species, as shown for mannitol symporters in celery (Noiraud et al., 2001). Later, phloem unloading in young leaves or fruit probably involves another apoplastic step with sorbitol transporters involved in partitioning and accumulation of sorbitol in sink tissues as reported in sour cherry (Gao et al., 2003). Carbon partitioning within fruit Early in fruit development, glucose and fructose are the most prominent sugars but they decline gradually while sucrose concentration increases rapidly and is dominant during stage III or the ﬁnal swell period (Moriguchi et al., 1990, 1992; Pavel and DeJong, 1993a;

Carbon Assimilation, Partitioning and Budget Modelling

Genard and Souty, 1996; Vizzotto et al., 1996; Lo Bianco et al., 1999a; Genard et al., 2003). Sorbitol and starch concentrations change less and remain relatively low throughout fruit growth. These ﬁndings are consistent with the concept that early spring growth in peach trees is largely dependent on stored carbohydrates that are mobilized after the release from dormancy and transported to the growing sinks through the xylem (as hexoses) (Loescher et al., 1990). Subsequently, phloem is reactivated and differentiated (Evert, 1960) and new photosynthates are transported primarily as sorbitol and sucrose (Moing et al., 1994). Peach domestication and hybridization appear to have resulted in large increases in fruit size (potential fruit growth; Quilot et al., 2002) and soluble sugar concentration as shown by comparative studies between wild species and commercial cultivars (Robertson et al., 1988; Moing et al., 2003). Concerning commercial cultivars, one study reporting genetic variation in sugar content of clingstone peach cultivars showed that sucrose was the dominant sugar even in the early stages of fruit growth (Brooks et al., 1993). It would be interesting to determine if the differences that have been reported for early fruit sugar concentrations between the freestone (Moriguchi et al., 1990, 1992; Pavel and DeJong, 1993a; Genard and Souty, 1996; Vizzotto et al., 1996; Lo Bianco et al., 1999a; Genard et al., 2003) and clingstone (Brooks et al., 1993) cultivars are consistent characteristics for the two fruit types. Our understanding of carbohydrate metabolism during later stages of peach fruit growth is less clear and there is confusion about whether peach fruit preferentially use sorbitol or sucrose as the primary source of transported carbohydrate. Several groups of researchers have attempted to follow the pattern of enzymes involved in peach fruit carbohydrate metabolism to try to discern the major source of carbon supplying fruit growth and to understand the mechanism of the rapid rise in sucrose concentration during peach development. Moriguchi et al. (1990) attributed the rapid rise of sucrose concentrations in peach fruits to increased sucrose synthase activity (operating in the synthesis direction; Moriguchi and Yamaki, 1988). They reported very low levels of sucrose phosphate synthase

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activity and did not ﬁnd decreasing acid invertase activity while sucrose accumulated, so they concluded that neither of these enzymes could account for the changes in sucrose concentrations. Moriguchi et al. (1990) also reported that sorbitol appeared to be converted to glucose by sorbitol oxidase and that both sucrose and sorbitol could be used to support fruit growth. Hubbard et al. (1991) reported similar enzyme activities for peach fruit, but in addition to increases in sucrose synthase activity they also detected sucrose phosphate synthase activity that could help account for the rise in sucrose concentrations. Subsequent research has reported decreasing sucrose synthase and invertase enzyme activities and fairly constant sucrose phosphate synthase activity while sucrose accumulates in the peach fruit (Vizzotto et al., 1996). The latter authors also conducted glucose and sucrose uptake studies with fruit mesocarp tissue and reported higher uptake rates for glucose than sucrose. They concluded that their results were consistent with the possibility that sorbitol and sucrose could be taken up by peach mesocarp tissue by either an apoplastic or symplastic route of phloem unloading. However, the recent cloning of sorbitol transporters in sour cherry fruit (Gao et al., 2003) is in favour of an apoplastic step. The mode of phloem unloading in peach fruit may depend on the fruit development stage as suggested in tomato (Ho, 1992). Recent research on the carbohydrate metabolism of fruit and vegetative sinks in peach has increased confusion over the role of sorbitol as a source of carbohydrate for supplying fruit growth. In contrast to Moriguchi et al. (1990), Lo Bianco et al. (1999a) reported that they could detect no sorbitol oxidase in peach mesocarp tissue during any stage of development and sorbitol dehydrogenase activity was present only during the last stage of fruit growth and then only in small amounts. Similar to reports of previous researchers, Lo Bianco et al. (1999a) noted that sucrose synthase and invertase activities were high early in the fruit development period and were low during stage III of fruit growth. However, data on general enzyme activity should be considered with care due to the possible presence of several enzyme isoforms. For instance,

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in apple fruit, four cDNAs encoding isoforms of NAD-dependent sorbitol dehydrogenase have been cloned (Park et al., 2002). The four corresponding genes were highly expressed at the late stage of apple fruit development. Moreover, post-translational regulation of invertases and sucrose synthases may be involved as suggested in other fruits (Tanase et al., 2002; Zhou et al., 2003c). On the other hand, Yamada et al. (2001), who cloned an NADdependent sorbitol dehydrogenase from peach fruit and studied its expression during development, proposed that the activity of NADdependent sorbitol dehydrogenase is regulated by the transcription of the gene. Genard et al. (2003) used an entirely different approach for analysing the changes in peach fruit sugar concentrations in response to assimilate supply, metabolism and dilution. They used the sugar model of Genard and Souty (1996), which predicts carbon partitioning into sucrose, sorbitol, glucose and fructose in peach mesocarp tissue by calculating rates of sugar transformation and computing concentrations of the various sugars, and compared the results with measured concentrations of carbohydrates in fruits. Based on their analysis, fruit carbohydrates differed in sensitivity to assimilate supply, metabolism and dilution (fruit volume). Sucrose was highly sensitive to assimilate supply and dilution effects but not subject to much metabolic transformation. Sorbitol was calculated to be the most important carbohydrate involved in peach fruit metabolism and consequently its concentration was generally low in spite of its high proportion in the assimilate supply. Glucose and fructose represented a transitory storage/metabolic pool. Their assessment appears to be in conﬂict with the hypothesis of Lo Bianco et al. (1999a) regarding the role of sorbitol as a carbon source for fruit growth but provides an insightful synthesis that is in agreement with most of the other literature on peach fruit carbohydrate metabolism. Carbon partitioning within vegetative growing sink organs Meristematic tissues in vegetative peach buds appear to have higher uptake capacity for

glucose than sucrose or sorbitol (Maurel et al., 2004). However, Lo Bianco et al. (1999a) found sorbitol dehydrogenase activities in active root tips to be high and in shoot tips they were positively correlated with shoot growth rates. This factor and the corresponding periods of peak sink and enzyme activities led these researchers to hypothesize that, in peach trees, sucrose is the major form of carbohydrate used for fruit growth whereas sorbitol has a predominant role in supporting vegetative growth. There seems to be general agreement that sorbitol is a primary source of carbohydrates for vegetative sinks such as root tips, growing shoots (Lo Bianco et al., 1999b) and immature leaves (Moing et al., 1992). These ﬁndings appear to agree with similar studies with apple (Loescher et al., 1982; Yamaki and Ishikawa, 1986).

Carbon partitioning and mobilization in perennial parts It is well known that the majority of the overwintering storage of carbohydrates in fruit trees is in the form of starch that is found in the bark and wood of stems, trunk and roots (Stassen et al., 1981, 1982; Tromp, 1983; Oliveira and Priestley, 1988). Rafﬁnose and stachyose are also stored in Prunus perennial parts during winter (Gaudillère et al., 1992). Although the concentration of starch and soluble carbohydrates is often higher in the bark, storage in woody tissue accounts for the greatest proportion of stored carbohydrates in the tree (Stassen et al., 1982). There is little information speciﬁc for peach regarding partitioning to long-term storage or starch metabolism within sink organs. Descriptive studies have shown strong seasonal patterns in starch concentration with the highest levels occurring in the dormant season (Stassen et al., 1981; Jordan and Habib, 1996; Yano et al., 2000). Starch storage that occurs during the growing season is often considered a residual sink for carbohydrates that is active after all the growing sinks are satisﬁed (Grossman and DeJong, 1994b). However, there must be speciﬁc mechanisms that regulate starch metabolism in storage tissue and certainly this activity

Carbon Assimilation, Partitioning and Budget Modelling

should be considered to be as much of a sink as the growth of speciﬁc organs. This is true especially when one considers that winter storage and spring mobilization of carbohydrates is essential for tree survival, ﬂowering and initial organ growth. Although the essential nature of mobilization of stored carbon is readily apparent when one considers the annual cycle of a peach tree, the relative contribution of this part of the carbon budget to the functioning of the whole plant is generally underappreciated. In the stem of peach, 50% of starch was hydrolysed between October and December (Marquat et al., 1999). The early study of Petrov and Manolov (1973) using 14CO2 labelling in autumn demonstrated accumulation and mobilization of carbon reserves in peach. 13C is used nowadays as a tracer to study the distribution of 13C-labelled assimilates during dormancy following assimilation of 13CO2 during the preceding autumn. It is also used to follow mobilization and translocation of 13C- labelled assimilates in the following spring but there has been limited use of this technique with peach. During the winter dormant season, phloem transport in temperate deciduous trees is thought to become non-functional (Evert, 1960) and whatever long-distance transport of carbohydrate occurs is apparently through the xylem (Loescher et al., 1990). Sorbitol has been reported to be the primary carbohydrate present in the xylem of peach trees during the winter months but it declines in the spring when the hexoses, glucose and fructose, become more prevalent (Loescher et al., 1990; Maurel et al., 2004). As noted previously, meristematic tissues in peach buds and young fruit appear to have higher uptake capacity for glucose than sucrose or sorbitol (Vizzotto et al., 1996; Maurel et al., 2004). It has been reported that sorbitol is the primary carbohydrate source for the growth of young leaves (Moing et al., 1992) and shoot and root tips (Lo Bianco et al., 1999b). It would be interesting to know if this is true for the early spring ﬂush of growth as well, since sorbitol is apparently not found in large amounts in the early spring xylem transport stream. It is generally recognized that the ﬁrst several days of spring growth is dependent on carbohydrates mobilized from storage and thereafter there is

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thought to be a transition to dependence on current assimilates (Priestley, 1970). Carbohydrate partitioning at the whole-plant level Over the past couple of decades the concept that carbohydrate partitioning at the wholeplant level is primarily driven by growth and development of individual organs has become widely accepted (Gifford and Evans, 1981; Watson and Casper, 1984; Ho, 1988; Marcelis, 1994; Weinstein and Yanai, 1994; Lacointe, 2000). Grossman and DeJong (1994a) used this concept in the development of the PEACH model and later DeJong (1999) outlined four principles for applying this concept to logically understand carbon partitioning in peach (and other fruit) trees. The ﬁrst principle is that a tree is a collection of semi-autonomous organs and each organ has a genetically determined, organ-specific development pattern and growth potential. Although much emphasis is often placed on considering plants as highly integrated organisms, the concept of semi-autonomy among organs is widely recognized (White, 1979; Harper, 1980; Watson and Casper, 1984; Sprugel et al., 1991). Indeed, the primary morphological features that distinguish one species or cultivar (in the case of peach) from another are at the organ or sub-organ level (i.e. fruit or leaf shape and size, ﬂoral characteristics, etc.), not at the wholeplant level. Furthermore, although variation exists, the developmental patterns and growth rates of individual organs under speciﬁc environmental conditions are generally predictable and have been modelled. Models have been developed for the growth of peach fruit (DeJong and Goudriaan, 1989; Pavel and DeJong, 1993c; Grossman and DeJong, 1995b; Genard and Huguet, 1996; Genard and Souty, 1996), shoots and branches (Costes et al., 1993; Grossman and DeJong, 1995a; Genard et al., 1998; Lescourret et al., 1998) and roots (Bidel et al., 2000). Although tree pruning and training can drastically alter the shape of peach trees, they generally have very little effect on individual organ characteristics other than those explained by changes in the local microenvironment of the organs or changes

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in the availability of carbohydrates due to the proximity of other sinks. The fact that there appears to be some level of branch autonomy (Sprugel et al., 1991) in peach trees further reinforces this ﬁrst principle. Branch autonomy tends to functionally isolate some sinks from sources of carbohydrates. When sinks are manipulated through pruning or fruit thinning to create an apparent abundance of photosynthate in one part of the tree and an undersupply somewhere else, the carbon does not freely move to the location of greatest demand. When one scaffold of Y-shaped peach trees was defruited the remaining fruit on the fruited scaffold beneﬁted very little from the carbon that should have been available for fruit growth from the defruited scaffold (Marsal et al., 2003). Interestingly, scaffold diameter growth appeared to be one of the sinks that beneﬁted most from the removal of fruit, while root growth was only marginally affected. There is much to be learned about the movement of carbohydrates within the context of the whole tree. The role of branch autonomy in the early spring, when much of the carbon used for growth is mobilized from storage in the root, trunk and major branches and is presumably transported in the xylem, is also very poorly understood. Carbon partitioning at the branch level has been studied in peach explicitly with radioactive tracer studies (Corelli Grappadelli et al., 1996) and by manipulating leaf number and fruit load in isolated branches (Genard et al., 1998). Implicit conclusions about carbon partitioning within shoots have also been drawn from fruit thinning studies to determine optimal fruit positioning for fruit size (Spencer and Couvillon, 1975; Marini and Sowers, 1994). These studies support the idea that fruit are strong sinks for carbon within shoots but their inﬂuence on where recently ﬁxed carbon goes varies substantially within the local context of the stem unit. The second principle is that the genetic potential of an organ is activated or deactivated by organ-specific, endogenous and/or environmental signals. The semi-autonomous nature of individual organs is further demonstrated by the fact that individual organs on a tree can be experimentally activated by manipulating

factors that stimulate the growth of speciﬁc organs independently from processes occurring in organs elsewhere on the tree. For instance, exposing individual buds on a branch to rest-breaking treatments can induce bud break in those buds while similar buds on other parts of the tree remain inactive (Chandler, 1942). Similarly, grafting multiple cultivars with differing chilling requirements on to one trunk will not inﬂuence the inherent chilling exposure required for activation by the branch of each speciﬁc cultivar. Also, removing the apical meristem on a shoot will promote the activation of growth of lateral buds on the remaining part of the shoot while buds on other shoots are unaffected (Harris, 1983). Although the exact mechanisms of the environment and/or endogenous signals that activate growth are not fully understood, the primary site of activation is clearly at the organ or sub-organ level. This is certainly one area where hormones play key roles in inﬂuencing carbon partitioning at the whole-tree level, as suggested by data on hormone concentrations in xylem sap (Sorce et al., 2002). The third principle is that after an organ is activated, current environmental conditions and genetic growth potential interact to determine conditional organ growth capacity. Although often overlooked, ambient temperature is probably the single most important environmental factor inﬂuencing organ growth. The importance of temperature is related to the strong dependence of respiration on temperature. All real plant organ growth is dependent on metabolic activity and enzyme function, and these processes are linked to respiration. Plant respiration generally has a temperature response quotient (Q10) of about 2 (doubles for every 10°C increase in temperature between 5°C and 35°C; Amthor, 1989) and peach is no exception (Pavel and DeJong, 1993c; Grossman and DeJong, 1994a). Therefore, conditional growth capacity of any organ is highly dependent on ambient temperature. The conditional growth capacity of peach fruits growing under near-optimal ﬁeld conditions has been modelled for several peach cultivars using relative growth rate functions (DeJong and Goudriaan, 1989; Pavel and DeJong, 1993c; Grossman and DeJong, 1995a; Berman et al., 1998). That other environmental factors

Carbon Assimilation, Partitioning and Budget Modelling

such as water status can also have a substantial effect on organ growth is well documented (Bradford and Hsiao, 1982). Extension growth of peach shoots has been successfully modelled by considering temperature and dynamic changes in shoot water status (Berman and DeJong, 1997a; Basile et al., 2003). Although peach fruit growth is quite sensitive to water stress it is important to distinguish between growth in fresh versus dry matter since the former is much more sensitive than the latter (Berman and DeJong, 1997b; Girona et al., 2004). Nutrient availability also can strongly inﬂuence conditional organ growth capacity because certain nutrients are required as constituents for the growing organs. Accordingly, Saenz et al. (1997) have demonstrated that N availability can inﬂuence developmental patterns of peach fruit. Finally, realized organ growth is a consequence of conditional organ growth capacity, resource availability (assimilate and nutrient supply) and interorgan competition for those resources. When conditional growth capacity of an organ is set, organ growth should proceed at a rate equal to the conditional growth capacity as long as transport is not limited and enough resources (carbohydrates) are available to support that organ’s growth and the growth of all other competing organs. However, if the tree does not have enough carbohydrate to support the conditional growth capacity of all organs or carbohydrate transport within the tree is limited, then the growth of an individual organ will be a function of its ability to compete for available carbohydrates with other organs. Since ﬂowering and pollination are not major problems in the more productive peachgrowing regions, most peach cultivars set very heavy fruit loads. Therefore lack of available assimilates and inter-fruit competition for carbohydrates is generally the primary factor limiting realized fruit growth in mature peach trees and fruit thinning is essential to manage this competition (Dorsey and McMunn, 1928; Cain and Mehlenbacher, 1956; Johnson and Handley, 1989; Pavel and DeJong, 1993b; DeJong and Grossman, 1995; Grossman and DeJong, 1995b; Costa and Vizzotto, 2000). Certainly there are some limitations to carbohydrate transport within the tree (DeJong and Grossman, 1995; Marsal et al., 2003) but these

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are difﬁcult to quantify speciﬁcally. There is substantial evidence that peach fruit growth can compete effectively for carbohydrates with shoot, trunk and root growth when the crop loads are high and all fruit are considered as a collective sink (Proebsting, 1958; Grossman and DeJong, 1995a; Marsal et al., 2003). But there is some evidence to the contrary when pruning systems stimulate excess vegetative shoot growth (Grossman and DeJong, 1998). There is also clear documentation of the capacity of individual fruit organs to compete with each other and/or vegetative sinks at the local branch level (Genard et al., 1998). To complicate things further, the competitive ability of fruit for carbohydrates appears to vary with the stage of fruit development (DeJong and Grossman, 1995). Upon examining these four principles for understanding carbon partitioning it becomes apparent that phenological patterns of organ growth are the principal determinants of carbon partitioning in peach trees. When experiments are conducted involving different crop load treatments or some other treatment that dramatically favours the growth of one type of organ over others, biomass data collected at the end of the season appear to indicate that some organs are in direct competition with others (Proebsting, 1958; Chalmers and van den Ende, 1975). However, when seasonal patterns of growth are analysed, it is apparent that direct competition between different organ types is limited by temporal separation of growth activities (DeJong et al., 1987; Miller and Walsh, 1988; Rufat and DeJong, 2001; Berman and DeJong, 2003). Generally, in late-maturing peach cultivars shoot and root growth is the dominant sink shortly after bud break in the spring. This period is followed by a peak of fruit growth and then there is a resurgence of root growth (L. Pace, unpublished results) and shoot diameter growth after harvest (Grossman and DeJong, 1995a; Berman and DeJong, 2003). It is interesting that breeding efforts to create cultivars with early fruit ripening times has apparently interfered with the natural temporal separation of dominant sink activities in peach trees. The dominant period of fruit growth of earlymaturing peach cultivars often coincides directly with the early peak of shoot growth.

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This has increased the competition between fruit and shoot growth, resulting in decreased yield potential (DeJong et al., 1987; Grossman and DeJong, 1995a). There is also some evidence that selection for early-maturing cultivars has involved selection for decreases in total fruit growth potential and dry matter content and these factors also account for differences in yield potential between early- and late-maturing cultivars (Berman et al., 1998). The selection for early-maturing fruit has also increased the competition for carbohydrates between organs within the fruit such that seed development corresponds with the period of ﬂesh enlargement (Pavel and DeJong, 1993a) as well as increasing the individual fruit relative growth rates, so that the tree cannot support as many fruits at one time (Grossman and DeJong, 1995a,b).

Effect of biotic stress Biotic stress may also modify carbon partitioning through effects on sources and/or sinks. Photosynthesis is drastically reduced in powdery mildew-affected trees (Toma et al., 2003). Leaf injuries caused by silver mite decrease photosynthetic rate and have effects on fruit quality in the current year and in the next year (Kondo and Hiramatsu, 1999). Increased partitioning of dry weight and carbohydrate fractions from shoots to roots and shifts in proportional composition of individual sugars occurred in ‘Nemaguard’ rootstocks infested with nematodes (Olien et al., 1995). If parasitism was severe, reduced levels of carbohydrates in the above-ground part of the tree could result in tree injury or death at levels of environmental and biological stresses that do not injure healthy trees.

10.4 Modelling the Carbon Economy of Peach A host of environmental (biotic and abiotic) and endogenous factors can simultaneously inﬂuence carbon assimilation and partitioning within leaves, transport processes between sources and sinks, activation and conditional

growth capacity of individual organs, and the relative ability of organs to compete with each other for carbon. The only way to functionally understand and quantify the importance of these factors in an integrated system is to develop computer simulation models of that system. The work in this area with peach has been focused principally in two areas: models of fruit growth and of the whole tree. Models of fruit growth and carbon economy Conners (1919) ﬁrst described the doublesigmoid growth curve of peach fruit almost a century ago. In 1989, DeJong and Goudriaan demonstrated that the double-sigmoid growth curve could be modelled with relative growth rate functions and developed a quantitative computer simulation model of the carbohydrate requirements for peach fruit growth. This work estimated the respiratory growth coefﬁcient for peaches to be 0.309 mg CO2/ mg fruit dry weight and allowed for subsequent models to calculate total carbohydrate requirements for peach fruit growth and development (DeJong and Walton, 1989). Fruit respiration accounts for 16–20% of the carbohydrate required for producing a peach fruit. The carbohydrate demand for an individual peach fruit peaks just before harvest and can be as high as 1.3 g CHO per fruit per day. DeJong and co-workers focused on the development of simulation models for estimating the carbohydrate demand of the cohort of larger-sized fruit on a tree (thus quantifying the fruit potential carbohydrate demands). Meanwhile, Genard and co-workers concentrated on models that take into account the great variation in fruit growth among the whole population of fruit in a typical peach canopy. In 1993, Genard and Bruchou presented a multivariate approach to modelling peach fruit growth that investigated the effect of leaf:fruit ratio and between- and withintree variability in growth of individual fruits. Interestingly, their model showed that size differences among fruits within shoots accounted for more than half of the total variability in fruit size while leaf:fruit ratio was not a major factor. However, subsequent models documented the importance of leaf:fruit ratio

Carbon Assimilation, Partitioning and Budget Modelling

in determining the size of fruits on wellilluminated girdled shoots (Genard et al., 1998; Lescourret et al., 1998). Research by Genard and Souty (1996) produced a very interesting model of mesocarp sugar contents in relation to peach fruit growth. Using fruit ﬂesh dry weight data and a set of literaturebased conceptual assumptions for carbon partitioning into various sugars, these authors successfully modelled fruit ﬂesh sucrose, glucose, fructose and sorbitol contents and concentrations at different crop loads. They also used the model to estimate the contribution of each sugar to relative sweetness during the last 50 days of fruit development. Their model indicates that sucrose is the most important sugar in determining fruit sweetness at fruit maturity but that fructose is more important earlier in fruit development. Subsequently this model was linked to a model of fresh mass growth of peaches to simulate the effect of water supply on fruit sugar concentrations (Genard and Huguet, 1997) and to a model of carbon acquisition and partitioning for simulating the effects of light interception and fruit thinning on peach sweetness (Genard et al., 1999). Most recently this model was used to further distinguish the effects of assimilate supply, dilution and metabolism on fruit sugar concentrations (Genard et al., 2003). These models substantiate that sorbitol is the most important carbohydrate used for metabolism in peach fruit, while sucrose does not undergo metabolic transformation but is subject to a dilution effect during fruit development. Glucose and fructose constitute a transitory storage pool and their concentrations are closely related to metabolism. Collectively these models provide a substantial resource for understanding the inﬂuence of crop load and various environmental factors such as light exposure, water and temperature on the dynamics of growth and quality of peach fruit.

Modelling tree growth and carbon economy The fruit growth model of DeJong and Goudriaan (1989) was based on the premise that fruit growth potential is genetically controlled and can be approximated by modelling the

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relative growth rates of fruit on lightly cropped (sink-limited) trees. This led to the development of a carbon-based simulation model of reproductive and vegetative growth of whole peach trees. By conducting a series of ﬁeld experiments to collect fruit and vegetative growth and respiration data under varying crop load scenarios, Grossman and DeJong (1994a, 1995a,b,c) quantiﬁed the seasonal interactions between the various organ types, which were used to develop sub-models of seasonal carbohydrate demand by the fruit, shoots, major branches and trunks of mature peach trees. The sub-models of carbohydrate demand were linked with a sub-model of canopy photosynthesis to estimate carbohydrate supply and the result was a whole-tree model that predicted the daily partitioning of carbon into various organ types (Grossman and DeJong, 1994b). The PEACH model estimated that for the high-density central leader planting where the data were collected, an individual tree assimilated 33 kg CHO between bloom in early March and the beginning of leaf-fall in mid-October. This was equivalent to 4.1 kg CHO/m2/year. For a normally cropped, August-ripening cultivar (‘Cal Red’), the model estimated that approximately onethird of the annual carbohydrate budget went to maintenance respiration while two-thirds went to biomass growth and growth respiration. Simulated fruit growth, above-ground vegetative growth and root activity each consumed about one-third of the carbohydrate used for growth. However, the model also clearly showed that these patterns of carbohydrate use are dependent on crop management practices such as fruit thinning. Subsequently the PEACH model was used to estimate the effect of differences in seasonal air temperature patterns on carbon assimilation, crop growth and respiration and yield (DeJong et al., 1996). This work showed that it is likely that wholetree canopy photosynthesis may be enhanced in very warm climates but these conditions may not lead to increased yields since higher maintenance respiration rates may actually reduce the amount of carbohydrate available for growth. Berman et al. (1998) have also used this model to estimate the effect of fruit maturity date on yield potential of processing peaches grown in California. This work

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predicted that the yield potential of cultivars developed with fruit maturity dates earlier than the second week in July (the harvest period of the current earliest processing clingstone peaches in California) will be reduced by approximately 1.8 t/ha for each day that harvest is advanced unless the physiological characteristics of the trees that govern carbon partitioning are also substantially altered. The original PEACH model had two major limitations. The ﬁrst was that carbohydrate partitioning to root growth and development was not explicitly modelled and this problem still persists. However, the general patterns and quantities of dry matter partitioning to root growth and respiration that the model predicts are in general agreement with data on dry matter distribution in peach trees (Chalmers and van den Ende, 1975; Miller and Walsh, 1988; Grossman 1993; Rufat and DeJong, 2001). All of these reports indicate that root biomass of peach trees accounts for about one-quarter of the total tree biomass, depending on crop load and other management factors. Trees on size-controlling rootstocks appear to allocate a slightly higher proportion of their dry mass to roots (Salvatierra et al., 1998; Basile et al., 2003) but very limited data are available on this question. Kubota et al. (1990) monitored the movement of 13C-labelled photosynthates into peach roots and found a dwarﬁng rootstock (Prunus tomentosa) received a greater proportion of labelled carbon 120 h after feeding than did a vigorous rootstock (Prunus persica). This labelling pattern ﬁts biomass distribution data; however, it may be unwise to draw too strong conclusions since there were limited data and P. tomentosa dwarﬁng appears to be a result of partial scion incompatibility. The second major limitation of the current PEACH model is that all the individual organs of each type in a tree are modelled together as a mean organ of that type. Thus the proximity of individual organs to sources or sinks of carbohydrate or location-dependent environmental stimuli such as light are not accounted for. Allen et al. (2002) have begun developing a new, context-sensitive, visual graphics-based approach to explicitly model carbon transport and partitioning within peach tree canopies. This model takes

advantage of L-systems technology (Prusinkiewicz, 1998) to keep track of every organ that develops on a simulated graphic representation of a tree. Algorithms are being developed to govern the movement of carbohydrate into and out of each organ as the tree develops through several growing seasons. This research is still in the formative stage but it holds substantial promise as a platform for beginning to understand the integrated processes involved in carbohydrate partitioning to individual organs within the context of the whole tree. It should also provide a framework for incorporating the quality modelling of peach fruits (Genard et al., 2003) into integrated wholetree models of carbohydrate partitioning in peach.

10.5 Future Directions There are two areas of scientiﬁc investigation that are likely to have major impacts on our understanding of carbon assimilation, partitioning and budget modelling of peach trees in the next decade. These are the techniques of molecular genetics and physiology and the rapid advances in information technology. Peach is considered as the model species for structural and functional genomics of Rosaceae (Abbott et al., 2002; http://www.genome. clemson.edu/gdr/; see Chapter 4). Genomic resources including expressed sequence tags and a physical genetic map are being developed. Molecular physiology is just beginning to enlighten scientists about the regulation of: (i) enzyme activity within cells of source and sink tissues; and (ii) transport between source and sink tissues. This work will provide a more thorough understanding of the regulation of source and sink activities at the cellular level and unlock the current mysteries regarding the role of the various carbohydrates in the overall scheme of the carbon budget. One very interesting question in this regard is the purpose of having two major transport carbohydrates (sucrose and sorbitol) in the rosaceous species. The potential for application of the recent developments in computer technology has yet to be efﬁciently used in efforts to synthesize

Carbon Assimilation, Partitioning and Budget Modelling

the knowledge about numerous aspects of carbon assimilation and partitioning into an integrated model of peach tree growth and carbon economy. Much work can be done at several levels of organization by just using current knowledge, let alone incorporating the new information that is being developed using new molecular techniques. New sensor technology is now available to monitor hundreds of facets of growth and environmental parameters simultaneously, but this

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work will require an integrated intellectual framework to make it efﬁcient. Advancing efforts with functional/structural models to couple plant architectural models with physiological models should make that feasible in the near future (LeRoux et al., 2001). Moreover, the combination of genetic and ecophysiological models should also help to unravel the mechanisms of carbon partitioning involved in the elaboration of fruit quality (Quilot et al., 2002, 2004b).

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11

Orchard Planting Systems

L. Corelli-Grappadelli1 and R.P. Marini2 1Dipartimento 2Department

di Colture Arboree, University of Bologna, Bologna, Italy of Horticulture, The Pennsylvania State University, University Park, Pennsylvania, USA

11.1 Introduction 11.2 Evolution of Training and Pruning Principles Minimal pruning Summer pruning Cropping as a tool in training Intensiﬁcation of peach orchard systems 11.3 Light and Tree Physiology Photosynthetic characteristics Light interception and distribution Fruit quality Flower bud differentiation 11.4 Modern Orchard Systems Open vase Palmette Central leader Y-shaped tree Meadow orchards Protected cultivation 11.5 Effects of Training System and Planting Density on Yield Tree form effect on yield Effect of planting density on yield Effect of tree density plus tree form on yield 11.6 Future Trends

11.1 Introduction Peach is one of the most important temperate fruit tree crops, with a world production in 2003 of about 14.8 million t. Total peach plantings and output worldwide have nearly doubled 264

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since 1974, with China accounting for most of this change (FAOSTAT, 2004). Over the same period of time, output per hectare has increased from 9.7 to 10.4 t; in the most advanced countries, output generally exceeds 15 t/ha. This difference certainly reﬂects vast differences in

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

Orchard Planting Systems

production techniques, including the choice and management of the orchard design (the combination of cultivar, rootstock, training system, spacing, tree size). The orchard designs adopted worldwide vary widely; it is known that different training systems can have quite different productive potentials. A large number of studies have been undertaken globally since the mid-1950s to elucidate several aspects of tree performance in peach, and these have been reviewed recently (Marini and Corelli Grappadelli, 2006). This past half century has seen a broad change in the forms peach trees are trained to and in the way a given form is achieved, and all along constant increases in productivity and efﬁciency have accompanied these changes. The thrust behind this evolution has mostly been the economics of the operation. For peach growing to remain economically viable in the more advanced countries, particularly those in which agricultural land is at a premium, it is necessary to increase orchard efﬁciency and productivity. In this chapter the evolution of the training and pruning techniques that have accompanied and fostered the evolution of orchard training systems, as well as the scientiﬁc bases underpinning these technical achievements, are reviewed. Then follow a detailed discussion of the most widely adopted training systems and a forecast of future trends in this important part of peach cultivation.

11.2 Evolution of Training and Pruning Principles In modern orchards, shortening the initial unproductive period is emphasized: the sooner trees come into bearing, the sooner the economic burden on the orchard begins to be alleviated. Instrumental to this are high planting densities: even if each individual tree does not bear a large amount of fruit, the higher number of trees per hectare allows sizeable initial yields. Later on in the life of the orchard, the differences in yield between high- and lowdensity orchard designs tend to disappear because at this stage most orchards will intercept similar amounts of light, which translates into similar yields. The pruning techniques

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adopted in the training stage of the tree are the key to hastening bearing. Today, there is a consensus that the most important aspects include reducing the number of pruning cuts in the early years, avoiding heading cuts wherever possible, using summer rather than winter pruning to train the trees, and allowing cropping in the early years as a tool to reduce vegetative growth since this species lacks vigour-controlling rootstocks.

Minimal pruning In general, the fewer pruning cuts made to the tree in the ﬁrst 2 to 3 years from planting, the quicker the tree will come into bearing. The minimal amount of pruning favours the onset of the reproductive phase of the tree. This concept was ﬁrst promoted by extension agents and researchers in Italy in the early 1950s (Baldassari, 1950), who demonstrated the advantages of the so-called ‘potatura a tutta cima’ (no-heading-cuts pruning). Baldassari argued against excessive cuts in the early years because this would alter the equilibrium of the tree towards a vegetative response, but he also showed the advantage of leaving the leader of the tree (and of the branches) intact, in order to hasten the reproductive stage. Therefore, only thinning cuts removing entire shoots or branches should be made, whereas all heading cuts on 1-year-old wood (widely used to obtain regular branch formation in the open vase or regular palmette) were abandoned. This type of pruning approach quite effectively shortened the time needed for the transition of the tree from vegetative to reproductive growth. Following this strategy is best accomplished by planting well-feathered maiden trees: the best feathers can be selected to form the permanent tree structure. However, production of good maiden trees can be difﬁcult, as peach trees require high light to develop laterals and in the nursery peaches are often planted too closely. As a result, peach trees tend to grow quite tall (particularly on vigorous rootstocks) and may have only a few short laterals, often with narrow crotch angles or too high on the tree to start the ﬁrst tier of

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branches. Thinning out excessive feathers and cutting them back to the ﬁrst or second node may induce regrowth of laterals that can be used to start the permanent structure of the tree without resorting to heading back the leader. If there are no good laterals the leader could still be maintained, but summer pruning is required to check the growth of the higher current-season laterals by pinching. This needs to be repeated in the summer, so that good laterals are formed by lower buds during the ﬁrst year. This is not optimal because the ﬁrst season in the ﬁeld is spent trying to overcome the problem, rather than training the tree, but it can be preferable to cutting back the leader. Heading of the tree in the ﬁrst year should be performed only in the case of trees devoid of or with only poor laterals, or when the training system requires it (such as in the Y-trellis). When heading is necessary it should be done at planting, so that the tree may develop new laterals and have the entire season to regrow. When the newly formed laterals are long enough (around 20–30 cm) shoot selection is necessary to choose the shoot that will reform the tree.

Summer pruning Another important tool for shortening the unproductive period is summer pruning. This is mainly because summer pruning facilitates controlling the development of the tree in a ‘softer’ way: very often a cut can be avoided if the shoot can instead be bent, trained, twisted, pinched, etc. All these operations are far less ‘traumatic’ for the tree and cause less reaction than dormant pruning. As a result, the tree is less prone to vegetative growth reactions which can be the result of heavy cuts made during the winter. Another advantage is that the tree is not investing too many resources in structures that are not permanent. Summer pruning is a practice most important in the training phase of the orchard, when the trees are young and must reach their adult stage as quickly as possible. However, it is also important for some high-planting density systems where heavy shading can cause a loss of bearing wood in the lower parts of the

canopy. Because summer pruning removes foliage, this impacts not only current-season fruit growth but also the reserves for early growth in the next season. In general fruit colour formation can be improved by summer pruning, but fruit size and internal quality may suffer from the reduction in available assimilates. It is difﬁcult to devise a successful summer pruning strategy because of the many processes occurring simultaneously which depend on light, i.e. fruit growth, shoot growth, ﬂower bud differentiation and reserve accumulation.

Cropping as a tool in training Allowing the presence of fruit on the tree is increasingly used to train trees in a ‘soft’ manner. Traditionally, all fruit would be removed from young trees to improve the growth and establishment of the tree structure. This was done because the goal was to establish a durable, robust tree, which would last many years. As the goal has shifted towards less durable trees, cropping has been regarded as a natural means of containing tree vigour with minimal pruning. Peach trees can feather quite normally in the nursery, provided sufﬁcient light is available during the growing season (which may not always be the case, as indicated above). As a consequence, the potential exists for a certain number of fruit to be borne on the tree in the year of planting. The number of fruits to be left, however, must be small: the overriding goal is to control tree growth, not to produce high early yields. Up to ﬁve or six fruits per tree may be left in the year of planting. Cropping acts by altering partitioning of resources towards the growing fruit and away from vegetative growth.

Intensification of peach orchard systems Work with apple demonstrated the feasibility of increasing early yields by increasing the number of trees per hectare. The high-density orchards, based on smaller trees planted closer together, reach their full production potential more quickly than ordinary orchards; their

Orchard Planting Systems

early yields, however, are also substantial because of the high number of trees, which acts as a powerful multiplier of even small yields per tree. The increasing costs facing growers in some peach-producing countries have been a strong incentive for the change towards more intensive orchard systems (Sansavini, 1974; Bandoli, 1980). Since dwarﬁng rootstocks for peach do not currently exist, the trend towards high tree densities has never reached the levels that are commonly observed for apple, which is very frequently planted at above 2000–3000 and up to 7000–8000 trees/ha. However, the beneﬁts of high-density plantings can be reaped with peach as well. Wellfeathered trees from the nursery which are minimally pruned, for example, can produce a proﬁtable crop in the year of planting. In addition, as indicated above, growers can use cropping as a powerful tool to control tree vigour. It is interesting that the most commonly used rootstock in Italy for almost two decades has been the vigorous ‘GF 677’ peach × almond hybrid. The reason for this apparent contradiction is that, as peach wood dies quickly under conditions of low light, the vigorous rootstock provides the potential for regrowth from shaded inner sections of the canopy when light conditions are improved by pruning.

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cally active radiation (PAR; 400 to 700 nm) (Marini and Marini, 1983; DeJong and Doyle, 1985). The only report of whole-tree CER shows saturation at about 1600 µmol/m2 per second of PAR (Giuliani et al., 1998). This may be due to the fact that whole-canopy CER takes into account respiring organs such as wood and fruits in addition to leaves, and also reﬂects the various net photosynthesis rates attained by leaves that are at different light levels. Leaf mass per area (LMA; the ratio of leaf dry weight to leaf area) is lower for shaded than for non-shaded leaves and was found to be a biological integrator of cumulative light exposure for a leaf until midseason (Marini and Barden, 1981). LMA of leaves exposed to a range of light levels for 18 days was linearly related to light level, and CER measured under saturating light was related to LMA. The CER and LMA of leaves shaded for 18 days and then exposed to full sun for 26 and 4 days, respectively, were similar to those of non-shaded leaves (Marini and Sowers, 1990). Leaf nitrogen content was related to the light environment of a leaf, and leaf nitrogen can be reallocated from shaded leaves to more exposed leaves of the tree canopy (DeJong and Doyle, 1985). These data indicate that the redistribution of leaf nitrogen is a means for maximizing whole-tree carbon gain.

11.3 Light and Tree Physiology Light interception and distribution Light is the driving factor for all plants on the planet. Dry mass production of a plant depends on the amount of light intercepted (Monteith, 1977), but in fruit trees the relationships between light intercepted and yield are fairly complex because they depend on the photosynthetic characteristics of a species and on the amount of light intercepted and distributed within a canopy. It is therefore necessary to review these aspects brieﬂy before discussing peach orchard systems.

Photosynthetic characteristics The peach exhibits a C3 photosynthetic carbon ﬁxation pathway; the carbon exchange rate (CER) of peach leaves saturates at about 800 µmol/m2 per second of photosyntheti-

Mathematical models indicate that the amount of light intercepted by a tree sets its maximum potential for yield, as the latter cannot exceed the former; however, the actual yield produced by a tree will also reﬂect the inﬂuence of temperature, the tree’s vegetative/reproductive equilibrium, its hormonal balance, and its nutritional and water status. From the standpoint of light alone, orchard productivity is inﬂuenced by the relationships between orchard design (i.e. tree form, tree spacing and row orientation) and available light, which depends on average sun position. The goal is to ensure concurrent high light interception and good distribution throughout the canopy. Modelling work in apple (Cain, 1972; Jackson and Palmer, 1972; Jackson and Middleton, 1988) has indicated that two ways exist to

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increase the amount of light intercepted by a tree: either by increasing the density of the canopy (which causes poor distribution within the canopy) or by increasing the orchard’s leaf area index (LAI; ratio of leaf area to unit of land area) by planting a greater amount of trees of smaller size (which allows for good transmission of the light to all the parts of a tree). This work has laid the theoretical foundation for high-density plantings of apple and other crops worldwide, including peach. Lakso (1994), drawing upon results from many studies in different parts of the world, showed apple yields to be linearly related to the percentage available light intercepted by the tree. Interestingly, above 50% light interception the relationship appears less tight. One of the reasons this could be attributed to illustrates the effect of vegetative growth versus planting density. Low-cropping trees often partition more resources to vegetative growth, which increases their light interception without a concurrent increase in yield. On the other hand, orchard designs based on many small trees, capable of high light interception and distribution within their smaller canopies, may retain greater crop loads (Robinson, 1997). The amount of light intercepted and its distribution depend not only on the amount available at the particular latitude, but also on the type of weather prevailing during the summer. In the north-eastern USA, for example, or in northern Europe, conditions prevailing in the summer include many hours of hazecloudiness which cause a shift in the proportion of diffuse/direct light available. This in turn has an effect on the amount of light that can reach the internal positions of the canopy. Lakso and Musselmann (1976) reported for upstate New York that maximum light penetration to the interior canopy occurs under a mix of direct and diffuse radiation rather than under maximum direct light conditions. On the other hand, Mediterranean climates such as Italy, California and Spain normally have very high amounts of direct light and this may largely alter these relationships. Fruit quality parameters for apples developing in a cloudless, high direct radiation environment of Washington State showed different relationships with light levels than fruits from the midAtlantic states (Campbell and Marini, 1992).

Reported light distribution patterns vary between different fruit tree forms. In general, the outer periphery of the canopy intercepts and reﬂects a high proportion of the incoming radiation, and this causes different light distribution proﬁles for different training systems. Light was distributed in a U-shaped pattern along a horizontal cross-section of the canopy for central leader trees (Porpiglia and Barden, 1980; Marini and Barden, 1982) and in a W-shaped pattern in open vase type trees (Marini and Marini, 1983). These studies showed that in all systems light penetration declines rapidly from the tree periphery towards the tree centre. Most often the zone which receives adequate light for high fruit quality is within about 1.5 m from the outside of the tree (Marini and Barden, 1982; Kappel et al., 1983). Relatively high light levels were measured in the centre of open vase trees (Marini and Marini, 1983) and following pruning or shearing of hedgerow systems in the summer (Kappel et al., 1983; Marini, 1985). The light levels within the canopy vary also with height from the ground, as the upper layers of leaves will project a shadow on those below, and with time of the day. Génard and Baret (1994) showed the variations in the amounts of light transmitted to shoots in open vase peach trees to be a function of position in the canopy and of time of day. Wellexposed shoots were mostly located at the top of the tree and were relatively erect. Shoots located in the outer parts of the canopy were slightly but signiﬁcantly more sunlit than others. Some shoots were exposed to light almost all day while other shoots were in sunlight very little. About 30% of the shoots received <30% of the incoming light. Light transmitted to the shoots did not depend on shoot compass direction. Drooping shoots were preferentially shaded by horizontal and erect shoots above and next to their position on the branch. Virtually all orchard systems far from intercept all of the total light available to them. Among the reasons for this are the need to allow room between rows for equipment access and the need to set adequate spacing to accommodate the height and girth of the trees: if trees were very closely spaced together, only the upper layers of their canopies would receive any light. In apple, experimental

Orchard Planting Systems

orchards have been reported to achieve greater than 80% light interception (several authors, cited in Robinson, 2003), but an average for the industry is certainly much less. In many cases, well-managed orchards may approach 50% interception of available light. In peach, Grossman and DeJong (1998) measured the daily patterns of intercepted photosynthetic photon ﬂux (PPF) in four peach training systems in California, which varied in planting density. The intercepted PPF was relatively constant during mid-day hours (from 09.00 to 15.00 h) for all training systems. The high-density Kearney Agricultural Center V (KAC-V; 1196 trees/ha) system and the cordon system (919 trees/ha) both intercepted more light than the low-density KAC-V (919 trees/ha). The open vase (299 trees/ha) system intercepted the least light. The high-density KAC-V and cordon systems intercepted nearly twice as much light as the open vase system, but no system intercepted much more than 50% of the available light. Robinson and Lakso (1991) also found that Y-shaped apple trees intercepted more light than conical-shaped

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trees (70% versus 55% available light). This training system is also capable of high light interception in peach. Corelli Grappadelli et al. (unpublished results) have measured light interception of three training systems (palmette, delayed vasette and Y-trellis) at standard commercial densities. The Y-trellis had 50% greater light interception from the second season, and in some seasons has reached about 80% interception. The delayed vasette and the palmette were always lower, in particular the palmette, which was normally below 50% (Fig. 11.1). More information is needed to determine the relationship between light interception and peach yield per hectare. Only then can orchard systems be developed that capture the optimum amount of light. Fruit quality Peach fruit quality depends on its position within the canopy, because this inﬂuences the amount of light intercepted by the fruit and the leaves near the fruit. The sensitivity of the

Light interception (% available)

100

80

60

40 Delayed vasette Palmette Y-trellis

20

0 0

2

4 6 Year of planting

8

10

Fig. 11.1. Light interception pattern for a 9-year-old ‘Red Gold’ orchard, grafted on clonal seedlings, trained in three different forms: delayed vasette (5.0 m × 3.7 m; 545 trees/ha), palmette (5.0 m × 2.8 m; 727 trees/ha) and Y-trellis (5.0 m × 1.6 m; 1274 trees/ha). The common spacing between rows in this trial was dictated by a drain tile system which had spacing between tiles of 5 m. Light interception was measured once a year, around summer solstice. The slight decreases for all systems after the seventh year are due to reform pruning applied to keep the trees from expanding excessively. (From CorelliGrappadelli et al., unpublished results.)

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peach to light varies during the season: shading portions of trees during the ﬁnal 6 weeks before harvest (Marini and Sowers, 1990; Marini et al., 1991) and measuring light interception by fruit during the ﬁnal swell (Lewallen and Marini, 2003) allowed the identiﬁcation of critical light levels for various aspects of peach fruit quality. Flore and Kesner (1982) also described critical light levels for various aspects of peach tree growth and fruit quality. These critical light levels are presented in Table 11.1.

Flower bud differentiation As discussed above, at high light interception levels canopies may tend to become too dense. If this is the case, the light-driven process of ﬂower bud differentiation may be hampered with a consequent negative impact on fruit quality, as well as yield. Levels of interception greater than 70% of available light have been reported for apple orchards, but at such levels light distribution may be inadequate for continued high yields of quality fruit (Jackson, 1980). Spurs of pome fruits require at least 30% of light to remain fruitful (Jackson, 1967), but leafy peach shoots must be exposed to adequate light to remain alive. Heavily shaded

portions of peach canopies are devoid of fruiting shoots because they die during the late summer. Flower bud density was also positively related to light levels from about 50 to 100 days after bloom (Marini and Sowers, 1990). Therefore, to maintain high production, light distribution in peach orchards is more important than in apple orchards.

11.4 Modern Orchard Systems In each fruit-growing area of the world, fairly speciﬁc environmental, technical, organizational and economic constraints may limit the choice of training system and orchard design that growers can adopt. These constraints affect the choice of cultivar, rootstock, tree training system and tree spacing, which results in what is normally deﬁned as an orchard system. The successful grower is one who can adapt the various techniques for training and managing the tree to their local conditions. Because of this variability, while it can be said that peach training systems are derived from essentially four basic tree shapes, a great many variations of each of these shapes exist, which depend on the type of nursery tree (maiden, dormant budded, trees grafted in situ), the orchard site (particularly soil and

Table 11.1. A summary of critical light levels (percentage of full sun) for various aspects of peach leaf function and fruit quality. Light threshold (% of full sun)

Parameter

Response to light

Leaf size Leaf thickness Specific leaf weight Maximum CER Cold hardiness Fruit size Fruit colour Soluble solids Flesh firmness Flower densitya

Negative Positive Positive Positive Positive Positive Positive Positive None Positive

Flore and Kesner (1982)

Marini and Sowers (1990); Marini et al. (1991)

36 36 36 36 21 – 36 – – –

40 40 40 35 – 10 30 50 No response 23

CER, carbon exchange rate. aFlower bud formation was most affected by shade during the period 50 to 100 days after bloom.

Orchard Planting Systems

temperature conditions), the skill of the labour, etc. The shift towards higher densities in peach has required adaptations and changes in training systems, as each training system is ideally suited to a speciﬁc density. Therefore, if one scored training systems according to density of planting for example, almost a continuum could be found in terms of trees per hectare but with widely different training systems: from the very low-density open centre, to smaller vases, to the palmette, to various Y-trellis, V-form and slender spindle (fusetto) systems, up to meadow orchards. As only the most widely adopted training systems are described in this chapter, the reader should be aware that, for each of them, many variants can be found in the literature. One common feature of many intensive peach orchard systems is that they strive to bring the orchard into production as early as possible, for obvious economic reasons. If wellfeathered trees are planted, it is not uncommon to pick peaches in the year of planting (Sansavini and Neri, 2005). This is not only a way to reduce the unproductive period at the beginning of orchard life, but also serves the purpose of controlling tree vigour, thus helping in the training stage when peach trees tend to grow excessively. On the other hand, early bearing normally shortens the productive life of an orchard. In the intensive peach industries of southern European countries (Italy, Spain, France) this is not considered a disadvantage because it is desirable to renew orchards with cultivars with improved fruit quality and that expand the harvest season (Borras Escriba, 2001; Sansavini and Neri, 2005).

Open vase Open vase or open-centre trees have been most common in commercial orchards for more than 150 years (Cole, 1849). Worldwide, this system probably is the most adopted one occurring in the largest acreage. Open vase trees in California, USA usually have three primary scaffold branches, each with two secondary scaffolds; mature trees are fairly upright and are about 4 to 5 m tall (Rizzi, 1975). In eastern North America open vase and

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modiﬁed leader trees have three to six primary scaffold branches and bench cuts are used to develop low (2.2 to 3.2 m tall) spreading trees with tree densities of 220 to 550 trees/ha (Fig. 11.2/Plate 70). The open vase, with about 500 trees/ha, is the most important training system in Spain (Royo Díaz and Martínez Lopez, 1992), France (Hugard, 1986; Hilaire, 2003) and Greece. In Spain the variants of the open vase include the ‘vaso Italiano’, ‘vaso de plataformas’ and ‘vaso Californiano’. The main difference is in the angle of the branches and the hierarchy of the secondary branches. Trees of the Italian vase are spaced more widely because the branches are trained to be more horizontal. The ‘vaso de plataformas’ has more upright scaffold branches (35 to 40° from the vertical) and each carries three tiers of secondary branches; up to four in the ﬁrst tier and decreasing to two in the top tier. The height of the tree is about 3 m. The ‘vaso Californiano’ features three fairly upright scaffold branches (15 to 20° from vertical), each with two secondary scaffolds (Royo Díaz and Martínez Lopez, 1992). In Italy, the open vase has long been among the most popular training systems in both the northern and southern growing districts (Giovannini and Monastra, 1995; Sansavini et al., 2000). The traditional opencentre tree is no longer adopted as its density is too low (400 trees/ha and less) and the yields are consequently low, particularly in the early years. In addition, that system requires detailed pruning, which is too expensive and delays bearing (Sansavini and Neri, 2005). A variant of the open centre which is adopted in some parts of Italy is the delayed vase. This tree is based on the natural basitony of the young peach tree, and adopts all the modern principles of pruning: minimal pruning in the early years, no heading cuts, cropping as a tool to control tree vigour. Maintaining the tree leader for 3–4 years helps open up the lower branches, which naturally expand outwards, towards the light. At the same time, by producing fruit, the leader contributes to those important early yields. When a well-feathered tree from the nursery is used (feathers should not lack in the ﬁrst 50–70 cm from the ground, where the ﬁrst whorl of branches is formed), this tree requires

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Fig. 11.2. Traditional open vase tree form.

very little pruning in the ﬁrst and second seasons. Summer pruning is preferentially adopted during training, and must be performed throughout the life of the orchard to maintain bearing wood inside the canopy (Mascanzoni, 1998). This is important to maintain the low bearing zone of the tree, which is one of the main advantages of this form. The leader is removed only after the third, or sometimes the fourth, season, thus the name ‘delayed’. The number of branches retained may vary from four to six, arranged in two whorls. Tree density is about 550 trees/ ha. In vigorous soils this vase can be difﬁcult to maintain low, within 2.2 to 2.5 m of the ground, while it does very well with lowvigour cultivar/rootstock combinations or in low-vigour environments. A variant of the vase that is sometimes used in Italy and Spain is the so-called ‘forma libera’ or free shape (Sansavini, 1980; Royo Díaz and Martínez Lopez, 1992; Sansavini and Neri, 2005). The tree is totally unpruned in the ﬁrst 3 to 4 years, which makes it very productive early on, but in severe need of reform pruning after this initial period. Because the tree develops a bushy appearance, very often it is pruned

back to form a vase, which reduces yield in the years immediately following this reform pruning. This is the main reason for its limited adoption. In general, the advantages of open vase and open-centre trees are in the limited number of trees per hectare (which helps reducing planting costs), the lack of a trellis system and, at least for some of them, the low height, which makes it possible to prune, thin and pick from the ground without using ladders (they do not lend to platforms at all). The disadvantages include low early yields (if the trees are headed back and severely pruned during training), late frosts since the short trees are more prone to freezing damage, and greater difﬁculty performing some cultural practices, such as herbicide applications and mowing, because of the spread of the tree (Mascanzoni, 1998). Palmette Hedgerow training systems from which the palmette was derived were in use in French gardens in the 1700s (Sansavini and Neri,

Orchard Planting Systems

2005). Hedgerows were introduced in commercial orchards in Italy in the early 1900s, but the modern palmette training system was introduced by Baldassari (1950), an innovative grower in Ferrara (northern Italy), who switched to this training system from the traditional vase- or pyramid-shaped fruit trees to improve orchard efﬁciency and profitability. This system proved to be more productive and less expensive than the traditional vase (Fideghelli, 1969) and ideally suited to the use of platforms for pruning, thinning and picking, which greatly improved labour efﬁciency over the use of ladders needed for the other systems. The palmette found its greatest diffusion in Italian peach orchards and to a lesser degree in other countries, especially Spain and France. In some important peach districts of Italy it is still the leading training system for peach (Sansavini et al., 2000). The palmette is normally formed from a well-feathered tree, which is planted without heading cuts and with some thinning cuts in case there are too many laterals or they are too crowded. The tree is allowed to grow freely in the ﬁrst year after planting; if it grows fast and develops sufﬁciently, the ﬁrst tier of branches can be selected during the ﬁrst summer, or else the choice is postponed to the second growing season. The following tiers are chosen during the second/third growing seasons, depending on the speed of tree development. The branches are selected according to height (no less than 80–100 cm from the ground or the nearest branch) and crotch angle, without complying with any

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geometric scheme. Selecting the branches in the summer has the advantage that they are easier to work with (if they have not already hardened) and will generally result in wider crotch angles, which are desirable from a mechanical as well as a growing (reduced vigour) point of view. Branch selection and positioning may require considerable time (Corelli Grappadelli et al., 1986) and represents one of the major drawbacks of this system compared with those based on a free structure without trellising (e.g. fusetto, delayed vasette, free shape). The branches are tied to the trellis, which provides support for the tree and a frame to form the structure of the hedge. The number of branches is reduced, sometimes to one tier, which is grown out and up to occupy the space between adjacent trees. Palmette trees are not slower to come into bearing compared with other systems (e.g. fusetto). If not headed in the ﬁrst year, canopy development will be the same as for any other training system (Table 11.2). When the tree is established, pruning the palmette is as rapid as other systems (Sansavini et al., 1980). The narrow canopy allows good light penetration (Corelli Grappadelli and Sansavini, 1989), the trellis helps maintain the shape, and throughout the life of the orchard the tree normally requires less summer pruning to retain bearing wood in the lower parts of the canopy. Typical densities for the palmette are between 600 and 900 trees/ha, with spacing varying between 4.5 m × 3.5 m and 4.0 m × 2.5 m, and a tree height of 3.5–4.5 m, depending on the cultivar/ rootstock combination and soil fertility.

Table 11.2. Annual and cumulative yield per tree and per hectare of ‘Flavorcrest’ peach trees trained as palmette, delayed vasette and free shape, planted at the density of 727 trees/ha, over the first four growing seasons. (From Corelli Grappadelli et al., 1986.) Yield per tree (kg) Training system

2nd year

3rd year

4th year

Palmette Delayed vasette Free shape

5.3a 6.3b 6.8b

7.3b 4.8a 9.7c

39.0a 35.4a 50.6b

Yield per hectare (t)

Sum of 2nd–4th years Sum of 2nd–4th years 51.6b 46.5a 67.1c

375a 338a 486a

a,b,cMeans within columns with unlike superscript letters were significantly different by the least significant difference test, a = 0.05.

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The suitability of the palmette for use with platforms helped it win over the taller and wider trees in the orchard of the 1960s and 1970s; but the capital investments required for platforms and for trellising became its weakness in the 1980s and 1990s, except for areas of high-vigour conditions where it is impossible to keep trees short and with the fruiting zone near the ground (Fig. 11.3/Plate 71).

Central leader While peach trees can be trained according to this system, for a number of reasons it is not well suited to peach: the trees become very large, they lose bearing wood in the low and inner canopy, their shape is not easy to maintain, and it can make the use of platforms difﬁcult. Therefore, peach trees are rarely trained to central leader (Fig. 11.4/Plate 72). Other systems have been proposed, derived from the central leader. The adaptation of the ‘axis central’ to peach in France (Hugard, 1981; Belluau and Lemaire, 1986) and the introduction of fusetto or free spindle in Italy (Bargioni et al., 1983) were attempts to increase peach tree densities to be similar, if not equal, to those of apple (1000–2000 trees/ha). How-

Fig. 11.3.

Palmette tree form.

ever, both systems tend to suffer from excessive shading and loss of bearing wood in the lower part of the canopy, particularly after 4–5 years from planting and at the higher densities (Belluau and Lemaire, 1986; Loreti et al., 1989). The trees have a single vertical leader, are conical in shape and are about 3–3.5 m tall (Bargioni et al., 1983). The trees create a hedgerow (Fig. 11.5/Plate 73), well suited to picking platforms. Both systems feature a leader, with no permanent branches. Fruiting wood is retained on short branches, which are renewed every few years (Fig. 11.6/ Plate 74). Since central leader trees are closer to the natural growth habit of peach than the palmette, these training systems require less pruning during training (if the tree is adequately feathered) and their training is much easier. As a result, early yields are normally fairly high, which is their greatest advantage. However, summer pruning is required throughout the life of the orchard, as the lower fruiting zone tends to become bare because of excessive shading from the top of the tree. The difﬁculty in maintaining the fusetto within the limits set by the spacing and the loss of productivity when the trees become too shaded has limited its adoption. Today this system is only marginally adopted in Italy (Sansavini and Neri, 2005). A variant

Orchard Planting Systems

Fig. 11.4.

Fig. 11.5.

Fusetto orchard.

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Central leader tree form.

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Fig. 11.6.

of the fusetto has been proposed for southern Italy by Caruso et al. (1997) for early-ripening peaches in a long-season Sicilian growing district. The ‘dwarfed fusetto’ (as it is called by proponents) is a shorter tree than fusetto, and it is planted to lower density (about 700 trees/ ha) with reduced height (2.5–2.8 m). Pruning is done immediately after harvest, when fruitbearing wood is removed and headed back to the lowest current-season lateral. After harvest, the canopy is thus formed by short ‘stubs’ carrying current-season growth which will become next year’s bearing wood. The long vegetative season and very early (lowchill) cultivars are very important features of

Fusetto tree form.

this system, which relies on having sufﬁcient time in the season after harvest to develop the laterals that will carry next year’s crop. In their comparison of this system with a variant of the tatura trellis (free-standing tatura), however, the authors found that the dwarfed fusetto was not as satisfactory as the other system, since its per-hectare yields were about half without any gain in fruit quality (Caruso et al., 1997). Y-shaped tree To form Y-shaped trees, the leader is removed and only two primary scaffold branches are

Orchard Planting Systems

retained, which are trained to grow perpendicular to the row axis (Fig. 11.7/Plate 75). This system is suited to high densities, up to 2000 trees/ha, but most commonly densities range between 900 and 1500 trees/ha, with spacing between 4.0–4.5 m by 1.2–1.5 m (Chalmers et al., 1978; Corelli Grappadelli et al., 1986; Caruso et al., 1997, 2003). This tree form was ﬁrst adopted many years ago (Baldassari, 1950), but interest in it has been renewed by its potential for very high light interception (above 70%; Nuzzo et al., 2000). This system intercepts twice as much radiation as the palmette and the delayed vase in the second leaf (40% versus 20% incoming radiation) and maintains greater levels throughout the life of the orchard (65% versus 55% and 42% for Y-trellis, delayed vase and free palmette at the ninth leaf, respectively; Fig. 11.1). A variant of this system is the so-called ‘V’, where trees are planted at an angle from the horizontal, alternated along the row, so as to form a V-shaped canopy (Costa et al., 1989) perpendicular to the

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row axis. Densities for this system can be quite high, reaching 2000 trees/ha (4 m × 1.25 m). The tatura trellis (Chalmers et al., 1978) was developed for mechanical harvest of cling peaches and scaffold limbs are supported with a wire trellis. The Kearney Agricultural Center perpendicular-V (KAC-V) was developed for hand harvest and is not supported (DeJong et al., 1994). Typical tree densities are 900–1200 trees/ha and trees are about 5.5 m tall. The MIA trellis is a modiﬁcation of the V-shaped tree. The A-shaped canopy is developed by orienting the leaders at 60° from vertical and leaning trees in adjacent rows towards each other. The Y-trellis developed in southern Italy (Caruso et al., 2003) features a wider angle between the branches (45°, compared with 35° for the tatura trellis), which are allowed to converge and touch each other in the middle of the alley row, giving this system light interception in excess of 70% (Nuzzo et al., 2000) and very high productivity (Caruso et al., 2003). A particular version of the Y-trellis

Fig. 11.7. Y-shaped tree form. (Courtesy of D.R. Layne, Clemson, South Carolina, USA.)

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has been proposed by Caruso et al. (1997) for low-chill, early-season cultivars in a variant of the meadow orchard concept proposed by Erez (1976, 1978). The goal is to restrict growth and retain tree fertility, despite the smaller tree size, which is trained without a trellis. This free-standing tatura was dubbed the ‘fsTatura’ by the authors, who adopt a pruning technique calling for the heading of all 1-year-old wood above the most proximal, current-season lateral shoot. This is done immediately after harvest; with very earlyseason cultivars, the long season remaining allows for the differentiation of ﬂower buds on these shoots. The next spring, the shoots bloom and bear fruit. By adopting a vigorous rootstock (‘GF 677’) this cycle can be maintained. Yields in this system can be high, because of the high tree density (2000 tree/ ha). The average yield for the ﬁrst three harvest seasons was 18 t/ha, but the yield in the ﬁrst harvest (the third year from planting) was 14 t/ha (Caruso et al., 1997). The Y-trellis is the system used in protected cultivation in southern Italy because this shape is well adapted to the tunnels used, where the support arches are set along the row, and the vegetation expands out towards the dome of the tunnel. Tree spacing is reduced (4.5 m × 1.5 m) and tree densities are fairly high (about 1500 trees/ha), favouring precocity and high yields. For ‘Armking’ nectarine on seedling rootstock in the Basilicata region of southern Italy, Fideghelli et al. (1988) reported yields of 5.0 t/ha in the second season and up to about 30 t/ha at full production. Meadow orchards The meadow orchard, originally developed by Hudson (1971), was an ultra-high-density (about 100,000 trees/ha) full ﬁeld-cover orchard for apples intended for mechanical harvest by mowing the trees with their fruit as grass in a meadow. Production was based on a biennial cycle starting with a vegetative ﬂush followed by harvest the next season, after which the trees were cut back to a stump, to restart the cycle. Theoretically, the two primary advantages for the meadow orchard are that the yields of young orchards would be high

because the orchard space is ﬁlled quickly, and the fruiting zone would remain near the ground because the tree top would be periodically removed. The apple meadow orchard was not economical because apple trees cropped only every other year. Peaches seem better suited to a meadow orchard system for two reasons: (i) establishment costs are relatively low because peach trees can be produced from rooted cuttings (Couvillon and Erez, 1980); and (ii) peaches fruit on 1-year-old wood and may crop annually. Erez (1988) evaluated two variations of the meadow orchard in Israel: the ‘mechanized system’, developed for mechanized harvesting (Erez, 1976, 1978), and the ‘intensive system’ (Erez, 1988). The former system involved a 2-year cycle similar to apple, whereas in the intensive system the tree was trained to two main shoots and each winter one of the two shoots was headed back to a short stump to allow regeneration of new growth and ﬂower bud formation during the growing season. Therefore, each side of the tree fruited every second year. The second system appeared better for ﬂower bud differentiation, fruit set and yields, and suitable for late-season cultivars as well, whereas the mechanized system required very long growing seasons and was thus limited to early-maturing cultivars. Optimum tree spacing for the mechanized system is probably about 1.5 to 1.8 m between rows and 0.6 m between trees within the row. For the intensive system, trees should be spaced about 1.5 m × 0.5 m. A modiﬁed mechanized system was tested in Georgia, USA (Couvillon and Erez, 1982) with 9810 or 3924 trees/ ha. Early-maturing, but not late-maturing, cultivars regenerated enough ﬂower buds for annual production. Trees became deﬁcient in several elements and constant fertigation was needed to alleviate the problem. Although yields were high for a young orchard, fruit size was too small; the percentage of fruit >5.7 cm in diameter was only 12%, 46% and 7% for ‘Redhaven’, ‘Loring’ and ‘Blake’, respectively. In Florida, USA, Crocker et al. (1988) tested a meadow orchard with 3333 trees/ha, where trees were topped after harvest at 0.75 m above ground to leave the basal portion of scaffold branches. This system’s annual cropping and yields in young orchards were

Orchard Planting Systems

considerably higher than for traditional peach orchards. In Sicily, Caruso et al. (1997) have proposed a similar approach, which tries to exploit the peach vegetative vigour for earlyseason cultivars: immediately after harvest, all the fruiting wood is shortened, cut above the most basal lateral, current-season growth. This produces a tree which only has short stumps with fruiting wood at the start of the new season, similar to some of the grape training systems. Testing with fusetto and modiﬁed tatura has indicated the latter to be better suited to this type of management. Another alternative to encourage annual cropping is to cut alternate trees in the row after harvest (Evert, 1988). In Sicily, a study was conducted on a commercial farm where meadow orchard trees were grown under greenhouse cultivation (Bellini et al., 2000). Tree densities were 5000 trees/ha for the small vase trees and 3300 trees/ha for Y-trellis. ‘Maravilha’, a low-chill cultivar, was used. Trees were highly productive: average annual yields during the ﬁrst four seasons were 25 and 33 t/ha for trees trained as Y-trellis and small vase, respectively. The authors indicated that trees could be successfully grown at these very high densities, although maintaining a productive canopy required summer pruning several times per season, particularly with the denser small vase. Despite the potential, however, virtually no commercial meadow orchards exist, because of problems with tree survival and the lack of suitable, low-cost mechanical equipment that would be needed for their management. Protected cultivation This type of peach cultivation has been widely practised in southern Italy over the last few decades (and now also in China; see Chapter 2 of this volume), where climatic conditions allow the use of PVC tunnels (without heating) to advance ripening, particularly of early cultivars. Fruit can bring high prices because they reach the market when no other peaches are available. The ﬁrst studies in protected cultivation were reported in the early 1970s (Sansavini, 1974). In the early 1980s several research trials were established (Caruso et al., 1989; Bellini et al., 1997, 2000), dealing with

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different solutions regarding the type of greenhouse, cultivars and training systems. PVC-covered greenhouses were trialled, as well as tunnels. Today, most of this industry is under tunnels with the support arches placed in the row, and trees are trained to Y-trellis at about 1500 trees/ha (Fideghelli et al., 1988). Early-season cultivars are used, such as ‘Armking’, along with low-chilling requirement cultivars, because these allow the earliest pickings. A typically grown cultivar, according to these criteria, is ‘Maravilha’. Low-chill cultivars tend to have very high fertility index and percentage fruit set (Caruso et al., 1989; Bellini et al., 1997, 2000), which is not frequently the case with high-chill ones. There is a requirement for careful summer pruning of these trees, in order to maintain good ﬂower bud differentiation and good fruit quality traits; however, no authors report increased difﬁculties in management of the trees due to the enclosure, as far as pests and fungi are concerned. The vast majority of commercial orchards are based on the Y-trellis, although other systems have been trialled, for example the modiﬁed meadow orchard or low central axis (MMO and LCA, respectively; Caruso et al., 1989). The MMO is the same as described by Erez (1976), where the fruiting shoot is cut back after harvest and a new sprout is selected and trained for next year’s crop. The LCA, on the other hand, has a central axis where all fruiting shoots are inserted directly on the leader and they are pruned back to short stubs immediately after harvest, in order to stimulate the emission of a new fruiting shoot from below the cut made. This shoot will bear next year’s crop before being removed and the cycle restarted. In general, these studies have indicated that it is difﬁcult to retain high productivity with the MMO, since the continuous removal and formation of a new canopy rapidly depletes the tree of its bearing potential, and crops decline in a few years. Overall, there is agreement over the Y-trellis being a better performer (a fact certainly not lost to the industry) because of its early, high crops, sustained over the years, at a density much lower than its counterparts. An additional beneﬁt is that it does not require summer pruning to be performed immediately after harvest (such as is the case

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with the other ones), since here summer pruning is only needed to improve ﬂower bud differentiation on existing shoots by allowing more light inside the canopy. In addition to these considerations, this training system lends itself quite well to the structure of the tunnel, because the supporting arches can be placed within the tree rows and the inter-row is free for movement, an important consideration when operating equipment in otherwise fairly restricted space. The tunnels are covered after completion of the chill requirement, which is normally during January in southern Italy. Following closure of the tunnel, ﬂowering occurs in early February and, depending on the cultivar, harvest commences in mid- to late April. Thus fruit can be harvested about a month earlier than in traditional orchards. Yields are satisfactory, especially considering the premium prices received for early fruit. Fideghelli et al. (1988) reported an average yield of 20.9 t/ha over the ﬁrst 4 years for ‘Armking’. Studies were conducted in Nova Scotia and Ontario, Canada to assess the feasibility of growing peaches in heated greenhouses, with trees grown in large containers and in the soil in the two areas, respectively (Crowe et al., 1987; Miles and Leuty, 1988). In both areas, growing peaches outdoors is restricted by low winter temperatures and short growing seasons. In Ontario, three training systems were evaluated for 4 years and the tatura trellis had the highest yields. Compared with similar trees in the ﬁeld, yields were 40–80% higher in the greenhouse. Establishment costs were more than three times higher for protected culture, but due to higher yields and higher prices for early-season fruit, the protected culture system was more proﬁtable than the standard system. Given today’s energy prices, however, it is unlikely that the economics of a heated greenhouse peach orchard would justify its adoption. The study in Nova Scotia, Canada was carried out with early-season peach cultivars grown in large containers and overwintered in heated poly-covered houses (Crowe et al., 1987). Average annual yield was about 16 to 19 kg/tree from the third to the seventh year after planting. Although these yields were less than 30% of what would be expected of ﬁeldgrown trees in traditional peach-growing

regions, the system was considered to be profitable in regions where traditionally grown peaches are normally not proﬁtable. Protected cultivation is a commercial practice in southern Italy, where low-cost, nonheated, PVC-covered tunnels can be used because the climatic conditions allow for sufﬁcient natural heating of the greenhouses. If this were not the case, the cost of heating would totally offset the economics of this type of cultivation in that district. In areas where heating is required, the economic feasibility of protected peach culture may depend on the price of fuel to maintain trees at appropriate temperatures. Interest rates on the capital required to build protective structures may also impact the proﬁtability of these systems.

11.5 Effects of Training System and Planting Density on Yield Tree form effect on yield Comparison of different shapes is important to evaluate tree performance, especially a system’s capacity for early fruit production, a vital trait in highly intensive orchards. Often the training systems requiring the least initial pruning are most precocious and tend to have higher cumulative yields over the ﬁrst four to six seasons. Many trials have demonstrated this advantage for more ‘natural’ systems. The free shape, which is nearly non-pruned initially, the fusetto and sometimes the delayed vasette all require less early pruning and are more precocious than systems such as the palmette or the Y-trellis (Table 11.2) (Sansavini et al., 1980, 1985; Bargioni et al., 1985; Bassi et al., 1985; Corelli Grappadelli et al., 1986; Blay Coll, 1988; Toribio Mancebo, 1993). The higher yields of these systems are normally restricted to the ﬁrst 4 to 6 years; as orchards age yields tend to level off and become similar between these systems (Bassi et al., 1985). In other studies, the KAC-V and the cordon systems planted at the same density produced similar yields per hectare (Grossman and DeJong, 1998). When planted at low densities, open vase trees had higher yields per tree, but lower yield per unit of land area

Orchard Planting Systems

under the canopy or per unit of canopy volume than did central leader trees (Marini et al., 1995). In another experiment central leader and open vase forms were compared at low density (370 trees/ha) and at moderate density (740 trees/ha) (Marini and Sowers, 2000). The interaction between tree form and tree density was not signiﬁcant, and tree form had little effect on cumulative yield. Allison and Overcash (1987) compared central leader trees with a palmette trellis system planted at 1292 trees/ha. Training system did not inﬂuence cumulative yield during the ﬁrst 4 years. Menzies (1988) compared a palmette hedgerow with the Lincoln canopy, both at 1000 trees/ha: after 6 years cumulative yield was about 25% greater for the palmette system. Taylor (1988) compared six different training systems, all with 1680 trees/ha. Low temperatures eliminated the crop in the third year. Yields in the fourth year ranked from highest to lowest as follows: open vase > modiﬁed Belgian fence > tatura trellis > perpendicular fan > parallel fan > central leader. These results generally indicate that training system has little impact on peach yield. In apple, Robinson (1997) showed that yield differences between Y-trellis, slender spindle and palmette were related to light interception, because yield per unit of intercepted light energy was similar. In agreement with this, whole-canopy photosynthesis of peach trees was linearly related to the amount of light intercepted by the tree (Giuliani et al., 1998), irrespective of training system (Y-trellis, sprint palmette and delayed vase). The Y-trellis intercepted more light, had the highest photosynthetic rates and the highest yields over nine cropping seasons (L. Corelli Grappadelli, unpublished results). Therefore, when training systems planted at the same density do not show much difference in yield over the life of the orchard, this should not be surprising if they efﬁciently ﬁll the allotted space and intercept similar amounts of light.

Effect of planting density on yield Conventional orchards are planned to ﬁt the dimensions of mature bearing trees. As a

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result, trees require 2 years or more to ﬁll their allotted space and for the orchard to attain maximum yields, even if the trees are not pruned to hasten their development. Several experiments were performed where tree density, but not tree form, was varied. While some studies showed a positive response of yield to density (Reeder et al., 1980; Miles et al., 1999), several authors found that yield per hectare increased less than proportionally to tree density (Giulivo et al., 1984; DeJong et al., 1999; Marini and Sowers, 2000). Hutton et al. (1987) compared three training systems, each at three tree densities, and showed that the effect of tree density on yield varied with the training system, and in some cases increasing density caused a decrease in cumulative yield. Working with fusetto at varying tree densities (1250, 1665 and 2500 trees/ha) in Italy, Bargioni et al. (1985) concluded that 1665 trees/ha was optimum for their conditions. The density of 2500 trees/ha had slightly higher yield and was not justiﬁed from an economic point of view. As the cost of the trees is very often quite high, adding up to a substantial portion of the total planting costs in high-density orchards (particularly so for patented cultivars), it is easy to see that density does have an important impact on the ﬁnancial aspects of peach growing. Since maximum orchard productivity cannot be attained until trees ﬁll their allotted space, the larger that trees are allowed to grow the further apart they must be planted, and the longer it will take to reach full production. Planting small trees at higher tree densities combined with minimal pruning encourages earlier yields, but once trees ﬁll the allotted space, the capacity for yield will be limited by the amount of light that can be intercepted. That is why in virtually all the trials there is a poor relationship between the cumulative yield increase and tree density increase after the ﬁrst few seasons. Results with apples are similar. Palmer et al. (1989) compared systems with densities ranging from 2667 to 8889 trees/ha, trained as single-, double- and triple-row spindles and six-row beds of full ﬁeld mini-trees. They found after six cropping seasons that the highestdensity system, with 233% more trees/ha, produced only 38% more fruit. However, in

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the year after planting these trees yielded 14 to 20 t/ha, compared with 5 to 11 t/ha for the other systems. From the fourth season on, when the orchards were at full bearing, there were no differences in yield per year across all training systems. Training systems with small trees are better suited to high densities and in general they tend to have high early yields. Later on this advantage is lost and the risk of losing production due to excessive competition becomes a factor to be carefully evaluated. Because of the interaction between tree behaviour with site environmental conditions, the ideal tree density will vary with site and training system. Regardless of training system, in most of the studies with reported increases in yield, these were usually relatively minor as tree densities increased above 1000 trees/ha. Effect of tree density plus tree form on yield As discussed above, the choice of training system dictates the spacing that can be used and often it also deﬁnes the training strategy, i.e. the sequence of summer and winter pruning events that will lead to a fully developed tree. As a result, yield may be dramatically affected by the combination of these two factors, but not always in favour of the higher densities. Often the yields in the early years are in favour of the higher densities, irrespective of the system (Phillips and Weaver, 1975; Hayden and Emerson, 1988), but later on these differences may disappear or be reversed. Leuty and Pree (1980) continued the trial of Phillips and Weaver (1975) for another 4 years and found that cumulative yields were related to tree density only during the ﬁrst three fruiting years. After 9 years, increasing the tree population from 397 to 1157 trees/ha (290%) resulted in only a 12% increase in cumulative yield per hectare. Pruning and thinning costs were also related to tree density. They concluded that the beneﬁt of high density was mostly in the early years, but high density offered little economic advantage over the life of the orchard. Kappel et al. (1983) found fairly similar cumulative yields, over a 10-year period, for oblique fan (567 trees/ha), modiﬁed central leader (606 trees/ha), canted oblique fan (969

trees/ha) and open centre (381 trees/ha) (125, 111, 104 and 92 t/ha, respectively). Increasing tree density can have beneﬁcial effects at very low densities, because at these wide spacings the time needed to ﬁll the space allotted to the tree is much longer and therefore the performance of higher-density orchards is superior for longer periods of time. In their study, Layne et al. (1981) found that yield increased by up to 96% as tree density increased from 266 to 536 trees/ha. Hutton et al. (1987) compared three systems and found that the optimum tree density appeared to vary with tree form and was 1732 trees/ha for palmette hedgerow, 1234 trees/ha for tatura trellis and 1110 trees/ha for MIA trellis. Menzies (1988) reported higher cumulative yields for 6 years for palmette hedgerow (1000 trees/ha) and tatura trellis (2500 trees/ha) and lowest for open vase (500 trees/ha), with intermediate yields for Lincoln canopy (1000 trees/ha) and central leader (666 trees/ha). A similar advantage of high-density over lowdensity systems was reported by Grossman and DeJong (1998) working with trees trained as KAC-V, cordon (1196, 919 trees/ha) and open vase (299 trees/ha). Similar results were reported in a different study by DeJong et al. (1992). This study concluded that the practical advantages and disadvantages of the high-density systems are probably less related to crop yield than to orchard management considerations such as tree structural strength, uniformity, access to ladder work and simplicity of cultural operations. The primary advantage of high-density over low-density systems is that the orchard space is ﬁlled quickly and yields of young orchards are improved. DeJong et al. (1994) compared the KAC-V (909 trees/ha) with the traditional open vase system (298 trees/ha). Cumulative yields for the ﬁrst 3 years were about 44 t/ha for the KAC-V and 24 t/ha for the open vase, but after 8 years yields were 224 and 190 t/ha, respectively. Therefore, the increased yield due to high tree populations is temporary and the economic feasibility of such systems may depend on the cost of trees and the value of new cultivars where supply has not satisﬁed demand. The training strategy, which is a consequence of the choice of training system, can

Orchard Planting Systems

have a large impact on productivity, especially in the critical early years. The no-heading-cuts strategy demonstrates this. Open vase trees are normally headed in their ﬁrst season, and this causes delayed and low initial yields. The delayed vasette is not headed at planting, and its early yields can be substantial. Delayed vasette planted at 727 trees/ha had similar yield per tree in the second season to fusetto at the same density. Fusetto and Y-trellis planted at 1454 trees/ha had lower yields. The study was terminated after 4 years, due to tree mortality following a winter freeze, but through the third cropping season the delayed vasette still had high yields per tree. However, because of the planting density, this form had one of the lowest cumulative yields for the three seasons. Cumulative yields per hectare were 52.9, 64.4 and 50.1 t for the delayed vasette, fusetto and Y-trellis with 727 trees/ha, respectively. The fusetto and Y-trellis at 1454 trees/ ha had 96.1 and 77.3 t/ha, respectively (Corelli Grappadelli et al., 1986). High tree density, almost irrespective of training system, appears to be advantageous for yields in the early years. This is the result of the training techniques used, which stimulate early production, and the high number of trees per hectare. This advantage may be lost over the life of the orchard, particularly if the orchard is planted at intermediate densities and if it is maintained for more than 20 years. For this reason the choice of training system may have less to do with tree performance than with the equipment on the farm, labour availability, proﬁciency in training the tree into a given form, the cost of the trees and of establishing and maintaining various systems, and their impact on fruit size and quality.

11.6 Future Trends Researchers and commercial producers have extensively evaluated peach orchard systems. Unless new cultivars, rootstocks or plant growth regulators become available for controlling tree vegetative growth, future orchards will consist of low or moderate tree densities. The most common tree training systems (i.e. the open vase and its derivatives in the western

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hemisphere and much of Europe, the palmette in some European countries, the Y-trellis) will continue to be adopted, because radical departures from these systems are not foreseeable. Certainly, training and management strategies will continue to evolve to address the continuing need to improve early crops, to alleviate the economic burden of peach growing in those countries. It can be expected that peach orchard systems will evolve differently in different parts of the world, reﬂecting the economic and technological conditions in the different areas. Factors other than strictly horticultural or physiological will be of prime importance in determining the choice of the tree form. The previous experience with a given system, the cost and availability of land and skilled labour, and ownership of previously purchased materials and equipment are certainly equally important determinants of these decisions. Where land is available and relatively inexpensive, simply planting more hectares can enhance farm income, even if low-density, extensive (as opposed to intensive) systems are adopted. Where new orchard land is very expensive and largely unavailable, on the other hand, the pressure will be on increasing the farm income by increasing returns per unit of land area or per unit of input. Most developing countries with peach industries are located in the southern hemisphere and farmers obtain high wholesale prices for fresh fruit exported to developed countries during their off-season. Both land and labour are available and inexpensive, but labour is unskilled. Tree uniformity within an orchard will facilitate standardizing orchard operations performed by non-skilled labour. Orchard systems will evolve slowly unless economic conditions change. Small orchards dominate the peach industry in most of Europe and orchard owners do much of the routine work; farmers must perform most of the orchard operations because labour is very expensive. Although land and labour are already being used efﬁciently, there will be increasing economic pressure to improve efﬁciencies. Intensive orchard practices, performed by highly skilled labour, will be required to improve early bearing and yields per unit of land area. Minimal pruning, summer pruning and cropping in the early

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seasons are just examples of the shift in the techniques employed to obtain early production. These orchards, heavily exploited from early on, will be less durable than traditional ones; this is not perceived as a problem since it allows for cultivar renovation, although it poses the increasing problem of replant sites (release of allelopathic compounds, increases in soil-borne diseases, depletion of soil natural resources, etc.), which do lower tree performance. Peach growers in western North America grow mostly fairly tall (4.0 to 5.0 m) open vase trees that are planted at about 300 trees/ha. North American orchards are relatively large and workers are unskilled. Therefore, trees within an orchard will have to be uniform to facilitate orchard worker training. The cost of labour is increasing rapidly and California growers are starting to reduce tree height. As land and labour become increasingly scarce and expensive, peach orchard systems probably will evolve towards those found in Europe. Some type of hedgerow system that allows use of platforms (Fig. 11.8/Plate 76) may dominate the peach industry and, where platforms

Fig. 11.8.

Modern picking platform.

are not used, tree height will be limited to less than 3.0 m. At higher latitudes, where trees grow slowly and winter injury results in early tree mortality, tree densities will increase to allow rapid ﬁlling of orchard space. Modiﬁcations of existing orchard systems and development of new systems will require research breakthroughs. Rootstocks that provide a range of tree vigour and enhance carbon partitioning, such as those available for apple, may allow development of novel orchard systems. Plant growth regulators to control ﬂowering and vegetative growth, crop load or fruit ripening could be utilized in new orchard systems. Growers need trees that produce high yields of uniformly high-quality fruit that can be harvested tree-ripe. Improvements in other aspects of fruit quality such as fruit size, colour, soluble solids concentration, ﬂesh ﬁrmness and high concentrations of health-promoting compounds may improve peach consumption and lead to increased prices. There is a need for long-term studies to determine the proﬁtability of various orchard practices and orchard systems. More information on fundamental relationships in peach tree physiology

Orchard Planting Systems

is needed to develop new systems or to modify systems. The relationship between light interception and yield per unit land area has not been elucidated in peach. The scant data existing are relative to single-season, short-term observations; no long-term studies have been carried out comparing light interception and marketable yields of the leading training

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systems. Currently peach growers do not have fruit thinning strategies, nor practical methods for assessing in real time the progress of the crop and the performance of the orchard. A better understanding of partitioning is needed to develop better strategies for hand thinning and pruning that may alter carbon partitioning.

References Allison, M.L. and Overcash, J.P. (1987) Factors affecting hedgerow peach orchard establishment. Journal of the American Society for Horticultural Science 112, 62–66. Baldassari, T. (1950) La potatura dei fruttiferi. In: Zucchini, M. (ed.) Proceedings of II Convegno Provinciale Frutticolo. SATE, Ferrara, Italy, pp. 71–76. Bandoli, A. (1980) Untitled. In: Sansavini, S. (ed.) Proceedings of XV Convegno Peschicolo. Litografica Faenza, Faenza, Italy, pp. 312–313. Bargioni, G., Loreti, F. and Pisani, P.L. (1983) Performance of peach and nectarine in a high density system in Italy. HortScience 18, 143–146. Bargioni, G., Pisani, P.L. and Loreti, F. (1985) Ten years of research on peach and nectarine in a high density system in the Verona area. Acta Horticulturae 173, 299–310. Bassi, D., Brighenti, G. and Nardi, V. (1985) Training systems of Klamt cling peach: performance after 8 years – IV Contribution. Acta Horticulturae 173, 339–348. Bellini, E., Falqui, D. and Musso, O. (1997) La coltura protetta del pesco. L’Informatore Agrario 31, 41–50. Bellini, E., Falqui, D. and Musso, O. (2000) Comparison between two training systems in peach protected culture in Sicily. Acta Horticulturae 513, 427–433. Belluau, E. and Lemaire, A. (1986) Evaluation of nine years experimenting on high-density peach orchard in south east of France. Acta Horticulturae 160, 327–340. Blay Coll, J. (1988) Formación del melocotonero en un solo eje principal (fuseto). Fruticultura Profesional 15(5/6), 3–17. Borras Escriba, F. (2001) La peschicoltura spagnola nel mercato globale. In: Sansavini, S. and Lugli, S. (eds) Proceedings of XXIV Convegno Peschicolo. Grafiche MDM, Forlì, Italy, pp. 31–34. Cain, J.C. (1972) Hedgerow orchard design for most efficient interception of solar radiation. Effects of tree size, shade, spacing and row direction. Search Agriculture 2, 1–14. Campbell, R.C. and Marini, R.P. (1992) Light environment and time of harvest affect ‘Delicious’ apple fruit quality characteristics. Journal of the American Society for Horticultural Science 117, 551–557. Caruso, T., Di Marco, L., Giovannini, D. and Motisi, A. (1989) Trials on training systems for greenhouse cultivated peach trees. Acta Horticulturae 243, 345–352. Caruso, T., Giovannini, D., Marra, F.P. and Sottile, F. (1997) Two new planting systems for early ripening peaches (Prunus persica L. Batsch): yield and fruit quality in four low-chill cultivars. Journal of Horticultural Science 72, 873–883. Caruso, T., Di Vaio, C., Guarino, F., Motisi, A. and Nuzzo, V. (2003) Le tipologie d’impianto per la peschicoltura intensiva nell’Italia meridionale. In: Marra, F.P. and Sottile, F. (eds) Proceedings of IV Convegno Nazionale sulla Peschicoltura Meridionale. Panuzzo Prontostampa, Caltanissetta, Italy, pp. 44–51. Chalmers, D.J., van den Ende, B. and van Heek, L. (1978) Productivity and mechanization of the ‘Tatura Trellis’ orchard. HortScience 13, 517–521. Cole, S.W. (1849) The American Fruit Book. John P. Jewett, New York. Corelli Grappadelli, L. and Sansavini, S. (1989) Light interception and photosynthesis related to planting density and canopy management in apple. Acta Horticulturae 243, 159–174. Corelli Grappadelli, L., Brighenti, G., Palara, U., Ravaioli, F. and Sansavini, S. (1986) Esperienze su forme di allevamento del pesco per medie ed alte densità di impianto. Rivista di Frutticoltura 12, 55–60. Costa, G., Miserocchi, O., Succi, F. and Martelli, S. (1989) Forme di allevamento del pesco per impianti ad elevata densità di piantagione. Rivista di Frutticoltura 1, 63–66.

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Couvillon, G.A. and Erez, A. (1980) Rooting, survival, and development of several peach cultivars propagated from semi hardwood cuttings. HortScience 15, 41–43. Couvillon, G.A. and Erez, A. (1982) Production potential and tree regeneration in a peach meadow orchard in southeastern United States. Compact Fruit Tree 15, 166–169. Crocker, T.E., Sherman, W.B., Young, M.J. and McDermont, L.G. (1988) An experimental high-density system for low-chill peaches and nectarines. In: Childers, N. and Sherman, W.B. (eds) The Peach. Horticultural Publishers, Gainesville, Florida, pp. 432–433. Crowe, A.D., Henniger, D.R., Craig, W.E. and O’Regan, R.T. (1987) Containerized peach orchards are profitable and avoid winter injury. Compact Fruit Tree 20, 90–94. DeJong, T.M. and Doyle, J.F. (1985) Seasonal relationships between leaf nitrogen content (photosynthetic capacity) and leaf canopy light exposure in peach (Prunus persica). Plant, Cell & Environment 8, 701–706. DeJong, T.M., Day, K.R. and Doyle, J.F. (1992) Evaluation of training/pruning systems for peach, plum and nectarine trees in California. Acta Horticulturae 322, 99–105. DeJong, T.M., Day, K.R., Doyle, J.F. and Johnson, R.S. (1994) The Kearney Agricultural Center perpendicular ‘V’ (KAC-V) orchard system for peaches and nectarines. HortTechnology 4, 362–367. DeJong, T.M., Tsuji, W., Doyle, J.F. and Grossman, Y.L. (1999) Comparative economic efficiency of four peach production systems in California. HortScience 34, 73–78. Erez, A. (1976) Meadow orchard for the peach. Scientia Horticulturae 5, 43–48. Erez, A. (1978) Adaptation of the peach to the meadow orchard system. Acta Horticulturae 65, 245–250. Erez, A. (1988) Peach meadow orchard: two feasible systems. In: Childers, N. and Sherman, W.B. (eds) The Peach. Horticultural Publishers, Gainesville, Florida, pp. 424–431. Evert, D.R. (1988) A modified meadow system. In: Childers, N. and Sherman, W.B. (eds) The Peach. Horticultural Publishers, Gainesville, Florida, p. 434. FAOSTAT (2004) ProdStat: Crops. http://faostat.fao.org/site/567/default.aspx (accessed October 2004). Fideghelli, C. (1969) Confronto tra i sistemi di allevamento a vaso ed a palmetta del pesco. In: Baldini, E. (ed.) Proceedings of Convegno Giornate di studio sulla potatura degli alberi da frutto. Firenze, pp. 133–147. Fideghelli, C., Monastra, F. and De Salvador, R.F. (1988) Evoluzione delle forme d’allevamento e delle densità d’impianto in peschicoltura. In: Sansavini, S. (ed.) Proceedings of XVIII Convegno Peschicolo. Grafiche MDM, Forlì, Italy, pp. 63–81. Flore, J.A. and Kesner, C. (1982) Orchard design for stone fruit based on light interception. Compact Fruit Tree 5, 159–165. Génard, M. and Baret, F. (1994) Spatial and temporal variation of light inside peach trees. Journal of the American Society for Horticultural Science 119, 669–677. Giovannini, D. and Monastra, F. (1995) Tipologie d’impianto e forme di allevamento per la peschicoltura meridionale. In: Pavia, R., Della Strada, G. and Grassi, F. (eds) Proceedings of Convegno su ‘Ricerca e innovazione per la peschicoltura meridionale. Interstampa, Rome, pp. 195–211. Giuliani, R., Magnanini, E. and Corelli Grappadelli, L. (1998) Whole canopy gas exchange and light interception of three peach training systems. Acta Horticulturae 465, 309–317. Giulivo, C., Ramina, A. and Costa, G. (1984) Effects of planting density on peach and nectarine productivity. Journal of the American Society for Horticultural Science 109, 287–290. Grossman, Y.L. and DeJong, T.M. (1998) Training and pruning system effects on vegetative growth potential, light interception, and cropping efficiency in peach trees. Journal of the American Society for Horticultural Science 123, 1058–1064. Hayden, R.A. and Emerson, F.H. (1988) High density plantings for peaches. In: Childers, N. and Sherman, W.B. (eds) The Peach. Horticultural Publishers, Gainesville, Florida, pp. 404–411. Hilaire, C. (2003) The peach industry in France: state of the art, research and development. In: Marra, F.P. and Sottile, F. (eds) Proceedings of the First Mediterranean Peach Symposium. Panuzzo Prontostampa, Caltanissetta, Italy, pp. 27–34. Hudson, J.P. (1971) Meadow orchards. Agriculture 78, 157–160. Hugard, J. (1981) High density plantings in French orchards: development and current achievements. Acta Horticulturae 114, 300–307. Hugard, J. (1986) Main features of fruit production in the French Mediterranean area. Acta Horticulturae 160, 15–22. Hutton, R.J., McFadyen, L.M. and Warwick, J.L. (1987) Relative productivity and yield efficiency of canning peach trees in three intensive growing systems. HortScience 22, 552–560. Jackson, J.E. (1967) Variability in fruit size and colour within individual trees. Annual Report of East Malling Research Station for 1966, 110–115.

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Jackson, J.E. (1980) Light interception and utilization by orchards. Horticultural Reviews 2, 208–267. Jackson, J.E. and Middleton, S.G. (1988) Progettazione del frutteto per la massima produttività e qualità. In: Youssef, J. (ed.) Proceedings of Conference ‘Coltura del melo verso gli anni ‘90’. Chiandetti, Udine, Italy, pp. 309–320. Jackson, J.E. and Palmer, J.W. (1972) Interception of light by model hedgerow orchards in relation to latitude, time of year and hedgerow configuration and orientation. Journal of Applied Ecology 9, 341–357. Kappel, F., Flore, J.A. and Layne, R.E.C. (1983) Characterization of the light microclimate in four peach hedgerow canopies. Journal of the American Society for Horticultural Science 108, 102–105. Lakso, A.N. (1994) Apple. In: Schaffer, B.S. and Anderson, P.C. (eds) Handbook of Environmental Physiology of Fruit Crops. Vol. I. Temperate Crops. CRC Press, Boca Raton, Florida, pp. 3–42. Lakso, A.N. and Musselmann, R.C. (1976) The effects of cloudiness on interior diffuse light in apple trees. Journal of the American Society for Horticultural Science 101, 642–644. Layne, R.E.C., Tan, C.S. and Fulton, J.M. (1981) Effect of irrigation and tree density on peach production. Journal of the American Society for Horticultural Science 106, 151–156. Leuty, S.J. and Pree, D.J. (1980) The influence of tree population and summer pruning on productivity, growth, and quality of peaches. Journal of the American Society for Horticultural Science 105, 702–705. Lewallen, K.S. and Marini, R.P. (2003) Flesh firmness and ground color in peach as influenced by light and canopy position. Journal of the American Society for Horticultural Science 128, 163–170. Loreti, F., Massai, R. and Morini, S. (1989) Further observations on high-density nectarine plantings. Acta Horticulturae 243, 353–360. Marini, R.P. (1985) Vegetative growth, yield, and fruit quality of peach as influenced by dormant pruning, summer pruning, and summer topping. Journal of the American Society for Horticultural Science 110, 133–139. Marini, R.P. and Barden, J.A. (1981) Seasonal correlations of specific leaf weight to net photosynthesis and dark respiration of apple leaves. Photosynthetic Research 2, 251–258. Marini, R.P. and Barden, J.A. (1982) Light penetration on overcast and clear days, and specific leaf weight in apple trees as affected by summer or dormant pruning. Journal of the American Society for Horticultural Science 107, 39–43. Marini, R.P. and Corelli Grappadelli, L. (2006) Peach orchard systems. Horticultural Reviews 32, 63–110. Marini, R.P. and Marini, M.C. (1983) Seasonal changes in specific leaf weight, net photosynthesis, and chlorophyll content of peach leaves as affected by light penetration and canopy position. Journal of the American Society for Horticultural Science 108, 600–605. Marini, R.P. and Sowers, D.S. (1990) Net photosynthesis, specific leaf weight, and flowering of peach as influenced by shade. HortScience 25, 331–334. Marini, R.P. and Sowers, D.S. (2000) Peach tree growth, yield, and profitability as influenced by tree form and tree density. HortScience 35, 837–842. Marini, R.P., Sowers, D.S. and Marini, M.C. (1991) Peach fruit quality is affected by shade during final swell of fruit growth. Journal of the American Society for Horticultural Science 116, 383–389. Marini, R.P., Sowers, D.S. and Marini, M.C. (1995) Tree form and heading height at planting affect peach tree yield and crop value. HortScience 30, 1196–1201. Mascanzoni, G. (1998) Evoluzione e problematiche del ‘vaso ritardato’ nel pesco. In: Sansavini, S. and Errani, A. (eds) Frutticoltura ad alta densità. Edagricole, Bologna, Italy, pp. 237–245. Menzies, A.R. (1988) Evolution of peach tree forms in New South Wales, Australia. In: Childers, N. and Sherman, W.B. (eds) The Peach. Horticultural Publishers, Gainesville, Florida, pp. 446–465. Miles, N.W. and Leuty, S.J. (1988) Protected peach culture. In: Childers, N. and Sherman, W.B. (eds) The Peach. Horticultural Publishers, Gainesville, Florida, pp. 380–386. Miles, N.W., Guarnaccia, R. and Slingerland, K. (1999) High density peach production in Ontario. New York Fruit Quarterly 7(4), 1–5. Monteith, J.L. (1977) Climate and the efficiency of crop production in Britain. Philosophical Transactions Royal Society of London Bulletin 281, 277–294. Nuzzo, V., Dichio, B., Palese, A.M. and Xiloyannis, C. (2000) Sviluppo della chioma ed intercettazione radiativa in piante di pesco allevate ad Y trasversale ed a vaso ritardato nei primi tre anni dall’impianto. In: Failla, O. and Piagnani, I. (eds) Proceedings of V giornate Scientifiche SOI. Edizioni Tecnos, Milan, Italy, pp. 319–320. Palmer, J.W., Bünemann, G., Sansavini, S., Wagenmakers, P.S. and Winter, F. (1989) The international planting systems trial. Acta Horticulturae 243, 231–241. Phillips, J.H.H. and Weaver, G.M. (1975) A high-density peach orchard. HortScience 10, 580–582.

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Porpiglia, P.J. and Barden, J.A. (1980) Seasonal trends in net photosynthetic potential, dark respiration, and specific leaf weight of apple leaves as affected by canopy position. Journal of the American Society for Horticultural Science 105, 920–923. Reeder, B.D., Bowen, H.H. and Aldred, W.H. (1980) Peach tree training and spacing. HortScience 15, 580– 581. Rizzi, A.D. (1975) Training and modifying peach trees in California for mechanical handling. In: Childers, N. and Sherman, W.B. (eds) The Peach. Horticultural Publishers, Gainesville, Florida, pp. 214–225. Robinson, T.L. (1997) Interaction of tree form and rootstock on light interception, yield and efficiency of ‘Empire’, ‘Delicious’ and ‘Jonagold’ apple trees trained to different systems. Acta Horticulturae 451, 427–436. Robinson, T.L. (2003) Apple-orchard planting systems. In: Ferree, D.C. and Warrington, I. (eds) Apples: Botany, Production and Uses. CAB International, Wallingford, UK, pp. 345–407. Robinson, T.L. and Lakso, A.N. (1991) Bases of yield and production efficiency in apple orchard systems. Journal of the American Society for Horticultural Science 116, 188–194. Royo Díaz, J.B. and Martínez Lopez, T. (1992) Sistemas de formación en melocotonero. Fruticultura Profesional 46, 22–31. Sansavini, S. (1974). Indirizzi tecnico-agronomici della peschicoltura romagnola. L’Italia Agricola 1–2, 1–47. Sansavini, S. (1980) Impianti e allevamento del pesco: analisi e prospettive delle tendenze in atto. In: Sansavini, S. (ed.) Proceedings of XV Convegno Peschicolo. Litografica Faenza, Faenza, Italy, pp. 63–116. Sansavini, S. and Neri, D. (2005) Forme di allevamento e potatura del pesco. In: Sansavini, S. and Fideghelli, C. (eds) Manuale di Peschicoltura. Edagricole, Bologna, Italy, pp. 115–143. Sansavini, S., Bassi, D. and Giunchi, L. (1980) Prove comparative di allevamento del pesco da industria. In: Sansavini, S. (ed.) Proceedings of XV Convegno Peschicolo. Litografica Faenza, Faenza, Italy, pp. 267– 278. Sansavini, S., Corelli Grappadelli, L. and Giunchi, L. (1985) Peach yield efficiency as related to tree shape. Acta Horticulturae 173, 139–158. Sansavini, S., Corelli Grappadelli, L., Costa, G., Lugli, S., Marangoni, B., Tagliavini, M., Ventura, M., Abeti, D., Ferali, S., Marani, G., Mascanzoni, G., Molducci, S., Proni, R., Sama, A., Spada, G., Vitali, S., Turroni, P., Minguzzi, A. and Randi, M. (2000) Ricostituzione degli impianti e nuovi indirizzi produttivi della peschicoltura romagnola. In: Sansavini, S. and Lugli, S. (eds) Proceedings of XXIII Convegno Peschicolo. Grafiche MDM, Forlì, Italy, pp. 62–74. Taylor, B.H. (1988) Promising high density peach systems in Illinois. In: Childers, N. and Sherman, W.B. (eds) The Peach. Horticultural Publishers, Gainesville, Florida, pp. 491–498. Toribio Mancebo, F. (1993) Juntos, pero bien formados. Albear (1), 20–27.

12

Crop Load Management R.P. Marini1 and G.L. Reighard2

1Department

of Horticulture, The Pennsylvania State University, University Park, Pennsylvania, USA 2Department of Horticulture, Clemson University, Clemson, South Carolina, USA

12.1 Introduction 12.2 Fruit Growth and Development 12.3 Quantifying Crop Load 12.4 Modifying Crop Load Pre-bloom Bloom Post-bloom 12.5 Crop Load Interactions with Stresses Tree density Water stress Leaf-feeding arthropods High temperatures Low temperatures 12.6 Future Directions

12.1 Introduction Crop load management is an important aspect of peach production. Most peach trees produce thousands of ﬂowers and, if conditions are favourable, may set several thousand fruit per tree. If all these fruit are allowed to develop, the weight of the fruit will break branches and the fruit will be small and have low sugar concentrations. To avoid overcropping, the number of fruit per tree must be managed. In descriptions of North American peach production during the 18th and 19th centuries there is no mention of fruit thinning (Cole, 1849; Fitz, 1872), but accounts indicate trees

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were productive for only a few years and orchards were replanted frequently. The reasons for early tree mortality were probably tree-boring insects, disease and winter damage, as well as limb breakage due to overcropping. Fruit thinning is now a standard commercial practice, and fruit are most commonly removed by hand. Hand removal of excess fruit is the most expensive preharvest activity in peach production, but it is absolutely necessary to produce a saleable crop. During the last half-century the peach industry has been searching for less expensive ways to remove unwanted fruit. This chapter provides a discussion of peach tree physiology, which is

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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needed to fully understand the concept of fruit thinning, and the literature leading to the recommendation for fruit thinning is reviewed. We also review the various methods that have been developed to thin peach trees and some of the factors inﬂuencing the efﬁcacy of these practices, and we provide some suggestions for future research.

12.2 Fruit Growth and Development During the late season, especially after fruit harvest, photoassimilate is translocated from leaves to the woody portions of the tree, where it is stored as starch. Spring growth of roots, cambium, shoots and fruit all depend on the reserve carbohydrates. Unlike some other deciduous fruit trees, peach trees bloom before there is much leaf development. Whole-tree photosynthesis is insufﬁcient to support earlyseason growth of the tree and fruit. Most of the energy for early-season fruit growth is derived from reserve carbohydrates, and fruits must compete with other parts of the tree and with each other for carbohydrates. Peach fruit growth is traditionally divided into three stages (Tukey, 1933; Chalmers and van den Ende, 1975; Zucconi, 1986; Gage and Stutte, 1991). The ﬁrst stage is a period of rapid fruit growth from bloom to about 50 days after bloom, when the stony endocarp (pit) hardens. The length of the ﬁrst stage depends on cultivar and temperature. Fruit growth during this stage is primarily due to cell division, but some cell expansion and intercellular space formation occurs during the second half of this stage. The duration of the second stage depends on the maturity date of the cultivar. Stage II may last a few days in very earlymaturing cultivars or up to 2 months in latematuring cultivars. During this stage there is little increase in fruit size, but fruit dry weight continues to increase due to endocarp development, which requires a considerable amount of assimilate. The third stage is a period of rapid fruit size increase as the mesocarp cells expand. This ﬁnal stage is often called the ‘ﬁnal swell’, lasts several weeks before harvest and is the time of rapid sugar accumulation. Fruits compete with other growing parts of the tree for assimilates. Grossman and DeJong

(1995a,b) identiﬁed periods of resource-limited fruit growth. For an early-maturing cultivar, resource limitation began about 38 days after bloom and continued through harvest, which was 84 days following bloom. For the latematuring cultivar, the ﬁrst period was similar to the early-season cultivar but a second period occurred during the last 28 days of the ﬁnal swell, 126 to 154 days after bloom. Suppressed fruit growth caused by resource limitations was only temporary and fruit growth resumed normally when resources became available. The primary objective of crop load management is to minimize resource limitations for fruit growth in proper balance with vegetative development. Because fruit size is related to the number of cells per fruit and resources are limited during the second half of stage I, it is most important to remove excess fruit during the ﬁrst half of stage I to encourage cell division of the remaining fruit. It is also important to minimize stresses during the ﬁnal swell of late-season cultivars to ensure maximum increases in fruit size.

12.3 Quantifying Crop Load Peach thinning to improve fruit size has been practised for many years. Early in the 20th century it was known that fruit size was related to the number of leaves per fruit, but the nature of this relationship was not known. Beach (1903; cited by Overholser and Claypool, 1931) reported a correlation between size of peach leaves and fruit. Small-fruited cultivars had smaller leaves than large-fruited cultivars. Based on apple thinning research in the 1920s, several researchers performed experiments during the 1930s to determine the precise relationship between leaf area or leaf number and size and quality of peach fruit. Weinberger (1931) removed varying numbers of fruit from ringed branches on peach trees to develop eight ratios of leaf to fruit in early July in Maryland. He reported a curvilinear response, where fruit size increased at a decreasing rate as leaves per fruit increased from 10 to 75. From 30 to 75 leaves per fruit, the response was nearly linear; the increasing fruit volume per leaf was about 0.75 cm3 for ‘Elberta’ and 0.17 cm3 for ‘Early Crawford’.

Crop Load Management

Sugars and acidity also increased with increasing numbers of leaves per fruit. Based on this study, 30 to 40 leaves per fruit seemed adequate for producing large, high-quality peaches. A similar experiment performed the next season produced similar results for fruit development; and shoots on limbs with high leaf: fruit ratio produced more ﬂower buds and had higher starch levels in the wood (Weinberger and Cullinan, 1932). Similar results were reported for ringed limbs in North Carolina, where fruit size and quality increased as the number of leaves per fruit was increased from 10 to 45 (Jones, 1932). In Washington State, Overholser and Claypool (1931) thinned branches to varying numbers of leaves per fruit in mid-June on ringed and non-ringed limbs. There was a gradual increase in fruit size as leaves per fruit increased from 25 to about 80, but there was little increase in fruit size with more than 85 leaves per fruit. The increase in fruit size was greater and more consistent for girdled limbs. These experiments show that there is a positive relationship between number of leaves per fruit and fruit size, but there are problems with the methodology and the leaf area per fruit required to produce large fruit is still unknown. These often-cited leaf:fruit ratios may not be very accurate because there was no consideration of the efﬁciency of a leaf and whether or not it was in a high light environment. The leaf:fruit ratios were established fairly early in the season. Normally leaf number per tree increases until late season, so the number of leaves early in the season is low but increases as the season progresses. Most of these experiments were performed with girdled limbs, and girdling is known to improve fruit size and to advance maturity. The crop load on non-treated limbs was not reported and the non-treated limbs may have inﬂuenced fruit on treatment limbs. The authors usually did not indicate if the fruit were all harvested on the same date, or if they were harvested on the basis of some maturity factor such as ground colour. Fruit on heavy-cropped trees usually mature later than fruit on light-cropped trees. Because fruit continue to grow every day until harvest, it is important to harvest fruit at the proper stage of maturity to compare treatments in peach experiments.

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Shoemaker (1933) was the ﬁrst to show experimentally that early thinning and heavy thinning to a spacing of 15 to 20 cm between fruit was more proﬁtable than later thinning and less severe thinning. The increased fruit size resulted in a higher crop value, which offset the increased cost of thinning and the slight loss of yield.

12.4 Modifying Crop Load Numerous methods to reduce crop load have been evaluated (Byers et al., 2003). Gould (1918) summarized peach-growing practices across the USA at the turn of the 19th century and reported that the need for peach thinning was a ‘complete oneness of opinion’ but ‘not . . . in all cases with regard to practice’. No matter which thinning method is employed, the primary objective is to reduce the crop to levels that promote adequate fruit size at a reasonable cost. Under commercial growing conditions, maximizing fruit size can be accomplished by selecting appropriate cultivars and by using various cultural practices before bloom, during bloom or after bloom. Pre-bloom Several factors occurring before bloom can inﬂuence crop load and fruit size at harvest. These factors include environmental conditions and several cultural practices. In some years low winter temperatures may kill some of the ﬂower buds, resulting in low numbers of fruit per tree. A frost that kills a portion of the ﬂower buds or ﬂowers during bloom will result in improved fruit size of the remaining fruit. However, peach growers try to minimize the impact of low temperatures because freezes and frosts often reduce crop loads below profitable levels, but there are several methods to reduce the number of blossoms to lower thinning costs and improve fruit size at harvest. Genetics An important consideration when choosing a cultivar is the inﬂuence of genetics on fruit size. Commercial peach producers are aware

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that some cultivars produce larger-sized fruits than others. Scorza et al. (1991) identiﬁed the factors associated with the inherent size of different cultivars. They found that the number of cells per fruit was higher for large-fruited cultivars than for small-fruited cultivars. Differences in fruit size were due to cell numbers rather than cell size, and these differences were apparent in the ﬂower buds during the autumn before bloom. Flower buds of large-fruited cultivars had 2.5 times as many cells in mid-October than small-fruited cultivars and the difference in cell numbers per fruit remained consistent until harvest. Before planting a new cultivar, growers should learn as much as possible about the inherent ability of a cultivar to produce fruit of marketable size with yields that are proﬁtable. Growers must also realize that the ideal crop load will vary for different cultivars. Johnson and Handley (1989) thinned an earlyseason, a mid-season and a late-season cultivar to varying numbers of fruit per tree and estimated average fruit weight at harvest. They found that average fruit weight was linearly related to number of fruit per tree and the decrease in fruit size for each additional fruit per tree (slope of the line) was similar for all three cultivars. In general, the average fruit weight was reduced by 0.49 to 0.58 g for each additional fruit that was left on the tree. Slopes reported for other experiments were similar (Cain and Mehlenbacher, 1956; Westwood and Batjer, 1958), indicating that this relationship is fairly robust for different cultivars, seasons and locations. For a given tree size and crop load, average fruit weight is determined by the inherent characteristics of the cultivar. For example, with 600 fruit per tree, average fruit weight was 100 g, 150 g and 220 g per fruit for ‘May Crest’, ‘June Lady’ and ‘Elegant Lady’, respectively. To obtain an average fruit weight that is acceptable for fresh fruit sales (130 g), ‘May Crest’ trees must be thinned to only 190 fruit, ‘June Lady’ can be thinned to 1000 fruit per tree and ‘Elegant Lady’ can support 2000 fruit per tree. These results indicate that potential marketable yield per tree, which is a function of number of fruit per tree and fruit size, will be higher for large-fruited cultivars. However, potential marketable yield

per unit land area will likely depend on the number of fruit per canopy volume per unit land area, which is related to tree density and tree size. This is an area that needs additional work and should also include a comparison of orchard training systems. Cultivars also vary in their ability to produce ﬂower buds. For a given cultivar, earlyseason fruit set and the need for fruit thinning are positively related to the number of ﬂowers per tree, and fruit set varies from year to year depending on a number of factors. Peach cultivars differ inherently in ﬂower bud number (Blake, 1943; Werner et al., 1988). In a peach cultivar trial in New Jersey, USA, the number of ﬂowers per metre of shoot length varied from 30 for ‘Slaybaugh Special’ to 54 for ‘Springold’ (L. Miller, New Jersey, 1983, personal communication). Flower density for the same cultivar was also quite variable from year to year. During a 5-year period the number of ﬂowers per metre of shoot length for ‘Garnet Beauty’ ranged from three to 45. These differences in ﬂower density were due to the tendency of a cultivar to produce ﬂower buds and the ability of buds of a cultivar to survive the winter. Flower bud density is also negatively related to the previous season’s crop load. Non-thinned shoots, especially at the basal nodes, had ﬂower bud densities 25% lower than hand-thinned trees (Byers et al., 1990). Fruit set is also quite variable from year to year depending on weather conditions. Fruit set per 100 ﬂowers was about 35 (Byers and Lyons, 1985; Byers and Marini, 1994), 54 (Marini, 1985) and 60 (Byers et al., 1990) in three different experiments. Due to differences in bloom density, some cultivars have lower fruit densities than others. Plant growth regulators The bloom density inherent in a given cultivar may also be modiﬁed with applications of plant growth regulators. Late-summer and autumn application of gibberellic acid (GA3) killed ﬂower buds (Stembridge and LaRue, 1969), but applications during early to midsummer inhibited ﬂower bud initiation at the lower nodes in peach (Edgerton, 1966; Byers et al., 1990) and nectarine (Garcia-Pallas et al., 2001). A commercial formulation of GA3,

Crop Load Management

Release LC®, reduced ﬂower bud formation and improved fruit size in commercial peach orchards (Southwick et al., 1998a,b). It was registered for commercial use in California by Abbott Laboratories, Inc. and later as Ralex® by Valent BioSciences Corp. for several years. However, the registration was withdrawn due to inconsistent results and discouraging grower experiences. Dormant-season application of vegetablebased oils (e.g. soybean) has been used safely and effectively to pre-bloom thin peach ﬂower buds (Myers et al., 1996; Moran et al., 2000) but has produced inconsistent results when applied under commercial orchard conditions (Reighard et al., 2003b; Andris et al., 2004). Flower buds on peach cultivars have been prebloom thinned by 15 to 40% at rates of 6%, 7% and 8% (v:v) of soybean oil–water in grower orchards in South Carolina (Muriu Njoroge, 2002; Reighard et al., 2003a). The 8% rate has been the most cost-effective for the majority of cultivars. However, differences in cultivar sensitivity and annual environmental effects (i.e. winter temperatures) have lessened the efﬁcacy in some years, and thus commercial acceptance of this practice is limited at this time. Other chemicals have also been applied during the dormant season to thin ﬂower buds but sometimes led to over-thinning because they are dependent on concentration and temperature. These include ethephon (e.g. Ethrel), which is absorbed by the buds and breaks down into ethylene but can cause excessive bud mortality if applied during unseasonably warm temperatures especially in autumn (Williams, 1989). This potential risk may be one of the reasons why it has not been labelled for peach in the USA. Hydrogen cyanamide (e.g. Dormex), which is labelled for dormantseason application in some fruits to augment inadequate chilling, has also been examined experimentally as a thinner. It can effectively thin ﬂower buds, but the timing and rate are critical in peach or else over-thinning can occur (Fallahi et al., 1990; Powell, 1994).

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by 50% reduced the need for hand thinning without reducing fruit size (Marini, 2002). Pruning to remove more than 50% of the length of a shoot resulted in reduced fruit size. Retaining only one-ﬁfth as many shoots as the number of fruits desired per tree, and thinning fruit so that ﬁve fruit were retained per shoot after hand thinning, reduced the need for hand thinning, improved fruit size and increased proﬁt more than normal pruning and hand thinning (Marini, 2003). Bloom During bloom, peach producers have an opportunity to remove blossoms by physical means or they can reduce fruit set with chemicals. Physical removal Many commercial peach producers reduce early-season crop load by removing ﬂowers during bloom. When ﬂower buds are in the pink stage until shuck split, buds, ﬂowers and young fruit can be removed with ﬁngers or by running a stiff brush along one side of the shoot. The object is to remove about half of the ﬂowers. Baugher et al. (1988) demonstrated that dragging curtains of large-diameter ropes over the trees during bloom physically removed enough blossoms to reduce hand-thinning costs and improved fruit size enough to be costeffective. Mechanical rope-thinning attachments for tractors are available from commercial vendors and are routinely used by peach growers. However, trees need to be pruned carefully to a spreading open-vase shape to allow the ropes to fall freely through the tree to obtain adequate thinning throughout the canopy. High-pressure water spray systems to remove blossoms were investigated by R. Byers (1995, Virginia, personal communication) for blossom thinning. This approach was never adopted to a large extent, in part due to the large volume of water required and some concern about damage to scaffolds by the water.

Pruning

Chemicals

Another method of reducing the number of ﬂower buds per tree is by pruning off shoots with ﬂower buds. Heading all fruiting shoots

Several strategies for modifying numbers of ﬂowers per tree at bloom have been investigated. Spraying trees during bloom with

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chemicals that kill ﬂower parts and prevent fertilization is relatively inexpensive, but results are often inconsistent (Byers and Lyons, 1982, 1985; Byers et al., 2003). A number of caustic chemicals, herbicides and surfactants have been examined as bloom thinners. Some growers used sodium dinitro-o-cresylate (DNOC) but results were mixed. The material was often applied when about 20% of the pistils were showing and again when the ﬁnal 20% of the ﬂowers were open, in an attempt to eliminate about 40% of the crop. Although, with experience, some large growers produced acceptable results with 1-aminomethanamide dihydrogen tetraoxosulfate, the registration on this material has never been approved on peach and was removed on apple. Wilthin®, a sulfcarbamide, is another caustic chemical that is labelled for use as a thinner (Myers et al., 1993), but it has performed inconsistently some years (Greene et al., 2001) and requires close attention to the handling and application procedures listed on the label. Research with Wilthin® (R. Byers, Virginia, 1997, personal communication) indicated that dilute applications should be made with an air-blast sprayer (1000–2000 l/ha, depending on tree size and spacing) at the rate of 7.5–15 l Wilthin®/ha when about 90% of the ﬂowers have opened and about 10% of the buds are in the pink stage of development. Proper timing is critical for consistent results in the east, but in California the timing may be less critical. Ammonium thiosulfate (ATS), a liquid fertilizer, has been widely researched as a means of ‘burning’ or desiccating ﬂower parts to reduce ﬂower numbers and fruit set (Johnson, 1998; Byers, 1999; Greene et al., 2001). However, there is no ATS label to thin peach ﬂowers and its somewhat inconsistent performance probably accounts for corporate disinterest in pursuit of a label. In spite of the lack of interest by agrichemical companies, ATS research as a bloom thinner continues in many tree fruit regions in the USA because of its availability, low cost, user safety and general effectiveness. Other chemicals, especially surfactants, have also been tested for thinning properties. The surfactant ArmoThin® (N,N-bis-2-(whydroxypolyoxyethylene/polyoxypropylene) ethyl alkylamine) was tested in the 1990s as a

bloom thinner, but was never used commercially (Southwick et al., 1998b). Another surfactant still under investigation is a dodecyl ether of polyethylene glycol (i.e. Tetgitol™ TMN-6, also known as Surfactant WK or DuPont WK). It has shown promise in thinning ﬂowers in orchard trials in the southeastern USA, but it has not been registered for thinning peaches (Ebel et al., 1999; Wilkins et al., 2004). It should be kept in mind that the effectiveness of air-blast application of any potential thinning agent is expected to vary with the amount of water applied, air temperature, humidity, surfactants, stage of ﬂower/ fruit development, orchard training system or other factors. Many of these products are commercially available, but growers should not use them for peach thinning unless they are registered for peach thinning because the results are inconsistent and trees may be injured.

Post-bloom Although thinning before or during bloom has the greatest impact on fruit size, postbloom thinning allows one to ﬁrst assess fruit set and minimize the potential for overthinning. Hand Hand thinning has been the most common method of reducing the crop load on peach trees for many years. The general rule of thumb has been to space fruit about 12, 15 and 20 cm apart for large-, medium- and small-fruit cultivars, respectively. In some regions distance between fruit is not considered, rather fruit number per shoot is varied depending on shoot location in the canopy or season of harvest. The number of fruit retained per shoot can be two or three in the bottom of the tree, three or four in the middle of the tree, and ﬁve in the top of the tree. Fruit retained per shoot may also vary from three for early-season cultivars, to four to six for late-season cultivars. Spacing fruit to a given distance or to a given number per shoot requires adequate pruning to remove excess fruiting shoots. An alternative approach may be to retain a certain number

Crop Load Management

of fruit per hectare; the desired number would vary with the cultivar and with the desired fruit size at harvest. Based on data published by Johnson and Handley (1989) in California, to obtain fruit that are 6.3 cm in diameter trees should be thinned to 70,000, 345,000 and 690,000 fruit/ha for small-, medium- and large-sized cultivars. If 7.0 cm fruit are desired, then the crop load should be reduced to about 70,000 and 140,000 fruit/ha for medium- and largefruited cultivars, respectively. These fruit numbers should probably be reduced by about 30% in the eastern USA, where tree canopies are smaller and there is less available light than in California. Small-fruited cultivars do not have the potential to produce 7.0 cm diameter fruit, even at very low crop loads. The small fruit size associated with early-season cultivars may be due to cell numbers or the short duration of fruit growth. The earlier trees are thinned, the greater the effect will be on fruit size. Havis (1962) demonstrated that reducing the crop load before or during bloom maximizes fruit size, and hand thinning becomes less effective for each day after bloom that thinning is delayed. In general, early-season cultivars are smallfruited and require earlier and more severe thinning than late-season cultivars. This is why so much emphasis has been placed on methods to reduce ﬂower density at bloom. It is difﬁcult to ﬁnd orchard workers who do a good job of hand thinning. Hand thinning requires a large labour force with good supervision and can cost from $375 to $1875/ha at $9/h depending on tree size and fruit set (G. Reighard, 2006, South Carolina, personal communication). Estimates for California are about $1514 (Hasey et al., 2004) to $2423 per hectare (Day et al., 2004). Therefore researchers and growers have been looking for ways to reduce thinning costs. Rather than removing small fruit solely by hand, some growers use rubber hoses, plastic baseball bats or padded sticks to knock fruit off the tree, followed by ﬁnal hand thinning. This method is less expensive than hand thinning alone, but it does not facilitate the selective removal of insect-injured and small fruit. Fruit removal with bats or sticks is most efﬁcient if delayed until fruits are large enough to be shaken off when the limb is struck.

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The effect of thinning on fruit size is related to the time of thinning. Generally the earlier the thinning is accomplished, the greater the effect on ﬁnal fruit size. However, Dorsey and McMunn (1935) demonstrated that even thinning later in the season is beneﬁcial. They thinned trees at various times during the season starting 64 days after bloom when the pits were hardening. They found that thinning up to 4 weeks before harvest increased the percentage and the yield of large fruit. During a drought, commercial peach producers without irrigation sometimes remove a portion of the crop during the ﬁnal swell to improve the size of the remaining fruit. The typical instructions for thinning peaches are to space the fruit relatively evenly along the fruiting shoot. However, the distance between fruit and the distribution of fruit along the shoot do not affect fruit size (Corelli Grappadelli and Coston, 1991; Marini and Sowers, 1994; Ben Mimoun and DeJong, 1999). Marini and Sowers (1994) reported that fruit on long shoots tended to be larger than fruit on short shoots and fruit on shoots with lateral shoots tended to be larger than fruit on shoots with only a terminal shoot. Heavily cropped branches on lightly cropped trees also had larger fruit than heavily cropped branches on heavily cropped trees. Therefore, the number of fruit per tree is more important than the distribution of fruit on the tree, because fruit size depends on photosynthate from leaves in the immediate vicinity of the fruit as well as photosynthate from more distant parts of the tree. Mechanical Some large peach growers use mechanical tree shakers or branch shakers to remove excess fruit, but smaller growers cannot justify the cost of a shaker. For this method to be successful, trees must be properly trained. About 60 cm of space between the ground and the lowest scaffold branches is required to attach the clamp to the trunk. Trees with no more than four scaffold branches and without willowy branches or many sub-scaffolds are most conducive to shaking. Shakers can injure the bark and predispose the tissue to Cytospora canker infection. Hand thinning is usually

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required for touch-up. Attempts to do all of the thinning with a shaker may result in overthinning, and there is a tendency to remove the largest fruit. A good shaker operator, working with well-trained trees, can remove 50–80% of the fruit, while the rest must be removed by hand. As with baseball batting, small fruit are difﬁcult to remove by shaking and so shakers must be used towards the later stages of thinning, which may be too late for early-season or small-fruited cultivars (Kamas et al., 1998). Chemicals Successful post-bloom apple thinning with chemicals led to a search to identify similar materials for peaches. Since the 1940s researchers have tested many apple thinners on peach, including naphthalene acetic acid (NAA), naphthylacetamide, carbaryl, and others. Early attempts to thin peach trees with NAA at bloom or shortly after bloom were somewhat successful, and Murneek and Hibbard (1947) showed that NAA was most effective when applied about 30 days after full bloom. Kelly (1955) applied NAA at concentrations of 30 to 50 ppm and found that NAA at 30 or 40 ppm thinned peaches when applied at about 14 days after shuck off in two of three experiments. Edgerton and Hoffman (1952) reported that NAA applied a month after bloom caused more thinning than DNOC at bloom, but the concentration of NAA that provided adequate thinning varied from 20 to 40 ppm depending on the cultivar. Research results with NAA were so inconsistent that interest shifted to the carbamate compounds. Horsfall and Moore (1956) evaluated eight formulations of carbamates as post-bloom peach thinners, and chloro IPC showed the most promise. Although the level of thinning was sometimes acceptable, results varied with season and cultivar, and some shoots were not thinned well, causing fruit clustering. None of these materials proved to be consistently effective post-bloom thinners for commercial use. During the 1970s and 1980s ethylene-releasing compounds were tested. Ethephon caused fruit thinning, but also often caused partial defoliation and tree injury. Another ethylene- releasing agent, CGA-15281 (2-chlorethylmethyl-bis(phenylmethoxy)silane),

provided fairly consistent fruit thinning with little leaf drop in the south-eastern USA (Gambrell and Sims, 1983), but in the mid-Atlantic states defoliation was often a problem. The product was never developed because the company responsible went out of business. Research on apples, and to a lesser extent on peach, indicated that natural or chemically induced fruit abscission might be accentuated by limiting photosynthesis. Therefore, Byers et al. (1984) shaded peach trees and also sprayed trees with photosynthesis-inhibiting herbicides, such as terbacil. Covering the trees with 92% shade cloth from 31 to 41 days after bloom, but not earlier, reduced fruit set severely and improved fruit size slightly. Terbacil applied at the rate of 500 ppm and at 35 days after bloom caused over-thinning with no defoliation. Although this approach was quite innovative and showed great promise, no chemical company was willing to register a herbicide for peach thinning. Pruning Harmon (1933) was the ﬁrst to demonstrate that pruning could inﬂuence fruit size and quality. In a 4-year experiment he compared non-pruned trees with trees that were pruned, and then the number of shoots per tree was varied by cutting back the shoots by varying amounts. As pruning became more severe, there were fewer fruits set per tree and fruit size increased, but yield per tree was highest for moderately pruned trees. The author indicated that from an economic standpoint the least expensive thinning of fruit is done by pruning. Hand thinning is a necessary accompaniment to adjust the number of fruits to the leaf area of the tree. Marini (2002, 2003) followed up on this pruning work. Heading all fruiting shoots on a tree by 50% while dormant, pruning reduced fruit set and hand-thinning costs, and sometimes improved fruit size, compared with not heading shoots. Heading to remove more than 50% of each shoot further reduced fruit set, but negatively affected fruit size. Pruning to retain varying numbers of shoots per tree also had an impact on fruit size. As the number of shoots retained per tree declined, fruit set and the need for hand thinning was reduced and fruit size increased.

Crop Load Management

When only about 100 shoots were retained per tree, the combination of reduced thinning costs and improved fruit size resulted in a net proﬁt $6000/ha greater than for trees with 250 shoots. This practice is commonly followed in California (K. Day, California, 2000, personal communication), but the concept is new for growers in the eastern USA. Following more research to identify the appropriate crop loads for different cultivars, it should be possible to prune trees to a given number of shoots per hectare and then thin the trees to a given number of fruit per shoot to obtain the desired number of fruit per hectare. The V-shaped tree would be particularly well suited to this approach because the simple tree structure facilitates pruning to a speciﬁc number of shoots per tree (DeJong et al., 1994).

12.5 Crop Load Interactions with Stresses A number of tree stresses can have a negative impact on fruit size. If these stresses can be predicted early in the season, crop load can be reduced to minimize the effects of stress.

Tree density To take advantage of high production during the early years after orchard establishment, some peach growers have started to increase the number of trees per hectare. Standard tree densities are about 300 to 350 trees/ha, but newer plantings may have as many as 1300 trees/ha. Giulivo et al. (1984) planted peach and nectarine trees at densities ranging from 1250 to 2000 trees/ha. Normally fruit size is negatively related to fruit density (number of fruit/cm2 trunk cross-sectional area). However, they found that both fruit size and fruit density were negatively related to tree density. The reduction in fruit size was related to a reduction in fruit relative growth rate during stage I of fruit development. In a study of peach orchard systems, Grossman and DeJong (1998) reported that the dry weight of individual fruits was inversely related to tree density, but it may have been a function of

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yield per hectare. Their data indicate that tree form as well as tree density may inﬂuence fruit size. In another study, fruit size and the percentage of marketable yield were inversely related to tree density (Marini and Sowers, 2000). Even when adjusted for number of fruits per hectare, fruit weight was higher for low-density trees than for high-density trees. The reason for reduced fruit weight may be increased competition for water and nutrients between trees or increased shading in close plantings. Whatever the reason, these data indicate that high-density peach plantings should be dormant-pruned or thinned more aggressively than low-density plantings.

Water stress Both crop load and water availability affect peach fruit size, but there is little information available concerning the combined effects of water stress and crop load. Both Morris et al. (1962) and Girona et al. (2002) showed that the effects of crop load and irrigation on fruit size were additive, rather than interactive; however, at heavy crop loads only a small percentage of harvested fruit from non-irrigated trees were of marketable size. Berman and DeJong (1996) performed an experiment with widely differing crop loads to study the effects of water stress on fruit growth. Fresh weight, which is analogous to fruit size, for all crop loads was reduced by water stress to a similar extent. However, the reduction in fruit dry weight by water stress was greatest for high crop loads. The reduction in dry weight on heavy-cropped trees was probably due to resource-limited conditions resulting from the combination of a high carbon demand and water-reduced photosynthesis. These data indicate that irrigated orchards can support heavier crop loads than non-irrigated orchards.

Leaf-feeding arthropods Arthropods that feed on peach foliage would theoretically reduce photosynthesis and fruit size and quality. In apple, the negative effect

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of indirect pests increased as population levels increased (Marini et al., 1994). For non-fruiting sour cherry trees, Layne and Flore (1992) showed that trees could compensate for up to 20% defoliation with minor effects on carbon assimilation. However, much less information is available for peach. Seasonal accumulations of 8900 cumulative European red mite-days did not inﬂuence fruit size or quality of ‘Cresthaven’ peaches (McClernan and Marini, 1986), but more information is needed on the effects of other indirect pests, such as Japanese beetle and two-spotted spider mite, and of diseases such as bacterial leaf spot, on peach fruit size and quality.

the warmest Augusts recorded at the Southeast Regional Climate Center, Columbia, South Carolina since 1900. In late July and into August, growers irrigated primarily only lateseason cultivars, which were still unpicked even though August rainfall was 5.3 cm below normal and trees were showing heat stress. In the subsequent growing season (i.e. 2000), an abnormally high incidence of fruit doubling occurred in some of the non-irrigated, earlyand mid-season cultivars (C.R. Carr III and L.F. Holmes III, South Carolina, 2000, personal communication).

Low temperatures High temperatures Unusually high temperatures during applications of soybean oil in January (>28°C) in South Carolina gave signiﬁcantly higher ﬂower bud thinning and increased fruit size at harvest (Lennon, 2004). In addition, temperatures from bloom to 30 days after bloom affect fruit development rates and can be used to predict harvest maturity date (Ben Mimoun and DeJong, 1999). In California during 2004, abnormally high temperatures at and after bloom advanced fruit maturity by 10–14 days. However, fruit size was decreased by one to two sizes below normal. The high temperatures advanced fruit development much quicker than normal so the trees’ carbohydrate reserves had probably already become limiting before growers initiated thinning (DeJong, 2005). This dilution of reserves to the rapidly developing fruit crop reduced potential fruit growth early in stage I, and the fruit never recovered by harvest time. High temperatures (>38°C) during ﬂower bud initiation after harvest in late summer can also negatively affect next year’s ﬂower buds. Postharvest reduction of irrigation in August was shown by Handley and Johnson (2000) not only to increase water stress and leaf temperature, but also increased fruit doubles and deep sutures the following year. In South Carolina, mean 24 h temperatures during August 1999 averaged 27.7°C, or 2°C above normal, in the Ridge peach region, which was one of

Thinning during bloom may increase shoot growth and ﬂower bud density for next year’s crop and also increase the cold tolerance of buds (Byers and Marini, 1994). Thus, thinning during bloom may be more important for northern regions that are prone to lowtemperature injury during the winter and for cultivars that naturally produce low ﬂower bud densities.

12.6 Future Directions During the 20th century the need for peach crop load management was clearly demonstrated and fruit thinning became a standard commercial practice. Researchers have described in detail the physiology of fruit growth and development, and this basic information was used to develop fruit thinning programmes. Future market demands will ultimately inﬂuence orchard practices such as crop load management. Assuming the demand for large fruit continues, fruit size should be an important criterion for peach breeders. Small and medium-sized cultivars are rapidly becoming non-proﬁtable for some markets. The demand for large fruit will increase the need for early and aggressive fruit thinning. Growers will continue to search for fruit thinning methods that are less expensive than hand thinning. More research is needed to develop chemicals that can be applied pre- and post-bloom to reduce ﬁnal

Crop Load Management

fruit set. This will require a better understanding of how the efﬁcacy of these materials interacts with climatic factors, the condition of the tree and the physiological development of the fruit. We also need a better understanding of the relationship between fruit size and number of fruit per unit of land area or unit of

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canopy volume for different cultivars, different orchard systems, and irrigated and nonirrigated orchards. After obtaining these types of information, researchers and growers can develop fruit thinning strategies to obtain the most proﬁtable crop load for speciﬁc situations and for different markets.

References Andris, H.L., Johnson, R.S., Klassen, K. and Day, K. (2004) Stone fruit thinning with soybean oil. 2004 California Tree Fruit Agreement Annual Research Report. California Tree Fruit Agreement, Reedley, California, pp. 47–51. Baugher, T.A., Elliot, K.C., Blizzard, S.H., Walter, S.I. and Keiser, T.A. (1988). Mechanical bloom thinning of peach. HortScience 23, 981–983. Beach, S.A. (1903) Correlation between different parts of the plant in form, color, size, and other characteristics. In: Proceedings of the International Conference on Plant Breeding and Hybridization Memoirs, Vol. 1. Horticultural Society of New York, New York, p. 63. Ben Mimoun, M. and DeJong, T.M. (1999) Using the relation between growing degree hours and harvest date to estimate run-times for PEACH: a tree growth and yield simulation model. Acta Horticulturae 499, 107–114. Berman, M.E. and DeJong, T.M. (1996) Water stress and crop load effects on fruit fresh and dry weights in peach (Prunus persica). Tree Physiology 16, 859–864. Blake, M.A. (1943) Classification of fruit bud development on peaches and nectarines and its significance in cultural practice. New Jersey Agricultural Experiment Station Bulletin No. 706. Byers, R.E. (1999) Effects of bloom-thinning chemicals on peach fruit set. Journal of Tree Fruit Production 2, 59–78. Byers, R.E. and Lyons, C.G. Jr (1982) Flower bud removal with surfactants for peach thinning. HortScience 17, 377–378. Byers, R.E. and Lyons, C.G. Jr (1985) Peach flower thinning and possible sites of action of desiccating chemicals. Journal of the American Society for Horticultural Science 110, 662–667. Byers, R.E. and Marini, R.P. (1994) Influence of blossom and fruit thinning on peach flower bud tolerance to an early spring freeze. HortScience 29, 146–148. Byers, R.E., Lyons, C.G. Jr, Del Valle, T.B., Barden, J.A. and Young, R.W. (1984) Peach fruit abscission by shading and photosynthetic inhibition. HortScience 19, 649–651. Byers, R.E., Carbaugh, D.H. and Presley, C.N. (1990) The influence of bloom thinning and GA3 sprays on flower bud numbers and distribution in peach trees. Journal of Horticultural Science 65, 143–150. Byers, R.E., Costa, G. and Vizzotto, G. (2003) Flower and fruit thinning of peach and other Prunus. In: Janick, J. (ed.) Horticultural Reviews, Vol. 28. Wiley, New York, pp. 351–392. Cain, J.C. and Mehlenbacher, J.R. (1956) Effects of nitrogen and pruning on trunk growth in peaches. Proceedings of the American Society for Horticultural Science 67, 139–143. Chalmers, D.J. and van den Ende, B. (1975) A reappraisal of the growth and development of peach fruit. Australian Journal of Plant Physiology 2, 623–634. Cole, S.W. (1849) The American Fruit Book. John P. Jewett, New York. Corelli Grappadelli, L. and Coston, D.C. (1991) Thinning pattern and light environment in peach tree canopies influence fruit quality. HortScience 26, 1464–1466. Day, K.R., Andris, H.L., Klonsky, K.M. and DeMoura, R.L. (2004) Sample costs to establish and produce peaches. http://coststudies.ucdavis.edu/files/peachesjv2004.pdf (accessed July 2005). DeJong, T.M. (2005) Using physiological concepts to understand early spring temperature effects on fruit growth and anticipating fruit size problems at harvest. Summerfruit Autumn, 10–13. DeJong, T.M., Day, K.R., Doyle, J.F. and Johnson, R.S. (1994) The Kearney Agricultural Center perpendicular ‘V’ (KAC-V) orchard system for peaches and nectarines. HortTechnology 4, 362–367. Dorsey, M.J. and McMunn, R.L. (1935) Peach thinning investigations V: a study of late thinning. Proceedings of the American Society for Horticultural Science 33, 280–283.

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Ebel, R.C., Caylor, A., Pitts, J. and Himelrick, D.G. (1999) ‘Surfactant WK’ for thinning peach blossoms. Fruit Varieties Journal 53, 184–188. Edgerton, L.J. (1966) Some effects of gibberellin and growth retardants on bud development and cold hardiness of peach. Proceedings of the American Society for Horticultural Science 88, 197–203. Edgerton, L.J. and Hoffman, M.B. (1952) The effect of thinning peaches with bloom and post-bloom sprays on the cold hardiness of the fruit buds. Proceedings of the American Society for Horticultural Science 60, 155–159. Fallahi, E., Kilby, M. and Moon, J.W. (1990) Effects of various chemicals on dormancy, maturity and thinning of peaches. In: Deciduous Fruit and Nut. University of Arizona, Series P-83. University of Arizona, Tucson, Arizona, pp. 121–128. Fitz, J. (1872) The Southern Apple and Peach Culturist. J.W. Randolf and English, Richmond, Virginia. Gage, J. and Stutte, G. (1991) Developmental indices of peach: an anatomical framework. HortScience 26, 459–463. Gambrell, C.E. and Sims, E.T. (1983) Results of eight years with CGA-15281 as a postbloom thinner for peaches. Journal of the American Society for Horticultural Science 108, 605–608. Garcia-Pallas, I., Val, J. and Blanco, A. (2001) The inhibition of flower bud differentiation in ‘Crimson gold’ nectarine with GA3 as an alternative to hand thinning. Scientia Horticulturae 90, 265–278. Girona, J., Marsal, J., Mata, M., Arbones, A. and Mata, A. (2002) The combined effect of fruit load and water stress in different peach fruit growth stages (Prunus persica L). Acta Horticulturae 584, 149–152. Giulivo, C., Ramina, A. and Costa, G. (1984) Effects of planting density on peach and nectarine productivity. Journal of the American Society for Horticultural Science 109, 287–290. Gould, H.P. (1918) Peach Growing. The Macmillan Company, New York. Greene, D.W., Hauschild, K.I. and Krupa, J. (2001) Effect of blossom thinners on fruit set and fruit size of peaches. HortTechnology 11, 179–183. Grossman, Y.L. and DeJong, T.M. (1995a) Maximum fruit growth potential and seasonal patterns of resource dynamics during peach growth. Annals of Botany 75, 553–560. Grossman, Y.L. and DeJong, T.M. (1995b) Maximum fruit growth potential following resource limitation during peach growth. Annals of Botany 75, 561–567. Grossman, Y.L. and DeJong, T.M. (1998) Training and pruning systems effects on vegetative growth potential, light interception, and cropping efficiency in peach trees. Journal of the American Society for Horticultural Science 123, 1058–1064. Handley, D.F. and Johnson, R.S. (2000) Late summer irrigation of water-stressed peach trees reduces fruit doubles and deep sutures. HortScience 35, 771. Harmon, F.N. (1933) Relation of pruning and thinning to fruit size and yield of Paloro peaches. Proceedings of the American Society for Horticultural Science 30, 219–222. Hasey, J., Duncan, R., Norton, M., Konsky, K.M. and Livingston, P. (2004) Sample costs to produce cling peaches: Sacramento and San Joaquin valleys, extra-early harvested varieties. http://coststudies.ucdavis. edu/files/peachessacsjv2004.pdf (accessed July 2005). Havis, A.L. (1962) Effects of time of fruit thinning of Redhaven peach. Proceedings of the American Society for Horticultural Science 80, 172–176. Horsfall, F. and Moore, R.C. (1956) Isopropyl N-(3 chlorophenyl)-carbamates and other carbamates as fruit thinning sprays for Halehaven, Ambergem, and Elberta peaches. Proceedings of the American Society for Horticultural Science 68, 63–69. Johnson, R.S. (1998) ATS works well as bloom thinner on stone fruits. Good Fruit Grower 49, 14–15. Johnson, R.S. and Handley D.F. (1989) Thinning response of early, mid-, and late-season peaches. Journal of the American Society for Horticultural Science 114, 852–855. Jones, I.D. (1932) Further observations on influence of leaf area on fruit growth and quality in the peach. Proceedings of the American Society for Horticultural Science 29, 34–38. Kamas, J., McEachem, G., Stein, L. and Roe, N. (1998) Peach Growing in Texas. http://aggie-horticulture. tamu.edu/extension/peach/peach.html (accessed July 2005). Kelly, V.W. (1955) Time of application of naphthaleneacetic acid for fruit thinning of the peach in relation to the June drop. Proceedings of the American Society for Horticultural Science 66, 70–72. Layne, D.R. and Flore, J.A. (1992) Photosynthetic compensation to partial leaf area reduction in sour cherry. Journal of the American Society for Horticultural Science 117, 279–286. Lennon, S.F. (2004) Integrated pest management strategies for reducing pesticide-related risks and increasing production efficiency in South Carolina peaches. MSc thesis, Clemson University, Clemson, South Carolina.

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McClernan, W.A. and Marini, R.P. (1986) European red mite on yield, fruit quality, and growth of peach trees. HortScience 21, 244–246. Marini, R.P. (1985) Vegetative growth, yield, and fruit quality of peach as influenced by dormant pruning, summer pruning, and summer topping. Journal of the American Society for Horticultural Science 110, 133–139. Marini, R.P. (2002) Heading fruiting shoots before bloom is equally effective as blossom removal in peach crop load management. HortScience 37, 642–646. Marini, R.P. (2003) Peach fruit weight, yield, and crop value are affected by number of fruiting shoots per tree. HortScience 38, 512–514. Marini, R.P. and Sowers, D.L. (1994) Peach fruit weight is influenced by crop density and fruiting shoot length but not position on the shoot. Journal of the American Society for Horticultural Science 119, 180–184. Marini, R.P. and Sowers, D.L. (2000) Peach tree growth, yield, and profitability as influenced by tree form and tree density. HortScience 35, 837–842. Marini, R.P., Pfeiffer, D.G. and Sowers, D.S. (1994) Influence of European red mite (Acari: Tetranychidae) and crop density on fruit size and quality and on crop value of ‘Delicious’ apples. Journal of Economic Entomology 87, 1302–1311. Moran, R.E., Deyton, D.E., Sams, C.E. and Cummins, J.C. (2000) Applying soybean oil to dormant peach trees thins flower buds. HortScience 35, 615–619. Morris, J.R., Kattan, A.A. and Arrington, E.H. (1962) Response of Elberta peaches to the interactive effects of irrigation, pruning, and thinning. Proceedings of the American Society for Horticultural Science 80, 177–189. Muriu Njoroge, S. (2002) Crop load manipulation in peach: comparison of soybean oil, ammonium thiosulfate and hand-thinning strategies. MSc. thesis, Clemson University, Clemson, South Carolina. Murneek, A.E. and Hibbard, A.D. (1947) Investigations on thinning of peaches by means of caustic and hormone sprays. Proceedings of the American Society for Horticultural Science 50, 206. Myers, R.E., Deyton, D.E. and Sams, C.E. (1996) Applying soybean oil to dormant peach trees alters internal atmosphere, reduces respiration, delays boom, and thins flower buds. Journal of the American Society for Horticultural Science 121, 96–100. Myers, S.C., King, A. and Savelle, A.T. (1993) Bloom thinning of ‘Winblo’ peach and ‘Fantasia’ nectarine with monocarbamide dihydrogensulfate. HortScience 28, 616–617. Overholser, E.L. and Claypool, L.L. (1931) The relation of leaf area per peach to physical properties and chemical composition. Proceedings of the American Society for Horticultural Science 28, 5–17. Powell, A.A. (1994) Action Program for Dormex Application on Peaches. Alabama Cooperative Extension Service Agriculture & Natural Resources Timely Information FN-94-1. Auburn University, Auburn, Alabama. Reighard, G.L., Ouellette, D.R. and Brock, K.H. (2003a) Economic analysis of soybean oil application to delay peach bloom and pre-bloom thin peach flowers. In: Reighard, G. (ed.) Annual Peach Research Report Vol. III. South Carolina Peach Council, Columbia, South Carolina, pp. 104–113. Reighard, G.L., Njoroge, S.M., Lennon, S., Ouellette, D. and Brock, K. (2003b) Reducing peach (Prunus persica) flower bud numbers with a mid-winter application of soybean oil. In: Proceedings of the 30th Annual Conference of the Plant Growth Regulation Society of America. The Plant Growth Regulation Society of America, LaGrange, Georgia, p. 28. Scorza, R.L., May, G., Purnell, B. and Upchurch, B. (1991) Differences in number and area of mesocarp cells between small- and large-fruited peach cultivars. Journal of the American Society for Horticultural Science 116, 861–864. Shoemaker, J.S. (1933) Certain advantages of early thinning of Elberta. Proceedings of the American Society for Horticultural Science 30, 223–224. Southwick, S.M., Weis, K.G., Yeager, J.T., Rupert, M.E. and Hasey, J.K. (1998a) Chemical thinning of cling peach. Acta Horticulturae 465, 647–654 Southwick, S.M., Weis, K.G., Yeagor, J.T., Hasey, J.K. and Rupert, M.E. (1998b) Bloom thinning of ‘Loadel’ cling peach with a surfactant: effects of concentration, carrier volume, and differential applications within the canopy. HortTechnology 8, 55–58. Stembridge, G.E. and LaRue, J.H. (1969) The effect of potassium gibberellate on flower bud development in the ‘Redskin’ peach. Journal of the American Society for Horticultural Science 94, 492–495. Tukey, H.B. (1933) Growth of peach embryo in relation to growth of fruit and season of ripening. Proceedings of the American Society for Horticultural Science 30, 209–218. Weinberger, J.H. (1931) The relation of leaf area to size and quality of peaches. Proceedings of the American Society for Horticultural Science 28, 18–22.

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Weinberger, J.H. and Cullinan, F.P. (1932) Further studies on the relation between leaf area and size of fruit, chemical composition, and fruit bud formation in Elberta peaches. Proceedings of the American Society for Horticultural Science 29, 23–27. Werner, D.J., Mowrey, B.D. and Chaparro, J.X. (1988) Variability in flower bud number among peach and nectarine cultivars. HortScience 23, 578–580. Westwood, M.N. and Batjer, L.P. (1958) Size of Elberta and J.H. Hale peaches during the thinning period as related to size at harvest. Proceedings of the American Society for Horticultural Science 72, 102–105. Wilkins, B.S., Ebel, R.C., Dozier, W.A., Pitts, J. and Boozer, R. (2004) Tergitol TMN-6 for thinning peach blossoms. HortScience 39, 1611–1613. Williams, K.M. (1989) Peach bloom delay using fall applications of Ethrel and Pro-Gibb. Acta Horticulturae 254, 151–154. Zucconi, F. (1986) Peach. In: Monselise, S.P. (ed.) Handbook of Fruit Set and Development. CRC Press, Boca Raton, Florida, pp. 303–321.

13

Nutrient and Water Requirements of Peach Trees R.S. Johnson

Department of Plant Sciences, University of California, Davis, California, USA

13.1 Introduction 13.2 Nutrient Requirements Diagnostic methods Nitrogen Phosphorus Potassium Calcium Magnesium Sulfur Zinc Boron Iron Manganese Copper 13.3 Peach Water Requirements Water stress

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13.1 Introduction

of water. Thus, information has been developed to help orchard managers deal with these suboptimal conditions. This chapter deals with the management of nutrients and water under both optimal and suboptimal conditions. As there has been increasing concern in recent years over environmental protection, the challenge is to supply adequate amounts of nutrients and water for good production, but guard against excessive amounts that might lead to environmental contamination.

When grown on fertile soils well supplied with nutrients and provided with adequate amounts of water, peach trees are very vigorous and productive. Many locations around the world where peaches are grown enjoy these conditions. However, there are also situations of peach orchards growing in more challenging soils (infertile, high pH, low in micronutrients, etc.) or with insufﬁcient supplies

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13.2 Nutrient Requirements As with all other plants, peach trees require at least 16 essential elements for optimum growth and productivity. A deﬁciency of any one of these nutrients can lead to problems with production, fruit quality, vegetative growth or tree health. Some deﬁciencies are extremely rare in ﬁeld-grown peach trees and information is limited. However, in general, the deﬁciency threshold for each nutrient has been determined (see Table 13.1 below), as well as a standard method of sampling. In recent years, research has focused on improved sampling methodologies in an effort to better diagnose and predict nutritional problems. Also, there has been much research effort directed towards improved nutrient uptake efﬁciency so that environmental contamination can be minimized and orchard proﬁtability maximized. This chapter presents the standard information developed over many years as well as recent research efforts.

Diagnostic methods There is a need to sample nutrient levels in the tree so corrective measures can be implemented in a timely manner. Leaf symptoms

Table 13.1. Peach deficiency thresholds and sufficiency ranges that have been set by various researchers. Values for mid-shoot leaves collected in mid-summer and expressed on a dry weight basis.

Nutrient

Deficiency threshold

Sufficiency range

N (%) P (%) K (%) Ca (%) Mg (%) S (%) Zn (ppm) B (ppm) Fe (ppm) Mn (ppm) Cu (ppm)

2.2–2.4 0.09–0.12 0.75–1.0 1.0 0.10–0.30 0.09 10–20 15–30 – 20 3

2.6–3.5 0.14–0.40 2.0–3.0 1.5–3.0 0.30–0.80 0.14–0.40 20–50 30–70 80–250 40–200 5–16

can be used as a diagnostic tool, but often deﬁciency symptoms do not develop until serious damage to the tree or crop has already occurred. Also, loss in productivity can occur without any leaf symptoms for some nutrients. Therefore, a more predictive method would be desirable. The standard method that has been developed for peaches, as well as most other plants, is a mid-summer sample of mature, mid-shoot leaves. Batjer and Westwood (1958) sampled ‘Elberta’ peach leaves throughout the whole growing season and found relatively constant values of most nutrients during the period from 100 to 125 days after bloom (Fig. 13.1/Plate 77). They recommended this as a stable period for leaf sampling, when consistent values could be obtained from year to year. Researchers from many different peachgrowing areas around the world followed the same general protocol and came up with remarkably similar values for most nutrients in healthy orchards (Leece et al., 1971). Thus, this has become the standard procedure for peach orchards and will be referred to for each nutrient throughout this chapter. However, the method does have drawbacks and considerable efforts have been made in recent years to develop alternative approaches. The biggest drawback is one of timing: 100 to 125 days after bloom is generally too late in the season to apply any corrective measures for yield and fruit quality in that year. An early-season or even dormant sampling would be preferable. Flower sampling for Fe content showed promise as a predictor of iron chlorosis, although there was variability among sites (Sanz et al., 1997a) and the absolute values changed considerably from year to year (Sanz et al., 1997b). Deﬁciency thresholds have been proposed for most nutrients but have not been validated in commercial orchards (Sanz et al., 1995). Sanz and Montañes (1995) correlated ﬂower nutrient levels with leaf nutrient levels at both 60 and 120 days after bloom and reported signiﬁcant correlations with most nutrients. Similar results were also obtained by correlating the two dates with each other (Montañes and Sanz, 1994). They also found that leaf nutrients at 60 days after bloom tended to correlate better with yield than later dates (Sanz et al., 1992b).

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N, P, Zn K

Mn, Mg, B, CI

Ca

Apr

May

June

July

Aug

Sept

All these relationships still need to be more widely tested before they can be used reliably. There is also the possibility of using dormant shoots or roots as an early predictor of tree nutrient status (Johnson et al., 2006). Researchers have also been evaluating more sophisticated methods of analysing nutrient data. Both the diagnosis and recommendation integrated system (DRIS) and the deviation from optimum percentage (DOP) method have been applied to peach trees with some success. The DRIS approach uses nutrient ratios and products to come up with a series of indices that theoretically stay constant over time (Walworth and Sumner, 1987). The DOP approach simply quantiﬁes the deviation of a given sample from a theoretical optimum (Montañes et al., 1993). Generally, the DOP method has been found to be more useful because its results are unambiguous and it provides some guidelines for how much fertilizer may be needed to correct a deﬁciency (Monge et al., 1995; Sanz, 1999). Before any new protocol or approach can be widely adopted, it will be important to relate it to the various components of yield and fruit quality so there is a physiological basis for its implementation. In summary, good progress has been made with various approaches to sampling nutrients in peach trees. However, none has yet shown consistent enough results to replace the standard method of sampling mature leaves in mid-summer.

Oct

Fig. 13.1. Generalized shapes of concentration curves of mineral nutrients in the leaf during growing season. Curves show trends, not actual levels, for the northern hemisphere.

Nitrogen N is a critical element for plant life since it is found in many important compounds including amino acids, proteins, enzymes, nucleic acids (component of DNA) and chlorophyll. It is the one nutrient that needs to be applied universally to peach orchards throughout the world. Although annual applications may not always be necessary, continued productivity can only be maintained with regular applications of N fertilizers. Peach trees respond very dramatically to N. With heavy fertilization, and under favourable environmental conditions, extreme vegetative growth and a very dense canopy will result (much more than for most other fruit trees). Therefore, care must be taken to prevent both over- and underfertilization. In recent years, many growers have cut back substantially on the amount of N applied to their peach orchards. At one time, recommended rates of 200 kg N/ha or more were common (Daane et al., 1995; Tagliavini et al., 1996). Current recommendations are often around 100 kg N/ha or even less (Tagliavini and Marangoni, 2002). There are at least three explanations for this change in practice. First, growers have become more environmentally aware and are striving to minimize nitrate pollution in groundwater and runoff. Second, the subtle effects of over-fertilization, which have generally been recognized in the past,

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have only recently been clearly documented (Weinbaum et al., 1992; Daane et al., 1995). Finally, improvements in N application efﬁciency have recently been demonstrated and are being adopted by many growers. N deﬁciency is identiﬁed by vegetative growth with light green or yellow leaves. A characteristic red coloration generally develops on shoots and leaf blades (Fig. 13.2/Plate 78). Often this discoloration takes on the form of red or brown spots on the leaves. Fruit produced under low N are smaller but have increased red colour compared with fruit produced with high N (Fig. 13.3/Plate 79) (Ballinger et al., 1966; Johnson and Uriu, 1989). Even though ﬂower density and fruit set are generally not affected by N, overall yields are decreased because of reduced fruit size and less fruiting sites due to shorter shoots. With severe deﬁciency, fruit are more astringent and ﬁbrous and of inferior eating quality (Proebsting et al., 1957; Ballinger et al., 1966). When N levels are too high, the most obvious problems arise from excessive vegetative growth (Lobit et al., 2001). The resultant shading causes less red coloration on the fruit, a delay in maturity and can lead to extensive

Fig. 13.2.

dying out of fruiting shoots on the inside and bottom of the canopy (Ballinger et al., 1966). Furthermore, pruning costs are more and it has been demonstrated that yields and fruit size are not increased compared with more moderate fertilization rates (Daane et al., 1995). Also, many pest and disease problems tend to be exacerbated at high N levels (Daines et al., 1958; Jafar, 1958; Daane et al., 1995). Despite the widespread belief that high N harms fruit quality and storability, there are few scientiﬁc studies to support this claim (Claypool, 1975). Greater water loss due to a thinner cuticle has been reported, but often researchers have found no differences in ﬁrmness, soluble solids content, acidity, bruising potential or internal breakdown (Daane et al., 1995). Because of the increasing concern with N pollution in the environment much attention has been paid to tactics for improving N uptake efﬁciency in peach trees. One approach that has shown promise is the use of foliar urea. Early studies showed potential for many fruit trees such as apple, but it did not appear to work as efﬁciently for peach (Weinberger et al., 1949; Norton and Childers, 1954; Leece and Kenworthy, 1971; Swietlik and Faust, 1984).

Red coloration on the leaves and stems of a nitrogen-deficient peach shoot.

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Fig. 13.3. Smoother finish and more red coloration on fruit from low-nitrogen trees (top row) compared with high-nitrogen trees (bottom row).

Recently, using more precise techniques (such as 15N), it has been demonstrated to be an effective method of supplying N to peach trees, especially when applied in the autumn before leaf senescence (Rosecrance et al., 1998a; Furuya and Umemiya, 2002). Estimates of 60–70% uptake of foliar urea have been reported as long as the application is not made too late in the season (Rosecrance et al., 1998b; Tagliavini et al., 1998). Much of that N is then mobilized out of the leaf and stored in perennial structures of the tree for use by new growth the next spring. Many of the early studies used low concentrations of urea solutions (generally 1% or less) in order to avoid phytotoxicity. Only a small percentage of total N needs could be supplied in this way and may be part of the reason for apparent failure of these studies. Recent approaches have used higher concentrations (5–10%) or multiple sprays in the autumn when leaf phytotoxicity is not a major concern and have shown substantial increases in stored N. Attempts to supply total N needs through foliar urea led to a decrease in fruit size, but the approach of replacing half of soil-applied N with autumn foliar urea showed no loss of productivity or fruit quality (Johnson et al., 2001). Therefore,

this is one strategy available to growers for reducing the potential of environmental pollution by substantially reducing soil-applied fertilizers, without risking a loss of production. Furthermore, it has been demonstrated that the urea spray can be combined with other materials commonly applied in the autumn such as Zn, thus making it a practical strategy as well (Johnson and Andris, 2001). Some recommendations now include autumnal foliar urea sprays as a supplement to the standard soil applications (Rombola et al., 1995; Tagliavini and Marangoni, 2002). Other approaches to improving N utilization efﬁciency involve more precise timing, placement and amounts of soil-applied N fertilizers. Applying fertilizers through a lowvolume irrigation system (fertigation) has generally demonstrated that considerably less fertilizer (sometimes about half) can be used compared with broadcast fertilization and still have the same growth and leaf N response (Smith et al., 1979; Neilsen et al., 1999). Even when using broadcast fertilization, splitting the applications into several smaller amounts increases efﬁciency. N uptake by mature peach orchards has been estimated to be between 0.5 and 1.0 kg N/ha/day

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during the period from rapid shoot growth until early autumn (Rufat and DeJong, 2001). Furthermore, this fairly constant uptake rate appears to be similar for early- and latematuring varieties (Policarpo et al., 2002). The uptake rate is much lower early in the spring and late in the autumn, especially after leaves begin to senesce. This information could be used as a guide to help meter out small amounts of fertilizer based on tree demand throughout the season. Tagliavini et al. (1996) developed a fertilization strategy based on this concept combined with soil sampling at three different periods to estimate N available to trees. The method was used in 15 different orchards and the resulting fertilizer usage was 50% that of other orchards in the area with no noticeable reduction in yield or growth. In the future, these types of approaches will be increasingly important as more environmentally sound practices will be required. Severe deﬁciency is generally found at mid-summer leaf N concentrations below 2.2 to 2.4% (Table 13.1) (Leece et al., 1971; Johnson and Uriu, 1989; Weir and Cresswell, 1993; Robinson et al., 1997). In the past, adequate or normal levels have usually been set at 3.0 to 3.5% (Leece et al., 1971; Weir and Cresswell, 1993; Robinson et al., 1997). However, with increased concerns over environmental contamination, and with recent studies documenting the negative aspects of high N, it is advisable in most situations to keep leaf N concentrations slightly below 3.0% (Johnson and Uriu, 1989). Phosphorus P is the key factor in compounds that store, transfer and utilize energy in plants. It is also found in nucleic acids, the building blocks for DNA. There have only been a few reports of P deﬁciency in ﬁeld-grown peach trees around the world (Lilleland, 1932; Veerhoff, 1948) and fertilization with this nutrient has often been ineffective (Proebsting and Kinman, 1933; Ballinger et al., 1966). Even in soils where ﬁeld crops have dramatically responded to P fertilization, peach trees (and other fruit and nut trees) have shown no response (Lilleland et al., 1942). Nevertheless, there are soils very low in P where peach trees have shown a

growth response to added P (Lilleland and Brown, 1940). In addition, there are a few documented situations of peach trees responding to P even when soil or tree levels have indicated adequate amounts (Taylor, 1975; Neilsen et al., 1990). Generally the response has been one of increased growth, and untreated trees in these situations have shown no leaf deﬁciency symptoms. Thus, although many consider it unnecessary, some local recommendations call for P fertilization as a standard practice, especially at planting (Van Niekerk and Pienaar, 1967; Sánchez, 1999; Gil Salaya, 2000). P deﬁciency has been induced in young trees growing in sand culture. One of the ﬁrst symptoms is a reduction in growth with no abnormal leaf symptoms (Weinberger and Cullinan, 1936; Lilleland and Brown, 1940). With more severe deﬁciency, leaves develop a dark purplish-green colour (Fig. 13.4/Plate 80) and are narrow, leathery and ﬂat (Cullinan and Batjer, 1943). Fruit ripen earlier and have a greenish ground colour with poor eating quality (Shear and Faust, 1980). A mid-summer leaf P level below 0.09 to 0.11% is generally considered deﬁcient (Table 13.1) (Lilleland and Brown, 1940; Leece et al., 1971; Shear and Faust, 1980; Robinson et al., 1997). We have found a reduction in growth below 0.12% P in bearing peach trees growing in sand culture (R.S. Johnson, unpublished results). Healthy trees are usually between 0.14 and 0.25% P (Robinson et al., 1997), with some of the most productive orchards often in the lower part of this range (Lilleland and Brown, 1942). Problems of excess P can be encountered at leaf levels above about 0.40% (Leece et al., 1971; Robinson et al., 1997). High P can exacerbate a Zn deﬁciency situation (Ballinger et al., 1966). When needed, any P-containing fertilizer is effective at raising the P level in trees. Taylor and Issell (1976) found soil applications to be more effective than foliar applications at improving the P status of peaches. Potassium K is very mobile within plants and can move readily in and out of cells. Because of this characteristic, K plays an important role in maintaining cell turgor and in the opening

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Fig. 13.4. Purple coloration and leathery texture of a phosphorusdeficient peach leaf.

and closing of stomata. It is also the activator of many different enzyme systems. At one time, K deﬁciency was widely reported throughout many peach-growing areas of the world (Scott, 1939; Boynton, 1944; Lilleland et al., 1962; Ballinger et al., 1966). Although it can still be a problem in some stone fruit orchards (such as prunes in California), it is generally not a major concern in modern peach orchards (Johnson and Uriu, 1989; Weir and Cresswell, 1993). The deﬁciency can be easily corrected with K-containing fertilizers, which are often recommended as a standard practice (Tagliavini and Marangoni, 2002). The amount of K in peach fruits is relatively large so K removal from the orchard can be substantial with highly productive trees. The most characteristic symptom of K deﬁciency is a pale green leaf colour and leaf rolling that appears in mid-summer (Fig. 13.5/Plate 81) (Dunbar and Anthony, 1937; Lilleland et al., 1962; Weir and Cresswell, 1993). Eventually necrosis can occur at the

leaf margins, producing a ‘scorched’ appearance. With severe deﬁciency, shoot growth is inhibited, leading to a small, unthrifty-looking tree. The shoots are thin and reddish and few ﬂower buds are initiated (Dunbar and Anthony, 1937). The fruit produced are smaller (Lilleland et al., 1962), advanced in maturity and have poor colour. There is some controversy over the effect of K on fruit quality. Several studies have shown a positive correlation between leaf K and fruit acidity (Kwong and Fisher, 1962; Cummings and Reeves, 1971) or between leaf K and fruit colour (Cummings, 1965), but no relationship with fruit soluble solids content. Others have shown no effect of K on ﬁrmness, keeping quality or acidity (Weinberger, 1929). Tagliavini and Marangoni (2002) have suggested that peach trees might beneﬁt from more efﬁcient K fertilization using fertigation. They provide evidence that fruit size, per cent soluble solids content and colour can all be improved even when the trees are not deﬁcient in K (1.35–1.6% K).

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Pale colour and leaf rolling caused by potassium deficiency in peach leaves.

A mid-summer leaf K value below 0.75 to 1.0% (Table 13.1) indicates a deﬁnite deﬁciency and K fertilization will generally provide a positive response (Boynton, 1944; Ballinger et al., 1966; Shear and Faust, 1980). Values between 1.0 and 2.0% are considered low or marginal (Leece et al., 1971; Weir and Cresswell, 1993; Robinson et al., 1997) and increasing the level may be beneﬁcial in some situations. Most normal, productive peach trees are between 2.0 and 3.0% K. Correction of K deﬁciency is accomplished with soil applications of various formulations of K-containing fertilizers. Generally the recommendation is to make a single application every 3 to 4 years (Weir and Cresswell, 1993). Fertigation has been shown to be a more efﬁcient method of supplying K to trees (Johnson and Uriu, 1989). Care should be taken to prevent over-application of K to peach trees. Although K toxicity has not been reported, an excess can easily lead to cation imbalance in the soil and cause

deﬁciencies of other nutrients such as Mg (Weir and Cresswell, 1993). Calcium Ca is a major constituent of cell walls and membranes and plays a role in their proper functioning. It is also involved with pollen germination, cell division, environmental signalling and protecting cells from toxins. Ca deﬁciency is generally not a problem with peach trees. Even though dozens of Ca-related disorders have been identiﬁed in other horticultural species (Shear, 1975), none have been reported in the scientiﬁc literature for peaches. Likewise, Ca deﬁciency in ﬁeld-grown trees has not been documented (Shear and Faust, 1980; Johnson and Uriu, 1989; Weir and Cresswell, 1993). Symptoms of Ca deﬁciency have been induced in hydroponically grown peach

Nutrient and Water Requirements

seedlings (Edwards and Horton, 1979) and in small fruiting trees grown in sand culture (Abdalla and Childers, 1973). One of the ﬁrst symptoms to appear is a reduction in root growth. Subsequent roots that develop are often swollen and stubby. Early leaf symptoms include marginal leaf chlorosis, which develops into necrosis and eventually leads to defoliation. Some shoot tips die back. Fruits on Ca-deﬁcient trees are smaller, lower in sugar, ﬁrmer and have poorer colour and ﬂavour. Deﬁciency thresholds for peach leaves have generally been set at 1.0% (Table 13.1) (Shear and Faust, 1980; Weir and Cresswell, 1993; Robinson et al., 1997) even though this has never been conﬁrmed in the ﬁeld. Abdalla and Childers (1973) found optimum fruit quality in sand culture trees at leaf values greater than 2.0%. Because Ca is found in cell walls, it has been associated with cell rigidity and fruit ﬁrmness. Addition of Ca has successfully delayed softening of various fruits (Pooviah et al., 1988) and reduced decay (Conway, 1982). Results with peaches have not been very consistent. There have been several reports that preharvest applications of Ca sprays have reduced fruit rot, maintained ﬁrmness and improved ﬂavour, aroma and appearance of peaches (Bhullar et al., 1981; Robson et al., 1989; Adaskaveg et al., 1992; Biggs et al., 1997). Others, however, have measured no beneﬁt from as many as 10 to 12 sprays of Ca throughout the season (Conway et al., 1987; Crisosto et al., 2000). Conway et al. (1987) were able to dramatically increase (two- to fourfold) the Ca content of fruit using pressure inﬁltration, which reduced decay by 40 to 60%. However, the treatment caused injury to the surface of the fruit. Likewise, Wills and Mahendra (1989) used a similar procedure and increased fruit storage life from 11.1 to 14.4 days, but induced the same skin damage. Therefore the procedure is unlikely to have commercial value. Magnesium Mg is a part of the chlorophyll molecule and also acts as an activator of many different enzymes. In most peach-growing areas of the world Mg deﬁciency is not considered a major

311

problem. The disorder can occur in some locations with very sandy acidic soils, especially if there is extensive leaching by high rainfall or excessive irrigation (Beyers and Terblanche, 1971d; Weir and Cresswell, 1993). Also, Mg deﬁciency can be induced by heavy applications of K- and Ca-containing fertilizers. These nutrients compete with Mg for cation exchange sites in the soil. In fruit-growing areas where Mg deﬁciency occurs, peach is considered to be less affected than other fruit trees and vines (Beyers and Terblanche, 1971d). Mg deﬁciency symptoms start as a pale green discoloration at the tips and margins of older leaves (Fig. 13.6/Plate 82). The affected area develops into a bright yellow chlorosis and eventually some marginal necrosis may occur. Reddish brown areas may develop within the chlorotic areas. A triangular area at the base of the leaf remains green (Beyers and Terblanche, 1971d; Weir and Cresswell, 1993). Additional symptoms have been described as interveinal necrotic spotting which starts as areas on the leaves that appear to be water-soaked (McClung, 1953). Some defoliation can occur, starting with basal leaves. Unless the disorder becomes severe, normal extension growth continues and tree productivity is not reduced. With severe deﬁciency shoot growth stops, ﬂower bud formation is inhibited and yield is greatly decreased. The fruit that develop are small, have poor colour and often fail to mature. Deﬁciency symptoms develop at midsummer leaf levels below 0.20 to 0.25% Mg (McClung, 1953; Shear and Faust, 1980; Johnson and Uriu, 1989; Weir and Cresswell, 1993; Robinson et al., 1997) although some researchers have set the deﬁciency threshold as low as 0.10% or as high as 0.30% (Table 13.1) (Leece et al., 1971; Sánchez, 1999). If correction is necessary, soil-applied fertilizers or foliar sprays containing Mg have proved effective. Fertilizers applied to the soil may take 2 to 3 years to completely eliminate symptoms, while foliar applications act faster but provide a more temporary response (Beyers and Terblanche, 1971d). Sulfur S is a part of two amino acids and thus is a component of many proteins and enzymes.

312

R.S. Johnson

Fig. 13.6. Discoloration on leaf margins and tip caused by magnesium deficiency.

It can be supplied to peach trees from many sources including fertilizers, soil amendments, pesticides, irrigation water, acid rain and even atmospheric pollutants. Therefore, S deﬁciency has seldom been encountered in peach-growing areas and often is not included in nutrient deﬁciency threshold tables. A few researchers have estimated the optimum range to be about 0.17 to 0.40% (Leece et al., 1971; Robinson et al., 1997). An early study, working with young potted trees, set the deﬁciency threshold at 0.01% (100 ppm) (Benson et al., 1963). Recently, a more thorough experiment determined the threshold to be much higher (Finch et al., 1997). These researchers set the threshold at 0.09% (Table 13.1) with adequacy levels ranging from 0.14 to 0.25%. There have been a few sketchy reports of S deﬁciency in the ﬁeld (Shear and Faust, 1980; Johnson, 1993) and some evidence of positive growth responses to S applications (Powell et al., 1995; Finch et al., 1997). Description of deﬁciency symptoms has mainly come

from potted tree experiments (Benson et al., 1963; Finch et al., 1997). Symptoms of S deﬁciency are very similar to N deﬁciency, with reduced growth and smaller, yellow leaves. The main difference is that S deﬁciency tends to start with young leaves at the tip of the shoot. Also, with severe S deﬁciency, necrosis can develop along leaf margins. Zinc Zn is involved in many functions in plants as it has been found in over 80 proteins. One of its roles is in the formation of the plant hormone auxin. A lack of auxin leads to stunting of leaves and shoots, one of the characteristic symptoms of Zn deﬁciency. The importance of Zn in peach trees was ﬁrst discovered in California with the identiﬁcation of a ‘little leaf’ disorder (Chandler et al., 1931). This disorder was subsequently associated with Zn deﬁciency (Chandler, 1937) and has since

Nutrient and Water Requirements

been found in almost all peach-growing areas on many different soil types around the world (Takkar and Walker, 1993; Swietlik, 1999). It is considered a major problem in Australia (Weir and Cresswell, 1993) and many locations in North America (Bell and Childers, 1954). Peach trees are more sensitive to this disorder than many other crops (Swietlik, 1999). Initial symptoms of the deﬁciency include interveinal chlorosis (Fig. 13.7/Plate 83) which is hard to distinguish from Mn deﬁciency (Bollard, 1953; Woodbridge, 1954). As the disorder becomes more severe, shortened internodes and narrow, pointed leaves at the end of shoots give the characteristic rosetting or little leaf symptoms (Fig. 13.8/Plate 84). Often leaves have a wavy margin. Eventually defoliation of older leaves and twig dieback can occur and fruit production is greatly reduced. What fruit are produced have a tendency to be smaller, more ﬂattened and break down earlier than normal (Chandler, 1937). Zn toxicity is rare but can be induced by over-fertilization with Zn chelates (Wallace et al., 1983). Early surveys of Zn-deﬁcient peach orchards generally found mid-summer leaf

Fig. 13.7.

313

Zn levels to be below 10 to 15 ppm. However, sometimes leaf levels as high as 25 ppm were reported (McClung, 1954) and some healthy orchards without symptoms tested as low as 6 to 10 ppm (Bollard, 1953; McClung, 1954; Woodbridge, 1954). Therefore, there has not been general agreement on establishing a deﬁciency threshold. In reviewing the literature for peach, Shear and Faust (1980) set the threshold at 12 ppm. However, others have often used higher values of 15 ppm (Leece et al., 1971; Johnson and Uriu, 1989; Robinson et al., 1997) or even 20 ppm (Sánchez, 1999; Gil Salaya, 2000) (Table 13.1). One problem with setting the threshold too high is that unnecessary corrective measures might be imposed. Sánchez and Righetti (2002) found many highyielding fruit orchards had Zn levels between 12 and 16 ppm, and concluded that either the generally accepted threshold of 18 to 20 ppm is too high or mid-summer leaf sampling does not adequately reﬂect the Zn status of the tree. Generally, the recommended treatment for Zn deﬁciency is foliar applications of ZnSO4. However, suggested rates and timing vary considerably (Bell and Childers, 1954;

Zinc deficiency symptoms of interveinal chlorosis on a peach leaf.

314

Fig. 13.8.

R.S. Johnson

Rosetting or ‘little leaf’ symptoms of zinc deficiency in peaches.

McClung, 1954; Johnson and Uriu, 1989; Weir and Cresswell, 1993; Neilsen and Neilsen, 1994). Soil applications have also been effective but require much higher rates (Bell and Childers, 1954; Mann et al., 1986). Soil-applied Zn chelates have shown efﬁcacy but are generally considered less cost-effective than ZnSO4 (Arce et al., 1992). Perhaps a better understanding of mycorrhizal association with peach roots could help improve Zn uptake efﬁciency. Gilmore (1971) showed that some cultures of mycorrhizae were more effective than others at alleviating Zn deﬁciency symptoms in peach seedlings. In the past, it has been widely accepted that Zn is not very mobile within the plant and that foliar treatments may never correct a root deﬁciency (Swietlik, 2002a). However, recent research has demonstrated the movement of Zn into roots of peach trees from a foliar application in autumn (Sánchez et al., 2006). Clearly, more research is needed and should focus on critical periods for Zn supply in the tree (Swietlik, 2002b) and the behaviour of Zn in the soil and plant, so that effective treatments can be made with a minimal impact on the environment.

Boron B is an essential nutrient for plant growth and development, but its exact physiological role is still poorly understood. When deﬁcient it can affect many plant processes including pollen tube growth, sugar transport, meristem growth, cell wall synthesis, hormone production and membrane integrity. B deﬁciency is widespread around the world, having been reported in at least 132 crops from over 80 countries (Shorrocks, 1997), and is often considered to be a major problem. However, peach is much less sensitive than most other plants and only a few cases have been documented in the ﬁeld (McLarty and Woodbridge, 1950; McClung and Clayton, 1956; Ballinger et al., 1966). More recent research indicates that B is very mobile in sorbitol-rich plants such as peach and apple (Brown and Hu, 1996). An easily translocated compound is formed from B and sorbitol (and other sugar alcohols) that accounts for this mobility (Hu et al., 1997). This provides at least part of the explanation for why peach is less sensitive than many other plants to B deﬁciency. However, peach is generally considered to be

Nutrient and Water Requirements

even less sensitive than many other sorbitolproducing fruit trees such as apple and pear (Ballinger et al., 1966; Weir and Cresswell, 1993), so additional factors may be involved. The high mobility of B in peach also makes it more sensitive to toxicity than many other crops (Gupta et al., 1985). Although there are few reports of B toxicity in the ﬁeld for peach orchards, care needs to be taken to prevent it from happening when applying B fertilizers, as there appears to be a rather narrow range between deﬁciency and toxicity. The reports of B toxicity in the literature have been associated with excessive soil applications (Williams and Veerhoff, 1948; McLarty and Woodbridge, 1950; Cibes et al., 1955; Dye et al., 1984). Furthermore, once B toxicity has been induced, it can take several years to alleviate the problem (Hernandez and Childers, 1956). Even though B can be leached from the soil fairly easily, it appears that this nutrient can be stored in relatively large amounts in peach trees (Dye et al., 1984), thus carrying on the problem from one year to the next. The ﬁrst symptom of B deﬁciency is the dying back of shoots and twigs in the spring (McLarty and Woodbridge, 1950; Ballinger et al., 1966; Kamali and Childers, 1970). These shoots apparently grew normally the year before. In fact, there appears to be no warning of the disorder beforehand such as gumming or necrosis. The ﬁrst sign of a problem occurs when buds on the shoots fail to break in the spring. These buds slowly turn brown and die and the stem tissue may continue to look normal for another couple of weeks before drying up. This dieback can occur over a large portion or even the whole tree. Vegetative buds that do survive often produce normal growth, although the ﬁrst leaves to develop may be narrow and small, with edges rolled inward. McClung and Clayton (1956) described somewhat different symptoms. They did not see shoot dieback initially. Instead, the vegetative buds grew but produced highly distorted shoots with small leaves and shortened internodes. The leaves were often asymmetrical with irregular and chlorotic margins. In extreme cases these shoots would die gradually, leading to dieback by early summer. In less severe cases the shoots eventually produced normal growth by mid-summer.

315

Fruit set is often greatly reduced by B deﬁciency (McClung and Clayton, 1956) as is generally seen for all fruit trees (Shear and Faust, 1980). The fruit that do develop can appear normal on the outside, but necrotic areas may occur around the pit and the fruit may ripen early. Fruit set and fruit disorders often occur without any leaf symptoms, indicating the particular sensitivity of reproductive processes to B deﬁciency (Shear and Faust, 1980). B toxicity has symptoms that can easily be confused with B deﬁciency (Dye et al., 1984; Neilsen et al., 1985). As with the deﬁciency, the ﬁrst sign of toxicity is shoot dieback in the spring or early summer (McLarty and Woodbridge, 1950; Cibes et al., 1955; Dye et al., 1984). Leaves produced can be small and crinkled. Sometimes they have small necrotic areas near the midrib which eventually drop out, leaving a perforated appearance. In sand culture, leaves became wrinkled and necrotic along the entire margin (Haas, 1929). Other symptoms include cankers along the shoots, profuse gumming and rough and cracked bark. Often fruit that develop are malformed, showing lopsided growth, cracking and prominent sutures. Using mid-summer mature leaf samples to establish thresholds for B deﬁciency and toxicity has not been very straightforward. First, there is not always a good correlation between symptom severity and leaf B content (McClung and Clayton, 1956). Second, the effects of B deﬁciency on fruit set and fruit disorders are sometimes evident without any apparent leaf symptoms (McClung and Clayton, 1956). Williams and Veerhoff (1948) found improvements in fruit size by applying B to peach trees showing no deﬁciency symptoms. Thus, it may be difﬁcult to determine the effect of B on more subtle processes in the plant. Nevertheless, researchers have generally established deﬁciency thresholds at about 15 to 20 ppm (McLarty and Woodbridge, 1950; Ballinger et al., 1966; Leece et al., 1971; Shear and Faust, 1980; Weir and Cresswell, 1993; Robinson et al., 1997; Gil Salaya, 2000), with some as high as 30 ppm (Table 13.1) (Sánchez, 1999). For toxicity, the threshold is generally set to about 80 to 100 ppm (McLarty and Woodbridge, 1950; Leece et al., 1971; Robinson et al., 1997), but others have suggested damage may occur

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R.S. Johnson

as low as 50 ppm (Neilsen et al., 1985). Improvements in the sampling procedure could be very helpful, since there appears to be such a narrow range of B for optimum performance. Dye et al. (1984) found spring leaves to be more diagnostic of B toxicity than midsummer leaves. For most ﬁeld crops, newly emerged leaves are generally used for B determination (Bell et al., 2002). Alternatively, fruit tissue could be useful for diagnosis since B accumulates there in B-mobile plants such as peach (Hernandez and Childers, 1956; Dye et al., 1984; Shu et al., 1994). This approach has proved effective in another Prunus species, almond (Nyomora et al., 1997). Correction of B deﬁciency is best achieved by foliar applications. Soil applications can also be effective, but many factors such as soil pH and texture can affect B availability, making this method less predictable. Furthermore, due to the extreme sensitivity of peach to B toxicity, damage has been reported even at recommended rates of soil application. Recommended rates vary from 10 to 30 kg/ha, but often only every third to ﬁfth year. Recommended foliar rates range from 0.5 to 2 kg/ha. Although studies with labelled B have shown leaf and fruit uptake to be less than 0.5% (Shu et al., 1993, 1994, 1997), this rate appears to be enough to correct B deﬁciency. For correcting B toxicity it is necessary to leach excess B from the soil. This may take three times more water than is needed for other salts because B can be adsorbed by soil particles (Gupta et al., 1985). Iron Fe in plant cells can easily be transformed from one oxidation state to another, giving up (or capturing) energy in the process. Thus, its main role is in transferring energy during the processes of photosynthesis and respiration. It is very rare for Fe to be deﬁcient in orchard soils. However, under calcareous soil conditions with high pH (7.5 to 8.5), Fe can become immobilized within the tree, leading to a condition called lime-induced or iron chlorosis. Peach trees are particularly susceptible to this type of Fe deﬁciency and it is a major problem in many peach-growing areas around the world

(Ballinger et al., 1966; Razeto, 1982; Byrne, 1988). In some locations it affects more than half the orchards and is considered the main nutritional disorder for fruit trees (Sanz et al., 1992a; Tagliavini et al., 2000). Peach trees are considered more susceptible than most other fruit species to Fe deﬁciency (Razeto, 1982). The characteristic symptoms of iron chlorosis are a ‘netting’ appearance on the leaves, where the veins remain green but all areas in between turn yellow (Fig. 13.9/Plate 85) (Johnson and Uriu, 1989; Weir and Cresswell, 1993). It starts with young leaves but can eventually spread to the whole tree. Severely affected leaves become bleached as they lose chlorophyll. Eventually these leaves develop burnt spots and extensive shoot dieback can occur. With severe deﬁciency, shoot growth, ﬂowering, fruit production and fruit size are greatly decreased (Beyers and Terblanche, 1971c; Sanz et al., 1997b). This disorder does not appear to be a straightforward Fe deﬁciency as the total Fe level in mid-summer leaves does not correlate well with deﬁciency symptoms (Shear and Faust, 1980; Abadia et al., 2000). Apparently, various factors such as pH and bicarbonate levels can cause the Fe in the plant to become unavailable (Köseoglu, 1995; Morales et al., 1998). Attempts to correlate available Fe with symptoms have shown promise (Abadia et al., 1985) but have not always been successful (Rashid et al., 1990). Therefore, it has been a challenge to develop a diagnostic tool for quantifying the problem. There has been some limited success with using leaf Fe values from leaves collected in the spring rather than mid-summer. Recently, ﬂower analysis has been proposed and good correlations have been shown between ﬂower Fe values and mid-summer symptoms (Sanz et al., 1997a; Abadia et al., 2000). However, absolute levels vary considerably from year to year, so recommendations cannot yet be made. Others have had less success with this approach (Toselli et al., 2000). Perhaps other nutrients are involved in the disorder and a multiple regression formula will need to be developed. Igartua et al. (2000) have proposed using the K:Zn ratio in addition to ﬂower Fe for diagnosing iron chlorosis. Correction of iron chlorosis has also proved to be challenging. Foliar applications

Nutrient and Water Requirements

317

Fig. 13.9. ‘Netting’ symptom of iron chlorosis on a peach leaf; veins remain green while the rest of the leaf has turned yellow.

with various materials have given variable results and, when effective, provide only temporary correction of symptoms (Razeto, 1982; Reed et al., 1988; Vizzotto and Costa, 1995). Trunk injection treatments have tended to work a little better, but are much more labourintensive and still do not correct the problem permanently (Ballinger et al., 1966; Yoshikawa, 1988). Soil application of chelated materials such as Fe EDDHA (ethylenediaminedi(o-hydroxyphenyl)acetic acid) has been one of the more effective treatments, but it is very expensive (Beyers and Terblanche, 1971c; Reed et al., 1988; Sanz et al., 1992a). Apparently, lower rates can be used if application is made through a low-volume irrigation system (Razeto, 1982). Ultimately, the best solution is to lower soil pH with acidifying amendments. This can be prohibitively expensive for the whole soil mass, but also works if only a small portion of the soil is acidiﬁed (Razeto, 1982; Johnson and Uriu, 1989). Selection of rootstock can make a big difference as some stocks are more resistant to iron chlorosis (Kester and Asay, 1986; Stylinanides et al., 1989). ‘GF 677’ and

other peach–almond hybrids have performed well on sites prone to this disorder (Syrgiannidis, 1985; Byrne, 1988).

Manganese Mn plays an important role in photosynthesis and also activates a number of enzyme systems. Mn deﬁciency has been documented in most peach-growing areas around the world. Generally, the symptoms observed have been quite minor, and are not considered a serious problem since yield and vegetative growth are not noticeably affected (Epstein and Lilleland, 1942; Boynton et al., 1951; Woodbridge and McLarty, 1951; Beyers and Terblanche, 1971a; Rogers et al., 1974; Johnson and Uriu, 1989; Weir and Cresswell, 1993; Gil Salaya, 2000). Severe deﬁciency has also been reported (Beyers and Terblanche, 1971a), but is rare. Symptoms start as small, irregularly shaped, light green spots in the interveinal and marginal areas of older leaves. Eventually these

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R.S. Johnson

spots grow together while the area along the veins and midribs remains green, giving the characteristic ‘herringbone’ pattern of Mn deﬁciency (Fig. 13.10/Plate 86). Generally fruit size, leaf size and shoot growth are not affected. Severe symptoms include dieback of terminals and premature defoliation with a marked reduction in ﬂowering and fruit set. Almost all nutrient deﬁciency tables indicate 20 ppm in mid-summer leaves to be the threshold for peaches (Table 13.1) (Leece et al., 1971; Shear and Faust, 1980; Johnson and Uriu, 1989; Weir and Cresswell, 1993; Robinson et al., 1997). Most researchers have found that a foliar spray of MnSO4 in the spring is the most effective method of alleviating symptoms (Boynton et al., 1951; Woodbridge and McLarty, 1951; Beyers and Terblanche, 1971a; Gil Salaya, 2000).

other fruit trees (Anderssen, 1932), this nutrient never seems to create major problems in modern peach orchards. Perhaps this is due to the widespread use of Cu as an effective and inexpensive broad-spectrum pesticide (Epstein and Bassein, 2001). Where Cu deﬁciency has been reported, it was more of a problem on other fruit trees such as apple, pear and citrus (Beyers and Terblanche, 1971b). Deﬁciency symptoms start with a pale green to bright yellow discoloration between the veins of leaves in the spring. Eventually growing shoot tips wither and die back, and multiple bud development below leads to abnormal branching and a bushy appearance. Extensive dieback of branches can occur. Affected trees often have a light or no crop. The deﬁciency threshold has generally been set at 3 ppm Cu in mid-summer leaves (Table 13.1) (Shear and Faust, 1980; Weir and Cresswell, 1993; Robinson et al., 1997).

Copper The main role of Cu in plants is energy transfer during photosynthesis, but it is also involved in several other plant processes. Despite a very old report of severe Cu deﬁciency in peach and

Fig. 13.10. green.

13.3 Peach Water Requirements Peach trees tend to have high water requirements compared with other fruit trees. Most experts

Manganese deficiency symptoms on a peach leaf; bands along the main veins remain

Nutrient and Water Requirements

agree that China is the location where peaches evolved (Faust and Timon, 1995). The areas of China with heavy concentrations of native trees are often quite humid. Thus, it seems likely that peaches evolved under conditions of abundant water and are therefore not very water-conservative or resistant to water stress (Proebsting and Middleton, 1980). From a practical perspective, orchard managers have often found supplemental irrigation to be beneﬁcial, even in locations with high rainfall (Feldstein and Childers, 1965; Reeder et al., 1979; Horton et al., 1981; Layne et al., 1981; Layne and Tan, 1984). One of the biggest beneﬁts has been an increase in fruit size (Daniell, 1982). Other beneﬁts have included more uniform fruit ripening (Feldstein and Childers, 1965) and less winter injury and tree disease (Layne and Tan, 1984). In colder climates, if supplemental irrigation is continued too late in the season so the tree does not harden off as well, ﬂower bud hardiness and tree survival can be reduced (Layne et al., 1994). Supplemental irrigation has also shown substantial beneﬁts with young trees (Black et al., 1977; Daniell, 1982; Renquist, 1987), even when there was no subsequent advantage once the trees matured (Layne et al., 1981, 1994). Generally, the trees grew considerably better and thus came into production much earlier. One study has shown no beneﬁt from irrigation in a humid climate, but the experimental site had a shallow water table (1–2 m) and wetter than normal conditions during the 4 years of the experiment (Layne et al., 1996). Too much water can lead to problems with peach trees as they are considered one of the most sensitive fruit species to waterlogging and anaerobic soil conditions (Andersen et al., 1984; Alvino et al., 1986; Schaffer et al., 1992). Therefore, in heavier soils or those with an impermeable hardpan layer, irrigation management is much more critical. Even in lighter-textured soils, overirrigation can lead to iron chlorosis symptoms (Johnson and Uriu, 1989) and greater probability of diseases such as Phytophthora root rot (Teviotdale et al., 1989). In drier peach-growing areas around the world, irrigation is a standard practice. Much research has been conducted to determine the

319

amount of water to apply to an orchard of peach trees. Orchards lose water through soil evaporation and through transpiration from the leaves. The combination of these two is termed evapotranspiration (ET) and can be affected by several factors. First, weather conditions can have dramatic effects on orchard ET. In a hot, sunny and dry climate, trees will use much more water than under cool, cloudy and humid conditions. The combined effect of weather conditions can be estimated by evaporation from an open body of water (pan evaporation) or by measuring water loss from a reference crop, typically mown grass. The latter is termed ET0 and is derived from weather station parameters. When orchard ET is compared with ET0 (or pan evaporation), a fairly constant ratio is obtained and is called a crop coefﬁcient, Kc. Using various measures of tree water use such as drainage lysimeters or root zone soil moisture depletion, Kc values well over 1.0 (Chalmers et al., 1983; Natali et al., 1985b; Tormann and Heyns, 1988) and even as great as 1.5 (Boland et al., 1993) have been reported for peach trees. Maximum Kc values less than 1.0 have also been measured, but often under less than optimum conditions such as under fertilized or isolated trees (Worthington et al., 1984; Garnier et al., 1986), or under conditions of high rainfall (Strabbioli, 1992a). Using a weighing lysimeter (Phene et al., 1991), which provides the most accurate measure of tree water use, mid-summer Kc values of 1.1 to 1.2 (based on ET0) have been reported for unstressed trees (Ayars et al., 2003; Johnson et al., 2005). Thus, healthy peach orchards use a large amount of water. Supplemental irrigation of more than 1000 mm may be required in hot, dry areas (Ayars et al., 2003). Another factor affecting orchard ET is leaf area development, as it has been shown that tree water use is directly proportional to light interception by the canopy (Johnson et al., 2000; Goodwin et al., 2006) (Fig. 13.11). Since peach trees are pruned hard, it takes several months for the canopy to develop fully. Therefore, the seasonal Kc pattern for peach starts low, about 0.1 to 0.2, early in the season (Ayars et al., 2003). Kc values then increase steadily as leaf area and therefore canopy light interception continue to expand (Fig. 13.12).

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1.6 1990

1991

1992

1993

1994

1.4 1.2

Kc

1.0 0.8 0.6 0.4 0.2 0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Proportion of midday light interception Fig. 13.11. Mature peach tree crop coefficients (Kc) as a function of the proportion of available light intercepted by the canopy at midday. Equation of the regression line is y = 1.59x + 0.082, R2 = 0.86. (Adapted from Ayars et al., 2003 with permission of Springer Science Publishers, The Netherlands.)

1.4 Crop Coefficient (Kc)

1.2 y = 0.0087x – 0.4263 R2 = 0.9835

1.0 0.8 0.6 0.4 0.2 0.0 0

50

100

150

200

250

300

Day of year Fig. 13.12. Seasonal pattern of crop coefficients (Kc) for mature peach trees (average from 2001 to 2003) as calculated from a weighing lysimeter. Each point is a weekly average. Regression line is for data collected from bud break to early July (about day 180). Equation of the regression line is y = 0.0087x – 0.4263, R2 = 0.9835. (Adapted from Johnson et al., 2005 with permission from California Agriculture, Oakland, California, copyright 2005 U.C. Regents.)

In contrast, values for other deciduous trees that are not pruned as heavily have generally been reported to be much higher early in the season (Allen et al., 1998). Some have reported seasonal tree water use to follow the doublesigmoid pattern of fruit growth (Chalmers et al., 1983; Klein, 1983; Boland et al., 1993) but this is not supported by weighing lysimeter

data. Both a late-season cultivar (Ayars et al., 2003) and an early-season cultivar (Johnson et al., 2005) had similar seasonal patterns of water use that reﬂected canopy growth and not fruit growth. A couple of approaches to modelling peach tree water use have been proposed. One is based on light interception of the canopy as it develops (Johnson et al., 2002, 2004).

Nutrient and Water Requirements

The other approach is based on the stages of fruit growth of various varieties (Klein, 1993). Irrigation needs for young trees depend strongly on the irrigation delivery system as soil evaporation can become a major component of ET. The transpiration component is proportional to canopy light interception (Fig. 13.13), similar to mature trees (see Fig. 13.11). However, the soil evaporation component depends on how much of the soil surface is wetted, and can be very large under ﬂood or furrow irrigation systems. A drip system can save substantial amounts of applied water on young trees (Fereres et al., 1982). Generally, with efﬁcient irrigation systems (drip or microsprinklers), researchers have found young tree ET to be about 50% greater than the value for transpiration alone shown in Fig. 13.13 (Black et al., 1977; Fereres et al., 1982; Renquist, 1987). In other words, a canopy shading 20% of the orchard ﬂoor would have a Kc value of about 0.45 (0.30 + 50% = 0.45).

Water stress Water stress can have many negative effects on the growth and productivity of peach trees. With severe stress, photosynthesis and vegetative growth are greatly reduced, leading to diminished fruit production. Xylem cavitation becomes increasingly severe as water stress progresses. Ameglio et al. (1998) reported 100% embolism at a xylem water

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potential of −3.0 MPa. In arid regions without supplemental irrigation, peach trees tend to die faster than other fruit trees unless they are pruned severely to reduce leaf area and crop load (Proebsting and Middleton, 1980). Heavy crop loads have been shown to lead to greater water stress (Berman and DeJong, 1996; Naor et al., 1999) due to higher stomatal opening in fruited versus non-fruited trees (DeJong, 1986). Fruit quality is also affected by water stress as fruit size is reduced and abnormal ﬂower buds can develop, leading to such disorders as fruit doubles and deep sutures (Patten et al., 1989; Handley and Johnson, 2000; Naor et al., 2005). Even normal-appearing fruit are often astringent and lacking in red coloration under severe water stress (Proebsting and Middleton, 1980). Severe postharvest water stress can reduce yield in the subsequent season (Naor et al., 2005). If a more moderate water stress condition is imposed and carefully managed, some beneﬁcial results can be achieved. Since peach trees are inherently very vigorous, heavy pruning is required every year. Therefore, moderate reductions in vegetative growth induced by water stress would generally be considered beneﬁcial since they could reduce pruning and improve light penetration though the canopy. Furthermore, ﬂowering and fruit set have been reported to increase (Chalmers et al., 1985; Larson et al., 1988) or remain unchanged (Besset et al., 2001) with moderate water stress, so continued productivity would not be a problem. As stomatal conductance decreases

0.6 0.5

Kcb

0.4 0.3 0.2 0.1 0 0

5

10 15 20 25 Per cent light interception

30

35

Fig. 13.13. Crop coefficients of transpiration alone (no soil evaporation) or basal crop coefficients (Kcb) of a 1-year-old peach tree as predicted by per cent light interception of the canopy at solar noon. R2 of the regression line is 0.987. (Adapted from Johnson et al., 2002 with permission from the International Society of Horticultural Science, Belgium.)

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with stress, some have reported no reduction in carbon assimilation, thus leading to greater water use efﬁciency (Cheng et al., 1996). Theoretically, under moderate stress, irrigation water savings could be achieved without reducing productivity. However, fruit fresh weight is very sensitive to water stress, so it can be reduced while fruit dry weight is not affected (Girona et al., 2004). With a light or moderate crop load, Berman and DeJong (1996) found water stress reduced fruit fresh weight but not dry weight. With a heavy crop load, both were reduced. An increase in fruit sugar concentration has generally been associated with moderately stressed peach trees (Gelly et al., 2004). Often this is simply a matter of concentrating the sugars as fruit water content decreases. Thus, increased sugars come at the expense of decreased fruit fresh weight (Crisosto et al., 1994; Besset et al., 2001). However, it has been reported that greater sugar concentration can occur without a loss of fruit size (Kobashi et al., 1997). Kobashi et al. (2000) documented an increase in sorbitol, sucrose and total sugars with moderate but not severe stress. Increased fruit growth could occur under these conditions due to lower osmotic and therefore greater turgor potential. This appears to be the basis for a few reports of improved fruit size with imposed stress, even though most studies have shown decreased fruit size with any level of water stress. Strategies for imposing water stress The potential beneﬁts that can be achieved with moderate water stress have led to a couple of strategies for imposing water stress in commercial peach orchards. One approach is to focus on the period after harvest of earlymaturing varieties. With no fruit on the tree, the strategy is to save water while minimizing problems with productivity and fruit quality in the following season and to prevent permanent tree damage. A second approach is to impose stress during the growth of the fruit in such a way that no decrease (or even an increase) in fruit size occurs. This strategy has proved difﬁcult to implement and may only be successful under certain conditions. Imposing water stress after harvest of an early June-maturing peach cultivar has been

achieved for four successive years in California (Johnson et al., 1992). The orchard was on a deep sandy loam soil under ﬂood irrigation. By the end of the season, measures of water status (stomatal conductance, leaf water potential, trunk growth and diurnal shrinkage) indicated substantial stress, but premature defoliation was minimal and subsequent yields were not reduced (Larson et al., 1988). Pruning weights were only slightly reduced since the majority of vegetative growth occurs early in the season. The biggest drawback to this practice was a substantial increase in fruit doubles the following year in the most severe water-stressed treatment. By relieving latesummer water stress during the carpel differentiation period, fruit doubles and the associated defect of deep sutures were reduced to levels of the well-watered control (Handley and Johnson, 2000; Naor et al., 2005). Thus, signiﬁcant irrigation water savings can be achieved without sacriﬁcing yield, fruit quality or tree health. The level of stress can become severe enough to cause defoliation and reduce yield in the following year (Naor et al., 2005). A threshold of −2.0 MPa for midday stem water potential in late summer (August in Israel and California) has been proposed to minimize productivity and fruit quality problems (Naor et al., 2005; Naor, 2006). The second approach to imposing water stress has generally been referred to in the literature as regulated deﬁcit irrigation (RDI). It involves deﬁcit irrigation during the slow growth phase (or stage II) of a late-season peach and also corresponds to the period of rapid shoot growth. During the ﬁnal, rapid stage of fruit growth (stage III), full irrigation (or greater) is applied through harvest. The theory, which is not well substantiated, states that the deﬁcit irrigation will inhibit vegetative growth to a greater extent than fruit growth. Perhaps osmotic adjustment in the fruit will also occur during this time. Then, once the stress is alleviated during stage III, fruit will grow at an increased rate due to less competition from shoots or greater turgor pressure (Behboudian and Mills, 1997). Studies from Australia reported positive results using RDI, with fruit size increased by as much as 30% compared with fully irrigated controls (Chalmers et al., 1981; Mitchell and Chalmers, 1982).

Nutrient and Water Requirements

Other researchers have not had the same success, as fruit size either was reduced by RDI (Girona, 1989) or showed no signiﬁcant increase (Li et al., 1989; Strabbioli, 1992b; Boland et al., 1993). Nevertheless, the water savings of 35 to 40% were substantial in these studies. Thus, RDI offers a viable strategy for water conservation, especially in locations where water is scarce or very expensive. The RDI strategy needs reﬁnement before it can be applied widely. There are still many questions about the details of how to implement this approach under different conditions. For example, the timing of stress imposition and alleviation are not clear. Li et al. (1989) have shown evidence that better results were obtained by starting the stress earlier than stage II. Also, alleviation of stress may need to be started well ahead of stage III in situations where roots are deep or water penetration into the soil is poor. Girona et al. (1993) reported that a period of 3 weeks after resumption of full irrigation was needed before midday leaf water potential recovered completely. Research is also needed on the factors inﬂuencing osmotic adjustment in the fruit. It appears the degree of stress may have some inﬂuence

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(Kobashi et al., 2000). The rate at which stress develops may also be important (Natali et al., 1985a; Olien and Flore, 1990). It has been suggested that the success of RDI by researchers in Australia may be due to the ability to quickly impose and relieve stress under the shallow soil conditions of their experiment (Johnson and Handley, 2000). Most of the RDI studies did not report measurements of plant water status. This makes it difﬁcult to transfer information from one location or soil type to another and expect the same results. For future experiments it will be important to assess the stress level being experienced by the tree. The measurement that has probably shown the best consistency and correlation with tree performance has been midday stem water potential (Garnier and Berger, 1985; McCutchan and Shackel, 1992). Not only is it a good indicator of the stress level in the tree, but it also correlates well with midday stomatal closure (Marsal and Girona, 1997), tree water use (Johnson et al., 2005) and fruit size (Naor et al., 1999, 2001). It is proving to be a useful indicator of stress in a wide range of fruit and nut trees (Shackel et al., 1997; Naor, 2006).

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Chandler, W.H., Hoagland, D.R. and Hibbard, P.L. (1931) Little-leaf or rosette in fruit trees. Proceedings of the American Society for Horticultural Science 28, 556–560. Cheng, L., Cheng, S., Shu, H. and Luo, X. (1996) Effect of mild water stress on CO2 assimilation and water use efficiency of field-grown peach trees. Acta Horticulturae 374, 121–125. Cibes, H.R., Hernandez, E. and Childers, N.F. (1955) Boron toxicity induced in a New Jersey peach orchard. Part I. Proceedings of the American Society for Horticultural Science 66, 13–20. Claypool, L.L. (1975) Plant nutrition and deciduous fruit crop quality. HortScience 10, 45–47. Conway, W.S. (1982) Effect of postharvest calcium treatment on decay of ‘Delicious’ apples. Plant Disease 66, 402–403. Conway, W.S., Greene, G.M. II and Hickey, K.D. (1987) Effects of preharvest and postharvest calcium treatments of peaches on decay caused by Monilinia fructicola. Plant Disease 71, 1084–1086. Crisosto, C.H., Johnson, R.S., Luza, J.G. and Crisosto, G.M. (1994) Irrigation regimes affect fruit soluble solids concentration and rate of water loss of ‘O’Henry’ peaches. HortScience 29, 1169–1171. Crisosto, C.H., Day, K.R., Johnson, R.S. and Garner, D. (2000) Influence of in-season foliar calcium sprays on fruit quality and surface discoloration incidence of peaches and nectarines. Journal of the American Pomological Society 54, 118–122. Cullinan, F.P. and Batjer, L.P. (1943) Nitrogen, phosphorus, and potassium inter-relationships in young peach and apple trees. Soil Science 55, 49–60. Cummings, G.A. (1965) Effect of potassium and magnesium fertilization on the yield, size, maturity, and color of Elberta peaches. Proceedings of the American Society for Horticultural Science 85, 133–140. Cummings, G.A. and Reeves, J. (1971) Factors influencing chemical characteristics of peaches. Journal of the American Society for Horticultural Science 96, 320–322. Daane, K.M., Johnson, R.S., Michailides, T.J., Crisosto, C.H., Dlott, J.W., Ramirez, H.T., Yokota, G.Y. and Morgan, D.P. (1995) Excess nitrogen raises nectarine susceptibility to disease and insects. California Agriculture 49, 13–18. Daines, R.H., Cohoon, D.F., Leone, I. and Brennan, E. (1958) Control of fusicoccum canker of peach by nutrition, defoliation, and protective fungicides. Phytopathology 48, 400–407. Daniell, J.W. (1982) Effect of trickle irrigation on the growth and yield of ‘Loring’ peach trees. Journal of Horticultural Science 57, 393–399. DeJong, T.M. (1986) Fruit effects on photosynthesis in Prunus persica. Physiologia Plantarum 66, 149–153. Dunbar, C.O. and Anthony, R.D. (1937) Two cases of potassium deficiency in peach orchards in South Central Pennsylvania. Proceedings of the American Society for Horticultural Science 35, 320–325. Dye, M.H., Buchanan, L., Dorofaeff, F.D. and Beecroft, F.G. (1984) Boron toxicity in peach and nectarine trees in Otago. New Zealand Journal of Experimental Agriculture 12, 303–313. Edwards, J.H. and Horton, B.D. (1979) Response of peach seedlings to calcium concentration in nutrient solution. Journal of the American Society for Horticultural Science 104, 97–99. Epstein, E. and Lilleland, O. (1942) A preliminary study of the manganese content of the leaves of some deciduous fruit trees. Proceedings of the American Society for Horticultural Science 41, 11–18. Epstein, L. and Bassein, S. (2001) Pesticide applications of copper on perennial crops in California, 1993 to 1998. Journal of Environmental Quality 30, 1844–1847. Faust, M. and Timon, B. (1995) Origin and dissemination of peach. Horticultural Reviews 17, 331–379. Feldstein, J. and Childers, N.F. (1965) Effects of irrigation on peaches in Pennsylvania. Proceedings of the American Society for Horticultural Science 87, 145–153. Fereres, E., Martinich, D.A., Aldrich, T.M., Castel, J.R., Holzapfel, E. and Schulbach, H. (1982) Drip irrigation saves money in young almond orchards. California Agriculture 36, 12–13. Finch, C.R., Byrne, D.H., Lyons, C.G. and Pennington, H.D. (1997) Sulfur nutrition requirements of peach trees. Journal of Plant Nutrition 20, 1711–1721. Furuya, S. and Umemiya, Y. (2002) The influence of chemical forms on foliar-applied nitrogen absorption for peach trees. Acta Horticulturae 594, 97–103. Garnier, E. and Berger, A. (1985) Testing water potential in peach trees as an indicator of water stress. Journal Horticultural Science 60, 47–56. Garnier, E., Berger, A. and Rambal, S. (1986) Water balance and pattern of soil water uptake in a peach orchard. Agricultural Water Management 11, 145–158. Gelly, M., Recasens, I., Girona, J., Mata, M., Arbones, A., Rufat, J. and Marsal, J. (2004) Effects of stage II and postharvest deficit irrigation on peach quality during maturation and after cold storage. Journal of the Science of Food and Agriculture 84, 561–568.

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Kamali, A.R. and Childers, N.F. (1970) Growth and fruiting of peach in sand culture as affected by boron and a fritted form of trace elements. Journal of the American Society for Horticultural Science 95, 652–656. Kester, D.E. and Asay, R.N. (1986) ‘Hansen 2168’ and ‘Hansen 536’: two new Prunus rootstock clones. HortScience 21, 331–332. Klein, I. (1983) Drip irrigation based on soil matric potential conserves water in peach and grape. HortScience 18, 942–944. Klein, I. (1993) Irrigation modeling of peach and nectarine. Acta Horticulturae 349, 225–228. Kobashi, K., Gemma, H. and Iwahori, S. (1997) Effect of water stress on fruit quality and endogenous abscisic acid (ABA) content in peach fruit. Environmental Control Biology 35, 267–274. Kobashi, K., Gemma, H. and Iwahore, S. (2000) Abscisic acid content and sugar metabolism of peaches grown under water stress. Journal of the American Society for Horticultural Science 125, 425–428. Köseoglu, A.T. (1995) Investigations of relationships between iron status of peach leaves and soil properties. Journal of Plant Nutrition 18, 1845–1859. Kwong, S.S. and Fisher, E.G. (1962) Potassium effects on titratable acidity and the soluble nitrogenous compounds of ‘Jerseyland’ peach. Proceedings of the American Society for Horticultural Science 81, 168–171. Larson, K.D., DeJong, T.M. and Johnson, R.S. (1988) Physiological and growth responses of mature peach trees to postharvest water stress. Journal of the American Society for Horticultural Science 113, 296–300. Layne, R.E.C. and Tan, C.S. (1984) Long-term influence of irrigation and tree density on growth, survival and production of peach. Journal of the American Society for Horticultural Science 109, 795–799. Layne, R.E.C., Tan, C.S. and Fulton, J.M. (1981) Effect of irrigation and tree density on peach production. Journal of the American Society for Horticultural Science 106, 151–156. Layne, R.E.C., Tan, C.S. and Hunter, D.M. (1994) Cultivar, ground-cover, and irrigation treatments and their interactions affect long-term performance of peach trees. Journal of the American Society for Horticultural Science 119, 12–19. Layne, R.E.C., Tan, C.S. and Hunter, D.M. (1996) Irrigation and fertilizer application methods affect performance of high-density peach orchards. HortScience 31, 370–375. Leece, D.R. and Kenworthy, A.L. (1971) Effect of potassium nitrate foliar sprays on leaf nitrogen concentration and growth of peach trees. HortScience 6, 171–173. Leece, D.R., Cradock, F.W. and Carter, O.G. (1971) Development of leaf nutrient concentration standards for peach trees in New South Wales. Journal of Horticultural Science 46, 163–175. Li, S.-H., Huguet, J.-G., Schoch, P.G. and Orlando, P. (1989) Response of peach tree growth and cropping to soil water deficit at various phenological stages of fruit development. Journal of Horticultural Science 64, 541–552. Lilleland, O. (1932) Experiments in K and P deficiencies with fruit trees in the field. Proceedings of the American Society for Horticultural Science 29, 272–276. Lilleland, O. and Brown, J.G. (1940) The phosphate nutrition of fruit trees. II. Continued response to phosphate applied at the time of planting. Proceedings of the American Society for Horticultural Science 37, 53–57. Lilleland, O. and Brown, J.G. (1942) The phosphate nutrition of fruit trees. IV. The phosphate content of peach leaves from 130 orchards in California and some factors which may influence it. Proceedings of the American Society for Horticultural Science 41, 1–10. Lilleland, O., Brown, J.G. and Conrad, J. P. (1942) The phosphate nutrition of fruit trees. III. Comparison of fruit tree and field crop responses on a phosphate deficient soil. Proceedings of the American Society for Horticultural Science 40, 1–7. Lilleland, O., Uriu, K., Muroaka, T. and Pearson, J. (1962) The relationship of potassium in the peach leaf to fruit growth and size at harvest. Proceedings of the American Society for Horticultural Science 81, 162–167. Lobit, P., Soing, S., Genard, M. and Habib, R. (2001) Effects of timing of nitrogen fertilization on shoot development in peach (Prunus persica) trees. Tree Physiology 20, 35–42. McClung, A.C. (1953) Magnesium deficiency in North Carolina peach orchards. Proceedings of the American Society for Horticultural Science 62, 123–130. McClung, A.C. (1954) The occurrence and correction of zinc deficiency in North Carolina peach orchards. Proceedings of the American Society for Horticultural Science 64, 75–80. McClung, A.C. and Clayton, C.N. (1956) Boron in relation to foliar and fruiting abnormalities of peach. Plant Disease Reporter 40, 542–548. McCutchan, H. and Shackel, K.A. (1992) Stem-water potential as a sensitive indicator of water stress in prune trees (Prunus domestica L. cv. French). Journal of the American Society for Horticultural Science 117, 607–611.

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McLarty, H.R. and Woodbridge, C.G. (1950) Boron in relation to the culture of the peach tree. Scientific Agriculture 30, 392–395. Mann, M.S., Sidhu, B.S., Chahil, B.S. and Mann, S.S. (1986) Effect of different rates of zinc applied to soil and foliage of peach (Prunus persica Batsch) on zinc concentration in leaves, fruit yield and quality. In: Chadha, T.R., Bhutani, V.P. and Kaul, J.L. (eds) Advances in Research on Temperate Fruits. Dr Y.S. Parmar University of Horticulture and Forestry, Solan, India, pp. 189–191. Marsal, J. and Girona, J. (1997) Relationship between leaf water potential and gas exchange activity at different phenological stages and fruit loads in peach trees. Journal of the American Society for Horticultural Science 122, 415–421. Mitchell, P.D. and Chalmers, D.J. (1982) The effect of reduced water supply on peach tree growth and yields. Journal of the American Society for Horticultural Science 107, 853–856. Monge, E., Montañes, L., Val, J. and Sanz, M. (1995) A comparative study of the DOP and the DRIS methods, for evaluating the nutritional status of peach trees. Acta Horticulturae 383, 191–199. Montañes, L. and Sanz, M. (1994) Prediction of reference values for early leaf analysis for peach trees. Journal of Plant Nutrition 17, 1647–1657. Montañes, L., Herar, L., Abadia, J. and Sanz, M. (1993) Plant analysis interpretation based on a new index: deviation from optimum percentage (DOP). Journal of Plant Nutrition 16, 1289–1308. Morales, F., Grasa, R., Abadia, A. and Abadia, J. (1998) Iron chlorosis paradox in fruit trees. Journal of Plant Nutrition 21, 815–825. Naor, A. (2006) Irrigation scheduling and evaluation of tree water status in deciduous orchards. Horticultural Reviews 32, 111–165. Naor, A., Klein, I., Hupert, H., Grinblat, Y., Peres, M. and Kaufman, A. (1999) Water stress and crop level interactions in relation to nectarine yield, fruit size distribution, and water potentials. Journal of the American Society for Horticultural Science 124, 189–193. Naor, A., Hupert, H., Greenblat, Y., Peres, M., Kaufman, A. and Klein, I. (2001) The response of nectarine fruit size and midday stem water potential to irrigation level in stage III and crop load. Journal of the American Society for Horticultural Science 126, 140–143. Naor, A., Stern, R., Peres, M., Greenblat, Y., Gal, Y. and Flaishman, M. (2005) Timing and severity of postharvest water stress affect following-year productivity and fruit quality of field-grown ‘Snow Queen’ nectarine. Journal of the American Society for Horticultural Science 130, 806–812. Natali, S., Xiloyannis, C. and Pezzarossa, B. (1985a) Relationship between soil water content, leaf water potential and fruit growth during different fruit growing phases of peach trees. Acta Horticulturae 171, 167–180. Natali, S., Xiloyannis, C. and Mugano, M. (1985b) Water consumption in high density peach trees. Acta Horticulturae 173, 413–420. Neilsen, G.H. and Neilsen, D. (1994) Tree fruit zinc nutrition In: Peterson, A.B. and Stevens, R.G. (eds) Tree Fruit Nutrition (Short Course Proceedings). Good Fruit Grower, Washington State Fruit Commission, Yakima, Washington, pp. 85–93. Neilsen, G.H., Yorstan, J., van Lierop, W. and Hoyt, P.B. (1985) Relationships between leaf and soil boron and boron toxicity of peaches in British Columbia. Canadian Journal of Soil Science 65, 213–217. Neilsen, G.H., Hogue, E.J. and Yorston, J. (1990) Response of fruit trees to phosphorus fertilization. Acta Horticulturae 274, 347–359. Neilsen, G.H., Neilsen, D. and Peryea, F. (1999) Response of soil and irrigated fruit trees to fertigation or broadcast application of nitrogen, phosphorus, and potassium. HortTechnology 9, 393–401. Norton, R.A. and Childers, N.F. (1954) Experiments with urea sprays on the peach. Proceedings of the American Society for Horticultural Science 63, 23–31. Nyomora, A.M.S., Brown, P.H. and Freeman, M. (1997) Fall foliar-applied boron increases tissue boron concentration and nut set of almond. Journal of the American Society for Horticultural Science 122, 405–410. Olien, M.E. and Flore, J.A. (1990) Effect of a rapid water stress and a slow water stress on the growth of ‘Redhaven’ peach trees. Fruit Varieties Journal 44, 4–11. Patten, K., Nimr, G. and Neuendorff, E. (1989) Fruit doubling of peaches as affected by water stress. Acta Horticulturae 254, 319–321. Phene, C.J., Hoffman, G.J., Howell, T.A., Clark, D.A., Mead, R.M., Johnson, R.S. and Williams, L.E. (1991) Automated lysimeter for irrigation and drainage control. In: Lysimeters for Evapotranspiration and Environmental Measurements. IR Div/ASCE, Honolulu, Hawaii, pp. 28–36. Policarpo, M., Di Marco, L., Caruso, T., Gioacchini, P. and Tagliavini, M. (2002) Dynamics of nitrogen uptake and partitioning in early and late fruit ripening peach (Prunus persica) tree genotypes under a Mediterranean climate. Plant and Soil 239, 207–214.

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Pooviah, B.W., Glenn, G.M. and Reddy, A.S.N. (1988) Calcium and fruit softening: physiology and biochemistry. Horticultural Reviews 10, 107–152. Powell, J.C., Lyons, C.G. and Haby, V.A. (1995) Effects of copper, zinc, and sulfur application to peach trees on coastal plain soil. Communications in Soil Science and Plant Analysis 26, 1637–1648. Proebsting, E.L. and Kinman, C.F. (1933) Orchard trials of nitrogen and phosphorus. Proceedings of the American Society for Horticultural Science 30, 426–430. Proebsting, E.L. Jr and Middleton, J.E. (1980) The behavior of peach and pear trees under extreme drought stress. Journal of the American Society for Horticultural Science 105, 380–385. Proebsting, E.L. Jr, Carter, G.H., Ingalsbe, D.W. and Neubert, A.M. (1957) Relationship between leaf nitrogen and canning quality of Elberta peaches. Proceedings of the American Society for Horticultural Science 69, 131–140. Rashid, A., Couvillon, G.A. and Jones, J.B. (1990) Assessment of Fe status of peach rootstocks by techniques used to distinguish chlorotic and non-chlorotic leaves. Journal of Plant Nutrition 13, 285–307. Razeto, B. (1982) Treatments for iron chlorosis in peach trees. Journal of Plant Nutrition 5, 917–922. Reed, D.W., Lyons, C.G. Jr and McEachern, G.R. (1988) Field evaluation of inorganic and chelated iron fertilizers as foliar sprays and soil application. Journal of Plant Nutrition 11, 1369–1378. Reeder, B.D., Newman, J.S. and Worthington, J.E. (1979) Effect of trickle irrigation on peach trees. HortScience 14, 36–37. Renquist, R. (1987) Evapotranspiration calculations for young peach trees and growth responses to irrigation amount and frequency. HortScience 22, 221–223. Robinson, J.B., Treeby, M.T. and Stephenson, R.A. (1997) Fruits, vines and nuts. In: Reuter, D.J. and Robinson, J.B. (eds) Plant Analysis, An Interpretation Manual, 2nd edn. CSIRO Publishing, Collingwood, Australia, pp. 349–382. Robson, M.G., Hopfinger, J.A. and Eck, P. (1989) Postharvest sensory evaluation of calcium treated peach fruit. Acta Horticulturae 254, 173–176. Rogers, E., Johnson, G. and Johnson, D. (1974) Iron-induced manganese deficiency in ‘Sungold’ peach and its effects on fruit composition and quality. Journal of the American Society for Horticultural Science 99, 242–244. Rombola, A.D., Quartieri, M., Tagliavini, M., Iannone, C., Zavalloni, C. and Marangoni, B. (1995) Slowrelease N fertilizers and foliar application of urea in the peach orchard. In: Atti del XXII Convegno Peschicolo. Società Orticola Italiana, Cesena, pp. 195–201. Rosecrance, R.C., Johnson, R.S. and Weinbaum, S.A. (1998a) The effect of timing of post-harvest foliar urea sprays on nitrogen absorption and partitioning in peach and nectarine trees. Journal of Horticultural Science & Biotechnology 73, 856–861. Rosecrance, R.C., Johnson, R.S. and Weinbaum, S.A. (1998b) Foliar uptake of urea-N by nectarine leaves: a reassessment. HortScience 33, 158. Rufat, J. and DeJong, T.M. (2001) Estimating seasonal nitrogen dynamics in peach trees in response to nitrogen availability. Tree Physiology 21, 1133–1140. Sánchez, E.E. (1999) Nutricion mineral de frutales de pepita y carozo. Publicacion del Instituto Nacional de Tecnologia Agropecuaria. Estacion Experimental Alto Valle de Rio Negro, Macrorregion Patagonia Norte, Argentina. Sánchez, E.E. and Righetti, T.L. (2002) Misleading zinc deficiency diagnosis in pome fruit and inappropriate use of foliar zinc sprays. Acta Horticulturae 594, 363–368. Sánchez, E.E., Weinbaum, S.A. and Johnson, R.S. (2006) Comparative movement of labeled nitrogen and zinc in 1-year-old peach [Prunus persica (L.) Batsch] trees following late-season foliar application. Journal of Horticultural Science & Biotechnology 81, 839–844. Sanz, M. (1999) Evaluation of interpretation of DRIS system during growing season of the peach tree: comparison with DOP method. Communications in Soil Science and Plant Analysis 30, 1025–1036. Sanz, M. and Montañes, L. (1995) Flower analysis as a new approach to diagnosing the nutritional status of the peach tree. Journal of Plant Nutrition 18, 1667–1675. Sanz, M., Cavero, J. and Abadia, J. (1992a) Iron chlorosis in the Ebro River Basin, Spain. Journal of Plant Nutrition 15, 1971–1981. Sanz, M., Heras, L. and Montañes, L. (1992b) Relationships between yield and leaf nutrient contents in peach trees: early nutritional status diagnosis. Journal of Plant Nutrition 15, 1457–1466. Sanz, M., Val, J., Monge, E. and Montañes, L. (1995) Is it possible to diagnose the nutritional status of peach trees by chemical analysis of their flowers? Acta Horticulturae 383, 159–163. Sanz, M., Belkhodja, R., Toselli, M., Montañes, L., Abadia, A., Tagliavini, M., Marangoni, B. and Abadia, J. (1997a) Floral analysis as a possible tool for the prognosis of iron deficiency in peach. Acta Horticulturae 448, 241–245.

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Sanz, M., Pascual, J. and Machin, J. (1997b) Prognosis and correction of iron chlorosis in peach trees: influence on fruit quality. Journal of Plant Nutrition 20, 1567–1572. Schaffer, B., Andersen, P.C. and Ploetz, R.C. (1992) Responses of fruit crops to flooding. Horticultural Reviews 13, 257–301. Scott, L.E. (1939) Response of peach trees to potassium and phosphorus fertilizers in the Sandhill Area of the Southeast. Proceedings of the American Society for Horticultural Science 36, 56–60. Shackel, K.A., Ahmadi, H., Biasi, W., Buchner, R., Goldhamer, D., Gurusinghe, S., Hasey, J., Kester, D., Krueger, B., Lampinen, B., McGourty, G., Micke, W., Mitcham, E., Olson, B., Pelletrau, K., Philips, H., Ramos, D., Schwankl, L., Sibbett, S., Southwick, S., Stevenson, M., Thorpe, M., Weinbaum, S. and Yeager, J. (1997) Plant water status as an index of irrigation need in deciduous fruit trees. HortTechnology 7, 23–29. Shear, C.B. (1975) Calcium-related disorders of fruits and vegetables. HortScience 10, 361–365. Shear, C.B. and Faust, M. (1980) Nutritional ranges in deciduous tree fruits and nuts. Horticultural Reviews 2, 142–163. Shorrocks, V.M. (1997) The occurrence and correction of boron deficiency. Plant and Soil 193, 121–148. Shu, Z.-H., Oberly, G.H. and Cary, E.E. (1993) Time course study on the mobility and pattern of distribution of foliar-applied boron in peaches. Journal of Plant Nutrition 16, 1661–1673. Shu, Z.-H., Oberly, G.H., Cary, E.E. and Rutzke, M. (1994) Absorption and translocation of boron applied to aerial tissues of fruiting ‘Reliance’ peach trees. HortScience 29, 25–27. Shu, Z.-H., Oberly, G.H. and Cary, E.E. (1997) Absorption, movement and distribution of boron applied to peach (Prunus persica L. Batsch) fruits. In: Bell, R.W. and Rerkasem, B. (eds) Boron in Soils and Plants. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 209–212. Smith, M.W., Kenworthy, A.L. and Bedford, C.L. (1979) The response of fruit trees to injection of nitrogen through a trickle irrigation system. Journal of the American Society for Horticultural Science 104, 311–313. Strabbioli, G. (1992a) Peach water requirements in Central Valley. Acta Horticulturae 315, 203–210. Strabbioli, G. (1992b) The influence of regulated deficit irrigation (RDI) on the growth and productivity of peach trees. Acta Horticulturae 315, 211–217. Stylinanides, D.C., Tsipourides, C.G. and Michailides, Z.S. (1989) Resistance to iron deficiency of five peach rootstocks. Acta Horticulturae 254, 185–187. Swietlik, D. (1999) Zinc nutrition in horticultural crops. Horticultural Reviews 23, 110–178. Swietlik, D. (2002a) Zinc nutrition of fruit crops. HortTechnology 12, 45–50. Swietlik, D. (2002b) Zinc nutrition of fruit trees by foliar sprays. Acta Horticulturae 594, 123–129. Swietlik, D. and Faust, M. (1984) Foliar nutrition of fruit crops. Horticultural Reviews 6, 287–355. Syrgiannidis, G. (1985) Control of iron chlorosis and replant diseases in peach by using the GF 677 rootstock. Acta Horticulturae 173, 383–388. Tagliavini, M. and Marangoni, B. (2002) Major nutritional issues in deciduous fruit orchards of Northern Italy. HortTechnology 12, 26–31. Tagliavini, M., Scudellari, D., Marangoni, B. and Toselli, M. (1996) Nitrogen fertilization management in orchards to reconcile productivity and environmental aspects. Fertilizer Research 43, 93–102. Tagliavini, M., Millard, P. and Quartieri, M. (1998) Storage of foliar-absorbed nitrogen and remobilization for spring growth in young nectarine (Prunus persica var. nectarine) trees. Tree Physiology 18, 203–207. Tagliavini, M., Abadia, J., Rombola, A.D., Abadia, A., Tsipouridis, C. and Marangoni, B. (2000) Agronomic means for the control of iron deficiency chlorosis in deciduous fruit trees. Journal of Plant Nutrition 23, 2007–2022. Takkar, P.N. and Walker, C.D. (1993) The distribution and correction of zinc deficiency. In: Robson, A.D. (ed.) Proceedings of the International Symposium on Zinc in Soils and Plants. Kluwer Academic Publishers, Boston, Massachusetts, pp. 151–164. Taylor, B.K. (1975) Response of newly planted peach and apple trees to superphosphate. Australian Journal of Agricultural Research 26, 521–528. Taylor, B.K. and Issell, L.G. (1976) Comparative effects of foliar- and root-applied phosphorus on one-year-old peach trees. Australian Journal of Experimental Agriculture and Animal Husbandry 16, 596–599. Teviotdale, B.T., Ogawa, J.M., Nyland, G. and Kirkpatrick, B.C. (1989) Diseases. In: LaRue, J.H. and Johnson, R.S. (eds) Peaches, Plums, and Nectarines: Growing and Handling for Fresh Market. University of California Division of Agriculture and Natural Resources, Publication No. 3331. University of California, Oakland, California, pp. 118–132. Tormann, H. and Heyns, D.J. (1988) Effect of progressive soil water tension on soil water availability, vegetative growth and crop yield of ‘Independence’ nectarines grown in lysimeters. The Deciduous Fruit Grower 38, 430–434.

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14

Orchard Floor Management Systems T.J. Tworkoski and D.M. Glenn

USDA-ARS, Appalachian Fruit Research Station, Kearneysville, West Virginia, USA

14.1 Introduction 14.2 Components Orchard ﬂoor preparation before planting Weed effects Weed management Orchard ﬂoor management effects on insects and small mammals Management of ground covers, row middles and drive alleys Ground cover interactions with irrigation and fertilization 14.3 Management Systems Year-round vegetation-free orchard ﬂoor Vegetation-free tree rows with vegetated drive alleys Permanent vegetation management by mowing 14.4 Orchard Floor Inﬂuences Effects of management systems on the environment Orchard ﬂoor management interactions with the peach tree

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14.2 Components

The orchard ﬂoor is the soil and understorey vegetation of an orchard ecosystem. Orchard ﬂoor management decisions can affect the prevalence of weeds, insects, small mammals, disease, soil fertility, water availability, and potential for erosion and pollution. Appropriate management of the orchard ﬂoor is important for economic success of the grower and sustainability of the orchard environment. This chapter considers individual system management components, their integration and their inﬂuences when managing a peach orchard ﬂoor.

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An orchard ﬂoor management programme should begin before tree planting with an understanding of potential biological pests and of abiotic soil conditions. Site preparation can avoid or reduce problems associated with the orchard ﬂoor of young peach orchards. Particular attention should be addressed to weed ﬂora, water availability, soil pH and structure, the presence of hard pans and long-term nutrient needs, which have been discussed elsewhere in this book.

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

Orchard Floor Management

Pre-plant management of weeds and soils Weed competition can signiﬁcantly reduce the growth rate of young peach trees and delay time to ﬁrst cropping year. Prior to planting, weeds that can adversely affect peach trees should be identiﬁed and targeted for control. Perennial weeds are problematic because many reproduce vegetatively and spread in undisturbed soils beneath peach trees. The management of perennial weeds like johnsongrass (Sorghum halepense (L.) Perse.), poison ivy (Toxicodenron radicans (L.) Kutze) and Virginia creeper (Parthenocissus quinquefolia (L.) Planch.) can require two or more herbicide or cultivation treatments (Tworkoski and Young, 1990). In addition, weeds such as yellow nutsedge (Cyperus esculentus L.) are not controlled by herbicides labelled for bearing peach trees. Repeated cultivations or herbicide applications prior to planting can avoid injury to newly planted peach trees. Annual weeds also compete with young peach trees and harbour insect and disease pests that injure peach trees and fruit (Duffus, 1971; Weller et al., 1985; Skroch and Shribbs, 1986). Establishing a grass sod in the year or two prior to planting can help reduce perennial weed and weed seed banks. The weed seed bank in the soil can be reduced if weeds are not allowed to ﬂower. Mowing in conjunction with competition from the grass cover selects against many broadleaved weeds while favouring grass. Grass sod also improves the organic matter, soil structure and other soil properties, compared with bare or tilled soil. The species of grass used as a pre-planting cover should be adapted to the planting environment and subsequent sod management issues must be considered. Planting fruit trees in soil prepared with ‘K-31’ tall fescue (Festuca arundinacea Schreber) sod, killed before tree planting, reduced subsurface leaching of nitrate-N and also reduced the amount of herbicide used in young orchards (Biggs et al., 1997). However, if left as a ground cover, ‘K-31’ fescue can become competitive with peach trees (Welker and Glenn, 1988). Other ground covers such as common bermudagrass (Cynodon dactylon L.) may inhibit the growth of newly planted peach trees by competition and allelopathic effects (Weller et al., 1985).

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Less competitive but well-adapted grasses can also be sown where future tree rows are to be planted (Butler, 1986; Willmott et al., 2000). Several months before planting peach trees, the sod should be killed with a nonselective contact herbicide. In this killed sod, grass residue acts as a mulch to increase soil water availability, suppress weeds and enable water penetration into the soil (Welker and Glenn, 1988; Glenn and Welker, 1989b). The dead sod can break down after it has been killed but it may be removed where trees are planted to reduce habitat for rodents near tree trunks. A planting hole that has been dug with an auger may sufﬁce. Cultivation may still be necessary in narrow strips within the killed sod into which trees are planted. However, soil cultivation should be minimized to reduce bringing weed seed to the soil surface, where it may germinate. Additional weed and soil-borne disease control can be obtained by soil solarization in the vegetation-free strips. Clear, polyethylene plastic can be installed on the even surface of moist soil to elevate soil temperatures for 6 to 8 weeks during the warmest times of the growing season prior to planting. Soil sterilization has greatest promise in warm areas such as the south-east USA and California, where the required sterilization time can decrease as soil temperatures increase above 37°C. Improved plastic sheeting may enable soil sterilization to be used in cooler regions (Katan and DeVay, 1991). Raised beds Poor drainage can be mitigated with raised planting beds. In Ohio, yield of peach trees improved by 56% over 5 years when the trees were grown in raised beds rather than ﬂat areas (Funt et al., 1997). The improved yield may have been associated with reduced waterlogging problems that may stimulate shallow rooting, and greater root regeneration may have enabled the trees to exploit water from deeper soil when the shallow soil dried. Raised beds did not increase yield of young peach trees grown in sandy soil in New Jersey (Belding et al., 2003). Trees grown in raised beds in sandy soils may require supplemental irrigation but, in heavy soils, raised beds appear to beneﬁt trees by increasing gas exchange to

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the root system. The impact of raised beds on mature tree growth and susceptibility to wind throw requires further study.

Weed effects Yield loss due to weeds in established orchards Weeds can reduce yield in 3-year-old peach trees by 94% (Welker, 1984). Older peach trees were less susceptible to weed competition, but the competitive impact of weeds is likely to vary with weed species and the availability of potentially limiting resources (Layne et al., 1981; Glenn and Welker, 1989b; Tworkoski and Glenn, 2001). For example, peach yield is likely to decrease with weed competition under dry conditions. Yield reductions due to weed competition have been demonstrated in other temperate tree crops. In Alabama, cumulative yield of pecans over nine seasons increased by 358% in trees grown with weed control compared with trees grown without weed control (Foshee et al., 1997). However, the costs of complete weed control were not recovered from gains in yield until the eighth season after establishment. In New York, yield and growth of young apple trees increased as duration of weed control increased during the growing season (Merwin and Ray, 1997). Signiﬁcant beneﬁts were achieved by initiating weed control early in the growing season (e.g. May instead of June). When the orchard ﬂoor was maintained weed-free from bloom until 12 weeks after bloom, MacRae et al. (2007) found that fruit size, number and total yield of peach were greater than when the weedfree interval was shorter. Winter annual weeds, such as chickweed (Stellaria spp.), may not compete signiﬁcantly with established peach trees but they may threaten the economic viability of the crop by attracting or providing an overwintering habitat to insects (Lygus spp. and stink bugs) (Atanassov et al., 2002; Parker, 2003). These piercing–sucking insects can move from the weed and cause cat-facing damage to the exterior of fruit (Killian and Meyer, 1984). In California, mustard (Brassica spp.), wild radish (Raphanus raphanistrum L.) and vetch

(Vicia spp.) hosted Lygus hesperus, Lygus elisus and Calocoris norvegicus, which moved to trees and caused fruit damage (Pickel et al., 2002). Clean cultivation and effective control of broadleaved weeds can suppress these pests (Atanassov et al., 2002). Programmes that include cultivation for pest management must weigh possible adverse effects of cultivation on the ﬁne, shallow roots of peach trees. Flowering weeds also can disrupt the pollination of peach trees during bloom by attracting bees and other wild insects. Dandelions (Taraxacum officinale Wigg.) and chickweed may serve as alternative hosts for viruses such as Tomato ringspot virus, which can be transmitted to peach trees by nematodes and adversely affect peach trees (Powell and Forer, 1982; Skroch and Shribbs, 1986). Other weed species can support high populations of insects (e.g. aphids and leafhoppers) and nematodes that transmit viruses (Duffus, 1971). Nematodes such as root-knot nematode and dagger nematode can cause direct damage to peaches as well as vectoring disease. Based on Duffus’ (1971) observations, the general reduction of weeds will help reduce virus-induced diseases because nematodes and nematode-transmitted viruses have a diverse range of weed hosts. Benefits of weed-like vegetation Negative impacts of weeds are well documented but some invading plants that are characterized as weeds may have value. A potentially confounding effect of understorey vegetation is that although broadleaved weeds and grass can both deplete soil water, water deﬁcits may be ameliorated by the greater moisture penetration into soil covered with grass (Atkinson and White, 1981; Glenn and Welker, 1989b). Often understorey vegetation is classiﬁed as ‘weeds’ and ‘grasses’. This classiﬁcation can be relevant because grasses can compete with peach trees but they generally do not cause problems as disease and insect hosts. In addition, grouping broadleaved weeds together simpliﬁes management decisions but this form of general categorization should be scrutinized. There is evidence that some broadleaved vegetation may be beneﬁcial by providing habitat to

Orchard Floor Management

predatory insects that feed on herbivorous insects (see references within Haynes, 1980 and Atkinson and White, 1981; Wooldridge and Botha, 1991). Brown (2001) was able to increase biological control of insect pests on peach with buckwheat (Fagopyrum esculentum), dill (Anethum graveolens), tansy (Phacelia tanacetifolia) and a wildﬂower mix without increasing the damage by plant bugs or stink bugs (Brown, 2002). Some, perhaps many, broadleaved plants that are classiﬁed as weeds may have little impact on peach production or may even be viable ground covers. Improved knowledge of the impact of speciﬁc weed populations can contribute to efforts to manage weeds in the understorey community.

Weed management In established orchards, identiﬁcation and control of problem weeds should be based on impact potential. Some weeds pose signiﬁcant threats of competition (e.g. johnsongrass) whereas others do not (e.g. Whitlow grass (Draba verna L.) and nimblewill grass (Muhlenbergia schreberi J.F. Gmel.)) (Parker and Meyer, 1996). Weeds posing a signiﬁcant threat are often best managed while they are seedlings since large weeds can be highly competitive, become signiﬁcant seed sources and be difﬁcult to kill. The location of weeds in an orchard will also inﬂuence management strategies. In many established peach orchards the orchard ﬂoor is partitioned into areas below the trees (the tree row) and between the tree rows (drive alleys). It is possible that a plant which is desirable in the drive alley (e.g. fescue) may be a weed in the adjacent tree row. A widely used weed control technology in the USA is with synthetic chemical herbicides, but other techniques are available and are of increasing interest. Combinations of cultivation, ﬂaming, mulching and ‘natural product herbicides’ may be acceptable for use in ‘organic’ management. Herbicides Two general categories of herbicide include pre-emergence and post-emergence herbicides. The pre-emergence herbicides are applied to

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the soil prior to weed seed germination and are absorbed by the emerging weed seedling. Pre-emergence herbicides kill weed seedlings by different modes of action. Post-emergence herbicides kill weeds on contact and these also have different modes of action. Postemergence herbicides are useful for ‘spot’ applications to localized infestations of large or troublesome weeds such as perennial weed escapes. Pre-emergence and post-emergence herbicides can be applied together or separately in rotation to manage weeds. Numerous herbicides may be used to manage weeds in peach orchards but their use must comply with label instructions (Table 14.1). It is vital to distinguish between herbicides used in non-bearing and bearing peach trees because some herbicides will damage young trees with green bark. Decisions to apply herbicides should be based on scouting results and site history with the goal of maintaining weed populations to acceptable threshold levels. Thresholds can be based on the potential economic loss due to decreased yield or fruit quality or threat to labour operations associated with increased density of weed populations. As noted earlier, some winter annual weeds (e.g. chickweed) and ground covers (e.g. clover) harbour cat-facing insects such as stink bugs that pose an unacceptable risk to fruit quality. In southern locations of the USA these broadleaved plants can be managed with 2,4-D applications 8 weeks prior to bloom without damaging grass in drive alleys. It is generally known that yields decrease due to weed competition and that young peach trees are more susceptible than mature peach trees (Weller et al., 1985). However, little is known about economic threshold levels of weeds related to insect injury and yield loss for peach trees and there is a need for additional research in this area. Consecutive applications of the same herbicide or of different herbicides with the same mode of action may lead to the development of weed populations that are resistant to the class of herbicides being used (Welker, 1984). Combinations of herbicides with different modes of action have been found to be more effective in weed control than using a single herbicide (Welker, 1984). However, even repeat applications of the

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Table 14.1.

T.J. Tworkoski and D.M. Glenn

Herbicidesa currently recommended for peach culture in the USA.

Herbicide and active ingredient Pre-emergence Dichlobenil (Casoron) 2,6-dichlorobenzonitrile Diuron (Karmex) 3-(3,4-dichlorophenyl)-1,1-dimethylurea Isoxaben (Gallery) N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl] -2,6-dimethoxybenzamide Napropamide (Devrinol) N,N-diethyl-2-(1-naphthalenyloxy)propionamide Norflurazon (Solicam) 4-chloro-5-(methylamino)-2-(α,α,α-trifluorom-tolyl)-3(2H)-pyridazinone Oryzalin (Surflan) 3,5-dinitro-N4,N4-dipropylsulfanilamide Oxyflurofen (Goal) 2-chloro-1-(3-ethoxy-4-nitrophenoxy)4-(trifluoromethyl)benzene Pendimethalin (Prowl) N-(1-ethylpropyl)-3,4-dimethyl-2,6dinitrobenzenamine Pronamide (Kerb) 3,5-dichloro-N-(1,1-dimethyl-2-propynyl) benzamide Simazine (Princep and generics) 2-chloro-4,6-bis(ethylamino)-S-triazine Terbacil (Sinbar) 3-tert-butyl-5-chloro-6-methyluracil Post-emergence 2,4-D amine (generics) (2,4-dicholorophenoxy)acetic acid Fluazifop (Fusilade) (R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy]propanoate Glyphosate (Roundup/Touchdown) N-(phosphonomethyl)glycine MSMA (MSMA Arsonate) monosodium acid methanearsonate Paraquat (Gramoxone) 1,1′-dimethyl-4,4′-bipyridinium dichloride Scythe pelargonic acid Sethoxydim (Poast) 2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]3-hydroxy-2-cyclohexen-1-one aNot

Application

Established trees for control of broadleaved weeds, quackgrass and fescue Trees established at least 3 years in the orchard for control of annual broadleaved and grass weeds Control of broadleaved weeds in non-bearing trees

Established bearing and non-bearing trees for control of annual grasses and small-seeded broadleaved weeds Control of annual grasses and small-seeded broadleaved weeds Bearing and non-bearing trees for control of annual grasses and small-seeded broadleaved weeds Control of broadleaved weeds in established trees

Non-bearing established trees for control of annual grasses and small-seeded broadleaved weeds Control of grass and small-seeded broadleaved weeds in established trees Trees established at least 1 year in the orchard for control of annual broadleaved weeds Established trees for control of grass and broadleaved weeds

Control of annual and perennial broadleaved weeds in established trees Control of annual and perennial grasses in newly planted and established trees Control of broadleaved and grass weeds Selective control of annual and perennial weeds in non-bearing trees Control of broadleaved and small grass weeds Non-selective burn-down of weeds Control of annual and perennial grasses in established trees

endorsed by the US Department of Agriculture. Labels and state extension recommendations should be followed.

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Plate 74. Fusetto tree form. Plate 75. Y-shaped tree form (courtesy of D.R. Layne, Clemson, South Carolina, USA). Plate 76. Modern picking platform. Plate 77. Generalized shapes of concentration curves of mineral nutrients in the leaf during growing season. Curves show trends, not actual levels for the northern hemisphere. Plate 78. Red coloration on leaves and stems of nitrogen-deficient peach shoot.

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Plate 79. Smoother finish and more red coloration on fruit from low nitrogen trees (top row) compared to high nitrogen trees (bottom row). Plate 80. Purple coloration and leathery texture of phosphorus-deficient peach leaf. Plate 81. Pale colour and leaf rolling caused by potassium deficiency in peach leaves. Plate 82. Discoloration on leaf margins and tip caused by magnesium deficiency. Plate 83. Zinc deficiency symptoms of interveinal chlorosis on a peach leaf. Plate 84. Rosetting or ‘little leaf’ symptoms of zinc deficiency in peaches.

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Plate 85. ‘Netting’ symptom of iron chlorosis on a peach leaf. Veins remain green while the rest of the leaf has turned yellow. Plate 86. Manganese deficiency symptoms on a peach leaf. Bands along the main veins remain green. Plate 87. Ten-year-old ‘Sunhigh’ peach trees, originally planted in 2.4 m vegetation-free areas with composted poultry litter placed beneath some trees at a rate of 11.6 kg litter/m2 to a depth of 10 cm (1.1 kg N per tree). Photograph was taken the second season after application when some weeds had begun to grow through the mulch. Plate 88. Trees planted in cultivated (left) and killed-sod (right) strips. Killed sod provides weed suppression and improves water penetration. Plate 89. ‘Jersey Dawn’ and ‘Redskin’ peach tree, the same age (approximately 3 years after planting) but some planted and grown in 0.6 m (small trees in foreground) and others grown in 2.4 m (large trees) vegetation-free areas with K-31 fescue in drive alleys. Plate 90. Brown rot blossom blight of peach caused by Monilinia fructicola. Infected blossom with gumming and canker development at the base of the peduncle. Plate 91. Brown rot fruit rot of peach caused by Monilinia fructicola.

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Plate 92. Jacket rot of peach caused by Botrytis cinerea. The jacket (or shuck) is infected, but the immature fruit is still disease-free. Plate 93. Green fruit rot of peach caused by Monilinia fructicola. The decay spreads to neighbouring healthy fruit by contact. Plate 94. Apothecia of Sclerotinia sclerotiorum are produced on overwintering sclerotia (bottom). Ascospores are forcibly discharged in a spore cloud (reprinted, with permission, from Strand, 1999).

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Plate 95. Lesion of the shothole fungus Wilsonomyces carpophilus on peach twig where the pathogen overwinters. Sporodochia of the fungus in the centre of a stem lesion. Plate 96. Symptoms of shothole caused by Wilsonomyces carpophilus on peach fruit and leaf. Plate 97. Symptoms of scab caused by Fusicladosporium carpophilum on peach fruit. Plate 98. Sporulating stem lesion of peach rust caused by Tranzschelia discolor. Plate 99. Symptoms of peach rust caused by Tranzschelia discolor on peach leaves. Plate 100. Leaf lesions with uredinia of peach rust caused by Tranzschelia discolor.

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Plate 101. Symptoms of peach rust caused by Tranzschelia discolor on peach fruit. Plate 102. Peach leaf curl caused by Taphrina deformans. Plate 103. Advanced symptoms of peach leaf curl caused by Taphrina deformans with leaf deformation, discoloration, necrosis and a subtle white layer of sexually produced asci containing ascospores. Plate 104. Symptoms of peach leaf curl caused by Taphrina deformans on developing peach fruit.

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Plate 105. Peach twig with overwintering mycelium and embedded chasmothecia of powdery mildew caused by Podosphaera pannosa. Plate 106. Powdery mildew caused by Podosphaera pannosa on peach leaves. Plate 107. Powdery mildew caused by Podosphaera pannosa on developing peach fruit. Plate 108. Powdery mildew caused by Podosphaera pannosa on mature peach fruit. Plate 109. Powdery mildew caused by Podosphaera pannosa on developing nectarine fruit. Plate 110. Close-up of chasmothecia of powdery mildew caused by Podosphaera pannosa on peach twig.

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Plate 111. Symptoms of silver leaf disease caused by Chondrostereum purpureum on peach leaves. Left: diseased leaf. Right: healthy leaf. Plate 112. Cross-section through scaffold branch of peach infected by Chondrostereum purpureum. Plate 113. Peach tree with Leucostoma (Cytospora) or perennial cankers on scaffold branches (reprinted from Ogawa et al., 1995, with permission of APS). Plate 114. Leucostoma or perennial cankers caused by Leucostoma cincta (Cytospora cincta) around nodes of peach shoot (reprinted from Ogawa et al., 1995, with permission of APS). Plate 115. Pycnidia of Leucostoma cincta (Cytospora cincta) on cherry twig. Spore masses are exuded by some pycnidia on the upper part of the twig. Plate 116. Fungal gummosis caused by Botryosphaeria dothidea. Blisters develop around lenticels on young bark that develop in the second or third growing season of the tree.

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Plate 117. Fungal gummosis caused by Botryosphaeria dothidea. Gumming blisters and necrotic tissue under lenticels that develop under the bark. Plate 118. Fungal gummosis caused by Botryosphaeria dothidea. Lesions may coalesce and form extensive cankers with excessive gumming on lower peach tree trunks. Plate 119. Constriction canker caused by Phomopsis amygdali. One-year-old peach twigs with infections around buds. The lower twig shows the zonations around the infection site. Plate 120. Constriction canker caused by Phomopsis amygdali. Flagging and withering of blighted peach twigs distal to twig cankers. Plate 121. Cirri (tendrils) exuding from pycnidia of Phomopsis amygdali. Each cirrus is composed of abundant conidia of the pathogen. Plate 122. Dieback of peach tree in foreground affected by Phytophthora root and crown rot (reprinted, with permission, from Strand, 1999).

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Plate 123. Phytophthora crown rot on peach tree (reprinted, with permission, from Strand, 1999). Plate 124. Peach tree with an aerial infection of a Phytophthora sp. (reprinted, with permission, from Strand, 1999). Plate 125. Leaf symptoms of peach tree affected by Armillaria root rot. Plate 126. Armillaria-infected peach trees showing dieback. Plate 127. Mycelial fans of Armillaria sp. under the bark of infected peach tree. Plate 128. Rhizomorph of Armillaria mellea (top) and healthy root (bottom) (reprinted, with permission, from Strand, 1999).

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Plate 129. Basidiomes of Armillaria sp. at the base of infected peach tree. Plate 130. Verticillium-infected peach tree with wilting of branches (reprinted, with permission, from Strand, 1999). Plate 131. Cross-section through branch of Verticillium-infected peach tree with discoloured outer xylem (reprinted, with permission, from Strand, 1999). Plate 132. Orchard with trees affected by peach tree short life. Plate 133. Discoloured tissue under the bark of peach tree short life-affected tree.

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Plate 134. Rootstock sprouting from peach tree killed by peach tree short life. Plate 135. Postharvest brown rot of peach fruit caused by Monilinia fructicola. Plate 136. Postharvest grey mould of nectarine fruit caused by Botrytis cinerea. Plate 137. Postharvest Rhizopus rot of peach fruit caused by Rhizopus stolonifer with decay spreading by contact to healthy fruit (nesting). Plate 138. Postharvest Gilbertella rot of peach fruit caused by Gilbertella persicaria. Plate 139. Sour rot caused by Geotrichum candidum initiated in wounds of the skin.

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Plate 140. Anthracnose of peach caused by Colletotrichum acutatum showing circular rings where spores of the fungus are produced. Plate 141. Electron micrograph of phloem sieve tube occluded with cells of phytoplasma. Plate 142. Leaves of periwinkle (Catharanthus roseus), which can serve as an indicator plant for phytoplasmas, colonized by dodder (Cuscuta sp.), which serves as a transmission bridge. Plate 143. Dead peach buds and twig canker associated with bacterial canker. Plate 144. Branch death and sucker growth from the rootstock associated with bacterial canker. Plate 145. Wood with discoloured streaks and the collapse and wilt of newly emerged growth associated with bacterial canker.

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Plate 146. Small branch killed by Pseudomonas syringae pv. syringae with the canker extending into a larger limb. Plate 147. Water-soaked bark and lightly discoloured wood in early spring associated with bacterial canker. Plate 148. Discoloured wood approximately a week after occurrence of cold damage, with the bark easily separating and appearing undamaged. Plate 149. Non-fluorescent and fluorescent bacteria associated with the bacterial canker complex cultivated on King’s medium B. Plate 150. Chlorotic peach leaves with lesions caused by Xanthomonas arboricola pv. pruni. Plate 151. Newly formed, water-soaked, greyish, angular bacterial spot lesions on peach leaf caused by Xanthomonas arboricola pv. pruni.

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Plate 152. Bacteria streaming from leaf lesion caused by Xanthomonas arboricola pv. pruni. Plate 153. Newly formed, water-soaked bacterial spot lesions on peach fruit near the growth stage of pit hardening. Plate 154. Bacterial spot lesions on fruit at harvest confined to the fruit surface that developed from infections occurring after pit hardening. Plate 155. Bacterial spot lesions on fruit at harvest caused by early infections occurring soon after shuck split and before pit hardening. Plate 156. Bacterial spot spring canker (Xanthomonas arboricola pv. pruni) with a black, greasy appearance. Plate 157. Terminal dieback and black tip canker, summer cankers on current year’s twigs, lesions on leaves, and nodes where leaves have defoliated caused by Xanthomonas arboricola pv. pruni.

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Plate 158. Discoloured bark tissue of spring canker Xanthomonas arboricola pv. pruni. Plate 159. Crown gall caused by Agrobacterium tumefaciens on peach trees recently dug from a nursery. Plate 160. Peach tree expressing phony peach disease symptoms. Leaves are greener and denser and internodes are shortened giving the tree a compact, flat canopy with an ‘umbrella-like’ appearance (from R.F. Mizell, III). Plate 161. X-disease phytoplasma-infected peach with necrotic lesions non-uniformly distributed on rolled and pale green leaves. Plate 162. X-disease phytoplasma-infected trees exhibit a loss of vigour, leaves have a pale green colour and severely infected branches die. Plate 163. Tree infected with peach yellows phytoplasma showing a bushy appearance on ends of branches and premature colouring and ripening of fruit (from A. Ragozzino).

Orchard Floor Management

same combination of herbicides can result in population shifts and new weed problems (Tworkoski et al., 2000b). Long-term applications of the same herbicide may also contribute to herbicide residue carry-over, which can adversely affect the growth of newly planted peach trees (Tworkoski et al., 2000a; Tworkoski and Miller, 2001). Repeated control of weeds with pre-emergence herbicides and mechanical tillage may reduce soil structure, fertility and orchard productivity compared with ‘living’ and straw–hay mulches (Merwin et al., 1994) and killed-sod systems (Glenn and Welker, 1989b). Productivity loss may be associated with reduced organic matter and water inﬁltration, and with elevated soil temperatures in non-mulched sites. At the time of ﬂowering, heat absorbed during the day by vegetation-free orchard ﬂoors will radiate from the soil at night, warm the air and possibly reduce cold injury to peach blossoms. Thus, soil that is continuously bare may contribute to reduced long-term orchard productivity but time intervals without vegetation cover can protect current-year cropping. Herbicides which may be acceptable for organic growers have been developed. In general they are contact-active and may require repeated applications when established plants are being controlled. These herbicides include pelargonic acid (Scythe; Mycogen Corp., San Diego, California), vinegar (BurnOut; St Gabriels Laboratory, Orange, Virginia) and essential oil of clove (Matran; EcoSmart Technologies, Inc., Franklin, Tennessee). Essential oils of cinnamon, clove, summer savory and red thyme have herbicidal activity and may be useful as ‘natural product herbicides’ (Tworkoski, 2002). However, these herbicides can be expensive and may have limited efﬁcacy against some weeds. These herbicides appear to be most effective when applied to small weeds, generally early in the growing season. Mechanical and flaming techniques Mechanical weed control devices such as discs or cultivators can control ground vegetation in areas where the orchard ﬂoor is not maintained with ground covers, such as in tree rows. Where drive alleys are maintained in permanent ground cover, cultivation can be

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performed beneath trees but care is necessary to avoid damaging low branches or tree trunks. Where drive alleys are maintained in winter ground covers, shallow disking in early spring can eliminate or reduce competition and provide residual mulch. Shallow disturbance of the soil is necessary to minimize bringing new weed seed to the soil surface and to avoid damaging shallow peach roots. Mechanical cultivators have been developed that can till to the tree and reduce or avoid damaging the trunk (Weed Badger, Marion, North Dakota; The Green Hoe Co., Portland, New York). Flame weeding eliminates weeds by searing, not burning, the vegetation (Ames and Kuepper, 2004). Torches fuelled by kerosene or propane are pulled behind a tractor at a speed that will wilt vegetation. Drawbacks to ﬂaming include ﬁre and fuel hazards, potential tree injury, water and fuel requirements, and lack of uniform weed kill. Flaming is an alternative weed management technology that may be useful in organic systems. Hand and tractor-mounted ﬂame weeding equipment is commercially available (Flame Engineering, Inc., LaCrosse, Kansas; Thermal Weed Control Systems, Inc., Neillsville, Wisconsin). Mulching Organic mulches, such as straw, sawdust and composted animal waste, can be applied beneath fruit trees to suppress weeds (Fig. 14.1/ Plate 87). Composted poultry litter applied to a depth of 10 cm beneath peach trees suppressed soil-germinating weeds but additional control was necessary for weeds germinating in the mulch (Preusch and Tworkoski, 2003). Composted mulch that is applied in too deep a layer may have the undesirable effect of releasing signiﬁcant P to the soil (Preusch et al., 2002). A layer of newspaper or cardboard could be applied beneath the mulch to increase weed suppression (Ames and Kuepper, 2004) but moisture penetration may be impeded and, as this lower layer degrades, weeds can grow through the mulch (T.J. Tworkoski, personal observation). If the mulch is raked aside, the lower newspaper layer replaced and the mulch raked back, then weeds can be suppressed for a longer time. These are labour-intensive practices which may not be economically

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Fig. 14.1. Ten-year-old ‘Sunhigh’ peach trees, originally planted in 2.4 m vegetation-free areas with composted poultry litter placed beneath some trees at a rate of 11.6 kg litter/m2 to a depth of 10 cm (1.1 kg N/tree). Photograph was taken the second season after application when some weeds had begun to grow through the mulch.

viable for large-scale commercial operations. Other beneﬁcial effects of mulch include slow release of some nutrients, increased soil organic matter and improved soil structure (Haynes, 1980). Soil moisture retention is improved when mulch is applied to tree rows (Skroch and Shribbs, 1986). Compost mulch has also been shown to inhibit growth of the brown rot fungus, Monilinia fructicola (G. Wint) Honey, in the laboratory (Brown and Tworkoski, 2004). High microbial biodiversity in compost may increase competition for resources and reduce production of inoculum. Pine straw or hay applied beneath trees to a depth of 12 cm can provide some mulching beneﬁts; however, they may pose a ﬁre hazard. Organic material that can be used for mulch may not be widely available and transportation costs of the large quantities necessary for mulch may prohibit its use. These problems can be ameliorated if mulch can be obtained from ‘on-site’ activities such as growing sorghum sudangrass (Sorghum × drummondii (Steudel) Millsp. & Chase) for mulch (Ames and Kuepper, 2004). Cover crops between trees or in ﬁelds near the orchard can

be a source of organic mulch. Sickle bar mowers can cut ground covers, which can then be raked or blown beneath trees. To prevent the ground cover from becoming a weed problem in the tree rows, the ground cover in the drive alley should be mown before it produces seed. In addition, mulch should be kept at least 20–30 cm from the trunk to avoid rodent and collar rot injury to peach tree trunks (Ames and Kuepper, 2004). Inorganic mulches such as black plastic and geotextile sheets can effectively suppress weeds. Their use requires a greater initial investment than most organic mulches. Another drawback is that the waste fabric must be removed and disposed of, but this problem may be less signiﬁcant if longer-lived mulch is used. In the south-eastern USA, growers using black plastic and raised beds can achieve weed control for up to 2 years, provided weed seed has been killed with methyl bromide. Drip irrigation beneath the plastic is necessary in this system. Biological control of weeds in peach orchards has been attempted by planting a short-lived cover plant which grows quickly

Orchard Floor Management

and dies, resulting in weed suppression by competition and residue which acts as a mulch. An example of such smother crops is Brassica campestris, which was planted in May and suppressed early-season weeds while it was actively growing (Halbrendt, 1993). However, by July weed growth was similar to untreated plots. For success, smother crops require weed suppression for longer periods without competition that reduces yield of peach trees.

Orchard floor management effects on insects and small mammals Cover crops and weeds can provide food and habitat for rodents, insects, nematodes, microbes and viruses (Norris, 1986). Management of the orchard ﬂoor can inﬂuence the balance between organisms that are beneﬁcial and those that are harmful to peach production. Research has provided insight into orchard ﬂoor manipulation effects on insect populations and behaviour in apple and pear orchards but less is known in peach orchards. The potential impact of such pests or the beneﬁts of other insects should be considered in the selection of an orchard ﬂoor management system. Insect populations are directly and indirectly affected by the composition and abundance of ﬂora on the orchard ﬂoor (Alston, 1994). In peach, control of many annual broadleaved weeds and legumes is necessary because they provide habitat for tarnished plant bugs and stink bugs (LaRue and Johnson, 1989; Atanassov et al., 2002; Ames and Kuepper, 2004). In apple orchards, broadleaved weeds such as common mallow (Malva neglecta Wallr.), ﬁeld bindweed (Convolvulus arvensis L.), knotweed (Polygonum spp.), morning glory (Ipomoea spp.), prickly lettuce (Lactuca serriola L.), puncture vine (Tribulus terrestris L.) and white sweetclover (Melilotus alba Medikus) enhanced phytophagous mites that are detrimental to tree productivity (Alston, 1994). Phytophagous mites were managed to economically acceptable levels by reducing these host broadleaved weed species to less than 12% of ground cover while maintaining ground cover of at least 50% of other ground cover species (orchardgrass (Dactylis glomerata L), red fescue (Festuca rubra L.) and

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lucerne (Medicago sativa L.)) which harbour predatory mites. Research has demonstrated that ground covers such as mustards (Brassica spp.), buckwheat (Fagopyrum spp.), dwarf sorghum (Sorghum spp.) and various members of the Apiaceae (Umbelliferae) and Asteraceae (Compositae) families can attract more beneﬁcial insects than pests. In addition to ﬂoristic effects, management of the orchard ﬂoor can inﬂuence insect behaviour and population demographics (Brown et al., 1997; Brown and Glenn, 1999). Mowing frequency can affect the population size of phytophagous and predacious insects, with increases of both groups resulting from decreased mowing in pear orchards in the north-western USA (Horton et al., 2003). There is a possibility of managing movement of natural enemies of insects into fruit tree canopies with cultural manipulation of the orchard ﬂoor, such as mowing. In California it is recommended that lucerne growing near a fruit crop not be mowed if there are Calocoris bugs feeding on the legume, since mowing may induce movement of Calocoris bugs into the tree canopy, where they may damage fruit (Ames and Kuepper, 2004). Increased research is needed to understand and improve the use of understorey vegetation as a tool for insect pest management in peach orchards. In addition to cover crops and weeds, mulches and herbicides that are part of the orchard ﬂoor management system can inﬂuence insect populations. Modiﬁcation of the orchard ﬂoor with composted mulch enhanced ground-foraging generalist predators, and predator activity may be enhanced when the orchard ﬂoor is disturbed or treated with herbicide (Brown and Tworkoski, 2004; Mathews et al., 2004). Mulch increased prey resources to support predator populations and herbicides enhanced habitat for predators with improved physical cover and microclimate effects. However, herbicide use can also decrease predatory insect populations. Integrated pest management (IPM) programmes that target control of the two-spotted spider mite (Tetranychus urticae Koch) with the predacious mite (Neoseiulus (Typhlodromus) fallacies (Garman)) should avoid use of 2,4-D amine, gramoxone and terbacil because these herbicides were more toxic to the predator and were likely to

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differentially decrease predator populations (Rock and Yeargan, 1973). Ground cover and mulch near tree trunks can lead to rodent damage in fruit orchards. In New York, meadow vole (Microtus pennsylvanicus Ord) density increased and young apple trees were injured in orchards with crown vetch (Coronilla varia L.), hay–straw mulch and red fescue (F. rubra L.) sod below trees (Merwin et al., 1999). Tree damage was controlled by reducing vegetation, trapping, and using tree guards and vole predators. In British Columbia, Canada, intensive weed control within an orchard reduced montane vole (Microtus montanus) abundance but a compensatory increase in other small mammal populations (deer mouse (Peromyscus maniculatus) and northwestern chipmunk (Eutamias amoenus)) was observed (Sullivan et al., 1998). Montane vole damage to apple trees was reduced with scent mixtures from ermine (Mustela erminea) (Sullivan et al., 1990). Such chemical repellants may have application to rodent control in peach orchards.

Management of ground covers, row middles and drive alleys The entire orchard ﬂoor, or a part of it, can be mulched, cultivated, treated with herbicide or maintained with ground covers. The tree rows can be maintained vegetation-free while the drive alleys between tree rows are managed with ground covers. Ideal ground covers should help control erosion, stand up to trafﬁc, require low maintenance, suppress weeds, improve soil quality and not compete with the peach trees. However, ground covers and mulch can reduce ﬂood and furrow irrigation efﬁciency and may not be used during the growing season, particularly under dry conditions in areas that include parts of California. Ground covers must adapt to climatic and edaphic conditions. In addition, management of drive alleys must be coordinated with tree rows. For example, ground covers in drive alleys may be cut to provide organic mulches beneath tree rows and they may also provide habitat for beneﬁcial insects such as predatory mites and spiders.

Generally, grass is more beneﬁcial to soil ﬂora and fauna than clean cultivation (Haynes, 1980). Grass ground covers with potential for use in drive alleys have been evaluated in terms of rate of grass establishment, height and spreading characteristics, root and water use traits, and tolerance to drought, heat, shade, cold and trafﬁc (Butler, 1986). Many growers in the eastern USA plant vigorous grasses on the orchard ﬂoor such as Kentucky bluegrass (Poa pratensis L.), fescue (Festuca elatior L.) and orchardgrass (D. glomerata L.) with herbicide strips in the tree row (Skroch and Shribbs, 1986). These cool-season grasses may not be the best choice as an orchard ﬂoor cover because they may require frequent mowing and can spread aggressively from drive alleys into tree rows (Willmott et al., 2000). In New Jersey, perennial ryegrass (Lolium perenne L.) and creeping red fescue (F. rubra L.) may succumb to infectious diseases or environmental stress and should not be used. A number of grass cultivars of tall, hard and chewings fescues (F. arundinacea Schreber, Festuca longifolia Thuill. and F. rubra, respectively) that require lower maintenance have been recommended (Willmott et al., 2000). In North Carolina, Parker and Meyer (1996) determined that peach tree growth was greater when grown with nimblewill grass (M. schreberi J.F. (Gmel.)) than in plots with weeds, centipedegrass (Eremochloa ophiuroides (Munro) Hack.) or bahiagrass (Paspalum notatum Flugge). Peach roots grew deeper and in greater number and lateral distribution in nimblewill grass or bare ground than in other grass treatments. In the Paciﬁc Northwest, most orchards use perennial grass with shallow roots as ground cover between tree rows and vegetation-free strips beneath trees (Granatstein, 2002). In the southern USA winter legumes such as vetch (Vicia spp.) and subterranean clover (Trifolium subterraneum L.) have been used as cover crops to improve soil physical and nutrient properties that can beneﬁt fruit trees (Hoyt and Hargrove, 1986). Subterranean clover had excellent reseeding ability, and may contribute N and organic matter to the orchard ﬂoor. However, the timing of nutrient release from legumes must support peach production without adversely affecting fruit quality or vegetative tree growth that

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can result from excessive N late in the season. In addition, some warm-season legumes may compete with trees for water and harbour phytophagous insects. None the less, after weighing costs and beneﬁts, legumes may play a role in sustainable practices for peach orchard ﬂoor management. Subterranean clover has been proposed as a useful ground cover for drive alleys in peach orchards in warm locations where winter temperatures do not drop below –18°C (Ames and Kuepper, 2004). The subterranean clover reseeds in early summer and dies in the heat of late summer to produce a weed-suppressive mulch in Arkansas and California. The clover has also provided a habitat for beneﬁcial insects. Ground covers with different species composition, including broadleaved weeds, favour diverse arthropod communities that have been useful for IPM in orchards (Wooldridge and Botha, 1991). Such broadleaved plants may serve as alternative food sources for predatory mites that feed on thrips, aphids and other mite species. However, ground cover ﬂora must be managed to reduce injury from phytophagous insects. Cat-facing injury by stink bugs (Pentatomidae) and tarnished plant bugs (Lygus lineolaris) was correlated with the presence of legumes such as vetch (Vicia spp.), clover (Trifolium spp.) and annuals such as chickweed, pepperweed (Lepidium spp.) and henbit (Lamium amplexicaule L.) (Killian and Meyer, 1984; Meyer, 1984). Some species of plants, if kept succulent, may be used as a trap crop to attract stink bugs away from the peaches (Brown, 2002). Spider mite (Tetranychus spp.) populations may also increase in these ground covers and migrate to peach trees when ground covers begin to senesce (Meagher and Meyer, 1990). Ring nematode (Mesocriconema xenoplax) may move from legumes as well as from weeds such as dandelion and purslane to peach roots (Zehr et al., 1986, 1990). Ground cover management is not restricted to vegetation management. Synthetic ground covers have been used to modify the orchard environment to enhance fruit quality. Reﬂective mulches have been applied in drive alleys to increase light intensity in orchards and to increase red colour of peaches. Reﬂecting ﬁlms can modify the composition of

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anthocyanins, ﬂavonoids, chlorophyll and carotenoids in apples (Ju et al., 1999). Layne et al. (2001) found increased red surface colour of peaches when metallized reﬂective ﬁlm was placed beneath peach trees 2 to 4 weeks before harvest. Peaches in the tree lower canopy were redder and overall price could increase by $1 per 11-kg box with increased colour. Estimated costs for the metallized mulch was $220/ha.

Ground cover interactions with irrigation and fertilization Irrigation combined with managed competition may increase peach tree productivity while reducing excess vegetative growth. In Australia, vegetative vigour was suppressed and yield was increased by intraspeciﬁc root competition from a high-density orchard planting in combination with restricted irrigation (Chalmers et al., 1981). Interspeciﬁc weed competition from ground cover can also dwarf young peach trees without reducing yield expressed on a trunk cross-sectional area basis (Glenn and Welker, 1996). Reducing tree size by manipulation of the orchard ﬂoor ground cover requires close management of fertilizer and water inputs. In older, 8-year-old peach trees, grass sod competition reduced total yield and yield of large fruit (>65 mm) in West Virginia (Glenn and Welker, 1996). In Ontario, Canada, permanent drive alleys with creeping red fescue combined with trickle irrigation increased total yield and yield of large fruit (Layne and Tan, 1988). Yield decreased when peach trees were grown with grassed drive alleys but without irrigation. Yield and the fruit in large size classes increased with irrigation when ground covers were present but the economic balance of irrigation costs and yield beneﬁts should be analysed. It is likely that supplemental fertilizer will be needed in productive orchards, regardless of the ground cover used, and fertilizer applications must be prescribed on the basis of appropriate soil and leaf analyses. In addition to fertilizer applications, soil nutrients can be manipulated by partial or complete kill of ground covers or by addition of organic

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mulches. In Europe, a permanent ground cover of white clover (Trifolium repens) was mowed regularly under older trees or winter rye was sown under young trees in late summer, followed by mechanical removal in spring (Bloksma, 2000; Bloksma and Jansonius, 2002). The permanent ground cover and late summer sowing provided a means of transferring soil N from late summer/autumn to the following spring. Organic mulches of bark, grass and composted waste may also provide a slow release of nutrients while conserving water and suppressing weeds throughout the year. However, organic mulches can increase the balance of C to N in the soil and immobilize nutrients from soil-applied fertilizer.

14.3 Management Systems The primary goal of orchard ﬂoor management systems is to control understorey vegetation and manage resources to ensure the economic success and sustainability of the orchard. Selection of the type of ground cover, its spatial and temporal distribution, and the method of control are critical aspects that must be integrated for orchard ﬂoor management. The ground may be completely covered with permanent vegetation or be controlled by cultivation, mulch or herbicides so that some portion of the ground cover remains (Hogue and Neilsen, 1987). This section considers the integration of several of the previously described management components in management systems. Year-round vegetation-free orchard floor Beneﬁts and disadvantages of different orchard ﬂoor management systems have been reviewed (Haynes, 1980; Skroch and Shribbs, 1986; Hogue and Neilsen, 1987). Continuous, clean cultivation of the orchard ﬂoor aerates the soil and eliminates competition but loss of organic matter, breakdown of soil structure, increased potential for erosion and destruction of shallow tree roots will occur. In dry areas where irrigation is the primary source of water for peach crops, year-round vegetation-free conditions have been used. Year-round tillage is used in

California to control weeds, save water and provide ditches for furrow and ﬂood irrigation (Vossen and Ingals, 2002). Soil compaction resulting from repeated cultivations can occur. Rip cultivation may then be necessary with shanks deep enough to break through the cultivated layer and allow water to penetrate the soil proﬁle. However, deep cultivation can require heavy equipment, which may contribute to further soil compaction. East of the Rocky Mountains, the practice of clean cultivation in bearing peach orchards declined during the middle part of the 20th century (Fogle et al., 1965). However, in South Carolina and Georgia, some large peach producers returned to a herbicide-maintained bare orchard ﬂoor system (D.R. Layne, South Carolina, 2004, personal communication). In other eastern locations, in place of complete removal of vegetation, ground covers were grown as permanent or temporary components of the orchard ﬂoor. Ground cover vegetation increases soil organic matter, structure and water penetration, but ground covers must be managed to control competition and reduce pests that are associated with them.

Vegetation-free tree rows with vegetated drive alleys In the USA the orchard ﬂoor beneath peach trees is often maintained free of weeds with herbicides and drive alleys may contain temporary or permanent ground covers (Elmore et al., 1997). Management decisions regarding the orchard ﬂoor before and shortly after planting will affect the composition and management of the orchard ﬂoor in a mature orchard. Establishment of the orchard floor In preparation for planting, a ground cover of grass sod should be installed as a fallow crop for at least 2 years to adjust soil pH and to decrease numbers of nematodes, weed seeds and soil pathogens. The goal of a 2-year fallow period should be pursued but growers may reduce time to replant based on economic pressures on the available land. Several months before planting (e.g. September before an April planting), tree rows are laid out and sod

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is killed with a post-emergence, non-selective and non-residue herbicide (e.g. glyphosate). The killed sod can improve growth of newly planted peach trees due to increased organic matter and water penetration, while acting as a mulch to suppress weeds (Welker and Glenn, 1988, 1990; Glenn and Welker, 1989a) (Fig. 14.2/Plate 88). Planting peach trees in killed sod increased growth by 120% and fruit yield by 160% during the ﬁrst 3 years after planting, compared with vegetation-free strips maintained by cultivation or herbicides (Glenn and Welker, 1989a). Often sod is killed only where trees are to be planted so that living grass remains as the foundation for drive alleys. The width of the killed-sod area in tree rows will strongly affect peach tree growth and branch angle (Welker and Glenn, 1989, 1991). Tree size decreases as killed-sod width is reduced below 2 m. Proximity of living sod to the planted peach tree can regulate competition and subsequently affect tree size and yield (Welker and Glenn, 1989, 1991). Newly planted peach trees were signiﬁcantly dwarfed by 1 m and not by 3 m vegetation-free strips. Dwarfed trees were as efﬁcient (i.e. yield per unit trunk cross-sectional area) as large trees. ‘Cultural

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dwarﬁng’ of peach trees by sod competition may enable growers to increase tree density and yield per hectare with trees that require less pruning. Yield efﬁciency of peach trees increased as the size of vegetation-free ground area increased to 9 m2 and then yield efﬁciency remained constant, suggesting that closer tree spacing within a row can increase yield per hectare (Welker and Glenn, 1989). Reduced vegetation-free ground area has reduced sprout growth and pruning needed to maintain tree size (Glenn and Welker, 1996). All ground covers are not equally competitive and selection of a ground cover will inﬂuence the dwarﬁng effect on planted peach trees. Planting peach trees into subterranean clover (T. subterraneum L.) resulted in reduced growth and leaf N, P and K compared with trees planted in a herbicide-treated strip. However, tree growth recovery was observed in the second year after planting (Stasiak and Rom, 1991). Young peach orchards may require up to three seasons until they bear fruit. During this establishment time, crops such as potatoes, strawberries and other vegetables can be interplanted within row middles to provide income and offset initial expenditures. For example, up to four seasons of horticultural crops were

Fig. 14.2. Trees planted in cultivated (left) and killed-sod (right) strips. Killed sod provides weed suppression and improves water penetration.

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harvested prior to the ﬁrst year of commercial peach production (Leuty, 2003). Intercropping requires careful management, is labourintensive and is not amenable to moderate- or high-density plantings that are commonly used. In addition, pesticide drift from one crop to another that it is not registered for is a potential problem. Finally, the tree crop can be inadvertently damaged while managing or harvesting the crop planted in the row middle.

models that determine action thresholds for vegetation control. Weed suppression was more critical early in the season rather than late in the season for apple production (Merwin and Ray, 1997). In North Carolina, MacRae et al. (2007) noted that when the orchard ﬂoor was kept weed-free with paraquat during the ﬁrst 12 weeks after bloom for peach, fruit number, size and total yield were greater than for weed-free periods of shorter duration.

Orchard floor composition of the established orchard

Vegetation-free tree rows in summer with control of cover crops

Grass is often used as permanent ground cover in drive alleys because it is amenable to management and harbours fewer pests than broadleaved ground covers. Although grass competition severely inhibits growth of newly planted peach trees, permanent sod in drive alleys of established trees is often less debilitating (Hill, 1962). The amount of competition can be managed based on the species of grass used, the size of the vegetation-free area within a tree row, suppressive treatment of the grass, irrigation and fertilization. Some grass cultivars (e.g. ‘K-31’ tall fescue) are highly competitive with peach trees and less competitive cultivars have been recommended for orchard ﬂoor cover. Used as a permanent and complete ground cover, orchard grass reduced peach yield by up to 37% but ‘Linn’ perennial ryegrass did not reduce yield in 8-year-old peach trees (Tworkoski and Glenn, 2001). Other non-competitive grasses have been recommended as suitable ground covers (see section on ‘Management of ground covers, row middles and drive alleys’ above; Willmott et al., 2000). Ground covers other than grass have been recommended for apple (Vossen and Ingals, 2002) but more research is needed to determine beneﬁts of forbs (herbaceous plants, excluding grasses) ground cover in peach. For example, common vetch has extraﬂoral nectaries on the stipules, which may provide nectar to beneﬁcial insects. Legumes and weeds are often controlled with herbicides although other techniques have been used (see ‘Weed effects’ above). Site conditions inﬂuence availability of nutrients and water and pest threats. These environmental conditions can be used to construct

Ground cover can positively affect orchard productivity and sustainability. As previously discussed, ground covers may provide a storage pool of nutrients that can be carried from one growing season to the next. In tree rows, early-season herbicide applications allowed N mineralization to begin. Grass cover that incorporated herbicide application for no-till control of ground covers may also be used to increase availability of Ca, Mg, K and P (Haynes and Goh, 1980). Grass cover can reduce leaching of Ca, Mg, K, P, NH+4 and NO –3 and management of grass, by frequent mowing, can contribute signiﬁcantly to mineral cycling and nutrient availability within an orchard (Haynes, 1980). Ground covers in drive alleys can be mowed, possibly chopped, and transferred to tree rows as mulch for weed suppression. However, large amounts of biomass may be needed to control weeds successfully (Elmore et al., 1993). One ground cover management strategy is to plant seed mixtures in late summer or autumn with one or two mowings in late winter or spring to control ground cover height. Ground covers are then killed by mowing close to the ground (e.g. legumes) and/or by tilling and incorporating ground covers into the soil the following spring. In Europe, lateseason ground covers included fodder radish (Raphanus sativus v. olieferus), turnip (Brassica rapa v. rapa), Phacelia (Phacelia tenacetifolia) and winter rye (Secale cereale) (Bloksma and Jansonius, 2002). In California, legume and legume/grass blends have also been sown in late summer, grown in autumn and winter, and mechanically killed with shallow soil disking or close mowing in the next growing season (Vossen and Ingals, 2002). The planted ground

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covers can be used as ‘green manure’ to suppress winter weeds and add N and organic matter to soil. If the mowed ground cover is not incorporated into soil it can be used as a mulch to suppress weeds in tree rows but fewer nutrients are added to soil in the short term. Total ground cover may require early spring cultivation in orchards that are furrow, ﬂood or sprinkler irrigated. In a review of orchard ﬂoor management systems, Hogue and Neilsen (1987) determined that organic mulching in tree rows combined with managed grass in drive alleys would provide the most beneﬁt for cropping and for soil properties. However, costs, rodent control and mulch availability must be considered. Signiﬁcant increase in consumer demand for reduced inputs of synthetic chemicals and for increased organic production presents new challenges for orchard ﬂoor management in peach orchards. Research is needed to discover and develop components for orchard ﬂoor management that can serve organic production systems. Components such as mechanical tillage and non-competitive ground covers that have been discussed will be useful, but additional tools are needed. Compatible cultural and genetic components can be integrated in the orchard ecosystem. Emergent traits of an ecosystem, such as productivity, nutrient cycling and nutrient loss to ground and surface water, can be optimized in orchards under organic and conventional management. Broad comparisons between systems, including energy inputs and extrinsic costs (e.g. CO2 emissions and topsoil loss), will eventually be needed to critically compare management systems. In the near term, improved understanding of nutrient dynamics and the relationships among antagonistic or synergistic organisms, and the manipulation of the orchard ecosystem to achieve grower goals will be likely areas for future progress in orchard ﬂoor management. Vegetation-free tree rows year-round In this management scheme drive alleys, not tree rows, are vegetated in winter. Tree rows may be kept vegetation-free year-round to reduce competition and eliminate pest habitat. Pre-emergence herbicide applied early in the growing season effectively controls weeds.

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Post-emergence herbicides, cultivation and ﬂaming may also be used effectively (see ‘Weed management’ above; Table 14.1). Vegetation in drive alleys can act as ﬁlter strips which foster vertical inﬁltration of surface water, which reduces pesticide runoff (Watanabe and Grismer, 2001). Another beneﬁt is that night-time air temperatures can be increased in early spring by radiant energy release from bare soil to reduce chances for frost damage. Disadvantages include surface compaction of soil, which can reduce water inﬁltration and break down soil structure in the absence of ground cover. Permanent vegetation management by mowing Permanent vegetation beneath peach trees requires management to prevent tall plants from growing into the peach canopy and disrupting orchard worker operations. The concept is to maintain low vegetation by planting ground covers with genetically based low stature or by reducing ground cover height by mowing. As young peach trees are very susceptible to competition, this approach seems more viable with older trees and irrigation may be necessary. Allelopathic interactions between ground cover and peach trees must also be monitored (Weller et al., 1985). In addition, pest problems and tree damage from mowing can result. In New Zealand, research identiﬁed dichondra, hard fescue and creeping red fescue as shallow-rooted, lowgrowing ground covers that were dense and could suppress new weed growth beneath fruit crops (Harrington et al., 2000a,b). Additional weed control, such as mowing or selective herbicides, was needed to control perennial weeds that could grow through these ground covers. Beneﬁts of improved soil quality and reduced herbicide use may justify permanent vegetation beneath peach trees in some applications. Also, permanent sod may recycle NO –3 near the soil surface and reduce NO –3 leaching that can pollute ground water (Wiedenfeld et al., 1999). White clover (Trifolium repens) mixed with sod may contribute N to soil after mowing and subsequent mineralization of organic matter (Bloksma, 2000). Supplemental fertilizer may be needed in early

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spring and summer if organic matter pools are small and the dynamics of nutrient movement in this system have yet to be clariﬁed. Shallow-rooted grasses such as Kentucky bluegrass (P. pratensis L.), annual bluegrass (Poa annua L.), fescue (F. elatior L.) and orchardgrass (D. glomerata L.) deplete less moisture from an orchard than deep-rooted sods (Skroch and Shribbs, 1986; Hogue and Neilsen, 1987). A variety of grasses and legumes can be used in California apple orchards that manage the understorey with mowing or cultivation (Vossen and Ingals, 2002). Similar species may have use in peach orchards. Combination of low ground cover or mulches with weed control (e.g. ﬂaming, mowing, natural product herbicides) merits closer scrutiny for organically acceptable practices (Weibel and Haseli, 2003).

14.4 Orchard Floor Influences Effects of management systems on the environment Ground cover can affect heat transfer and energy relationships in orchards (Snyder and Connell, 1993). Reducing vegetation allows greater absorption of solar energy by soil and increases radiant heating from the soil in the night-time. The resulting increase can help prevent freeze injury of ﬂowers in spring. The range and ﬂuctuation in soil temperature can affect root growth rates and frost injury to roots. Permanent sod cover of creeping red fescue in row middles reduced ﬂuctuations in daily soil temperatures and provided some frost protection compared with a system of clean cultivation in summer and temporary ground cover in winter (Tan and Layne, 1993). Irrigation lowered soil temperature in summer with evaporative cooling, and elevated soil moisture persisted to ameliorate soil temperatures in winter. Soil water availability to peach trees was increased when cultivated for two or more years compared with trees grown with permanent sod cover (Kenworthy, 1953). However, in the long run (25 years) sod cover improved soil water penetration and holding capacity compared with long-term cultivation.

Research demonstrated that this long-term effect was in part due to increased rainfall capture (less runoff) and improved soil properties (increased aggregate stability, macroporosity and microbial respiration) (Welker and Glenn, 1988; Glenn and Welker, 1989b). Orchard floor management interactions with the peach tree Orchard ﬂoor management will affect peach tree size. Obviously, nutrient availability will affect growth and yield but it can also inﬂuence growth in more subtle ways. Root density of young peach trees will decrease in sod (Glenn and Welker, 1991; Parker and Meyer, 1996). When maintained in weed-free alleys, trees exploit more of the grassed areas as they age (Atkinson, 1980). Competition might be manipulated, perhaps to the growers’ advantage, to affect branch angle, excessive vegetative growth and possibly tree architecture. Reduced peach root growth resulting from competing ground cover may alter rootproduced signals, which can affect shoot development and tree architecture. Grass competition altered both dry weight and N partitioning within branches of a 3-year-old peach tree; the proportion of the N and mass partitioned into fruit decreased as the size of the vegetation-free area decreased (Tworkoski et al., 1997). In contrast, the proportion of N and mass partitioned into stem and leaves increased or were unaffected as the size of the vegetation-free area decreased. The implication of these ﬁndings is that peach yield may be more sensitive than vegetative shoot growth to increased grass competition. Young peach trees can be dwarfed and growth of mature peach trees reduced when grown for several years with grass competition (Tworkoski, 2000; Tworkoski and Glenn, 2001) (Fig. 14.3/Plate 89). However, peach tree size (mass, trunk diameter and crown size) inﬂuenced shoot regrowth following pruning more than grass competition (Tworkoski, 2000). In this case, ground covers appeared to deprive peach trees of soil nutrients by exploiting the upper soil. Fruit yield was reduced when peach trees are dwarfed by competition from sod in drive alleys but the yield efﬁciency based

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Fig. 14.3. ‘Jersey Dawn’ and ‘Redskin’ peach trees, the same age (approximately 3 years after planting) but some planted and grown in 0.6 m (small trees in foreground) and others grown in 2.4 m (large trees) vegetation-free areas with ‘K-31’ fescue in drive alleys.

on tree size (kg yield/cm2 trunk area) and water use (kg yield/cm water use plus precipitation) was not changed (Glenn and Welker, 1996). High-density plantings might, therefore, be attained by dwarﬁng peach trees with grass competition. The cumulative yield of such plantings has not yet been determined. Orchard ﬂoor management of peach has undergone a signiﬁcant change from complete mechanical control of vegetation to management of temporary and permanent vegetation with mechanical and chemical techniques. The future may incorporate ground covers that can be managed with environmentally appropriate techniques for weed control that enhance soil fertility and stability. These techniques will almost certainly be incorporated with information-based technologies and with computer models to help establish economic action thresholds for weed, water and nutrient management decisions. Management decisions are often based on increases in yield and cosmetic quality, but decisions can

include less evident gains from soil and water conservation and from biological regulation of pest populations. Such economic and environmental beneﬁts should be incorporated into future models that assist with orchard ﬂoor management decisions.

Disclaimer Mention of trade names or commercial products in this book chapter is solely for the purpose of providing speciﬁc information and does not imply recommendation or endorsement by the US Department of Agriculture.

Acknowledgement The authors thank Drs Fumiomi Takeda, Mark Brown and Mike Parker for critical reviews that improved this book chapter.

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Glenn, D.M. and Welker, W.V. (1991) Soil management affects shoot and root growth, nutrient availability, and water uptake of young peach trees. Journal of the American Society for Horticultural Science 116, 238–241. Glenn, D.M. and Welker, W.V. (1996) Sod competition in peach production: II. Establishment beneath mature trees. Journal of the American Society for Horticultural Science 121, 670–675. Granatstein, D. (2002) Tree Fruit Production with Organic Farming Methods. http://organic.tfrec.wsu.edu/ OrganicIFP/OrganicFruitProduction/OrganicMgt.PDF (accessed August 2007). Halbrendt, J.M. (1993) Research report: evaluation of a ‘Smother crop’ for orchard weed control. Pennsylvania Fruit News 73, 38–39. Harrington, K., Rahman, A., Hartley, J. and James, T. (2000a) Ground covers for orchards – past research. The Orchardist October, 54–57. Harrington, K., Rahman, A., Hartley, J. and James, T. (2000b) Ground covers for orchards – present research. The Orchardist November, 66–68. Haynes, R.J. (1980) Influence of soil management practice on the orchard agro-ecosystem. Agro-Ecosystems 6, 3–32. Haynes, R.J. and Goh, K.M. (1980) Seasonal levels of available nutrients under grassed-down, cultivated and zero-tilled orchard soil management practices. Australian Journal of Soil Research 18, 363–373. Hill, R.G. (1962) The effect of sod as a soil management practice upon the growth and yield of the peach. Ohio Agricultural Experiment Station Research Bulletin No. 903. Hogue, E.J. and Neilsen, G.H. (1987) Orchard floor vegetation management. Horticultural Reviews 9, 377–430. Horton, D.R., Broers, D.A., Lewis, R.R., Granatstein, D., Zack, R.S., Unruh, T.R., Moldenke, A.R. and Brown, J.J. (2003) Effects of mowing frequency on densities of natural enemies in three Pacific Northwest pear orchards. Entomologia Experimentalis et Applicata 106, 135–145. Hoyt, G.D. and Hargrove, W.L. (1986) Legume cover crops for improving crop and soil management in the southern United States. HortScience 21, 397–402. Ju, Z., Duan, Y. and Ju, Z. (1999) Effects of covering the orchard floor with reflecting films on pigment accumulation and fruit coloration in ‘Fuji’ apples. Scientia Horticulturae 82, 47–52. Katan, J. and DeVay, J.E. (eds) (1991) Soil Solarization. CRC Press Inc., Boston, Massachusetts. Kenworthy, A.L. (1953) Moisture in orchard soils as influenced by age of sod and clean cultivation. Michigan Quarterly Bulletin 35, 454–459. Killian, J.C. and Meyer, J.R. (1984) Effect of weed management on catfacing damage to peaches in North Carolina. Journal of Economic Entomology 77, 1596–1600. LaRue, J.H. and Johnson, R.S. (1989) Peaches, Plums, and Nectarines: Growing and Handling for Fresh Market. University of California Division of Agriculture and Natural Resources, Publication No. 3331. University of California, Oakland, California, p. 105. Layne, D.R., Jiang, Z. and Rushing, J.W. (2001) Tree fruit reflective film improves red skin coloration and advances maturity in peach. HortTechnology 11, 234–242. Layne, R.E.C. and Tan, C.S. (1988) Influence of cultivars, ground covers, and trickle irrigation on early growth, yield, and cold hardiness of peaches on Fox sand. Journal of the American Society for Horticultural Science 113, 518–525. Layne, R.E.C., Tan, C.S. and Fulton, J.M. (1981) Effect of irrigation and tree density on peach production. Journal of the American Society for Horticultural Science 106, 151–156. Leuty, T. (2003) Intercropping trees and annual crops. Ontario Ministry of Agriculture and Food. http://www. omafra.gov.on.ca/english/crops/facts/info_intercropping.htm (accessed August 2007). MacRae, A.W., Mitchem, W.E., Monks, D.W., Parker, M.L. and Galloway, R.K. (2007) Tree growth, fruit size, and yield response of mature peach to weed-free intervals. Weed Technology 21, 102–105. Mathews, C.R., Bottrell, D.G. and Brown, M.W. (2004) Habitat manipulation of the apple orchard floor to increase ground-dwelling predators and predation of Cydia pomonella (L.) (Lepidoptera: Tortricidae). Biological Control 30, 265–273. Meagher, R.L. and Meyer, J.R. (1990) Influence of ground cover and herbicide treatments on Tetranychus urticae populations in peach orchards. Experimental and Applied Acarology 9, 149–158. Merwin, I.A. and Ray, J.A. (1997) Spatial and temporal factors in weed interference with newly planted apple trees. HortScience 32, 633–637. Merwin, I.A., Stiles, W.C. and van Es, H.M. (1994) Orchard groundcover management impacts on soil physical properties. Journal of the American Society for Horticultural Science 119, 216–222. Merwin, I.A., Ray, J.A. and Curtis, P.D. (1999) Orchard groundcover management systems affect meadow vole populations and damage to apple trees. HortScience 34, 271–274.

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Meyer, J.R. (1984) Catfacing in peaches: effects of ground cover and surrounding vegetation. In: Proceedings of the 43rd Annual Convention of the National Peach Council. National Peach Council, Columbia, South Carolina, pp. 5–11. Norris, R.F. (1986) Weeds and integrated pest management systems. HortScience 21, 402–410. Parker, M.L. (2003) Growing peaches in North Carolina. http://www.ces.ncsu.edu/depts/hort/hil/ag30.html (accessed August 2007). Parker, M.L. and Meyer, J.R. (1996) Peach tree vegetative and root growth respond to orchard floor management. HortScience 31, 330–333. Pickel, C., Bentley, W.J., Hasey, J.K. and Day, K.R. (2002) Peach plant bugs. In: UC IPM Pest Management Guidelines: Peach. UC ANR Publication 3454. http://www.ipm.ucdavis.edu/PMG/r602300511.html (accessed August 2007). Powell, C.A. and Forer, L.B. (1982) Reservoirs of tomato ringspot virus in fruit orchards. Plant Disease 66, 583–584. Preusch, P.L. and Tworkoski, T.J. (2003) Nitrogen and phosphorus availability and weed suppression from composted poultry litter applied as mulch in a peach orchard. HortScience 38, 1108–1111. Preusch, P.L., Adler, P.R., Sikora, L.J. and Tworkoski, T.J. (2002) Nitrogen and phosphorus availability in composted and uncomposted poultry litter. Journal of Environmental Quality 31, 2051–2057. Rock, G.C. and Yeargan, D.R. (1973) Toxicity of apple orchard herbicides and growth-regulating chemicals to Neoseiulus fallacies and twospotted spider mite. Journal of Economic Entomology 66, 1342–1343. Skroch, W.A. and Shribbs, J.M. (1986) Orchard floor management: an overview. HortScience 21, 390–394. Snyder, R.L. and Connell, J.H. (1993) Ground cover height affects pre-dawn orchard floor temperature. California Agriculture 47, 9–12. Stasiak, M.J. and Rom, R.C. (1991) Subterranean clover (Trifolium subterraneum L.) ground cover affects on growth and foliar nutrients status of young peach (Prunus persica (L.) Batsch). HortScience 26, 77. Sullivan, T.P., Crump, D.R., Wieser, H. and Dixon, E.A. (1990) Comparison of release devices for stoat (Mustela erminea) semiochemicals used as montane vole (Microtus montanus) repellents. Journal of Chemical Ecology 16, 951–957. Sullivan, T.P., Sullivan, D.S., Hogue, E.J., Lautenschlager, R.A. and Wagner, R.G. (1998) Population dynamics of small mammals in relation to vegetation management in orchard agroecosystems: compensatory responses in abundance and biomass. Crop Protection 17, 1–11. Tan, C.S. and Layne, R.E.C. (1993) Irrigation and ground cover management effect on soil temperature in a mature peach orchard. Canadian Journal of Plant Science 73, 857–870. Tworkoski, T. (2000) Response of potted peach trees to pruning and grass competition. HortScience 35, 1209–1212. Tworkoski, T. (2002) Herbicide effects of essential oils. Weed Science 50, 425–431. Tworkoski, T.J. and Glenn, D.M. (2001) Yield, shoot and root growth, and physiological responses of mature peach trees to grass competition. HortScience 36, 1214–1218. Tworkoski, T. and Miller, S. (2001) Apple and peach orchard establishment following multi-year use of diuron, simazine, and terbacil. HortScience 36, 1211–1213. Tworkoski, T.J. and Young, R.S. (1990) Rate and time of triclopyr application to control Virginia creeper in a peach orchard. HortScience 25, 443–445. Tworkoski, T.J., Glenn, D.M. and Welker, W.V. (1997) Carbohydrate and nitrogen partitioning within one-year shoots of young peach trees grown with grass competition. HortScience 32, 1174–1177. Tworkoski, T.J., Welker, W.V. and Vass, G.D. (2000a) Soil residues following repeat applications of diuron, simazine, and terbacil. Weed Technology 14, 191–196. Tworkoski, T.J., Welker, W.V. and Vass, G.D. (2000b) Weed community changes following diuron, simazine, or terbacil application. Weed Technology 14, 197–203. Vossen, P. and Ingals, C. (2002) Orchard Floor Management. http://cesonoma.ucdavis.edu/HORTIC/orchard_ floor.pdf (accessed August 2007). Watanabe, H. and Grismer, M.E. (2001) Diazinon transport through inter-row vegetative filter strips: microecosystem modeling. Journal of Hydrology 247, 183–199. Weibel, F. and Haseli, A. (2003) Organic apple production – with emphasis on European experiences. In: Ferree, D.C. and Warrington, I.J. (eds) Apples: Botany, Production and Uses. CAB International, Cambridge, Massachusetts, pp. 551–583. Welker, W.V. (1984) The effects of oryzalin alone and in combination with diuron and simazine on young peach trees. HortScience 19, 824–826. Welker, W.V. and Glenn, D.M. (1988) Growth responses of young peach trees and changes in soil characteristics with sod and conventional planting systems. Journal of the American Society for Horticultural Science 113, 652–656.

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Diseases of Peach Caused by Fungi and Fungal-like Organisms: Biology, Epidemiology and Management J.E. Adaskaveg1, G. Schnabel2 and H. Förster3 1Department

of Plant Pathology, University of California at Riverside, Riverside, California, USA 2Department of Entomology, Soils, and Plant Sciences, Clemson University, Clemson, South Carolina, USA 3Department of Plant Pathology, University of California, Davis, California, USA

15.1 Introduction 15.2 Blossom, Foliage and Fruit Diseases Brown rot Jacket rot and green fruit rot Shot hole Scab Rust Peach leaf curl Powdery mildew 15.3 Trunk and Scaffold Diseases Silver leaf disease Leucostoma (Cytospora) canker Fungal gummosis Constriction canker 15.4 Root and Crown Diseases Phytophthora root and crown rots Armillaria root rot Verticillium wilt Peach tree short life 15.5 Postharvest Diseases Brown rot and grey mould Rhizopus rot, Gilbertella and Mucor decays Sour rot Management of postharvest decays 15.6 Other Diseases of Peach and Nectarine 15.7 Concluding Remarks 352

353 353 353 360 361 363 365 368 368 373 373 375 378 380 383 383 386 392 393 396 396 396 398 400 401 401

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

Diseases Caused by Fungi

15.1 Introduction A large number of fungal pathogens attack the blossoms, foliage, fruit, branches, trunks and roots of peach and nectarine trees. The diseases covered in this chapter are considered important diseases worldwide and are also found on other stone fruit crops. Most of them occur preharvest in the orchard and determine the overall productivity and fruit quality of the orchard during its lifespan, whereas others are major postharvest decays that have a tremendous annual economic impact after season-long inputs for production. Of the preharvest diseases discussed, some consistently cause annual losses in production. Others occur more sporadically and develop under speciﬁc climatic conditions. All of the diseases included in this discussion are caused by microorganisms that are heterotrophic and require water for growth. The organisms belong to two kingdoms, the True Fungi and the Stramenopila (Chromista). Both kingdoms previously were grouped together as ‘Fungi’ because of similarities in growth and mode of nutrient uptake, and because members of both kingdoms reproduce by spores. Members of the True Fungi discussed here belong to the phyla Zygomycota, Basidiomycota and, most importantly, Ascomycota. The phyla are characterized by the speciﬁc ways that sexual spores (zygospores, basidiospores and ascospores, respectively) are produced. These spores may be formed in fruiting structures called basidiomes (i.e. Basidiomycota) or ascoma (i.e. Ascomycota). Ascoma of the Ascomycota range from cup-shaped (apothecia) to ﬂask-shaped (perithecia) to spherical (cleistothecia, chasmothecia) bodies or are in cavities embedded in fungal tissue (ascostroma). In addition, asexual spores (sporangiospores in the Zygomycota, conidia in the Ascomycota and sometimes in the Basidiomycota, or somatic spores called chlamydospores for any group) may be formed. Dense survival structures formed by fungal mycelium (i.e. sclerotia) or by mycelium and host tissue (i.e. pseudosclerotia) may also be present. Commonly within the Ascomycota as well as other phyla, fungi have two different names, one for the asexual (anamorph) stage and another one for the

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sexual (teleomorph) stage. Within the Stramenopila, the phylum Oomycota contains important plant pathogens in the genus Phytophthora. These organisms generally are soil-borne and are adapted to wet environments, and thus are less of a problem when soil water content is managed. Organisms in the Oomycota produce asexual motile zoospores that are wall-less and ﬂagellate and are capable of swimming towards roots using chemotaxis. Zoospores form in a sac-like cell called a sporangium. Oospores are sexually produced spores that are surrounded by a thick wall. These cells, in addition to asexually produced chlamydospores, are survival structures. Pathogens that infect roots are commonly referred to as soil-borne organisms. Those that occur above ground commonly have airborne propagules that have adapted to rainsplash or wind dispersal. The purpose of this chapter is to provide the peach and nectarine horticulturalist with an overview of the major fungal diseases including a description of their distribution, the symptoms (description of disease) and signs (structures of the pathogen) involved with each disease, critical ecological and epidemiological information, and important management concepts and practices (Table 15.1). Also included are representative disease cycles for the major fungal groups, which visualize host–pathogen relationships over the growing season and illustrate the importance of the different fungal infection propagules. More detailed information on each of the diseases discussed can be found in the references provided, including some extensive book contributions (Snowdon, 1990; Ogawa and English, 1991; Ogawa et al., 1995; Strand, 1999).

15.2 Blossom, Foliage and Fruit Diseases Brown rot Brown rot is a major fungal disease of all commercially grown Prunus spp. in most regions of the world and can result in extensive crop losses (Batra, 1991). In areas with high rainfall, severe epidemics may occur in most years. In more arid locations, losses may be serious

Disease Blossom, foliage and fruit diseases Brown rot

Jacket rot and green fruit rot

Rust

Symptoms of economic significance

Primary managementb

Conidia, ascospores Conidia, ascospores? Conidia, ascospores Conidia Ascospores Conidia, ascospores Conidia, ascospores? Bud conidia Conidia, ascospores

Fruit decay Fruit decay Fruit decay Fruit decay Fruit decay Fruit decay Fruit decay Defoliation, fruit off-grades Defoliation, fruit off-grades

Sanitation, fungicides Sanitation, fungicides Sanitation, fungicides Sanitation, fungicides Orchard floor management, fungicides Sanitation, fungicides Sanitation, fungicides Fungicides Cultivar selection, fungicides

Conidia Conidia, ascospores Urediniospores (aeciospores?) Urediniospores (aeciospores?) Conidia, ascospores?

Fruit off-grades Defoliation Defoliation, fruit off-grades

Cultivar selection, fungicides Cultivar selection, fungicides Fungicides (removal of alternative host?)

Defoliation, fruit off-grades

Fungicides (removal of alternative host?)

Fusicladosporium carpophilum (= Cladosporium carpophilum) Wilsonomyces carpophilus Conidia

Fruit off-grades

Fungicides

Defoliation, fruit off-grades

Fungicides

Leucostoma cincta (Cytospora cincta) Leucostoma persoonii (Cytospora leucostoma) Chondrostereum purpureum

Branch dieback, tree decline and death Branch dieback, tree decline and death Branch dieback, tree decline and death

Sanitation, pruning practices

Monilinia fructicola Monilinia laxa Monilinia fructigena Botrytis cinerea Sclerotinia sclerotiorum M. fructicola M. laxa Taphrina deformans Podosphaera pannosa (= Sphaerotheca pannosa) Podosphaera leucotricha Podosphaera clandestina Tranzschelia discolor Tranzschelia pruni-spinosae

Scab

Shot hole Trunk and scaffold diseases Leucostoma (Cytospora) canker (syn. perennial canker) Silver leaf disease

Conidia (ascospores?) Conidia (ascospores?) Basidiospores

Sanitation, pruning practices Sanitation, pruning practices

J.E. Adaskaveg et al.

Peach leaf curl Powdery mildew

Important reproductive stages(s) for infectiona

Pathogen

354

Table 15.1. Common fungal diseases of peach and nectarine and important information on the biology, epidemiology and management of each disease.

Botryosphaeria dothidea (Botryosphaeria obtusa and Botryosphaeria rhodinia) Phomopsis amygdali

Ascospores and conidia

Branch dieback, tree decline and death

Sanitation and winter pruning (removal of alternative host?)

Conidia

Branch dieback, tree decline and death

Cultivar selection, sanitation and winter pruning, use of low-N fertilization and broad-spectrum fungicides

Root and crown diseases Armillaria root rot

Armillaria mellea

Rhizomorphs, mycelium

Armillaria ostoyae

Rhizomorphs, mycelium

Armillaria tabescens

Mycelium (rhizomorphs?)

Pseudomonas spp.

Bacterial cells

Root and crown rot, tree decline and death Root and crown rot, tree decline and death Root and crown rot, tree decline and death Tree decline and death

Cytospora spp.

Conidia (ascospores)

Site selection (avoidance), sanitation, soil fumigation Site selection (avoidance), sanitation, soil fumigation Site selection (avoidance), sanitation, soil fumigation Site selection (avoidance), soil fumigation, rootstocks Sanitation, pruning practices

Phytophthora cactorum

Zoospores, chlamydospores?

Phytophthora cambivora

Zoospores, chlamydospores? Zoospores, chlamydospores Zoospores

Peach tree short life

Phytophthora root and crown rots

Phytophthora cinnamomi Phytophthora citricola Phytophthora citrophthora Phytophthora cryptogea Phytophthora drechsleri

Zoospores, chlamydospores? Zoospores Zoospores, chlamydospores

Branch dieback, tree decline and death Root and crown rot, tree decline and death Root and crown rot, tree decline and death Root and crown rot, tree decline and death Root and crown rot, tree decline and death Root and crown rot, tree decline and death Root and crown rot, tree decline and death Root and crown rot, tree decline and death

Irrigation management (e.g. raised beds, sprinkler shields to prevent trunk wetness), rootstocks, fungicides Irrigation management, rootstocks, fungicides Irrigation management, rootstocks, fungicides Irrigation management, rootstocks, fungicides Irrigation management, rootstocks, fungicides Irrigation management, rootstocks, fungicides Irrigation management, rootstocks, fungicides

355

(Continued)

Diseases Caused by Fungi

Fungal gummosis (syn. peach blister canker or ibokawa byo) Constriction canker

356

Table 15.1. continued Symptoms of economic significance

Primary managementb

Phytophthora syringae

Zoospores, chlamydospores Zoospores

Verticillium wilt

Verticillium dahliae

Microsclerotia

Root and crown rot, tree decline and death Root and crown rot, tree decline and death Wilt

Irrigation management, rootstocks, fungicides Irrigation management, rootstocks, fungicides Site selection (avoidance), soil fumigation

Postharvest diseases Brown rot

M. fructicola

Conidia

Fruit decay

M. laxa

Conidia

Fruit decay

M. fructigena

Conidia

Fruit decay

Grey mould

B. cinerea

Conidia

Fruit decay

Gilbertella decay

Gilbertella persicaria

Sporangiospores

Fruit decay

Mucor decay

Mucor piriformis Mucor spp. Geotrichum candidum

Sporangiospores

Fruit decay

Arthroconidia

Fruit decay

Temperature management, sanitation, fungicides Temperature management, sanitation, fungicides Temperature management, sanitation, fungicides Temperature management, sanitation, fungicides Temperature management, sanitation, fungicides Temperature management, sanitation, fungicides Temperature management, sanitation

Pathogen Phytophthora parasitica

Sour rot aPropagules

with a question mark have a limited or unknown role in the disease cycle. practices with a question mark have a limited or poorly defined role in controlling the disease.

bManagement

J.E. Adaskaveg et al.

Important reproductive stages(s) for infectiona

Disease

Diseases Caused by Fungi

when environmental conditions are conducive for the pathogen to produce blossom blight and quiescent infections on developing fruit or brown rot of mature fruit when rains occur at harvest time. The disease is caused by three species of the genus Monilinia that can be differentiated by their cultural characteristics (Byrde and Willetts, 1977). Monilinia fructicola Winter (Honey), the cause of North American brown rot, is the main pathogen on peaches and other stone fruits in most regions, except in Europe, where it is not found (Batra, 1991). Monilinia laxa (Aderh. & Ruhl.) Honey causes European brown rot on peaches and other stone fruits worldwide, but generally is less important on peaches in areas where M. fructicola is also present. The third species, Monilinia fructigena Honey in Whetzel, is not present in North America. In Europe, its primary distribution area, it mainly occurs on pome crops and only occasionally on peach and nectarine. The brown rot disease cycle includes blossom and twig blights and, most economically important, pre- and postharvest fruit decay (Fig. 15.1). Primary inoculum sources in the spring are overwintering brown rot fruit mummies on the tree, which produce asexual conidia in sporodochia, and fruit mummies on the orchard ﬂoor, which produce sexual fruiting structures (apothecia) and spores (ascospores) (Biggs and Northover, 1985). Twig cankers and infected fruit peduncles can be additional sources of inoculum (Sutton and Clayton, 1972; Biggs and Northover, 1985). Blossom blight rarely reduces the crop load, but blighted blossoms and infected shoots provide secondary inoculum for fruit infections later in the season. Infections can occur over a wide temperature range with an optimum of 22.5–25°C (Biggs and Northover, 1988a; Tamm and Flückiger, 1993). Minimum wetness durations of 3–5 h are required at 20°C, whereas 18 h are needed at 10°C. The ﬁrst symptoms of blossom blight (Fig. 15.2/Plate 90) are necrosis of the anthers and browning of the ﬁlaments that proceeds to the ﬂoral tube, ovary and peduncle. Infections may extend into the twig, which may be girdled. As infected ﬂowers wilt and turn brown, they generally ﬁrmly stick to the twig in a gummy mass. In wet weather, infected

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ﬂowers become covered with greyish to tan sporodochia. Blossom infections by M. laxa, and less commonly by M. fructicola, may result in twig cankers that often show extensive gum formation at the advancing margin. The canker may girdle the twig, resulting in blight of the distal twig with leaves turning tan to brown and remaining attached. If the branch is not girdled, surrounding healthy tissue will produce callus. On large cankers, sporulation may continue for several years. Infection of fruit occurs by direct penetration through the cuticle, through suture cracks or other injuries, or indirectly through stomata. Susceptibility of fruit to infection by Monilinia spp. is high during the early stages of fruit development, decreases during green fruit stages and then increases again as fruit mature and ripen (Biggs and Northover, 1988b; Gradziel, 1994). On mature or ripening fruit, brown rot typically develops as a rapidly spreading, ﬁrm, brown decay (Fig. 15.3/ Plate 91). Under optimum conditions, decay of ripe peaches infected by M. fructicola may be visible within 48 h of infection. Quiescent infections that occur on developing fruitlets and on ripening fruit in less favourable environments (arid and semi-arid climates) may become active when fruit mature prior to or after harvest. Molecular techniques have been developed for the detection of quiescent fruit infections of stone fruit and for species identiﬁcation (Förster and Adaskaveg, 2000; Hughes et al., 2000; Boehm et al., 2001; Côte et al., 2004). Infections on green fruit that are injured by frost or insects or are dropped to the orchard ﬂoor, especially during late thinning, may sporulate and provide additional inoculum. Orchard sanitation practices that include removal of mummiﬁed fruit and infected twigs, as well as twigs with cankers, from trees are important components of an integrated management approach. In some peach production areas, removal of alternative hosts such as wild Prunus spp. may also be an effective strategy. No brown rot-resistant peach cultivars are available, but there are considerable differences in susceptibility among peach (cling and freestone) cultivars (Gradziel and Wang, 1993; Bassi et al., 1998). Protective fungicide treatments provide the best control for both blossom blight and fruit rot. The proper use

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Overwintering mummy on ground

Twig blight and rot of immature and mature fruit

Conidia

Conidia

Gumming

Overwintering mummy on tree

Blossom blight

Ascus and ascospores

Apothecia

Fig. 15.1. Disease cycle of brown rot of peach caused by Monilinia fructicola. The fungal pathogen overwinters in fruit mummies either on the tree or on the orchard floor. In spring, asexual conidia produced from mummies on the tree and sexual ascospores produced in asci that are formed in fruiting bodies (apothecia) on the ground are the primary inoculum. These spores are wind-dispersed to susceptible host tissues (e.g. blossoms) and germinate under favourable wetness and temperature conditions. Infections of blossom tissue can occur within 6–12 h at 15–20°C. After 3 to 5 days, blossoms become blighted. Diseased blossoms typically remain attached and the infection spreads into the peduncle and down into the twig. The infection continues with the formation of a twig canker that often develops a gumdrop as a host response. Conidia form on infected tissue and serve as secondary inoculum for infection of immature (green) and mature fruit. Fruit infections may also result in twig blight during severe outbreaks. (Drawing by J.E. Adaskaveg.)

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Fig. 15.2. Brown rot blossom blight of peach caused by Monilinia fructicola. Infected blossom with gumming and canker development at the base of the peduncle.

Fig. 15.3.

Brown rot fruit rot of peach caused by Monilinia fructicola.

of fungicides with local systemic activity protects ﬂowers and fruit, reduces the amount of sporulation formed on the infected tissue, and reduces sources of overwintering inoculum.

Blossom applications have to be done as susceptible ﬂower parts are exposed and before the occurrence of periods with conducive wetness and temperatures. Fungicides need

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not be applied to immature fruit unless wetness conditions are especially favourable for infection or injury caused by insects or cold has increased the likelihood of disease. Thus, insect control during this period may be an important consideration. Management of brown rot and several other pathogens is heavily dependent on fungicides and, thus, fungicide resistance management practices are essential to prevent the development of insensitive pathogen populations using the newer single-site mode of action materials. In some peach production areas, fungicide resistance has developed in populations of M. fructicola against the benzimidazoles and crop losses have occurred (Ogawa et al., 1988). More recently extensive shifts in effective concentrations (EC50 values) of the demethylation-inhibiting fungicides have also been observed in the ﬁeld (Zehr et al., 1999; Schnabel et al., 2004). Jacket rot and green fruit rot Decay of ﬂower parts resulting in jacket rot and subsequent green fruit rot can be a serious problem in wet years or in foggy production

areas with prolonged wetness periods during bloom. This disease can affect all stone fruit crops including peach and nectarine that are the least susceptible. One or several fungi including Monilinia spp., Botrytis cinerea Pers.: Fr. (teleomorph Botryotinia fuckeliana (de Bary) Whetzel) and Sclerotinia sclerotiorum (Lib.) de Bary commonly cause jacket rot and green fruit rot, depending on the geographical location and the presence of the pathogens. All of these fungi have a cosmopolitan distribution and thus this disease presumably occurs throughout temperate fruit-growing regions of the world wherever wetness occurs during the bloom period. The disease begins with the pathogens attacking the calyx (ﬂoral cup or later the ‘jacket’ or ‘shuck’ around the developing fruit), petals and other ﬂower parts, causing them to wither (Fig. 15.4/Plate 92). As fruit develop and come in contact with diseased blossom parts, the pathogens can grow into the healthy fruit. A brown lesion develops and spreads quickly into the small or immature fruit (Fig. 15.5/Plate 93). B. cinerea is characterized by greyish tufts of conidia on infected senescent or dying plant tissues or on sclerotia on the orchard ﬂoor. Germination of conidia occurs

Fig. 15.4. Jacket rot of peach caused by Botrytis cinerea. The jacket (or shuck) is infected, but the immature fruit is still disease-free.

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Fig. 15.5. Green fruit rot of peach caused by Monilinia fructicola. The decay spreads to neighbouring healthy fruit by contact.

with wetness over a wide temperature range with an optimum of 15–20°C. Wetness is not required if relative humidity is above 98%. With S. sclerotiorum, white mycelium develops on infected fruit and blossom tissues; no asexual spores are produced. Sexual spores of S. sclerotiorum are produced from apothecia that develop from sclerotia on the orchard ﬂoor (Fig. 15.6/Plate 94), especially under vegetation of cover crops. Ascospores are forcibly discharged from the apothecia following changes in relative humidity or by physical disturbance. Infection of ﬂoral parts by ascospores requires 48–72 h of wetness with temperature seldom being limiting. Sclerotia of this fungus only form after infected structures fall to the ground. Monilinia species can also cause green fruit rot after partial colonization of blossom tissue or after causing brown rot blossom blight. Spores of the jacket rot and green fruit rot fungi are wind-borne or are disseminated by splashing rain and germinate to infect the senescent blossom tissues. From infections of blossom tissues the pathogens can move into fruit tissue, provided that cool, wet weather occurs, which

delays the jacket from separating from the developing fruit and allows fungal growth. Removal of weeds and senescent plant tissues from the orchard ﬂoor is probably beneﬁcial in reducing inoculum levels for jacket rot and green fruit rot. Fungicide applications with materials effective against all green fruit rot pathogens during bloom, especially full bloom, are suggested to prevent losses.

Shot hole Shot hole disease of stone fruits occurs worldwide but is especially important in the peachproducing areas of the western USA. It is most important on peaches, nectarines and apricots. Outbreaks of the disease on peach occur following favourable environments and when no protective fungicide treatments were applied during the dormant season. Shot hole is caused by the imperfect fungus Wilsonomyces carpophilus (Lév.) Adaskaveg, Ogawa & Butler, which was previously

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Fig. 15.6. Apothecia of Sclerotinia sclerotiorum are produced on over wintering sclerotia (bottom). Ascospores are forcibly discharged in a spore cloud. (Reprinted, with permission, from Strand, 1999.)

classiﬁed in the imperfect genera Coryneum, Clasterosporium and Stigmina. Symptoms of shot hole occur on twigs, leaves and fruit (Wilson, 1937). The primary damage to peach is the killing of twigs and buds. In the absence of management practices, unsightly superﬁcial fruit infections render the crop unmarketable. On twigs, where the fungus overwinters, lesions ﬁrst appear as purplish spots 2–3 mm in diameter that enlarge up to 10 mm in diameter, turn brown and are slightly sunken (Fig. 15.7/ Plate 95). In the light tan centre of the lesions, asexual conidia of the fungus are produced in sporodochia in the spring. These conidia are the primary inoculum for new infections; they are rain-splash dispersed to developing blossoms and leaves. Conidia may remain

viable for several months when kept dry. Infected buds are another overwintering stage of the fungus where primary inoculum is produced in the spring and often throughout the season. Scales of infected buds turn dark and are sometimes covered with gummy exudates. Lesions on leaves and fruit also start out as small purplish spots that turn brown and expand up to 10 mm in diameter. During warm, dry weather, lesions on leaves abscise to produce the typical shot hole symptoms. Early dehiscence mostly eliminates the formation of sporodochia on shot hole lesions. In cool, wet environments, however, lesions remain attached to leaves and sporodochia commonly develop in the centre of each lesion. Infected leaves may drop but early defoliation of peach trees is rare. On fruit,

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Fig. 15.7. Lesion of the shot hole fungus Wilsonomyces carpophilus on peach twig, where the pathogen overwinters. Sporodochia of the fungus can be seen in the centre of a stem lesion.

lesions turn into raised, corky areas that do not extend into the mesocarp tissues (Fig. 15.8/ Plate 96). Conidia of the fungus germinate over a wide temperature range. Twig infections require at least 24 h of continuous wetness, whereas shorter wetness durations are required for leaf infections. Thus, at 20–25°C, leaf infections occur after 8–12 h of wetness. Epidemics of shot hole occur when high rainfall commonly occurs. For management of the disease in semi-arid climates like in California, dormant fungicide sprays to protect against twig and bud infections are applied in the autumn after leaf drop and before winter rains begin. In wetter climates, protective fungicides also have to be applied at leaf emergence and through fruit set.

Scab Scab is an important fungal disease of peaches, nectarines and other Prunus species in warm areas with high rainfall, such as the southeastern USA, or when orchards are irrigated by overhead sprinkler. The disease also has caused epidemics on peach in semi-arid areas like California in years with unusually high rainfall. Scab is caused by the fungus Venturia carpophila E.E. Fisher. The sexual stage has rarely been observed but the asexual stage, Fusicladosporium carpophilum (Thüm.) Partridge & Morgan-Jones (formerly Cladosporium carpophilum Thüm.), is common. Infections can occur on twigs, leaves and fruit, but symptoms are most noticeable on fruit. On twigs, where the fungus overwinters,

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Fig. 15.8. Symptoms of shot hole caused by Wilsonomyces carpophilus on peach fruit and leaf.

superﬁcial circular to oval lesions that are slightly raised develop on new succulent growth in the spring (Keitt, 1917; Bensaude and Keitt, 1928). These lesions initially appear as water-soaked spots, which darken with age and become brown and later purple to dark brown and have a raised border. At the end of the season, lesions are oval in shape and 3 mm × 5 mm to 5 mm × 8 mm in size. They persist throughout the host dormant period. In the following spring, during periods with relative humidity between 70 and 100%, the fungus produces abundant primary inoculum in the form of asexual conidia from olivaceous tufts of mycelium within the lesion (Lawrence and Zehr, 1982; Gottwald, 1983) especially after petal fall until mid-spring. Conidia are dispersed by wind and rain. They germinate between 15 and 30°C with an optimum temperature of 25–30°C (Lawrence and Zehr, 1982). Maximum conidial germination occurs in free water, but conidia can also germinate at 94–100% relative humidity. The

fungus does not survive in the twig lesions for more than a second season due to bark formation during twig growth. With unusually severe infections, new shoots of the host may die back. On leaves, symptoms may occur in early summer on the lower surfaces and are visible as irregular, blotchy lesions slightly darker in colour than the surrounding healthy tissue. Lesions turn olive green once sporulation of the fungus occurs. Infections of leaves are rarely severe enough to cause serious defoliation of trees. On fruits, small circular spots develop mainly on the upper, exposed surfaces (Fig. 15.9/Plate 97). They are 5–10 mm in diameter, are ﬁrst green and turn olive to black once the fungus sporulates and sometimes have a green to yellow halo. When fruit are severely infected, lesions coalesce and form large, superﬁcial blotches that make the fruit unmarketable. Although scab on peach and nectarine fruit may develop similar to bacterial spot caused by Xanthomonas arboricola pv. pruni (Smith) Vauterin, in

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Fig. 15.9. Symptoms of scab caused by Fusicladosporium carpophilum on peach fruit.

most early-season infections bacterial spot on fruit is visible as small, irregular, watersoaked brown spots that may occur anywhere on the fruit surface and later develop into deep, cavernous-appearing lesions. Management of scab is mainly accomplished with the use of fungicidal sprays that are applied at shuck split and every 2 weeks thereafter through early summer. In semi-arid climates, effective management can also be obtained by reducing inoculum dispersal and leaf wetness from foliar sprinkler irrigation. Sanitation by removing infected twigs is impractical because large numbers of overwintering lesions persist on fruiting wood. Pruning trees to allow adequate sunlight penetration and unimpeded air movement may improve scab management by facilitating rapid drying and good fungicide coverage.

Rust Peach rust occurs wherever stone fruit are grown. Incidence of the disease in different years and different peach production regions is highly variable and epidemics occur in years with excessive wetness during the growing

season. Rust is caused by two species of the biotrophic genus Tranzschelia, Tranzschelia discolor Tranz. & Lit. and Tranzschelia pruni-spinosae Pers., that differ in morphology of their teliospores. T. discolor is found worldwide, whereas T. pruni-spinosae is mainly found in Europe and the central and eastern USA (Dunegan, 1938). For T. discolor, different formae speciales have been described on different stone fruit hosts with strains on peach being designated as T. discolor f. sp. persicae. Although cross-infection of formae speciales among host species occurs, virulence is generally reduced. Tranzschelia spp. are macrocyclic, heteroecious rusts that alternate between species of Prunus and genera in the Ranunculaceae (buttercup family). In mild climates, the fungus can survive on Prunus spp. without infecting the alternative host. Because the uredinial stage is capable of repeated infections on Prunus spp., this host can be seriously damaged, causing economic losses. On peach, in addition to leaves and fruit, the fungus can infect stem tissues, which are important sources of primary inoculum in the spring (Fig. 15.10/Plate 98). Leaf infections develop as angular, yellow lesions with rustybrown urediniospore-producing pustules (uredinia) on the lower leaf surfaces (Goldsworthy

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Fig. 15.10. Sporulating stem lesion of peach rust caused by Tranzschelia discolor.

Fig. 15.11. Symptoms of peach rust caused by Tranzschelia discolor on peach leaves.

and Smith, 1931) (Figs 15.11 and 15.12/Plates 99 and 100). Late in the growing season, uredinia develop into telia that produce darkcoloured teliospores. Heavy leaf infection can

result in premature defoliation of the tree during autumn and stimulate ﬂowering, which may reduce tree vigour or productivity in the subsequent season. Symptoms on

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Fig. 15.12. Leaf lesions with uredinia of peach rust caused by Tranzschelia discolor.

Fig. 15.13. Symptoms of peach rust caused by Tranzschelia discolor on peach fruit.

immature fruit are green, circular lesions 2–3 mm in diameter (Fig. 15.13/Plate 101). On mature fruit, lesions are sunken with yellow halos and the mesocarp below the lesion is discoloured. Current-year peach stems are infected during outbreaks of the disease in

late autumn and the fungus survives as mycelium in symptomless stems during the winter. In early spring, infections are ﬁrst visible as water-soaked lesions. The epidermis then becomes raised and ruptures with the development of uredinia and urediniospores that

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function as primary inoculum for leaf infections. Later, as the stems grow in circumference, lesions split open lengthwise along the stems. Lesions will not continue to produce spores in the following season because infections are then delimited by a wound periderm. Stem lesions are superﬁcial and are not considered directly damaging to the tree. On peach, both species of Tranzschelia function as asexual fungi. Stages of the fungus that occur on the alternative host have not been observed in many locations and the aecial stage generally is not considered an important inoculum source. As described above, the fungi overwinter as mycelium in twigs, but may also survive as urediniospores on twigs or as uredinia on non-abscised leaves. Urediniospores germinate over a wide temperature range (8–38°C; 13–26°C is optimum) and require wetness or a saturated atmosphere. At 20°C, 18 h of wetness are required for adequate leaf infection. Thus, for the development of epidemics, the presence of viable spores and conducive periods of wetness are needed. For management of peach rust, preventive applications of fungicides are done before rain events during the spring. The emergence of sporulating stem lesions as indicated during monitoring programmes in the spring has been used as a starting date for fungicide applications (Soto-Estrada et al., 2003).

Peach leaf curl Peach leaf curl is a cosmopolitan disease and occurs wherever peaches and nectarines are grown. Economic losses have been reported historically, but crop losses in orchards treated with fungicides are now negligible. In mild climates the disease can consistently be observed, but its occurrence is more erratic in most other production areas. Peach leaf curl is caused by Taphrina deformans (Berk.) Tul. Symptoms occur mainly on newly formed leaves in the spring (Fig. 15.14/Plate 102). Leaves ﬁrst develop discoloured areas that thicken and then become wrinkled and puckered, causing the leaves to curl. Infected leaves can have a range of

colours from light green to yellow, red and purple (Fig. 15.15/Plate 103). They may be covered with a subtle white layer of sexually produced spore sacs (asci containing ascospores) and then turn brown and generally abscise. Defoliated trees will leaf out again, but fruit set will be sparse in the current year and the following season. Fruit infections are less common. They are characterized by irregular, raised green (initially) or reddish lesions (Fig. 15.16/Plate 104). The fungus overwinters in the asexual, yeast-like bud-conidia stage, which contaminates twigs and buds of the tree. Emerging leaves are infected when the fungus changes to a mycelial parasitic phase. Naked asci are then produced on the leaf surface and the sexual ascospores are forcibly discharged. These spores germinate and form more budconidia that contaminate twig tissues. Infections occur at temperatures of 10–21°C, but ascospores and bud-conidia can survive hot, dry conditions for several months. Periods of cool, wet weather during early bud development favour leaf curl disease. When temperatures at early leaf development are high, infections rarely become established. Peach leaf curl can be managed with one well-timed preventive fungicide application, either in late autumn after 90% of the leaves have fallen or in spring before bud swell. Treatments after infection or symptom development are ineffective. Sanitation and cultural practices do not provide control against this disease. Most peach and nectarine cultivars are susceptible to the disease, but there is a wide range of susceptibilities. Vigour of infected trees should be maintained by irrigation and N fertilization management, as well as reducing stress from crop load by extra thinning.

Powdery mildew Powdery mildew of peach and nectarine occurs worldwide, but is most damaging in semiarid growing areas. The disease can be caused by several different species of fungi that commonly occur on rosaceous plants (Yarwood, 1939). Three species have been reported on

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Fig. 15.14. Peach leaf curl caused by Taphrina deformans.

peach, with Podosphaera pannosa (Wallr.:Fr.) Braun & Takamatsu (formerly Sphaerotheca pannosa (Wallr.:Fr.) Lév.) being the most important. Podosphaera leucotricha (Ellis & Everh.) E.S. Salmon is less common, and Podosphaera clandestina (Wallr.:Fr.) Lév. has been reported on peach seedlings in the eastern USA, whereas P. tridactyla has been observed on peach in southern California (J.E. Adaskaveg and H. Förster, unpublished). Fruit infections caused by P. pannosa and P. leucotricha cause the most economic damage, but leaf infections are important sources of inoculum. In nurseries, powdery mildew leaf infections can cause signiﬁcant damage to seedlings and small trees. The susceptibility of peach and other stone fruit crops varies greatly among cultivars. The eglandular (without glands at the leaf base) peach cultivars are more susceptible than the glandular ones. Furthermore, in some cultivars, tissues also vary in their susceptibility with fruit being more or less susceptible than leaves,

depending on the mildew species involved and maturity of host tissue. Leaves, buds, green shoots and fruit are commonly attacked, but ﬂower infections are rare. On twigs, mildews are white and felt-like, even in the winter in mild climates (Fig. 15.17/Plate 105). The ﬁrst symptoms on peach leaves infected by P. pannosa are small, circular, white, web-like colonies that become powdery once masses of asexual conidia are produced in chains (Fig. 15.18/Plate 106). Leaves may then curl or become stunted. Older infections commonly result in leaf chlorosis and necrosis. Severe infections may result in defoliation. Fruit are susceptible from the early stages of development until pit hardening on peach, nectarine and plum, but not other Prunus spp. (Weinhold, 1961). White circular spots may enlarge, coalesce and cover large areas of the fruit (Figs 15.19–15.21/Plates 107–109). Infections usually result in some deformation of the fruit surface with depressed or slightly

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Fig. 15.15. Advanced symptoms of peach leaf curl caused by Taphrina deformans with leaf deformation, discoloration, necrosis and a subtle white layer of sexually produced asci containing ascospores.

Fig. 15.16. Symptoms of peach leaf curl caused by Taphrina deformans on developing peach fruit.

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Fig. 15.17. Peach twig with overwintering mycelium and embedded chasmothecia of powdery mildew caused by Podosphaera pannosa.

raised areas. Infections on peach fruit become necrotic after pit hardening, whereas on nectarine and occasionally also on peach the tissue remains green. Any fruit with blemishes caused by powdery mildew are generally unmarketable. Based on indirect evidence, P. leucotricha (mainly an apple pathogen) presumably is involved in causing another powdery mildew symptom on peach fruit known as ‘rusty spot’ (Daines and Trout, 1977, Ries and Royse,

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1978). With this disease, small, circular, orangerusty lesions develop on the fruit, which enlarge and may cover the entire fruit. No symptoms occur on leaves and stems. Lesion development has been related to rapid fruit growth. Incidence of the disease increases from shuck-fall stage of fruit development until 60 days after full bloom and epidemics typically last from 17 to 30 days (Furman et al., 2003a). P. pannosa overwinters as mycelium in shoots and in the inner bud scales (Weinhold, 1961). In milder climates, young twigs may be covered with dense mats of mycelium. During a recent winter in California we found for the ﬁrst time on peach the sexual fruiting bodies (chasmothecia, formerly referred to as erysiphaceous cleistothecia or perithecia) of the fungus, which were embedded in these mycelial mats (Fig. 15.22/Plate 110). In the spring, newly developing leaves become diseased as they emerge from infected buds. When chasmothecia are present, ascospores are released that also serve as primary inoculum. Because roses are an important host for the pathogen and disease is not always managed on this host, diseased roses can be major contributors to the development of epidemics of peach powdery mildew. Secondary infections by the wind-disseminated, asexual conidia occur throughout the growing season. Conidia germinate between 2°C and 37°C, with an optimum of 21°C. Conidia can germinate in free water and at relative humidity of 43–100%. Excessive durations of wetness will kill conidia of powdery mildew fungi. During periods with warm, humid conditions the disease can quickly develop into an epidemic. Management of powdery mildew is by cultural practices and the use of protective fungicide treatments. Less-susceptible cultivars should be planted in areas that commonly have a high incidence of disease. To reduce the relative humidity in the orchard, the frequency of irrigation periods should be minimized and low-angle sprinklers should be used to keep foliage dry. Fungicide applications are done from calyx (i.e. shuck) fall until the pit-hardening stage of fruit development for peach and nectarine. Adequate management of rusty spot was achieved with three to ﬁve fungicide applications (Furman et al., 2003b).

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Fig. 15.18. Powdery mildew caused by Podosphaera pannosa on peach leaves.

Fig. 15.19. Powdery mildew caused by Podosphaera pannosa on developing peach fruit.

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Fig. 15.20. Powdery mildew caused by Podosphaera pannosa on mature peach fruit.

Fig. 15.21. Powdery mildew caused by Podosphaera pannosa on developing nectarine fruit.

15.3 Trunk and Scaffold Diseases Silver leaf disease Silver leaf disease of peach is caused by the fungus Chondrostereum purpureum (Pers.:Fr.)

Pouz. The disease also affects a wide range of other cultivated and non-cultivated hardwood tree species, particularly willow and poplar. Silver leaf disease has been reported from most temperate-zone stone fruit production areas and can also be a problem in nurseries.

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Fig. 15.22. Close-up of chasmothecia of powdery mildew caused by Podosphaera pannosa on peach twig.

The fungus can also grow saprophytically on tree logs and prunings. Leaves of silver leaf-diseased trees become silvery in appearance (Fig. 15.23/Plate 111), which is most noticeable on new growth in the spring when damage by other diseases and pests does not obscure the symptoms. These symptoms occur soon after the pathogen invades the woody tissues. Silver leaf symptoms result from a toxin produced by the pathogen that causes the upper epidermis to separate from the palisade mesophyll layer of the leaf. The separated layers then reﬂect light differently from healthy tissue, giving leaves the silvery appearance. Infected leaves may then become necrotic and abscise. In the wood of infected trees, two symptoms occur, wood discoloration and white rot. Wood discoloration in branches is often angular to pieshaped in cross-section, whereas in the trunk the discoloration occurs in the older secondary xylem (Fig. 15.24/Plate 112). In white rot, the decayed wood becomes mottled to bleached white and eventually spongy soft. Substantial decay of the trunk may occur and extend into the scaffold branches and into the roots. Leathery fruiting bodies of the fungus may develop in bracket-like clusters on tree trunks and scaffold branches of living trees and on dead wood. They produce sexual basidiospores

that are the only known propagules of the fungus. They are wind-disseminated and function as inoculum in disseminating the organism. On peaches, fruiting bodies are not easily found, although they are thought to persist for up to 2 years, producing spores during warm, moist environments at any time of the year. Like most wood decay fungi, C. purpureum needs a fresh wound that exposes wood of the branch or trunk. Wind-disseminated spores of the fungus are deposited on the moist wood, germinate and quickly invade the xylem tissues of the wood. The fungus grows over a wide temperature range with an optimum of 25°C. Wood-exposing wounds are most susceptible in the ﬁrst week after injury. Wound healing, which prevents infection by the fungus, progresses at different rates in different climates and at different times of the year. A wide range of perennial hosts, inoculum production over a long period, the impossibility of protecting all wounded surfaces and the inability to eradicate established infections from tree trunks make silver leaf a difﬁcult disease to control. Management practices should therefore focus on starting with clean nursery stock and on preventing the establishment of the fungus by minimizing large wood-exposing wounds and using proper pruning practices. Sanitation measures to

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Fig. 15.23. Symptoms of silver leaf disease caused by Chondrostereum purpureum on peach leaves: diseased leaf (left) and healthy leaf (right).

reduce inoculum include removing and burning infected wood. The most effective pruning wound treatments are biocontrol agents such as Trichoderma spp., which act by pre-colonizing the wood and site-excluding the pathogen. Leucostoma (Cytospora) canker Leucostoma (Cytospora) or perennial canker is an important disease of stone fruit crops including peach and nectarine, especially in colder climates. It is also associated with the peach tree short life syndrome in the southeastern USA (see below) and is part of the apoplexy disease complex on stone fruits in Europe. The disease also occurs in the Paciﬁc Northwest of the USA, as well as in Canada, South America and Japan. Leucostoma canker

reduces the number of bearing branches, kills twigs and shortens tree life. Leucostoma canker is caused by Leucostoma cincta (Fr.:Fr.) Höhn. (syn. Valsa cincta (Fr.:Fr.) Fr.) (anamorph Cytospora cincta Sacc.) and Leucostoma persoonii Höhn. (syn. Valsa leucostoma (Pers.:Fr.) Fr.) (anamorph Cytospora leucostoma (Pers.:Fr.) Fr. These fungi produce a compound fruiting body that consists of a central pycnidium that produces hyaline asexual conidia. These conidia ooze from the pinhead-sized, black pycnidia to form long orangish tendrils (cirri). Perithecia develop in or under older stroma around the pycnidium. In the perithecia, sexual spores (ascospores) are formed. The pathogens infect small and large branches of trees (Fig. 15.25/Plate 113). Infections result in dieback that continues from

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Cross-section through scaffold branch of peach infected by Chondrostereum purpureum.

Fig. 15.25. Peach tree with Leucostoma (Cytospora) or perennial cankers on scaffold branches. (Reprinted from Ogawa et al., 1995, with permission of APS.)

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apical branches to the main scaffold branches and trunk. On small branches, lesions appear as sunken, zonate, discoloured areas that develop around dead buds or previous years’ leaf scars and are observed 2 to 4 weeks after bud break (Fig. 15.26/Plate 114). Amber gum may ooze from these lesions as they age and darken unless the branch dies. On large branches, scaffolds and trunks, conspicuous elliptical cankers develop. Copious amounts of gum may exude from the cankers and, with age, the bark dries and cracks form, exposing the blackened tissue beneath. If infections follow winter injury or develop on branches weakened from infections by other pathogens, gumming will not be associated with the cankers. Cankers typically develop concentric rings from alternation between canker

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extension and callus formation during dormant and growing seasons, respectively. Pycnidia erupt directly through the bark within the branch or trunk canker and give the surface of the bark a pimpled appearance (Fig. 15.27/Plate 115). Thus, pycnidia are not associated with bark lenticels. Discoloured wood, wilting and chlorotic and dehiscent leaves are other symptoms associated with Leucostoma canker. Conidia are the primary inoculum for the disease. They are most abundantly produced under cool, moist conditions of late autumn and early spring, but are present throughout the year if rainfall is sufﬁcient. Conidia are dispersed by rain, wind and possibly birds and wood-boring beetles. Germination requires the presence of free water or 100% relative

Fig. 15.26. Leucostoma or perennial cankers caused by Leucostoma cincta (Cytospora cincta) around nodes of peach shoot. (Reprinted from Ogawa et al., 1995, with permission of APS.)

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Fig. 15.27. Pycnidia of Leucostoma cincta (Cytospora cincta) on cherry twig. Spore masses are exuded by some pycnidia on the upper part of the twig.

humidity and a carbon source. Most infections occur on wood injured by sunburn, pruning, insects or rodents. Trees stressed by freezing, nutrient deﬁciency and infections by ring nematodes and bacterial canker are predisposed to the disease. Young vigorous trees are less susceptible. On older weakened trees many new infections may occur at the nodes of 1-year-old shoots. Because Leucostoma canker develops on weakened trees, requires injuries for infections and usually follows winter injury in cold climates and sunburn in warm climates, the management of Leucostoma canker requires an integrated approach of cultural and pest management practices. In both cold and warm climates, the disease can be kept to a minimum with good cultural practices that ensure tree vigour and hardiness. Painting trunks white with 100% acrylic latex paint prevents sunburn (‘south-west’) injuries and helps reduce Leucostoma canker. Trees should not be planted on heavy clay or shallow soils, where moisture and nutrient stress may occur. Fungicides have not been effective. In summary, management of Leucostoma canker is based on preventive measures that minimize improper pruning cuts (Biggs, 1989), winter injury, sunburn and insect damage, promote optimum tree health, and facilitate rapid wound healing.

Fungal gummosis Fungal gummosis of peach trees was ﬁrst described in the 1960s almost concurrently in the south-eastern USA and in Japan, but has since been reported in Australia and China. The disease is caused by Botryosphaeria dothidea (Moug.:Fr.) Ces. & De Not (anamorph Fusicoccum aesculi Corda). This fungal species has one of the largest host ranges of plant pathogenic fungi, but one physiological race of the pathogen is speciﬁc to peach. Other species of Botryosphaeria, Botryosphaeria rhodina (Cooke) Arx and Botryosphaeria obtusa (Schein.) Shoemaker, have also been reported to cause gummosis, but these organisms are primarily wound invaders that are not known to cause lenticel infections of the bark like B. dothidea (Pusey et al., 1995). Lenticel infections by B. dothidea occur primarily in the summer months, whereas wound infections by all three species may occur at other times during the growing season with wet weather and when inoculum is available. Characteristic symptoms of the disease are ﬁrst evident as blisters around lenticels on young bark (Fig. 15.28/Plate 116) and develop in the second or third growing season of the tree. Subsequently, blisters enlarge and necrotic lesions 5–15 mm in diameter develop around the lenticels, which later are

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Fig. 15.28. Fungal gummosis caused by Botryosphaeria dothidea. Blisters develop around lenticels on young bark, which develop in the second or third growing season of the tree.

sunken and exhibit excessive gum exudation (Fig. 15.29/Plate 117). Lesions may coalesce and form extensive cankers (Fig. 15.30/Plate 118). On young branches blisters 1–6 mm in diameter develop around lenticels, but there is no gumming. Symptoms generally ﬁrst occur on the trunk and then on scaffold branches or even on smaller fruiting branches. Trees in general good health will form a periderm around infection sites and diseased tissue is walled off from healthy tissue. Fungal gummosis can signiﬁcantly suppress tree growth and fruit yield on susceptible peach cultivars (Beckman et al., 2003). Branches and entire trees in poorly managed orchards, however, may die. B. dothidea overwinters in diseased bark and woody tissues. The pathogen produces

asexual conidia in pycnidia and sexual ascospores in ascostroma perithecia in branch and trunk cankers. Under wet conditions abundant conidia may be produced, which are disseminated by splashing irrigation water or rain. For management of the disease, dead trees and infected wood should be removed or destroyed (e.g. by burning, shredding or ﬂail-mowing) to reduce inoculum sources. Winter pruning is encouraged to avoid periods when inoculum is present. During the summer, inoculum is commonly present and pruning at this time may result in rapid colonization of wounds by any of the three species of Botryosphaeria. Fungicide applications may prevent infections, but may not be costeffective in many areas.

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Fig. 15.29. Fungal gummosis caused by Botryosphaeria dothidea. Gumming blisters and necrotic tissue under lenticels, which develop under the bark.

Constriction canker Peach constriction canker, also known as Fusicoccum canker, is a disease caused by the anamorphic fungus Phomopsis amygdali (Del.) Tuset & Portilla (previously known as Fusicoccum amygdali Del). The disease has been reported from the mid-Atlantic region of the USA, European countries (the UK, France, Italy, Portugal, Bulgaria), North Africa (Tunisia), South America (Argentina, Brazil) and Japan. Historically, constriction canker was devastating to peach production in the midAtlantic states in the mid-1900s. Some peach cultivars such as ‘Golden Jubilee’ were so severely affected that the disease prevented its cultivation in New Jersey. Oddly, in the

1970s, the disease virtually disappeared in the USA but it caused extensive tree decline and death in Italy. Recently, constriction canker has reappeared in southern New York and New Jersey. The pathogen has also been reported on almond in Europe and in California. Symptoms develop primarily on twigs and leaves. Typically, stem infections develop on 1-year-old shoots as reddish-brown or pale brown, sunken, elliptical lesions around buds or nodes (Fig. 15.31/Plate 119). This is in contrast to cankers caused by brown rot blossom blight, which develop from infected blossoms. The sunken lesions of constriction canker enlarge (2–8 cm) to form cankers with alternating light and dark brown rings or zones. Subsequently, the twigs are girdled (i.e.

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Fig. 15.30. Fungal gummosis caused by Botryosphaeria dothidea. Lesions may coalesce and form extensive cankers with excessive gumming on lower peach tree trunks.

constriction canker) and develop a blighted appearance. Lesions of constriction canker also exude some gum and sometimes can be confused with brown rot infections, but the latter disease causes more profuse gumming from infections. The fungus produces a toxin (fusicoccin) that is distally translocated from twig cankers and contributes to leaf wilting and yellowing on blighted twigs (Fig. 15.32/ Plate 120). On leaves, the disease develops as brown, zonate, circular to irregular spots that have black asexual pycnidia in the centre. The pathogen is restricted to leaf lesions in the summer but may continue to develop into the vascular tissue in the autumn. Brown, ﬁrm fruit decay has also been reported but both leaf and fruit infections are considered of minor importance.

Infections may develop throughout the growing season with unusually wet weather. Lesions commonly develop in spring and autumn, but under favourable environmental conditions (i.e. wet weather) lesion numbers may continue to increase into summer. High N levels within trees also favour the disease. The pathogen produces numerous conidia in long tendrils or cirri from pycnidia (Fig. 15.33/Plate 121) during wet weather. The conidia are rainsplash dispersed and germinate over a wide range of temperatures (5–36°C). Although the optimal temperature range for fungal growth is 29–30°C, successful host infection occurs mainly at 5–15°C. In autumn, infections occur through leaf scars and during the growing season through buds, scars on bud scales, stipules and fruits, or directly through young shoots.

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Fig. 15.31. Constriction canker caused by Phomopsis amygdali. One-year-old peach twigs with infections around buds. The lower twig shows the zonations around the infection site.

Fig. 15.32. Constriction canker caused by Phomopsis amygdali. Flagging and withering of blighted peach twigs distal to twig cankers.

Peach cultivars differ widely in their susceptibility to constriction canker. Thus, planting of less-susceptible cultivars is an important consideration in establishing an orchard in areas where the disease is a problem. Fertilization programmes that carefully regulate N to low or moderate levels decrease host susceptibility. Judicious pruning of infected branches and careful removal of prunings

from the orchard help reduce inoculum and prevent the spread of infections, but this may not be economically feasible and results may be inconsistent (Lalancette and Robison, 2002). The use of fungicides (e.g. benzimidazoles, captan, captafol, chlorothalonil) applied before bud break and in the autumn is effective for disease management (Lalancette and Robison, 2002). The extensive use of benzimidazoles

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Fig. 15.33. Cirri (tendrils) exuding from pycnidia of Phomopsis amygdali. Each cirrus is composed of abundant conidia of the pathogen.

and captan for management of brown rot and scab during the growing season has probably contributed to the reduced occurrence of constriction canker in the past. The increased use of newer fungicides that have a lower persistence in the orchard environment may be responsible for the recent increase of the disease. In addition, fungicides are not commonly applied in late summer and autumn, when a signiﬁcant amount of infections may occur during wet weather.

15.4 Root and Crown Diseases Phytophthora root and crown rots Phytophthora root and crown rots are destructive soil-borne diseases of stone fruits that occur worldwide in nurseries and orchards. Trees can be affected at all ages and infections often result in tree death. The identiﬁcation of diseases caused by Phytophthora spp. has improved over past decades due to better detection methods including the development of selective media. The incidence of disease has increased because orchards are established in less than optimal locations that have poor soil drainage or use improper irrigation practices. Phytophthora root and crown rots

can be caused by a number of species in the genus Phytophthora (Wilcox and Ellis, 1989), fungal-like organisms that are not closely related to the ‘true’ fungi and are classiﬁed in a separate kingdom (Chromista or Stramenopila). Species include Phytophthora cactorum (Lebert & Cohn) J. Schröt., Phytophthora cambivora (Petri) Buisman, Phytophthora cinnamomi Rands, Phytophthora citricola Sawada, Phytophthora citrophthora (R.E. Sm. & E.H. Sm.) Leonian, Phytophthora cryptogea Pethybr. & Lafferty, Phytophthora drechsleri Tucker, Phytophthora megasperma Drechs., Phytophthora parasitica Dastur and Phytophthora syringae (Kleb.) Kleb. In a particular location, several species of Phytophthora may be present endemically; other species may be introduced by infested irrigation water, soil or plant material. When free water is present, all species commonly produce sporangia that release numerous asexual zoospores and they may also form resistant chlamydospores and sexual oospores. Ecologically, the different species differ in their geographic distribution, their characteristic temperature optimum, their capability to cause root and/or crown rots, their seasonal occurrence and in their virulence. Trees infected by Phytophthora spp. show poor terminal growth and leaves are small, chlorotic and sparse (Fig. 15.34/Plate 122). Fruit may be undersized, highly coloured and

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Fig. 15.34. Dieback of peach tree in foreground affected by Phytophthora root and crown rot. (Reprinted, with permission, from Strand, 1999.)

sunburned. Trees either show dieback and decline progressively over several seasons or die suddenly in late spring or summer following years with excessive wet weather. These symptoms are often not very characteristic and may be confused with other diseases and disorders. Mild symptoms of root and crown rot are not always noticeable and yet yield is reduced. Crown rots develop at the root crown and/or at the base of the trunk (Fig. 15.35/Plate 123). The bark is killed and discoloration may extend into the outer layers of the xylem tissues. As the decay expands, a canker develops that is often accompanied

by the production of copious amounts of amber to brown gum. Cankers have distinct borders between diseased and healthy tissues. If the canker encircles the trunk, the tree is girdled and dies. If the lesion ceases expansion or the pathogen dies, callus tissue will grow into the dead areas of the bark in an attempt to heal the wound. Cankers are usually limited to the crown tissues, but sometimes may extend up the trunk and occasionally into scaffold branches. Aerial cankers develop when inoculum is disseminated by rain or sprinkler water to upper parts of the tree, especially the scaffold crotches, where water tends to accumulate

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Fig. 15.35. Phytophthora crown rot on peach tree. (Reprinted, with permission, from Strand, 1999.)

(Fig. 15.36/Plate 124). Infected roots exhibit decay, sometimes extending to the crown. On feeder roots, portions of the outer cortical tissue are disintegrated, leaving only the white, hair-like stele protruding from the decaying outer tissue. Phytophthora spp. are mainly soil-borne organisms (Fig. 15.37). They survive as chlamydospores, hyphae or oospores in root debris in the soil. At high soil moisture levels, the fungi produce abundant sporangia that release numerous zoospores. Zoospores are motile and are attracted by root exudates to host plant roots, where they encyst and infect mainly the ﬁne feeder roots. After each rain or irrigation new generations of sporangia are produced, which will restart the disease cycle. Zoospores are considered the main infective propagules, but other structures (i.e. chlamydospores, oospores) may also cause infections.

Although Phytophthora spp. are pathogenic on their own, in many cases Phytophthora root rots are increased with root injuries caused by nematodes or other organisms. Phytophthora root and crown rots are managed by the use of resistant rootstocks, careful soil water management and by fungicides. A considerable degree of resistance among stone fruit rootstocks is available, but none is immune. Because the zoospores are dependent on water for movement, the disease is greatly affected by soil water management. Ideally, orchards should be established on well-drained soils that are never watersaturated for more than 24 h. In soils with poor drainage, trees should be planted on ridges or raised beds. Flood or furrow irrigation increases the disease, whereas irrigating with micro-sprinklers and allowing the surface soil to dry between irrigations will reduce

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Fig. 15.36. Peach tree with an aerial infection of a Phytophthora spp. (Reprinted, with permission, from Strand, 1999.)

root rot. In addition, sprinklers should never be directed towards tree trunks and crotches. Control of root and crown rots may also be achieved with the use of systemic fungicides that are applied to the soil, injected, or sprayed or painted on gummosis lesions. In problematic areas, fungicides together with nematicides or a soil fumigant should be used to protect replants during the ﬁrst 2 years of growth.

Armillaria root rot Armillaria root rot (syn. shoestring root rot, oak root rot) is an important disease of peaches and other stone fruits worldwide, but losses have been greatest in production

areas in North America. Many native, ornamental and agricultural woody plants are affected by Armillaria root rot. Trees can be killed at all ages. Severe outbreaks are often observed on land planted successively with peaches where inoculum was allowed to build up gradually (Savage et al., 1953) or where forest trees were recently removed. In contrast to Phytophthora root rot, Armillaria root rot is also common on well-drained soils. Early symptoms of Armillaria root rot include poor terminal growth and undersized, curled leaves on all major limbs (Fig. 15.38/Plate 125). Infected peach trees may collapse suddenly during summer months with a majority of leaves still attached (Fig. 15.39/ Plate 126). In older orchards with widely spaced trees, the disease may expand in a circular fashion, but in high-density orchards

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Symptoms of Phytophthora root and crown rot include gumming and necrosis under the bark of the lower trunk and necrotic roots Feeder roots are infected by zoospores and possibly chlamydospores

Gumming and necrosis

Symptoms of aerial Phytophthora cankers include gumming and necrosis under the bark

Gumming

Sporangia form from mycelium or germinating chlamydospores or oospores and release zoospores

Dying tree

Oospores and chlamydospores are produced by some species of Phytophthora in infected roots

Fig. 15.37. Disease cycle of Phytophthora root and crown rot of peach. Phytophthora spp. are mainly soil-borne organisms that survive as chlamydospores, mycelium (hyphae) or oospores in root debris in the soil. At high soil moisture levels, the fungi produce abundant sporangia with numerous motile zoospores that are attracted by exudates of host plant roots. Zoospores encyst on root surfaces and infect fine feeder roots. Tree crowns that are subjected to prolonged wetness from flood irrigation or heavy rain often develop crown rot. After each rain or irrigation new generations of sporangia are produced, which will restart the disease cycle. Zoospores are considered the main infective propagules, but other structures (i.e. chlamydospores, oospores) may also cause infections. Propagules of Phytophthora spp. are carried to aerial portions of trees by dust, soil particles and splashing water, where they can cause aerial Phytophthora cankers. Trees infected by Phytophthora spp. show decreased growth and may ultimately die. (Drawing by J.E. Adaskaveg and H. Förster.)

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Leaf symptoms of peach tree affected by Armillaria root rot.

Fig. 15.39. Armillaria-infected peach trees showing dieback.

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the disease often progresses along tree rows. White mycelial fans that develop in the cambium between the bark and wood on the crown are highly diagnostic signs of the disease (Fig. 15.40/Plate 127). In advanced stages of colonization, white rot wood decay occurs and the wood is soft, spongy and bleached whitish in colour (Morrison et al., 1991). The decay is a result of the degradation of cellulose, hemicellulose and lignin. Roots may have black, shoestring-like mycelial strands called rhizomorphs attached to the surface (Fig. 15.41/Plate 128). Armillaria tabescens, however, does not form such rhizomorphs under ﬁeld conditions (although they have been induced in the laboratory). Typically in late summer to early autumn clusters of brown mushrooms develop at the base of infected trees (Fig. 15.42/Plate 129). Until the late 1970s, Armillaria mellea (Vahl:Fr.) Kummer was considered the causal organism of Armillaria root rot. Based on compatibility assays, it was subdivided into ten biological species (Anderson and Ullrich, 1979) that have since been shown to be welldeﬁned morphologically and genetically dis-

Fig. 15.40.

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tinct. Three species of Armillaria are currently associated with peach. In North America, A. mellea sensu stricto (Vahl:Fr.) P. Kumm., Armillaria ostoyae (Romagn.) Herink and A. tabescens (Scop.) Dennis, Orton & Hora (syn. Clitocybe tabescens) have been found in California, Michigan and in the south-eastern USA, respectively. A. tabescens was also identiﬁed on peach in Japan (Fujii and Hatamoto, 1974). A. mellea and A. ostoyae are the predominant species in Europe. The species can be easily differentiated when fruiting bodies are available. In their absence, labour-intensive compatibility tests (Korhonen, 1978; Anderson and Ullrich, 1979) and, more recently, DNA diagnostics are being used for species identiﬁcation (Harrington and Wingﬁeld, 1995; White et al., 1998; Sierra et al., 1999). Previous DNA methods were limited in their usefulness for distinguishing A. tabescens from other species. Based on ITS1 sequence data, a PCR-based identiﬁcation technique was recently developed to distinguish A. tabescens from A. mellea (Schnabel et al., 2005). The disease cycle for Armillaria root rot is shown in Fig. 15.43. Armillaria spp. persist

Mycelial fans of Armillaria sp. under the bark of infected peach tree.

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Fig. 15.41. Rhizomorph of Armillaria mellea (top) and healthy root (bottom). (Reprinted, with permission, from Strand, 1999.)

Fig. 15.42.

Basidiomes of Armillaria sp. at the base of infected peach tree.

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Root-to-root contact and spread of disease in infection centres

Rhizomorph

Healthy root

Rhizomorphs growing from diseased to healthy tree (note: some species do not form rhizomorphs)

White rot of wood

Dying tree

Possibly, basidiospores infect wounded roots or exposed wood

Clusters of honey-coloured basidiomes with white spores and annulus on stipe (note: some species do not possess an annulus)

Basidium and basidiospores

Mycelial fan under bark and rhizomorph on root

Immature and mature basidiomes (mushrooms) at tree base

Fig. 15.43. Disease cycle of Armillaria root rot of peach caused by Armillaria spp. The pathogen persists in the soil as mycelium in infected roots or as rhizomorphs that are associated with tree roots, depending on the species of Armillaria involved. New infections of healthy roots originate from infected root segments in the soil, from root-to-root contact, or from contact with rhizomorphs. Basidiospores that are produced on the fruiting bodies are not considered major infection propagules in fruit orchards. Early symptoms of Armillaria root rot include poor tree growth. Infected peach trees may collapse suddenly during summer months with a majority of leaves still attached. White mycelial fans that develop in the cambium between the bark and wood on the crown are highly diagnostic signs of the disease. In advanced stages of colonization, white rot wood decay occurs and the wood is soft, spongy and bleached whitish in colour. Roots may have black, shoestring-like mycelial strands called rhizomorphs attached to the surface. Typically in late summer to early autumn clusters of brown mushrooms develop at the base of infected trees. (Drawing by J.E. Adaskaveg.)

in the soil for many years as mycelium in infected plant tissues or as rhizomorphs. The pathogens are most successful in invading healthy tissue if they ﬁrst become established

saprophytically. Thus, very young trees are often killed on replant sites or older trees after they have grown for 5 years or more. Infections of healthy roots originate from infected

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root segments in the soil, from root-to-root contact, or from contact with rhizomorphs. Spread by root-to-root contact or rhizomorphs was estimated to be 0.8–3.2 m/year (Kable, 1974). Basidiospores that are produced on the fruiting bodies are not considered major infection propagules in fruit orchards (Rizzo et al., 1998; Termorshuizen, 2000). A strategy to prevent the spread of Armillaria root rot disease from an infection centre is presented in Fig. 15.44. If tree rows are separated by a sod-middle, roots of trees are mostly conﬁned to the herbicide-treated strip and it is sufﬁcient to remove trees adjacent (dotted circles) to the infected tree within a row. If trees are grown on bare ground, roots are likely to spread evenly in all directions and all trees surrounding (dotted and waved circles) the infected tree should be removed. Management strategies for Armillaria root rot are not very effective. If sites are seriously infested they are usually abandoned. The most effective strategy is to avoid planting new orchards on infested soil. Options to manage the disease on replant sites are limited and often only marginally effective. Chemical control options with moderate efﬁcacy include pre- and post-planting fumigations to reduce inoculum in the soil (Munnecke et al., 1970; Savage et al., 1974; Adaskaveg et al., 1999); however, many fumigants face increased regulation and, in the case of methyl bromide for example, are scheduled for imminent phasing out. Cultural management practices include raking out old roots before

replanting, planting trees on raised beds and removal of trees surrounding an infection centre. Susceptibility differences in fruit tree rootstocks to Armillaria infection have been reported (Beckman et al., 1998), but none of the currently available rootstocks is immune.

Verticillium wilt Verticillium wilt of peach and other stone fruit crops caused by Verticillium dahliae Kleb. occurs in many parts of the world and can cause serious economic losses, although the disease has been recently more of sporadic occurrence. Many plants including tree and annual vegetable crops have been reported as hosts of this fungal pathogen. Peach and nectarine trees sometimes develop Verticillium wilt when planted in locations where highly susceptible crops such as cotton, tomato or peppers were grown for a number of years. The disease is most serious on young trees although some peach cultivars may recover with age. Mature trees are most susceptible in cooler climates. The soil-borne V. dahliae produces resistant structures (microsclerotia) that can survive in the soil for many years in the absence of hosts when soil temperatures are between 5 and 15°C and soil moisture-holding capacity is between 50 and 75%. Conidia are short-lived and are considered to have a minor role in infection and dissemination of the fungus

Tree row

Infected tree

Fig. 15.44. Strategy to prevent the spread of Armillaria root rot disease from an infection centre. If tree rows are separated by a sod-middle, roots of trees are mostly confined to the herbicide-treated strip and it is sufficient to remove trees adjacent (dotted circles) to the infected tree within a row. If trees are grown on bare ground, roots are likely to spread evenly in all directions and all trees surrounding (dotted and waved circles) the infected tree should be removed.

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from tree to tree. The fungus is found in the highest concentration at a soil depth of 15–30 cm but can be found as deep as 105 cm. The pathogen infects the roots of host plants in the spring and invades the vascular system, moving up through the xylem as mycelium and asexual conidia, interfering with water transport in the xylem. The ﬁrst symptom of Verticillium wilt is a sudden wilting of leaves on one or more branches during hot weather in the summer (Fig. 15.45/Plate 130). Subsequently, leaves yellow, brown and curl up. Sometimes older, lower leaves wither and fall before younger, upper leaves on the terminal ends of branches. Thus, young trees can be killed, but the primary symptoms on several-year-old trees are poor growth and low productivity. Longitudinally cut branches of diseased trees show brown to black streaks in the sapwood. In cross-sections, a portion of the outer xylem will be stained dark brown to black (Fig. 15.46/ Plate 131). In hot weather, the pathogen dies in the upper part of infected trees and the tree can recover with new growth the following season. The disease cycle, however, can recur each growing season. The most effective management practice for Verticillium wilt is to avoid planting orchards in soils where inoculum of the fungal pathogen

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has increased on other susceptible crops that have been grown for a number of seasons. Inoculum of the pathogen can be reduced using chemical fumigation, solarization, ﬂooding fallow ﬁelds, growing grass crops for several seasons, or any combination of these treatments. Rootstocks resistant to V. dahliae are unknown. Minimizing tree stress through maintenance of soil fertility and soil moisture will help trees tolerate the disease and encourage their recovery. Peach tree short life Peach tree short life (PTSL) is a disease complex characterized by sudden wilt and collapse of new growth and death of all aerial portions of the tree (see also Chapters 16 and 19). The disease is part of general replant disorders, which refer to problems that diminish tree growth and productivity. PTSL also affects other stone fruits and has been a serious threat to commercial peach growers in the south-eastern USA for more than 100 years (Chandler, 1969). The number of peach trees lost to PTSL in South Carolina roughly tripled when the soil fumigant DBCP (1,2dibromo-3-chloropropane) was no longer

Fig. 15.45. Verticillium-infected peach tree with wilting of branches. (Reprinted, with permission, from Strand, 1999.)

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Fig. 15.46. Cross-section through branch of Verticillium-infected peach tree with discoloured outer xylem. (Reprinted, with permission, from Strand, 1999.)

registered for use. The disease is similar to the bacterial canker complex in California with the exception of cold injury, which kills many trees with PTSL. Bacterial and nematode aspects are similar for the two diseases. The symptoms deﬁning the PTSL syndrome were established in the early 1970s. The canopy of a peach tree suddenly collapses before, during or just after bloom, usually 3–6 years after planting (Fig. 15.47/Plate 132). Tree sap often oozes out of scaffold limbs and trunk. On many limbs, the tissue just beneath the bark is discoloured (Fig. 15.48/Plate 133) and has a sour odour. Peripheral parts of the tree, although dying, may still reveal healthy tissue underneath the bark. Trees are killed only to the soil line. Later in the season, shoots from the living rootstock often emerge (Ritchie and Clayton, 1981) (Fig. 15.49/Plate 134). This is in contrast to trees infected with Armillaria root

rot, where root suckers do not emerge from the rootstock because it may be completely dead. PTSL is a complex disease with biotic and abiotic factors that may contribute to the disease directly or indirectly. The immediate causes of death can be cold injury (Nesmith and Dowler, 1976), bacterial canker caused by Pseudomonas syringae Van Hall, a combination of the two, and perhaps Cytospora canker. Cold injury in the south-eastern USA occurs in late winter after the rest period has been broken and physiological activity resumes. In a normal season, sufﬁcient chill-hours have accumulated by late January and peach trees can lose hardiness after periods of warm weather in the dormant season. Like frost injury, bacterial canker can affect all parts of a peach tree if the tree is stressed. Indirect factors that predispose trees to PTSL include the commonly found ring nematode (Mesocriconema

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395

Fig. 15.47. Orchard with trees affected by peach tree short life.

xenoplax (Raski) Loof and de Grisse) (Ritchie and Clayton, 1981), improper rootstock selection (Zehr et al., 1976) and time of pruning (Nesmith and Dowler, 1976), root injury, physical characteristics of the orchard site such as pH and soil structure, and planting on land previously used for peach production. The disease is most common in sandy soils. Losses are more frequent and severe in orchards where peaches or other stone fruits have been grown previously than in locations where peaches have not been grown before. In clay soils less difﬁculty is encountered when peach orchard sites are replanted. Ideally, peach plantings should be established on new ‘virgin’ land with no recent history of growing stone fruit. Site selection in any given region, however, is often compromised by other factors (e.g. urban encroachment, unsuitable microclimate, proximity to packinghouses). The complexity of the PTSL syndrome complicates attempts to effectively manage the disease in commercial orchards. A 10-Point Programme that emphasizes practices to enhance the health and vigour of peach trees was developed (Ritchie and Clayton, 1981). The programme consists of the following rec-

ommendations: (i) adjust pH to at least 6.5 before planting; (ii) cultivate subsoil before planting; (iii) fumigate on replant sites with sandy soil and other nematode-infested soils (see Chapter 19); (iv) continue to fumigate such soils at approximately 2-year intervals or as indicated by nematode populations; (v) select rootstocks tolerant or resistant to nematodes; (vi) purchase rootstocks that are certiﬁed to be free of nematodes or have been grown on fumigated soil; (vii) apply nutrients and lime as needed; (viii) delay pruning to late winter (February and March); (ix) use recommended herbicides for weed control; and (x) remove and burn all dead or dying trees. Alternatives to methyl bromide, such as chloropicrin and methyl iodide, are currently being explored as soil fumigants. Pre-plant fumigation is expensive and does not provide long-term control of nematodes. Currently, one of the most effective management strategies is the use of rootstocks such as the highly PTSL-tolerant ‘Guardian’ (BY520-9 line) (Okie et al., 1994), which is rapidly replacing other rootstocks in the south-eastern USA. This rootstock is also very resistant to the ring nematode. Unfortunately, the BY520-9 lines are genetically highly

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Fig. 15.48. Discoloured tissue under the bark of peach tree short life-affected tree.

diverse and research is ongoing to further select lines with horticultural characteristics similar or superior to commercial rootstocks (Wilkins et al., 2002).

15.5 Postharvest Diseases Brown rot and grey mould Worldwide, brown rot caused by M. fructicola, M. laxa and M. fructigena is the most important postharvest decay of peach and other

stone fruits and causes losses every year. Losses are especially high in areas where the more aggressive M. fructicola is present and, without management, large amounts of the crop may be destroyed. Grey mould, caused by B. cinerea, also occurs every year, but damage is generally less serious. Preharvest aspects of the brown rot and grey mould pathogens are discussed above. Fungal inoculum starts building up in the orchard when blossom blight and jacket rot or green fruit rot are not managed. At harvest time, when airborne and surface-deposited conidia gain entry through small wounds on the fruit, postharvest decay can result. Conidia germinate and start growing into the fruit within 4 to 6 h at 20–25°C. Some of the postharvest brown rot and grey mould decay originates from quiescent infections that occur during early fruit development and become actively growing when the fruit is maturing. Both decays are ﬁrm, brownish and develop rapidly (Figs 15.50 and 15.51/Plates 135 and 136). Fruit may be completely rotted after 3–4 days at 20°C. Both decays are not easily differentiated at the earlier stages, but decay caused by B. cinerea is of a slightly lighter brown to tan colour than the one caused by Monilinia spp. At advanced decay stages the fruit surface is covered with cottony fungal mycelium and conidia. Fungal structures of Monilinia spp. are of a light brown colour, whereas those of B. cinerea are grey. Brown rot decay on fruit in cold storage often appears black with little or no sporulation. The black-coloured areas (pseudosclerotia) consist of both fungal and host tissues.

Rhizopus rot, Gilbertella and Mucor decays Three fungal species in the Zygomycetes (order Mucorales) that also can cause signiﬁcant postharvest losses on peach and nectarine are Rhizopus stolonifer (Ehrenb.:Fr.) Vuill., Gilbertella persicaria (E.D. Eddy) Hesselt., Mucor piriformis E. Fisch and other species of Mucor. The three fungi are rarely a problem preharvest, except in warm, wet climates, where infections may already occur through injuries or cracks on ripening fruit on the tree. The spores of these

Diseases Caused by Fungi

Fig. 15.49.

Rootstock sprouting from peach tree killed by peach tree short life.

Fig. 15.50.

Postharvest brown rot of peach fruit caused by Monilinia fructicola.

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Fig. 15.51. Postharvest grey mould of nectarine fruit caused by Botrytis cinerea.

fungi are ubiquitous in soils and are easily wind-disseminated. Infections occur on mature fruit that are injured or bruised, especially during harvest and postharvest handling. Rhizopus-infected fruit are ﬁrst covered with a thick cottony mycelial layer that rapidly starts sporulating, forming tiny, black, terminal sporangia that contain large numbers of spores (Fig. 15.52/Plate 137). Fruit infected by R. stolonifer decay very rapidly and an entire fruit may turn into a soft, watery rot within 1–2 days at optimum temperatures. Likewise, a cottony mycelial mat, which is shorter than that of R. stolonifer, ﬁrst covers Gilbertellainfected fruit. Small, black, glistening sporangia are produced terminally on the mycelium (Fig. 15.53/Plate 138). Mucor-infected fruit ﬁrst look similar to Rhizopus rot, but sporangiophores are often longer and sporangia are tan to brown in colour. Fruit infections by these pathogens may spread quickly by hyphal contact to healthy fruit (nesting), destroying large numbers of fruit in a basket or box. R. stolonifer and G. persicaria do not grow at temperatures below 4°C. The optimum temperature range for growth of R. stolonifer is 21–27°C with a maximum of 33°C, whereas for G. persicaria the optimum range is 30–33°C with a maximum of 39°C. In contrast, the optimum range

for growth of M. piriformis is between 10 and 15°C and the fungus can grow at temperatures near freezing, but not at or above 27°C.

Sour rot Sour rot of peach, caused by Geotrichum candidum Link (teleomorph Galactomyces geotrichum (E.E. Butler and L.J. Petersen) Redhead and Malloch), has only been infrequently reported to cause problems of traditionally handled and marketed fruit (e.g. fruit picked, hydro-cooled, transported at low temperatures and displayed at markets). Fruit that are treeripened or pre-conditioned (fruit ripened after harvest for 1–2 days or until a pre-selected ﬁrmness is reached and then refrigerated) are more prone to the disease. Sour rot-like infections may also be caused by other yeasts and possibly other organisms that are not well characterized. Sour rot occurs mainly on ripe fruit but may also occur on severely injured immature fruit. Symptoms include a watery, soft decay with a thin layer of white mycelial growth on the fruit surface (Fig. 15.54/Plate 139). The decay may reach the pit and consume the entire fruit. Rotted fruit have a

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Fig. 15.52. Postharvest Rhizopus rot of peach fruit caused by Rhizopus stolonifer with decay spreading by contact to healthy fruit (nesting).

Fig. 15.53. Postharvest Gilbertella rot of peach fruit caused by Gilbertella persicaria.

characteristic yeasty to vinegary odour; however, other odours may develop with bacterial contamination that commonly occurs in the watery decay. G. candidum is a wound

pathogen that decays fruit after spores are deposited into injuries. The organism is widespread on organic material in the soil and is commonly found in dust or dirt on fruit

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Fig. 15.54.

Sour rot caused by Geotrichum candidum initiated in wounds of the skin.

surfaces. During harvest micro-wounds occur on the fruit and these injuries may function as infection sites. The minimum temperature for spore germination, growth and infection of the fungus is about 2°C, the optimum is 25–27°C, and the maximum is 38°C. Management of postharvest decays Management of postharvest decays requires an integrated approach with pre- and postharvest components that focus on maintaining a healthy crop, delaying fruit senescence, avoiding injuries to fruit, sanitation practices and fungicide use (Adaskaveg et al., 2002). Preharvest cultural practices include cultivar selection, fertilization, pruning, weed control, irrigation and sanitation (e.g. removal of diseased plant material such as fruit mummies). For brown rot, nectarines are more susceptible than peaches, and fresh market (i.e. freestone) peaches are typically more susceptible than canning (i.e. clingstone) peaches. Cultivar differences also exist, although no cultivar is completely resistant. Excess N fertilization is known to increase susceptibility to brown rot and other diseases. Orchard planting designs, pruning practices and orchard ﬂoor (including ground covers) management can signiﬁcantly alter the microclimate. Dense tree canopies can restrict air movement, increase

relative humidity, prolong leaf wetness duration and decrease pesticide efﬁcacy. Irrigation systems can also affect the incidence of disease. High-angle sprinklers should be avoided to prevent canopies and tree trunks from getting wet. Preharvest fungicide treatments are successfully used for management of brown rot and grey mould. Treatments that are applied 14 to 0 days before harvest help to protect wounds from infections that occur at harvest time. Fungicides with locally systemic action also can inactivate some of the brown rot and grey mould quiescent infections that only penetrate the fruit for several cell layers. After harvest it is important to remove all fruit from the trees and from the orchard ﬂoor. Additional sanitation practices include the removal of tree prunings and cleaning of harvest equipment, including bins, pick bags and trailers. Postharvest handling and marketing practices that minimize fruit injuries, utilize sanitation of fruit and equipment, and employ temperature management of harvested fruit are essential in any management programme. For minimizing injuries, shock-absorbing foam pads are used in most harvesting, handling and packing equipment. Pre-washing and hydro-cooling treatments that contain sodium hypochlorite or other oxidizing materials (e.g. ozone, chlorine dioxide) are used for fruit sanitation. Harvest bins are usually high-pressure washed or steam-treated. Other

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sanitizing materials for equipment, but not fruit, include quaternary ammonium compounds. Temperature management is critical to all postharvest handling systems for stone fruit crops. Stone fruits are best stored at 0°C. Low temperatures maximize the potential life of the fruit and slow fungal development. At 0°C, some decay fungi such as R. stolonifer and G. candidum will not grow, whereas others such as Monilinia spp. and B. cinerea are greatly reduced in their growth. Finally, postharvest fungicide treatments are used to ensure the prevention of decay from latent and active infections. These treatments also prevent the spread of decay between adjacent fruit (i.e. nesting) in packing containers. Without postharvest fungicide use, fruit usually cannot be stored safely at storage and display-shelf temperatures after long-distance transportation and marketing (Adaskaveg et al., 2002). New, safer postharvest fungicides are currently being registered in the USA that are highly effective against brown rot, grey mould and Rhizopus rot.

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masses of conidia that are disseminated by splashing rain. Fungicide sprays can be used to manage anthracnose where it is a problem. Other diseases listed in Table 15.2 include black knot caused by Apiosorina morbosa (Schwein.:Fr.) Arx, Botryosphaeria fruit rot caused by species of Botryosphaeria discussed above, Diplodina fruit rot caused by Diplodina persicae Horn & Hawthorne, frosty mildew caused by Mycosphaerella pruni-persicae Deighton, Leucotelium white rust caused by Sorataea pruni-persicae Tranzschel (formerly Leucotelium pruni-persicae (Hori) Tranzschel), Phymatotrichum root rot caused by Phymatotrichopsis omnivore (Duggar) Hennebert, Rosellinia root rot caused by Rosellinia necatrix Prill., Sclerotium stem rot caused by Sclerotium rolfsii Sacc., target leaf spot caused by Phyllosticta persicae Sacc., violet root rot caused by Helicobasidium mompa Tanaka, sour pit caused by Candida inconspicua (Lodder & Kreger-Van Rij) Meyer & Yarrow, and wood decay caused by a number of fungal species (over 56 species in North America) in the phylum Basidiomycota (Adaskaveg et al., 1993).

15.6 Other Diseases of Peach and Nectarine

15.7 Concluding Remarks

A number of additional diseases affecting different parts of peach and nectarine trees have been reported. Some of these diseases are limited in their geographic distribution, whereas others are widespread but do not limit peach and nectarine production. In favourable environments, however, many of these diseases can be economically important and limit crop production. Examples of these diseases are listed in Table 15.2. Anthracnose caused by Colletotrichum acutatum J.H. Simmonds and Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. occurs in areas and seasons with high rainfall and warm temperatures during fruit ripening. Circular lesions that are brown, ﬁrm and slightly sunken expand slowly over the fruit surface (Fig. 15.55/Plate 140). Another diagnostic feature is that the lesion in cross-section is coneshaped, hardened and is easily separated from the healthy mesocarp. Asexual fruiting structures of the pathogens (acervuli) are produced in concentric rings on the fruit surface, bearing

Numerous fungal and fungal-like organisms are pathogens of peach and nectarine. Many of these organisms have a worldwide distribution, whereas others occur only locally to regionally. Disease incidence is largely dependent on climatic conditions and the distribution of the causal microorganism in peach production areas, but also on the peach genotype. Many of the diseases are limiting to crop production if they are not managed effectively. Knowledge about peach diseases has increased over the years. New pathogens have been identiﬁed, described and studied at the biological, epidemiological and molecular levels. In most cases, they can be effectively managed. With worldwide trade and increased travel, the potential for diseases to spread and become limiting factors to peach production has also increased. In the immediate future, peach production will be dependent on the success of programmes that prevent pathogen movement and introduction to new

Disease

Pathogen

Blossom, foliage and fruit diseases Anthracnose

Geographical distribution

Colletotrichum acutatum and Widespread but infrequent Colletotrichum gloeosporioides Diplodina persicae South-eastern USA Mycosphaerella pruni-persicae Widespread but infrequent Leucotelium pruni-persicae Japan, Korea, China

Target leaf spot

Phyllosticta persicae

Italy, India, USA

Trunk, scaffold and branch diseases Black knot

Apiosorina morbosa

Eastern USA

Sclerotium stem rot

Sclerotium rolfsii

Wood decay fungi

Species in the Basidiomycota

Nursery disease, widespread in warm areas Widespread in older orchards

Root and crown diseases Phymatotrichum root rot Phymatotrichopsis omnivora

Rosellinia root rot

Rosellinia necatrix

Violet root rot

Helicobasidium mompa

Postharvest diseases Botryosphaeria fruit rot

Sour pit aManagement

Botryosphaeria dothidea, Botryosphaeria obtusa and Botryosphaeria rhodinia Torulopsis inconspicua

Primary management practicesa

Sunken, firm fruit lesions with concentric rings of sporulation zones Leaf and fruit spots White mildew on leaves Angular leaf lesions with rusty brown uredinia or white telia Leaf spot (target appearance)

Fungicides (removal of alternate host?)

Black, elongated swellings on twigs Stem cankers, wilting

Elimination of alternate hosts and judicial use of fungicides during active shoot growth Sanitation, fungicides

Wood rot – white and brown knots

Time of pruning, sanitation, removal of infected branches

Fungicides None Elimination of alternate host None

South-western USA and Mexico Dead roots are colonized by golden mycelial strands with cruciform hyphae Widespread in warm areas, Root rot, tree decline sporadic in the USA Japan, Korea, China Infected roots are colonized by purplish mycelium

Integrated approaches – plant in disease free areas, deep soil fumigation

South-eastern USA

Fruit decay (sunken soft lesions, no sporulation)

Preharvest disease management, sanitation, fungicides

Widespread

Fruit decay

None available

practices with a question mark have a limited or poorly defined role in controlling the disease.

Integrated approaches – soil fumigation, fungicides Integrated approaches – plant in disease free areas, soil fumigation, fungicides

J.E. Adaskaveg et al.

Diplodina fruit rot Frosty mildew Leucotelium white rust

Primary symptoms

402

Table 15.2. Other fungal diseases with variable importance in the production of peach and nectarine, their geographical occurrence, primary symptoms and management practices.

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Fig. 15.55. Anthracnose of peach caused by Colletotrichum acutatum showing circular rings where spores of the fungus are produced.

geographical areas. Quarantines that completely restrict plant movement, as well as controlled plant movement (e.g. the federal Inter-Regional No. 2 or IR-2 programme in the USA) and production certiﬁcation programmes for breeders and nurseries potentially will prevent or minimize harmful microorganisms from being spread while allowing exchange of diverse genetic plant material. Furthermore, new control practices based on biological and genetic information of host and pathogen, as well as on novel antimicrobial and host defence chemistries are continuing to be developed. Ultimately, with the promise of biotechnology, peach may be genetically modiﬁed similar to some other crops to ﬁt the demands for new varieties that are more tolerant of pests and diseases. Thus, although plant pathological aspects in peach production may become

more complex, the challenges will likely be met by an array of traditional and new host defence strategies.

Acknowledgements Special thanks to Drs N. Lalancette and L. Pusey for providing information and images on constriction canker and fungal gummosis, respectively. We also thank the University of California, Agricultural and Natural Resources (ANR) for providing images of Sclerotinia sclerotiorum, shot hole infections of peach twigs, Phytophthora root and crown rots, Verticillium wilt and rhizomorphs of Armillaria mellea and the American Phytopathological Society (APS) for providing images of Leucostoma canker.

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Keitt, G.W. (1917) Peach Scab and Its Control. USDA Bulletin No. 395. US Department of Agriculture, Washington, DC. Korhonen, K. (1978) Interfertility and clonal size in the Armillaria mellea complex. Karstenia 18, 31–42. Lalancette, N. and Robison, D.M. (2002) Effect of fungicides, application timing, and canker removal on incidence and severity of constriction canker of peach. Plant Disease 86, 721–728. Lawrence, E.G. and Zehr, E.I. (1982) Environmental effects on the development and dissemination of Cladosporium carpophilum on peach. Phytopathology 72, 773–776. Morrison, D.E., Williams, R.E. and Whitney, R.D. (1991) Infection, disease development, diagnosis, and detection. In: Shaw, C.G. and Kile, G. (eds) Armillaria Root Disease. USDA Forest Service Agricultural Handbook No. 691. US Department of Agriculture Forest Service, Washington, DC, pp. 62–75. Munnecke, D.E., Wilbur, W.D. and Kolbezen, M.J. (1970) Dosage response of Armillaria mellea to methyl bromide. Phytopathology 60, 992–993. Nesmith, W.C. and Dowler, W.M. (1976) Cultural practices affect cold hardiness and peach tree short life. Journal of the American Society for Horticultural Science 101, 116–119. Ogawa, J.M. and English, H. (1991) Diseases of Temperature Zone Tree Fruit and Nut Crops. University of California Division of Agriculture and Natural Resources, Publication No. 3345. University of California, Oakland, California. Ogawa, J.M., Manji, B.T., Adaskaveg, J.E. and Michailides, T.J. (1988) Population dynamics of benzimidazoleresistant Monilinia species on stone fruit trees in California. In: Delp, C.J. (ed.) Fungicide Resistance in North America. American Phytopathology Society Press, St. Paul, Minnesota, pp. 36–39. Ogawa, J.M., Zehr, E.I., Bird, G.W., Ritchie, D.F., Uriu, K. and Uyemoto, J.K. (1995) Compendium of Stone Fruit Diseases. American Phytopathology Society Press, St. Paul, Minnesota. Okie, W.R., Beckman, T.G., Nyczepir, A.P., Reighard, G.L., Newall, W.C. and Zehr, E.I. (1994) BY5209, a peach rootstock for the southeastern United States that increases scion longevity. HortScience 29, 705–706. Pusey, P.L., Kitajima, H. and Wu, Y. (1995) Fungal gummosis. In: Ogawa, J.M., Zehr, E.I., Bird, G.W., Ritchie, D.F., Uriu, K. and Uyemoto, J.K. (eds) Compendium of Stone Fruit Diseases. American Phytopathology Society Press, St. Paul, Minnesota, pp. 33–34. Ries, S.M. and Royse, D.J. (1978) Peach rusty spot epidemiology: incidence as affected by distance from a powdery mildew-infected apple orchard. Phytopathology 68, 896–899. Ritchie, D.F. and Clayton, C.N. (1981) Peach tree short life: a complex of interacting factors. Plant Disease 65, 462–469. Rizzo, D.M., Whiting, E.C. and Elkins, R.B. (1998) Spatial distribution of Armillaria mellea in pear orchards. Plant Disease 82, 1226–1231. Savage, E.F., Weinberger, J.H., Luttrell, E.S. and Rhoads, A.S. (1953) Clitocybe root rot – a disease of economic importance in Georgia peach orchards. Plant Disease Reporter 37, 269–270. Savage, E.F., Hayden, R.A. and Futral, J.G. (1974) Effect of soil fumigants on growth, yield and longevity of Dixired peach trees. University of Georgia, Research Bulletin 148, 3–22. Schnabel, G., Bryson, P.K., Bridges, W.C. and Brannen, P.M. (2004) Reduced sensitivity in Monilinia fructicola to propiconazole in Georgia and implications for disease management. Plant Disease 88, 1000–1004. Schnabel, G., Ash, J.S. and Bryson, P.K. (2005) Identification and characterization of Armillaria tabescens from the southeastern United States. Mycological Research 109, 1208–1222. Sierra, A.P., Whitehead, D.S. and Whitehead, M.P. (1999) Investigation of a PCR-based method for the routine identification of British Armillaria species. Mycological Research 103, 1631–1636. Snowdon, A.L. (1990) A Color Atlas of Post-Harvest Diseases and Disorders of Fruit and Vegetables. Vol. 1. General Introduction and Fruits. Wolfe Scientific Ltd, London. Soto-Estrada, A., Förster, H. and Adaskaveg, J.E. (2003) New fungicides and inoculum-precipitation based application strategies for managing peach rust in California. Plant Disease 87, 1094–1101. Strand, L. (1999) Integrated Pest Management for Stone Fruits. University of California Statewide Integrated Pest Management Program. University of California Agricultural and Natural Resources, Publication No. 3389. University of California, Oakland, California. Sutton, T.B. and Clayton, C.N. (1972) Role and survival of Monilinia fructicola in blighted peach branches. Phytopathology 62, 1369–1373. Tamm, L. and Flückiger, W. (1993) Influence of temperature and moisture on growth, spore production and conidial germination of Monilinia laxa. Phytopathology 83, 1321–1326. Termorshuizen, A.J. (2000) Ecology and epidemiology of Armillaria. In: Fox, R.T.V. (ed.) Armillaria Root Rot: Biology and Control of Honey Fungus. Intercept, Andover, UK, pp. 45–64. Weinhold, A.R. (1961) The orchard development of peach powdery mildew. Phytopathology 51, 478–481.

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White, E.E., Dubertz, C.P., Cruickshank, M.G. and Morrison, D.J. (1998) DNA diagnostic for Armillaria species in British Columbia: within and between species variation in the IGS-1 and IGS-2 regions. Mycologia 90, 125–131. Wilcox, W.F. and Ellis, M.A. (1989) Phytophthora root and crown rot of peach in the eastern Great Lakes region. Plant Disease 73, 794–798. Wilkins, B.S., Ebel, R.C., Dozier, W.A., Pitts, J., Eakes, D.J., Himelrick, D.G., Beckman, T. and Nyczepir, A.P. (2002) Field performance of Guardian (TM) peach rootstock selections. HortScience 37, 1049–1052. Wilson, E.E. (1937) The shot-hole disease of stone-fruit trees. California University Agriculture Experiment Station Bulletin 608, 3–40. Yarwood, C.E. (1939) Powdery mildews of peach and rose. Phytopathology 29, 282–284. Zehr, E.I., Miller, R.W. and Smith, F.H. (1976) Soil fumigation and peach rootstocks for protection against peach tree short life. Phytopathology 66, 689–694. Zehr, E.I., Luszcz, L.A., Olien, W.C., Newall, W.C. and Toler, J.E. (1999) Reduced sensitivity in Monilinia fructicola to propiconazole following prolonged exposure in peach orchards. Plant Disease 83, 913–916.

16

Diseases Caused by Prokaryotes – Bacteria and Phytoplasmas D.F. Ritchie,1 M. Barba2 and M.C. Pagani3

1Department

of Plant Pathology, North Carolina State University, Raleigh, North Carolina, USA 2Istituto per la Patologia Vegetale, Rome, Italy 3BASF Corporation, Research Triangle Park, North Carolina, USA

16.1 Introduction 16.2 Bacterial Diseases Bacterial canker complex Bacterial spot Crown gall Phony peach disease 16.3 Phytoplasma Diseases Peach X-disease Peach yellows Peach rosette Peach yellow leaf roll European stone fruit yellows 16.4 Summary

16.1 Introduction Bacteria and phytoplasmas are prokaryotic microorganisms. Prokaryotes lack a nucleus and other membrane-enclosed organelles. Both bacteria and phytoplasmas are singlecelled or capable of living as single cells. The cellular membrane of bacteria is surrounded by a rigid cell wall whereas phytoplasmas lack the cell wall, being enclosed only by a cellular membrane and thus varying in shape (i.e. pleomorphic). Phytoplasmas were previously known as ‘mycoplasma-like organisms’ and taxonomically are placed in the class

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Mollicutes, order Mycoplasmatales. Unlike mycoplasmas of humans and animals, phytoplasmas have not yet been cultured on synthetic media. In their plant hosts they are localized in phloem sieve tubes, which they can occlude completely (Fig. 16.1/Plate 141). Multiple years are usually required for entire colonization of woody plant hosts. Thus, at an early stage of infection, trees often express symptoms only on a single branch. Most phytoplasmas overwinter in the roots of the diseased plant. The phytoplasma environment is either inside the phloem vessels or in their phloemfeeding leafhopper or psyllid insect vectors.

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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Fig. 16.1. Electron micrograph of phloem sieve tube occluded with cells of phytoplasma.

In contrast, the bacterial pathogens of peach can all be cultured on synthetic media and except for Xylella fastidiosa, the phony peach pathogen, do not exhibit a high degree of host tissue speciﬁcity. Some bacterial pathogens can also exist on plant surfaces as epiphytes (Cross, 1966). Bacteria multiply through binary ﬁssion, resulting in large populations within days or even hours. The multiplication process for phytoplasmas is not totally understood, but may result from cellular fragmentation. Presently, there are four bacterial-caused diseases (Table 16.1) and ﬁve phytoplasmacaused diseases (Table 16.2) described on peaches. Phony peach is limited to the southeastern USA, but bacterial canker, bacterial spot and crown gall occur worldwide where favourable environments exist. The bacterial pathogens cause leaf and fruit spots, cankers, twig dieback, galls and tree death. Bacterial

canker and bacterial spot cause the greatest economic loss but their occurrence is sporadic and highly inﬂuenced by weather conditions. Phytoplasma-caused diseases are potentially devastating because once infection occurs there is no cure, fruit production and quality are reduced, and trees usually die within a few years after infection. Management of bacteria- and phytoplasma-caused diseases relies primarily upon pathogen exclusion using quarantines, certiﬁed pathogen-free plant material, host resistance if available, production site selection and vector control. Chemicals are limited mostly to Cu compounds, which can be phytotoxic to peach foliage, and the antibiotic oxytetracycline, which is used in some regions. Phytoplasmas cause vegetative and fruit disorders that are expressed throughout the entire tree or only in speciﬁc plant organs. Flowers and vegetative growth may emerge

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Table 16.1. Diseases caused by bacteria, the pathogens, typical symptoms and primary control methods. Disease

Pathogen

Typical symptoms

Primary control method(s)

Bacterial canker complex

Pseudomonas syringae pv. syringae, P. syringae pv. persicae Xanthomonas arboricola (syn. campestris) pv. pruni Agrobacterium tumefaciens Xylella fastidiosa

Cankers, shoot dieback, leaf and flower bud death, root injury, tree death Leaf and fruit lesions, leaf chlorosis and defoliation, twig cankers Galls on lower stem/trunk near soil line and on roots Flattened, compact canopy, shortened internodes, tree dwarfing, reduced fruit size and production

Exclusion, cultural practices that minimize tree stress

Bacterial spot

Crown gall Phony peach

prematurely in the spring, the internodes may be shortened, lateral buds may proliferate, and rosetting or premature defoliation may occur. Fruit number and size may be reduced, ripening may be non-uniform, fruit may drop prematurely and taste bland or bitter. Terminal dieback is common in the advanced stages of phytoplasma-caused disease and tissues have increased sensitivity to winter freezes. Trees exhibit stunting and a general decline and often die within 2–3 years after symptom onset. Phytoplasmas are transmitted by phloemfeeding insects such as leafhoppers and psyllids. These insects acquire the pathogen while feeding on infected plants. Insects generally remain infectious for life although trans-ovarian transmission (i.e. to offspring) has not been shown. Phytoplasmas can be transmitted by dodder (Cuscuta spp.) (Fig. 16.2/ Plate 142), but not mechanically in sap. They can be transmitted through use of infected propagative material but are not known to be transmitted in seeds and pollen. Historically, phytoplasmas were detected using indexing with indicator host plants such as periwinkle (Catharanthus roseus) (Fig. 16.2/ Plate 142), electron microscopy, or DAPI (4′,6′-diamidino-2-phenylindole) staining and epiﬂuorescence microscopy. Serological methods improved detection, but major advances occurred with the use of genomic-based hybridizations, PCR and nucleotide sequencing. All diagnostic protocols, however, must take into

Host resistance, bactericides, planting site selection Sanitation, exclusion, biocontrol Removal of diseased trees, eradication of secondary hosts

account that phytoplasmas generally occur in relatively low titres, are unevenly distributed within the tree, and their presence in different parts of a tree varies with plant growth stage. Diagnosis of phytoplasma-caused diseases solely on symptomatology can result in incorrect conclusions. Different phytoplasmas can cause similar symptoms. Environmental conditions, host plant nutrition and host genetic abnormalities also can produce symptoms similar to those caused by phytoplasmas. Phytoplasmas are classiﬁed into 15 groups comprising more than 40 subgroups (Lee et al., 2000; Montano et al., 2001). Those infecting peach belong to two very distinct groups. The ﬁrst is the apple proliferation (AP) group (group 16Sr X), which includes European stone fruit yellows (ESFY) and peach yellow leaf roll (PYLR). ESFY also belongs to subgroup B, whereas PYLR belongs to subgroup C. The second is the X-disease group (group 16Sr III), which includes peach X, peach yellows and peach rosette. Management and control strategies for all phytoplasma-caused diseases of peaches are similar. They begin with preventive measures including use of certiﬁed pathogen-free propagative material and the enforcement of quarantines for the pathogen and vectors. Where the disease is endemic, control of local vector populations and elimination of woody and herbaceous host plants that serve as reservoirs for both the phytoplasmas and the vector are recommended.

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Table 16.2. Diseases caused by phytoplasmas, the synonyms, classification, vector(s), geographical distribution and other woody, non-peach hosts. Hosts other than peach

Leafhoppers: Colladonus geminatus, Colladonus montanus, Fieberiella florii, Paraphlepsius irroratus Leafhopper: Macropsis trimaculata

Canada, USA

Sour and sweet cherry, Prunus virginiana

Canada, USA

Almond, apricot, Prunus salicina

Unknown

USA

Psyllid: Cacopsylla pyricola Psyllid: Cacopsylla pruni

USA

P. salicina, almond, apricot, cherry, ornamental and wild Prunus spp. None known

Synonyms

Taxonomic classification

Vector(s)

Peach X

Peach western X, peach yellow leaf roll

Group 16Sr III-A of Lee et al. (2000)

Peach yellows

Little peach, peach red suture

Peach rosette (PR)

None

Related to, but distinct from, peach X-disease phytoplasma Related to, but distinct from, peach X-disease phytoplasma

Peach yellow leaf roll (PYLR) European stone fruit yellows (ESFY)

None Peach yellows, European peach yellows, peach decline

Group 16Sr X-C of Lee et al. (2000) Group 16Sr X-B of Lee et al. (2000)

Europe

Almond, apricot, plum, Japanese plum, Prunus serrulata

D.F. Ritchie et al.

Geographical distribution

Disease

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Fig. 16.2. Leaves of periwinkle (Catharanthus roseus), which can serve as an indicator plant for phytoplasmas, colonized by dodder (Cuscuta spp.), which serves as a transmission bridge.

16.2 Bacterial Diseases Bacterial canker complex Bacterial canker and a decline syndrome affect peaches and other stone fruits worldwide. The disease is also known as bacterial gummosis, sour sap or blast, and has been recognized on stone fruit trees since the early 1900s (Cross, 1966). On peach, this disease is associated with bud, shoot and branch dieback and tree death (Davis and English, 1969). Bacterial canker is a component of the peach tree short life complex in the south-eastern USA (Peterson and Dowler, 1965; Ritchie and Clayton, 1981). The disease is also part of a decline syndrome in France and New Zealand (Prunier et al., 1970; Young, 1988). For infection and disease development, usually trees must be predisposed by adverse environmental or biological factors (Davis and English, 1969; Ritchie and Clayton, 1981; Cao et al., 2005). Symptoms are variable within individual trees and across the orchard. Healthy-appearing trees can exist next to dead or dying trees.

Symptoms usually are ﬁrst noticed in early spring as trees emerge from dormancy. Fruit and leaf buds may fail to open (Fig. 16.3/ Plate 143), be delayed in opening, or open and then cease growth, wilt and die back. This may occur on individual branches or the entire tree (Fig. 16.4/Plate 144). An elliptical canker may be observed at the base of killed buds (Fig. 16.3/Plate 143). Removal of the outer bark commonly reveals reddish-brown, water-soaked streaks in the wood (Fig. 16.5/ Plate 145). The discoloured tissue may extend a few centimetres or encompass an entire branch and extend into the trunk (Fig. 16.6/ Plate 146). There is an associated sour sap odour with the diseased tissue. Water-soaked areas may develop in the bark with the discoloured tissue beneath the surface of the outer bark (Fig. 16.7/Plate 147). Leaf and fruit symptoms have not been observed on peaches. Trees in their second to sixth growing season are more prone to the bacterial canker complex than are older trees. Injury from freezing temperatures produces symptoms similar to bacterial canker and may favour the infection

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Fig. 16.3. Dead peach buds and twig canker associated with bacterial canker.

Fig. 16.4.

Branch death and sucker growth from the rootstock associated with bacterial canker.

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Fig. 16.5. Wood with discoloured streaks and the collapse and wilt of newly emerged growth associated with bacterial canker.

Fig. 16.6. Small branch killed by Pseudomonas syringae pv. syringae with the canker extending into a larger limb.

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Fig. 16.7. Water-soaked bark and lightly discoloured wood in early spring associated with bacterial canker.

process. Cold injury causes the cambial area to develop a brown discoloration, with the bark often splitting and separating easily from the wood (Fig. 16.8/Plate 148). This characteristic contrasts with bacterial canker, where the diseased bark remains attached to the wood (Fig. 16.5/Plate 145). Symptoms of bacterial canker and cold injury merge as the season progresses and isolation of the bacterial pathogen becomes difﬁcult (Endert-Kirkpatrick and Ritchie, 1988). Where Pseudomonas syringae pv. syringae is involved, roots remain functional and often produce suckers (Fig. 16.4/ Plate 144). In contrast, for Pseudomonas syringae pv. persicae, roots also are attacked by the pathogen (Prunier et al., 1970; Young, 1988). Bacteria associated with bacterial canker and decline were ﬁrst investigated in Germany in 1907 as a disease of cherry trees. In 1911, a similar disease was reported in North America (Cross, 1966). Investigations of a bacterial disease of stone fruits in England in the 1920s

led to the description of two additional species, Pseudomonas prunicola and Pseudomonas mors-prunorum. It was concluded that, except for P. mors-prunorum, all such species were strains of the lilac pathogen P. syringae van Hall 1902 (Cross, 1966). Peterson and Dowler (1965) associated P. syringae with peach tree deaths in the south-eastern USA. Prunier et al. (1970) reported that a non-ﬂuorescent bacterium was associated with a peach decline syndrome in France and named the pathogen P. syringae pv. persicae. In 1967, a similar bacterial pathogen was associated with a decline syndrome of peaches, nectarines and Japanese plums in New Zealand (Young, 1988). Thus, at least two pathovars of P. syringae are associated with bacterial canker of peach trees: (i) P. syringae pv. syringae van Hall causes disease on many commercially grown Prunus spp. in addition to peach; and (ii) P. syringae pv. persicae is mostly limited to and possibly more aggressive on peach, but also

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Fig. 16.8. Discoloured wood approximately a week after the occurrence of cold damage, with the bark separating easily and appearing undamaged.

Fig. 16.9. Non-fluorescent and fluorescent bacteria associated with the bacterial canker complex cultivated on King’s medium B.

occurs on nectarine and plum. P. syringae pv. syringae utilizes inositol and lactate, ﬂuoresces on King’s medium B (Fig. 16.9/Plate 149) (Young and Triggs, 1994) and produces the

toxin syringomycin, while P. syringae pv. persicae does not utilize these two carbohydrates, is non-ﬂuorescent and produces the toxin persicomycin (Barzic, 1999).

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P. syringae consists of a ubiquitous group of bacteria that can exist internally as plant pathogens and externally as epiphytes (Cross, 1966; Dowler and Weaver, 1975). The pathogen can be disseminated by splashing rain, possibly through pruning, and with contaminated nursery stock. Infections of the woody portions of the tree are presumed to occur in autumn through leaf scars, with symptom expression in the following early spring as trees emerge from dormancy. Infection and disease development are favoured by wet and cool environmental conditions. Widespread infection and canker enlargement occur in trees with high water content (Vigouroux, 1999). Chemical sprays targeted at the pathogen have not adequately controlled bacterial canker on peaches. The best success has been achieved when management practices focus on alleviating predisposing factors (Davis and English, 1969; Ritchie and Clayton, 1981; Cao et al., 2005). These include selection of planting sites suited for peaches, proper rootstock and cultivar selection adapted to the growing region, reduction of nematode stress through the use of pre-plant soil fumigation and appropriate resistant rootstocks, and other cultural practices that minimize tree stress such as delaying pruning until late winter.

Bacterial spot Bacterial spot, also known as bacteriosis, bacterial leaf spot and bacterial shot hole, infects most Prunus species but causes signiﬁcant economic losses on peaches, nectarines and plums. Bacterial spot was originally described on Japanese plum (Prunus salicina Lindl.) from Michigan in 1903 (Smith, 1903). The disease occurs in most countries where peaches are grown including Argentina, Australia, Brazil, Canada, France, Italy, Japan, New Zealand, South Africa, the USA and Uruguay. Bacterial spot is most common and severe where peaches are grown in light, sandy soils and moist, warm environment conditions occur. Bacterial spot is caused by Xanthomonas arboricola (syn. campestris) pv. pruni (Smith) (Vauterin et al., 1995). The bacterium is a Gram-negative, strict aerobe having an optimal growth

temperature of 24–30°C. Growth on YDC medium (yeast–dextrose–calcium carbonate– agar) or SPA medium (sucrose–peptone–agar) for 48–72 h results in light yellow, lemoncoloured, mucoid colonies. Bacterial spot affects leaves, fruits and twigs. Leaf lesions and chlorosis are usually the ﬁrst and most obvious symptoms observed (Fig. 16.10/Plate 150). Lesions start as greyish, angular areas approximately 1–3 mm in width (Fig. 16.11/Plate 151). Lesion centres become purple and necrotic and, if centres abscise, leaves develop a shot-hole, tattered appearance. Leaves may become chlorotic and abscise. Lesions contain large numbers of bacteria and bacterial streaming can be observed when lesions are placed in a droplet of water and viewed at 100–200× under a microscope (Fig. 16.12/Plate 152). This is a quick diagnostic method to differentiate bacterial-caused lesions from those caused by other entities such as Cu or other pesticides. Lesions from pesticide injury are almost always circular, non-water soaked and not angular when compared with bacterial spot lesions. On highly susceptible varieties, multiple years of severe premature defoliation result in reduced numbers of fruit buds, reduced fruit crops and weakened trees. Fruit symptoms are ﬁrst visible as small, angular, water-soaked lesions 3–5 weeks after petal fall (Fig. 16.13/Plate 153). These early infections can develop into deep, cavernousappearing lesions (Fig. 16.14/Plate 155). Lesions that develop from later infections, especially those after pit hardening, tend to be conﬁned more to the fruit surface (Fig. 16.15/Plate 154). Bacterial spot lesions on fruit may be confused with peach scab lesions, which are darker in colour, circular and usually more restricted to the surface of the peach skin. Also, no bacterial streaming should be detected from peach scab. Spring cankers are ﬁrst visible near time of bloom and develop on the previous season’s twig growth, usually centred on a leaf scar (Fig. 16.16/ Plate 156). Leaf and ﬂower buds fail to open or the canker extends downward from the terminal bud, which fails to open, resulting in a ‘black tip’ canker (Fig. 16.17/Plate 157). Cankers may extend several centimetres from the dead buds and have a

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Fig. 16.10. Chlorotic peach leaves with lesions caused by Xanthomonas arboricola pv. pruni.

black, greasy, wet appearance. Cutting the outer bark reveals brownish, water-soaked bark that usually does not extend into the wood (Fig. 16.18/Plate 158), differentiating it from bacterial canker. During the growing season, cankers can develop on the current season’s twig growth; these are termed ‘summer cankers’ (Fig. 16.17/Plate 157). The pathogen overwinters on peach trees in association with buds, in protected areas on the woody tree surface, and in leaf scars that become infected during defoliation the previous season (Shepard and Zehr, 1994). Leaf-scar infections can result in spring cankers that become active as new leaf tissue emerges the following season, serving as a major source of primary inoculum. Moisture such as splashing or wind-blown rain or dripping of dew is essential for bacterial dissemination to newly emerging leaves and fruit. Fruit can become infected as they emerge from the shuck if there is adequate moisture. Frequent periods of rainfall and water congestion of plant tissues are important for leaf infection (Zehr and Shepard, 1996; Battilani

et al., 1999). Severe fruit infections are most common when rainfall or extended periods of water congestion occur during shuck split to near pit hardening (Ritchie, 1993). Bacterial spot is more severe where peaches are grown in sandy than in heavier soils. This may be associated with increased leaf and fruit injury from wind-blown sand, from physiological factors related to water potential, predisposition by nematodes, or a combination of these (Zehr and Shepard, 1996). Leaf infections occur as long as new leaf growth continues. The time from infection until symptom expression is inﬂuenced by temperature. Under optimal bacterial growth conditions, symptom expression may occur in 3–5 days but under cool conditions this may take up to 14 days. Peach cultivars vary greatly in susceptibility and the most effective control is through the use of host plant resistance (Werner and Ritchie, 1986). Unfortunately, many resistant varieties lack speciﬁc desirable fruit and marketing characteristics (Okie, 1998). Most varieties developed in dry regions where the disease

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Chemical controls have shown limited efﬁcacy but are most effective when management programmes are started before the infection of newly emerged leaves and fruits occurs, with success depending on weather conditions and disease pressure. Foliar-applied chemicals consist primarily of Cu-containing materials and in the USA also oxytetracycline (Ritchie, 1999). Peach foliage is very sensitive to Cu and severe phytotoxicity can result if misused. Cu use focuses on three to ﬁve applications from start of bud break through shuck split, when only a limited amount of foliage is present (Ritchie, 1999; Brannen et al., 2007). The rate of elemental Cu is reduced each subsequent application (Brannen et al., 2007). After shuck split, very low rates of elemental Cu or other materials registered for use in the region have shown some success. Sprays are usually applied at 7–14-day intervals, depending upon rainfall and disease pressure.

Crown gall

Fig. 16.11. Newly formed, water-soaked, greyish, angular bacterial spot lesions on peach leaf caused by Xanthomonas arboricola pv. pruni.

does not occur are highly susceptible and, when planted in regions where environmental conditions favour bacterial spot and the pathogen is present or is introduced, fruit loss can be severe. Once bacterial spot is established in an orchard, disease control can be very difﬁcult (Ritchie, 1999). Injury from blowing sand may be minimized by planting and maintaining appropriate ground covers in and near the orchard. Windbreaks appropriately placed to blunt the damaging effects of strong winds, while still allowing for air movement, may aid in reducing bacterial spot.

The greatest economic impact of this disease occurs in the nursery from culling of symptomatic trees. Galls commonly develop in the lower stem or trunk region at the root crown just below the soil line (Fig. 16.19/Plate 159), but can occur on roots and occasionally aerial plant parts. Galls may develop to several centimetres in diameter. Tissue of newly formed and expanding galls is soft and spongy. Young trees may be stunted and older trees may express symptoms typical of root problems. On mature trees, galls often are not discovered until the roots are exposed when trees are removed. As galls age, they become woody and usually are colonized by other microbes, resulting in decay. Agrobacterium belongs to the family of nitrogen-ﬁxing bacteria, Rhizobiaceae, and consists of several species of bacteria that induce hyperplastic plant growths. Agrobacterium tumefaciens, also known as biovar 2, is the species that induces galls in peach. Several selective media have been developed to aid in isolation and differentiation of the species (biovars) (Brisbane and Kerr, 1983) and

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Fig. 16.12. Bacteria streaming from leaf lesion caused by Xanthomonas arboricola pv. pruni.

Fig. 16.13. Newly formed, water-soaked, bacterial spot lesions on peach fruit near the growth stage of pit hardening.

PCR-based primers also have been developed (Haas et al., 1995). The tumourigenic ability is due to genes on a large bacterial plasmid termed

the Ti-plasmid. A segment of the Ti-plasmid (the T-DNA) is transferred to the plant cell via a conjugation-like process and incorporated into the plant genome. Loss of the Ti-plasmid

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Fig. 16.14. Bacterial spot lesions on fruit at harvest caused by early infections occurring soon after shuck split and before pit hardening.

Fig. 16.15. Bacterial spot lesions on fruit at harvest which are confined to the fruit surface and developed from infections occurring after pit hardening.

renders the A. tumefaciens strains nontumourigenic. Such strains are classiﬁed as Agrobacterium radiobacter. Infection requires wounds and is favoured by moist conditions and poorly drained soils. Although the Ti-plasmid DNA transfer is favoured by temperatures just below 20°C, gall development occurs more rapidly at temperatures greater than 20°C with galls visible

2–4 weeks after infection (Fullner et al., 1996). Crown gall is more common in temperate than tropical regions. Once plant cells are transformed, bacterial presence no longer is necessary for tumour development since the T-DNA replicates with the host DNA. Gene expression causes the plant to produce excess amounts of indoleacetic acid and cytokinin, which stimulate hyperplastic growth.

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Fig. 16.16. Bacterial spot spring canker (Xanthomonas arboricola pv. pruni) with a black, greasy appearance.

Fig. 16.17. Terminal dieback and black tip canker, summer cankers on current year’s twigs, lesions on leaves, and nodes where leaves have defoliated caused by Xanthomonas arboricola pv. pruni.

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Discoloured bark tissue of spring canker Xanthomonas arboricola pv. pruni.

Fig. 16.19. Crown gall caused by Agrobacterium tumefaciens on peach trees recently dug from a nursery.

Diseases Caused by Prokaryotes

Species of Agrobacterium are ubiquitous in the soil and can be isolated from agricultural and non-agricultural soils (Bouzar and Moore, 1987). The ability to exist in latent infections and in soil adhering to root surfaces allows for pathogen dissemination with nursery stock and through the movement of soil and water (Moore, 1976). Under experimental conditions, agrobacteria have survived in soil for more than 2 years, with survival negatively affected by soil temperatures greater than 34°C and acidic conditions. Crown gall is best controlled by prevention of infections. This starts with a pathogenfree nursery site, inspection of trees as removed from the nursery and the planting of quality, gall-free trees. Seed used for rootstocks can be treated using the appropriate biocontrol strain of A. radiobacter. Roots of trees also can be treated with this agent at planting time (Jones and Kerr, 1989). Removal of the galls does not necessarily prevent galls from occurring later, thus trees having galls should be destroyed. Once trees have been planted, infections can be minimized by avoiding practices that cause injuries (e.g. tillage) to the lower trunk and roots.

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Phony peach disease Phony (phoney) peach disease (PPD) reduces fruit quality and the economic life of trees. This disease is endemic in the south-eastern USA, where symptoms were ﬁrst described in 1890. Sporadic epidemics have occurred several times since then. Tree losses have occurred from eastern Texas to the southeastern Atlantic states, being most severe in Georgia, northern Florida and southern Alabama (Wells et al., 1983; Mizell et al., 2003). Diseased trees appear dwarfed compared with non-diseased trees. Dark green leaves on branches with shortened internodes give the tree a compact, ﬂattened, umbrella-like canopy (Fig. 16.20/Plate 160). Infected trees tend to bloom several days earlier than healthy trees and retain their leaves longer in autumn. Another typical symptom occurring 3–5 years after infection is the production of progressively smaller, more colourful, but nonmarketable fruit (Evert and Smittle, 1989). PPD is caused by the fastidious xylemlimited, Gram-negative bacterium, Xylella fastidiosa Wells et al. (Wells et al., 1983). Detection of X. fastidiosa was hampered because of

Fig. 16.20. Peach tree expressing phony peach disease symptoms. Leaves are greener and denser and internodes are shortened, giving the tree a compact, flat canopy with an ‘umbrella-like’ appearance. (Courtesy of R.F. Mizell III, University of Florida, Quincy, Florida, USA.)

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difﬁculty in culturing the pathogen. In 1973, PPD was ﬁrst associated with a rickettsia-like bacterium before ﬁnally being cultured in 1983. PCR primers have proved useful to identify naturally infected ﬁeld samples (Rodrigues et al., 2003). Genetically distinct strains of X. fastidiosa are responsible for a variety of economically important plant diseases. Strains of X. fastidiosa cause citrus variegated chlorosis (CVC), Pierce’s disease, PPD, plum leaf scald (PLS) and leaf scorch diseases in elms, almonds, maples, oleander, pear, oaks, sycamores and coffee (Nunes et al., 2003). A phylogenetic analysis based on partial sequences of the gyrB gene placed X. fastidiosa strains into three clusters: (i) grapevine-associated strains; (ii) citrus–coffee strains; and (iii) a cluster composed of all other strains (Rodrigues et al., 2003). A common aetiology between strains that cause PPD on peaches and PLS on plums was shown (Wells et al., 1981; Abrahams and Norton, 1994). Plants of more than 30 families can serve as natural reservoirs and secondary hosts for the pathogen. The most important for PPD are wild Prunus species and grasses such as johnsongrass (Sorghum halapense) (Mizell et al., 2003). X. fastidiosa enters the peach xylem tissue via the feeding of sharpshooter leafhopper vectors, primarily Homalodisca coagulata and Oncometopia nigricans. The polyphagous H. coagulata has a moderate feeding preference for plums and a low preference for peaches. Insect numbers also are reduced on trees that express PPD symptoms. The xylem ﬂuid chemistry of the scion/rootstock combination affects the feeding behaviour and performance of PPD vectors (Andersen et al., 1994). X. fastidiosa multiplies and spreads systemically throughout the xylem, occluding the vessels and restricting water movement (Mizell et al., 2003). X. fastidiosa is usually much more abundant in peach roots than in stems or leaves, which contrasts with plums, where it is homogeneously distributed throughout the tree (Evert and Smittle, 1989). This is considered important as it results in lack of secondary spread within peach orchards and, thus, peach may be a ‘dead-end’ host. There is no cure for PPD and so control is based on preventing spread through early detection and removal of diseased trees. Wild

plums within approximately 400 m should be removed and weeds controlled in and close to peach orchards to reduce reservoir hosts for the pathogen and the insect vectors. Severe summer pruning should be avoided since intense regrowth is attractive to leafhoppers. Control of leafhoppers with routine spraying has not proved effective. New orchards should not be established close to infected Prunus trees before removal and destruction of such trees (Mizell et al., 2003).

16.3 Phytoplasma Diseases Peach X-disease Peach X-disease was described in California in 1931. It also occurs in eastern fruit-growing areas of North America, where it continues to cause economic losses to stone fruits, but has not been reported outside North America (EPPO/CABI, 1997b). In addition to peach, the disease is economically important on tart and sweet cherries, Japanese plum (P. salicina), almonds and apricots, and occurs on some wild Prunus species (e.g. Prunus virginiana), which serve as important pathogen reservoirs (Kirkpatrick et al., 1995). Eastern and western strains of the pathogen are similar and the term X-disease is currently used to describe this group of yellows-inducing Prunus pathogens (Kirkpatrick et al., 1995). During the early stages of infection, trees show very irregularly distributed symptoms. The phytoplasma pathogen requires more than 2 years to colonize a mature tree completely (Kirkpatrick et al., 1995). Symptoms occur on the leaves as irregularly distributed yellow or necrotic spots (Fig. 16.21/Plate 161). The number of lesions increases during the season and lesion centres may abscise, creating a shot-hole appearance. Leaves are rolled and have a pale green colour, conferring an appearance of reduced tree vigour. Often infected leaves at the base of the shoots abscise, inducing a terminal rosetting (Fig. 16.22/Plate 162). Symptomatic branches are more sensitive to freezes and young trees can die within 1–3 years after infection (Gilmer and Blodgett, 1976). Fruit size and yield are

Diseases Caused by Prokaryotes

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Fig. 16.21. X-disease phytoplasmainfected peach with necrotic lesions non-uniformly distributed on rolled and pale green leaves.

Fig. 16.22. X-disease phytoplasma-infected trees exhibit a loss of vigour, leaves have a pale green colour and severely infected branches die.

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greatly reduced; remaining fruit ripen several days later than normal and often have an insipid ﬂavour. Grannet and Gilmer (1971) demonstrated the association of a phytoplasma with X-disease in various Prunus species. This phytoplasma belongs to the X-disease group (group 16Sr III) (Lee et al., 2000). Analysis of 16S rDNA of phytoplasmas associated with individual trees affected by little peach, red suture and rosette strongly suggests that these phytoplasmas are closely related, exhibiting greater than 99% similarity (Scott and Zimmerman, 2001), but the diseases are considered to be different because of epidemiological properties including geographical distribution, host range and insect vectors. The greatest potential for infection occurs during late spring and summer. Peach X-disease has been transmitted by grafting to several Prunus spp. and through dodder (Cuscuta spp.) to periwinkle and other herbaceous plants such as celery, carrot, parsley, tobacco and tomato (Gilmer and Blodgett, 1976). The primary method of ﬁeld dissemination is by leafhoppers, with Colladonus montanus, Colladonus geminatus, Fieberiella florii and Paraphlepsius irroratus considered the most important. Each vector has its own ecological niche, which characterizes the natural spread to peach orchards. For C. montanus, the probability to infect peach orchards is greater in areas where sugarbeet or other dicotyledonous plants are present because this vector overwinters and multiplies on these plants. Wild cherries, such as bitter cherry (Prunus emarginata) and chokecherry (P. virginiana), serve as reservoirs of this phytoplasma in the eastern USA where the vector is the cherry leafhopper, F. florii, which is very efﬁcient at transmitting the phytoplasma from wild cherries to peaches. In areas where P. irroratus is the primary vector, it feeds on infected monocotyledonous plants during the day and at night moves to peach or other woody hosts (Rosenberger and Jones, 1977; Kirkpatrick et al., 1995). Diseased peach trees should be removed and destroyed as soon as detected. Cultural practices that reduce the risk of disease spread include control of the leafhopper vector population and elimination of woody and herbaceous plants that serve as reservoirs for the

phytoplasma or that allow the vector to overwinter and multiply. In the eastern USA, removal of wild chokecherry within 200 m of orchards reduced disease incidence (Rosenberger and Jones, 1977). Peach yellows Peach yellows, little peach and red suture are caused by the same phytoplasma (Kirkpatrick, 1995b; EPPO/CABI, 1997c), although there are epidemiological differences (Larsen and Waterworth, 1995). Peach yellows epidemics with economic losses occurred during the 19th and early 20th centuries along the eastern US coastal states from Maryland to South Carolina. The disease has not been reported in far western and southern states (south of South Carolina) or outside the USA (EPPO/CABI, 1997c). Peach red suture, however, has been observed in eastern Canada, Russia and possibly France and Israel (Larsen and Waterworth, 1995). All cultivars of peach and nectarine are susceptible. Almonds, apricots and Japanese plum (P. salicina) can serve as reservoirs for the pathogen (EPPO/CABI, 1997c). Disease symptoms are as follows. ●

●

Peach yellows: Flowers and foliage of infected trees emerge 2–4 weeks earlier than on healthy trees. Leaves are small and narrow, inwardly rolled with a downward droop, chlorotic and may develop red spots. Latent-infected buds initiate new growth by producing multiple shoots, especially on the internal portion of the canopy, giving the tree a bushy appearance. Terminal dieback of twigs and branches is common in advanced stages of the disease. Severely diseased trees die within 2–4 years. Fruits ripen and colour several days earlier than normal (Fig. 16.23/ Plate 163) and, although of normal or larger size, have a bland or bitter ﬂavour (Pine and Gilmer, 1976). Little peach: Symptoms are similar as for peach yellows but differ in two distinctive characteristics. Young leaves initially are greener than normal and later become yellow. Fruits are reduced in size and ripen several days to 3 weeks later than normal (Pine and Gilmer, 1976).

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Fig. 16.23. Tree infected with peach yellows phytoplasma showing a bushy appearance on ends of branches and premature colouring and ripening of fruit. (Courtesy of A. Ragozzino.)

●

Red suture: Leaves develop a yellowishgreen appearance soon after petal fall and become greenish-bronze just before harvest. The most distinctive symptom occurs on fruits as a premature ripening and softening in the suture area, while the other part of the fruit remains green and hard. The suture area is prominent, bumpy, swollen, accompanied by an intense dark red to purple colour for red cultivars and a deep yellow for yellow cultivars, and an intense internal colour along the suture (Klos, 1976; Larsen and Waterworth, 1995). Fruit ﬂavour is often insipid.

Jones et al. (1974) demonstrated that a phytoplasma is responsible for the peach yellows symptoms. This phytoplasma belongs to the X-disease group (group 16Sr III) (Lee et al., 2000), but is distinct from the peach X-disease phytoplasma (Kirkpatrick, 1995b; EPPO/ CABI, 1997c). Phytoplasmas associated with little peach, red suture and western X-disease are more than 99% similar (Scott and Zimmerman, 2001). These phytoplasmas also are closely related to those causing peach rosette. Peach yellows was transmitted experimentally by grafting to several Prunus spp. and through dodder (Cuscuta spp.) to periwinkle

(Jones et al., 1974). Symptom expression is inﬂuenced by the site of inoculation. This phytoplasma moves downward more rapidly than upward. Hence, infection near the apical portion of the tree causes symptom expression much earlier than does infection nearer the soil (Pine and Gilmer, 1976). Peach yellows and little peach are transmitted by the plum leafhopper Macropsis trimaculata, whereas the vector of red suture is unknown (EEOP/CABI, 1997c). Because plums are the preferred host of M. trimaculata, latently infected plums may serve as reservoirs for transmission to peaches. This plum leafhopper vector does not occur in Europe (EEOP/ CABI, 1997c). Diseased peach trees should be removed and destroyed as soon as detected. Plums located near peach orchards should be carefully monitored and removed if they test positive for peach yellows.

Peach rosette Peach rosette (PR) was ﬁrst described in the state of Georgia, USA, in 1881, and later reported in other south-eastern states as far

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west as Texas (Kenknight, 1976). Initially, it was considered a southern strain of peach yellows. The disease has not been reported from western states or outside the USA (Kirkpatrick, 1995a). Kirkpatrick et al. (1975) demonstrated experimentally that a phytoplasma is responsible for the symptoms. The disease is sporadic in occurrence and currently considered of minor importance. The deﬁning symptom of PR is the shortening of internodes on new shoots, creating tight clusters of leaves that cause a rosette or witches’ broom appearance. In early summer, premature defoliation occurs at the base of the shoots, leaving tufts of young leaves near the shoot tip. The interior tree canopy fails to develop secondary shoots, resulting in a sparse appearance. Leaves are normal in size but may become chlorotic. Blossom and fruit production are reduced and the few fruits produced ripen irregularly and abscise prematurely. Infected trees generally survive the season that the infection occurred, but in severe cases die within a year after onset of symptoms (Kenknight, 1976; Kirkpatrick, 1995a). These two characteristics (sudden reduction of fruit production and tree death) are different from peach yellows. The PR phytoplasma belongs to the X-disease group (group 16Sr III) (Lee et al., 2000), but is distinct from the peach X-disease phytoplasma (Kirkpatrick, 1995a; EPPO/CABI, 1997a). Peach, Japanese plum (P. salicina) and wild plum species (Prunus augustifolia, Prunus hortulana, Prunus munsoniana) are important native hosts of PR (Kenknight, 1976). Rosette symptoms occurred within 4–11 months after experimental transmission to peach, plum, almond and cherry seedlings by grafting (Kirkpatrick et al., 1975). The PR phytoplasma has been transmitted through dodder to periwinkle, tomato and tobacco (Kenknight, 1976). Field surveys indicate spread from tree to tree, but infected peach trees apparently are not the primary reservoir of the phytoplasma since such trees generally die within a year after infection. Diseased peach trees are usually ﬁrst detected at the border of the orchard, suggesting that the pathogen is introduced from wild plums growing near the orchard. Infected plums survive for years and serve as reservoirs of the phytoplasma

(Kenknight, 1976; Scott and Zimmerman, 2001). No insect vector(s) has been identiﬁed. Control measures include removal and destruction of diseased trees as soon as detected. Wild plums should not be allowed to grow near peach orchards. Peach yellow leaf roll Peach yellow leaf roll (PYLR) and western X-disease are the two major phytoplasmacaused diseases of peaches in California (Blomquist and Kirkpatrick, 2002). Nyland and Schlocker (1951) ﬁrst reported PYLR in 1951. It apparently is restricted to a few northern California counties where it periodically has caused severe tree losses (Nyland and Schlocker, 1951; Purcell et al., 1981; Blomquist and Kirkpatrick, 2002). Until recently, PYLR was considered a different manifestation of peach X-disease. PYLR has been observed only on peach trees. Leaves of infected trees have normal size, but are yellow and roll downward with a tendency to curve toward the stem. The leaf midribs and lateral veins are enlarged and affected leaves abscise prematurely. Fruit production decreases, a rapid tree decline occurs, and the tree can die within 3 years after the onset of symptoms. Late-season leaf symptoms sometimes result in shot holes, thus resembling peach X-disease (Blomquist and Kirkpatrick, 2002). The PYLR phytoplasma is a member of the AP (apple proliferation) group (group 16Sr X) (Kison et al., 1997), which includes phytoplasmas infecting stone fruits in Europe (European stone fruit yellows, ESFY), pears (pear decline, PD) and apples (AP). Restriction fragment length polymorphism analysis of PCR-ampliﬁed rDNA differentiated the PYLR phytoplasma from the AP and ESFY phytoplasmas, but not from the PD phytoplasma (Kison et al., 1997). Worldwide, peach and pear orchards can be found adjacent yet PYLR occurs only in California, suggesting that the PYLR sub-strain of the PD phytoplasma evolved in California (Blomquist and Kirkpatrick, 2002). PYLR is most evident in peach orchards adjacent to pears, thus pear orchards are considered the primary reservoir for PYLR

Diseases Caused by Prokaryotes

(Purcell et al., 1981; Blomquist and Kirkpatrick, 2002). Psylla insects (Homoptera: Psyllidae) transmit phytoplasmas that belong to the AP group, which include the PD and the ESFY phytoplasmas (Carraro et al., 1998; Frisinghelli et al., 2000). PYLR phytoplasma also is transmitted by psylla, which is considered the primary vector (Blomquist and Kirkpatrick, 2002). In late summer to early autumn, psylla move from pears to the surrounding vegetation and thus transmit the PYLR phytoplasma to other hosts. The use of effective insecticides in pear orchards after fruit harvest for reducing lateseason psylla populations, thus restricting psylla movement to peach orchards, has effectively reduced PYLR in northern California (Blomquist and Kirkpatrick, 2002). European stone fruit yellows Decline diseases of apricot and Japanese plum were observed in France and Italy in the early 1900s and named apricot chlorotic leaf roll (ACLR) and plum leptonecrosis (PLN) or plum decline. Similar diseases were later described on peach and almond in Germany and Spain.

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Today, all these decline diseases are referred to as ESFY (European stone fruit yellows) (Lorenz et al., 1994). The disease occurs on Prunus species in all Mediterranean countries and as far north as Germany. It is economically the most important phytoplasma-caused disease of stone fruits in Europe (Poggi-Pollini et al., 2001). Symptoms that develop soon after infection are irregularly distributed on the branches inoculated by the insect vector. Two or more years are required to completely colonize a mature tree. The greatest potential for infection occurs in late summer (August–September) when symptoms are particularly evident on the foliage. Leaves of infected branches are small in size, roll longitudinally upward, are yellow to red in colour and thick and brittle (Fig. 16.24/Plate 164). Leaf midribs and lateral veins are enlarged and affected leaves may become necrotic and abscise prematurely (Fig. 16.25/Plate 165). Diseased trees have reduced vigour (Fig. 16.26/Plate 166), are more sensitive to winter freezes and decline gradually, with reduced fruit productivity (Poggi-Pollini et al., 2001). Early emergence of ﬂowers and leaves may occur during the winter, allowing for easy differentiation from

Fig. 16.24. Leaves on branch infected with European stone fruit yellows phytoplasma (left) are small in size, rolled upward longitudinally and have a pale yellow colour compared with leaves on a non-infected branch (right). (Courtesy of A. Ragozzino.)

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Fig. 16.25. Peach tree infected with European stone fruit yellows phytoplasma with leaf midrib and lateral veins enlarged and necrotic. (Courtesy of L. Giunchedi.)

healthy trees. Symptom expression is inﬂuenced by the virulence of individual phytoplasma strains and the susceptibility of the rootstock and scion. Some strains are very aggressive, especially when susceptible rootstocks (e.g. peach seedlings, ‘GF 677’, ‘Rubira’, ‘Montclar’, ‘Rutgers Red Leaf’) are used. These aggressive strains also cause high mortality when scions are grafted on to tolerant rootstocks (Kison and Seemüller, 2001). ESFY is caused by a phytoplasma belonging to the AP group (group 16Sr X) (Lee et al., 2000). It differs from the PYLR and X-disease phytoplasmas, which occur in North America (Dosba et al., 1991; Ahrens et al., 1993; Seemüller et al., 1998). The ESFY phytoplasma persists in the aerial portion of peach trees during the dormant season and can be dormant-bud

transmitted by grafting (Seemüller et al., 1998; Jarausch et al., 1999). Cross-inoculation experiments with phytoplasma isolates infecting various Prunus species suggest that ACLR, PLN and yellowing and decline of almond and peach have a common aetiology (Dosba et al., 1991). Ahrens et al. (1993) conﬁrmed that the phytoplasmas associated with naturally infected apricot, plum, almond and peach are closely related. The psylla, Cacopsylla pruni, is the major natural vector. The phytoplasma is acquired when the psylla feed on infected trees for 2–4 days and they remain infective until their death. A latent period of 2–3 weeks between acquisition and transmission may occur (Carraro et al., 1998). Several wild Prunus species (Prunus spinosa, Prunus cerasifera, Prunus domestica) serve as reservoirs for the ESFY

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Fig. 16.26. Two trees of the same age of cultivar ‘Baby Gold 7’. The tree in foreground is infected with the European stone fruit yellows phytoplasma (exhibiting reduced vigour); compare with the non-infected tree in the background. (Courtesy of A. Ragozzino.)

phytoplasma and as hosts for the insect vector (Carraro et al., 2002). Although ESFY is present in many European countries, spread currently is reduced through phytosanitary regulations. Other management practices include removal and destruction of diseased trees and eradication of wild Prunus spp. when identiﬁed, and the control of psylla populations.

16.3 Summary Although there are relatively few diseases of peach caused by bacteria and phytoplasmas,

these can cause serious economic fruit losses, render trees non-productive and shorten tree life. Diagnosis based on symptoms ranges from relatively easy for bacterial spot to difﬁcult or unreliable for the phytoplasma-caused diseases, for which conﬁrmation must include serological or genomic methods. Disease management is based on prevention and starts with pathogen exclusion from a region or individual orchard by use of quarantines and certiﬁed plant material. Antibacterial chemicals are few, have limited efﬁcacy and may produce unacceptable phytotoxicity. Host plant resistance, when available in adapted cultivars, is very effective.

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Andersen, P., Brodbeck, B. and Mizell, R. (1994) Influence of xylem fluid chemistry of Prunus spp. on the abundance and performance of adult Homalodisca coagulata. HortScience 29, 493. Barzic, M.R. (1999) Persicomycin production by strains of Pseudomonas syringae pv. persicae. Physiological and Molecular Plant Pathology 55, 243–250. Battilani, P., Rossi, V. and Saccardi, A. (1999) Development of Xanthomonas arboricola pv. pruni epidemics on peaches. Journal of Plant Pathology 81, 161–171. Blomquist, C.L. and Kirkpatrick, B.C. (2002) Identification of phytoplasma taxa and insect vectors of peach yellow leaf roll disease in California. Plant Disease 86, 759–763. Bouzar, H. and Moore, L.W. (1987) Isolation of different Agrobacterium biovars from natural oak savanna and tall grass prairie. Applied and Environmental Microbiology 53, 717–721. Brannen, P., Horton, D., Bellinger, B. and Ritchie, D. (2007) Southeastern Peach, Nectarine and Plum Pest Management and Cultural Guide. Georgia Extension Bulletin No. 1171 (revised annually). University of Georgia Cooperative Extension Service, College of Agricultural and Environmental Sciences, Athens, Georgia. Brisbane, P.G. and Kerr, A. (1983) Selective media for three biovars of Agrobacterium. Journal of Applied Bacteriology 54, 425–431. Cao, T., Duncan, R.A., McKenry, M.V., Shachel, K.A., DeJong, T.M. and Kirkpatrick, B.C. (2005) Interaction between nitrogen-fertilized peach trees and expression of syrB, a gene involved in syringomycin production in Pseudomonas syrinage pv. syringae. Phytopathology 95, 581–586. Carraro, L., Osler, R., Loi, N., Ermacora, P. and Refatti, E. (1998) Transmission of European stone fruit yellows phytoplasma by Cacopsylla pruni. Journal of Plant Pathology 80, 233–239. Carraro, L., Ferrini, F., Ermacora, P. and Loi, N. (2002) Role of wild Prunus species in the epidemiology of European stone fruit yellows. Plant Pathology 51, 513–517. Cross, J.E. (1966) Epidemiological relations of the pseudomonad pathogens of deciduous fruit trees. Annual Review of Phytopathology 4, 291–310. Davis, J.R. and English, H. (1969) Factors related to the development of bacterial canker in peach. Phytopathology 59, 588–595. Dosba, F., Lansac, M., Mazy, K., Garnier, M. and Eyquard, J.P. (1991) Incidence of different diseases associated with mycoplasmalike organisms in different species of Prunus. Acta Horticulturae 283, 311–320. Dowler, W.M. and Weaver, D.J. (1975) Isolation and characterization of fluorescent pseudomonads from apparently healthy peach trees. Phytopathology 65, 233–236. Endert-Kirkpatrick, E. and Ritchie, D.F. (1988) Involvement of pH in the competition between Cytospora cincta and Pseudomonas syringae pv. syringae. Phytopathology 78, 619–624. EPPO/CABI (1997a) Peach rosette phytoplasma. In: Smith, I.M., McNamara, D.G., Scott, P.R. and Holderness, M. (eds) Quarantine Pests for Europe, 2nd edn. CAB International, Wallingford, UK, pp. 1036–1038. EPPO/CABI (1997b) Peach X-disease phytoplasma. In: Smith, I.M., McNamara, D.G., Scott, P.R. and Holderness, M. (eds) Quarantine Pests for Europe, 2nd edn. CAB International, Wallingford, UK, pp. 1039–1043. EPPO/CABI (1997c) Peach yellows phytoplasma. In: Smith, I.M., McNamara, D.G., Scott, P.R. and Holderness, M. (eds) Quarantine Pests for Europe, 2nd edn. CAB International, Wallingford, UK, pp. 1044–1047. Evert, D. and Smittle, D. (1989) Phony disease influences peach leaf characteristics. HortScience 24, 1000– 1002. Frisinghelli, C., Delaiti, L., Grando, M.S., Forti, D. and Vindimian, M.E. (2000) Cacopsylla costalis (Flor 1861), as a vector of apple proliferation in Trentino. Journal of Phytopathology 148, 425–431. Fullner, K.J., Lara, J.C. and Nester, E.W. (1996) Pilus assembly by Agrobacterium T-DNA transfers genes. Science 273, 1107–1109. Gilmer, R.M. and Blodgett, E.C. (1976) X-disease. In: Virus Diseases and Noninfectious Disorders of Stone Fruits in North America. USDA Agriculture Handbook No. 437. US Department of Agriculture–Agricultural Research Service, Washington, DC, pp. 145–155. Grannet, A.L. and Gilmer, R.M. (1971) Mycoplasma associated with X-disease in various Prunus species. Phytopathology 61, 1036–1037. Haas, J.H., Moore, L.W., Ream, W. and Manulis, S. (1995) Universal PCR primers for detection of phytopathogenic Agrobacterium strains. Applied and Environmental Microbiology 61, 2879–2884. Jarausch, W., Lansac, M. and Dosba, F. (1999) Seasonal colonization pattern of European stone fruit yellows phytoplasmas in different Prunus species by specific PCR. Journal of Phytopathology 147, 47–54. Jones, A.L., Hooper, G.R., Rosenberger, D.A. and Chevalier, J. (1974) Mycoplasma-like bodies associated with peach and periwinkle exhibiting symptoms of peach yellows. Phytopathology 64, 1154–1156. Jones, D.A. and Kerr, A. (1989) Agrobacterium radiobacter strain K1026, a genetically engineered derivative of strain K84, for biocontrol of crown gall. Plant Disease 73, 15–18.

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Kenknight, G. (1976) Peach rosette. In: Virus Diseases and Noninfectious Disorders of Stone Fruits in North America. USDA Agriculture Handbook No. 437. US Department of Agriculture–Agricultural Research Service, Washington, DC, pp. 73–76. Kirkpatrick, B.C. (1995a) Peach rosette. In: Ogawa, J.M., Zehr, E.I., Bird, G.W., Ritchie, D.F., Uriu, K. and Uyemoto, J.K. (eds) Compendium of Stone Fruit Diseases. APS Press, St. Paul, Minnesota, pp. 56–57. Kirkpatrick, B.C. (1995b) Peach yellows. In: Ogawa, J.M., Zehr, E.I., Bird, G.W., Ritchie, D.F., Uriu, K. and Uyemoto, J.K. (eds) Compendium of Stone Fruit Diseases. APS Press, St. Paul, Minnesota, p. 57. Kirkpatrick, B.C., Uyemoto, J.K. and Purcell, A.H. (1995) X-disease. In: Ogawa, J.M., Zehr, E.I., Bird, G.W., Ritchie, D.F., Uriu, K. and Uyemoto, J.K. (eds) Compendium of Stone Fruit Diseases. APS Press, St. Paul, Minnesota, pp. 57–59. Kirkpatrick, H.C., Lowe, S.K. and Nyland, G. (1975) Peach rosette: the morphology of an associated mycoplasmalike organism and the chemotherapy of the disease. Phytopathology 65, 864–870. Kison, H. and Seemüller, E. (2001) Differences in strain virulence of the European stone fruit yellows phytoplasma and susceptibility of stone fruit trees on various rootstocks to this pathogen. Journal of Phytopathology 149, 533–541. Kison, H., Kirkpatrick, B.C. and Seemüller, E. (1997) Genetic comparison of the peach yellow leaf roll agent with European fruit tree phytoplasmas of the apple proliferation group. Plant Pathology 46, 538–544. Klos, E.J. (1976) Red suture. In: Virus Diseases and Noninfectious Disorders of Stone Fruits in North America. USDA Agriculture Handbook No. 437. US Department of Agriculture–Agricultural Research Service, Washington, DC, pp. 133–134. Larsen, H.J. and Waterworth, H.E. (1995) Peach red suture. In: Ogawa, J.M., Zehr, E.I., Bird, G.W., Ritchie, D.F., Uriu, K. and Uyemoto, J.K. (eds) Compendium of Stone Fruit Diseases. APS Press, St. Paul, Minnesota, pp. 55–56. Lee, I.M., Davis, R.E., Gundersen, E. and Rindal, D.E. (2000) Phytoplasmas: phytopathogenic Mollicutes. Annual Review of Microbiology 54, 221–255. Lorenz, K.H., Dosba, F., Poggi-Pollini, C., Llacer, G. and Seemüller, E. (1994) Phytoplasma diseases on Prunus species in Europe are caused by genetically similar organisms. Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz 101, 567–575. Mizell, R., Andersen, P., Tipping, C. and Brodbeck, B. (2003) Xylella fastidiosa diseases and their leafhopper vectors. University of Florida Cooperative Extension Service, ENY-683. http://edis.ifas.ufl.edu/BODY_ IN174 (accessed January 2008). Montano, H.G., Davis, R.E., Dally, E.L., Hogenhout, S., Pimental, J.P. and Brioso Paulo, S.T. (2001) Candidatus Phytoplasma brasiliense, a new phytoplasma taxon associated with hibiscus witches’ broom disease. International Journal of Systematic and Evolutionary Microbiology 51, 1109–1118. Moore, L.W. (1976) Latent infections and seasonal variability of crown gall development in seedlings of three Prunus species. Phytopathology 66, 1097–1101. Nunes, L., Rosato, Y., Muto, N., Yanai, G., da Silva, V., Leite, D., Goncalves, E., de Souza, A., Coletta-Filho, H., Machado, M., Lopes, S. and Costa, R. (2003) Microarray analyses of Xylella fastidiosa provide evidence of coordinated transcription control of laterally transferred elements. Genome Research 13, 570–578. Nyland, G. and Schlocker, A. (1951) Yellow leaf roll of peach. Plant Disease Reporter 35, 33. Okie, W.R. (1998) Handbook of Peach and Nectarine Varieties. USDA Agriculture Handbook No. 714. US Government Printing Office, Washington, DC. Peterson, D.H. and Dowler, W.M. (1965) Bacterial canker of stone fruits in the southeastern states. Plant Disease Reporter 49, 701–702. Pine, T.S. and Gilmer, R.M. (1976) Peach yellows. In: Virus Diseases and Noninfectious Disorders of Stone Fruits in North America. USDA Agriculture Handbook No. 437. US Department of Agriculture–Agricultural Research Service, Washington, DC, pp. 91–95. Poggi-Pollini, C., Bissani, R. and Giunchedi, L. (2001) Occurrence of European stone fruit yellows phytoplasma (ESFYP) infection in peach orchards in Northern-Central Italy. Journal of Phytopathology 149, 725–730. Prunier, J.P., Luisetti, J. and Gardan, L. (1970) Etudes sur les bacterioses des arbres fruitiers. II. Caracterisation d’un Pseudomonas non fluorescent, agent d’une bacteriose nouvelle chez le pecher. Annales de Phytopathologie 2, 168–197. Purcell, A.H., Nyland, G., Raju, B.C. and Heringer, M.R. (1981) Peach yellow leaf roll epidemic in northern California: effects of peach cultivar, tree age, and proximity to pear orchards. Plant Disease 65, 365–368. Ritchie, D.F. (1993) Time of peach fruit infection by Xanthomonas campestris pv. pruni. Phytopathology 83, 1376.

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Ritchie, D.F. (1999) Sprays for control of bacterial spot of peach cultivars having different levels of disease susceptibility, 1998. Fungicide & Nematicide Tests 54, 63–64. Ritchie, D.F. and Clayton, C.N. (1981) Peach tree short life: a complex of interacting factors. Plant Disease 65, 462–469. Rodrigues, J., Silva-Stenico, M., Gomes, J., Lopes, J. and Tsai, S. (2003) Detection and diversity assessment of Xylella fastidiosa in field-collected plant and insect samples by using 16S rRNA and gyrB sequences. Applied and Environmental Microbiology 69, 4249–4255. Rosenberger, D.A. and Jones, A.L. (1977) Spread of X-disease in Michigan peach orchards. Plant Disease Reporter 61, 830–834. Scott, S.W. and Zimmerman, M.T. (2001) Peach rosette, little peach, and red suture are diseases induced by a phytoplasma closely related to western X-disease. Acta Horticulturae 550, 351–354. Seemüller, E., Stolz, H. and Kison, H. (1998) Persistence of the European stone fruit yellows phytoplasma in aerial parts of Prunus taxa during the dormant season. Journal of Phytopathology 146, 407–410. Shepard, D.P. and Zehr, E.I. (1994) Epiphytic persistence of Xanthomonas campestris pv. pruni on peach and plum. Plant Disease 78, 627–629. Smith, E.F. (1903) Observations on a hitherto unreported bacterial disease, the cause of which enters the plant through ordinary stomata. Science (USA) 17, 456–457. Vauterin, L., Hoste, B., Kesters, K. and Swings, J. (1995) Reclassification of Xanthomonas. International Journal of Systematic Bacteriology 45, 472–489. Vigouroux, A. (1999) Bacterial canker of peach: effect of tree winter water content on the spread of infection through frost-related water soaking in stems. Journal of Phytopathology 147, 553–559. Wells, J., Raju, J., Thompson, J. and Lowe, S. (1981) Etiology of phony peach and plum leaf scald diseases. Phytopathology 71, 1156–1161. Wells, J., Raju, B. and Nyland, G. (1983) Isolation, culture and pathogenicity of the bacterium causing phony disease of peach. Phytopathology 73, 859–862. Werner, D.J. and Ritchie, D.F. (1986) Susceptibility of peaches and nectarines, plant introductions, and other Prunus species to bacterial spot. HortScience 21, 127–130. Young, J.M. (1988) Pseudomonas syringae pv. persicae from nectarine, peach, and Japanese plum in New Zealand. OEPP/EPPO Bulletin 18, 141–151. Young, J.M. and Triggs, C.M. (1994) Evaluation of determinative tests for pathovars of Pseudomonas syringae van Hall 1902. Journal of Applied Bacteriology 77, 195–207. Zehr, E.I. and Shepard, D.P. (1996) Bacterial spot of peach as influenced by water congestion, leaf wetness duration, and temperature. Plant Disease 80, 339–341.

17

Viruses and Viroids of Peach Trees

M. Cambra,1 R. Flores,2 V. Pallás,2 P. Gentit3 and T. Candresse4 1Instituto

Valenciano de Investigaciones Agrarias (IVIA), Department of Plant Protection and Biotechnology, Valencia, Spain 2Instituto de Biología Molecular y Celular de Plantas (IBMCP), Universidad Politécnica de Valencia–CSIC, Valencia, Spain 3Centre Technique Interprofessionnel des Fruits et Lègumes de Lanxade (CTIFL), La Force, France 4Institut National de la Recherche Agronomique, UMR GDPP–IBVM Equipe de Virologie, Villenave d’Ornon, France

17.1 Introduction 17.2 Sharka or Plum Pox Economic importance and geographic distribution Symptoms Causal agents and diagnosis Epidemiology Control 17.3 Ilarviruses Economic importance and geographic distribution Symptoms Causal agents and diagnosis Epidemiology Control 17.4 Tomato Ringspot Virus Economic importance and geographic distribution Symptoms Causal agent and diagnosis Epidemiology Control 17.5 Strawberry Latent Ringspot Virus Economic importance and geographic distribution Symptoms Causal agent and diagnosis Epidemiology Control 17.6 Peach Rosette Mosaic Virus Economic importance and geographic distribution Symptoms

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Causal agent and diagnosis Epidemiology Control 17.7 Peach Latent Mosaic Economic importance and geographic distribution Symptoms Causal agent and diagnosis Epidemiology Control 17.8 Peach Dapple Economic importance and geographic distribution Symptoms Causal agent and diagnosis Epidemiology Control 17.9 Peach Mosaic Economic importance and geographic distribution Symptoms Causal agent and diagnosis Epidemiology Control 17.10 Diseases of Unknown Aetiology and Experimental Infections in Peach Apricot latent virus, Peach sooty ringspot virus and Peach asteroid spot virus Apple chlorotic leaf spot virus Nepoviruses 17.11 Concluding Remarks and Perspectives

17.1 Introduction Viruses and viroids of peach trees incite over 20 different diseases, including some that result from mixed infections of different viruses. Agents belonging to these pathogen groups most likely are also involved in other diseases of uncertain aetiology. Some of the diseases caused by these graft-transmissible pathogens are economically important, particularly when they affect fruit quality or induce severe tree decline. On the other hand, some viruses and viroids that produce conspicuous symptoms on speciﬁc peach cultivars or other Prunus spp. do not cause phenotypic alterations on other peach cultivars or hosts. Most peach viruses and viroids do not spread naturally, although some viruses may be spread by aphid and nematode vectors or through pollen. The propagation of infected sources of plant material and their exchange

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over long distances is the main cause of the distribution of viruses and viroids in the peach industry worldwide. The use of symptomless infected trees for grafting purposes considerably contributes to the spread of viruses and viroids. Reliable techniques based on serological and molecular methods are available today for the detection of most peach viruses and viroids. These are gradually and successfully replacing the conventional biological methods (indexing) and are contributing directly to the control of the peach diseases based on the exclusive use of virus- and viroid-free propagation materials. This chapter on diseases caused by viruses and viroids includes 11 characterized agents that are responsible for the main viral problems in peach. The chapter also contains comments on diseases of unknown aetiology and on experimental infections of peach.

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17.2 Sharka or Plum Pox Economic importance and geographic distribution Sharka (pox in Slavic), or plum pox disease, is considered one of the most devastating diseases of stone fruit in terms of agronomic impact and economic importance (Dunez and Sutic, 1988; Németh, 1994). The disease is very detrimental in apricot, peach and plum trees because it reduces fruit quality and can result in premature drop of fruit. The estimated costs associated with sharka disease management in the last 30 years exceeded 10,000 million worldwide (Cambra et al., 2006). It is caused by Plum pox virus (PPV). The PPV epidemic originated in Eastern Europe: the disease was described for the ﬁrst time in about 1917 on plums and in 1933 on apricots, both growing in Bulgaria (Atanasoff, 1932, 1935). Since then, the virus has progressively spread to a large part of the European continent, around the Mediterranean basin and to the near and Middle East (Roy and Smith, 1994). It has been found in South and North America (Argentina, Chile, USA, Canada) (Roy and Smith, 1994; Levy et al., 2000; Thompson et al., 2001; Dal Zotto et al.,

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2006) and in Asia (Kazakhstan and China) (Spiegel et al., 2004; Navrátil et al., 2005). An update of PPV and sharka disease has been published (García and Cambra, 2007).

Symptoms In peach, symptoms may appear on petals, leaves and fruits. Discoloration of petals (colour breaking) can occur on the ﬂowers of some peach varieties (Figs 17.1 and 17.2/ Plates 167 and 168). Symptoms on leaves include mild light green discoloration, chlorotic spots, bands or rings, vein clearing or yellowing, and even leaf deformation (Figs 17.3 and 17.4, Plates 169 and 170), and are particularly evident in spring. Infected fruit show chlorotic spots or underpigmented yellow rings or line patterns (Figs 17.5, 17.6 and 17.7/Plates 171, 172 and 173). Fruit may become deformed or irregular in shape and develop either small brown or necrotic areas. Diseased fruit may show internal browning of the ﬂesh and have a reduced quality. In some cases the diseased fruit drop prematurely from the tree. The development of fruit in early varieties (May to June) is coincidental with the highest concentration of

Fig. 17.1. Discoloration symptoms of Plum pox virus type M on flowers of peach cultivar ‘Baby Gold 6’. (Courtesy of J.C. Desvignes, La Force, France.)

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Fig. 17.2. Colour break symptoms of Plum pox virus type M on flower petals of peach cultivar ‘Gladys’. (Courtesy of M.A. Cambra, Zaragoza, Spain.)

Fig. 17.3. Leaf symptoms of Plum pox virus on ‘GF 305’ peach seedlings used as indicator plant.

PPV in the tree in Mediterranean climates. Viral titre decreases later in summer (July to September), when the fruit of late varieties are developing. Consequently, there is a broad general trend for early-ripening varieties to

be much more sensitive and to show more severe symptoms on fruit than later-maturing varieties. Plum pox disease symptoms in peach vary considerably with the cultivar, age of the

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Fig. 17.4. Leaf symptoms of Plum pox virus type M on peach cultivar ‘Royal Gem’.

Fig. 17.5. Fruit symptoms (underpigmented yellow rings) caused by Plum pox virus in peach cultivar ‘Springcrest’.

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Fig. 17.6. Chlorotic rings and line pattern caused by Plum pox virus in fruit of nectarine cultivar ‘Arm King’.

Fig. 17.7. Chlorotic spots and underpigmented yellow rings caused by Plum pox virus in fruits of peach cultivar ‘Catherine’. (Courtesy of M.A. Cambra, Zaragoza, Spain.)

plant, climatic conditions (temperature) and PPV type. Causal agents and diagnosis PPV is a member of the viral genus Potyvirus in the family Potyviridae (López-Moya and García, 1999). PPV particles are ﬂexuous rods about 700 nm in length and 11 nm in width.

They are composed of a single-stranded RNA molecule of about 10,000 nucleotides in length coated by up to 2000 subunits of a single coat protein. The virus’s expression strategy, typical of potyviruses, includes translation of a unique, long, open reading frame into a large polyprotein that is processed after translation by three viral proteinases to yield nine or ten mature viral proteins. In recent years, knowledge of the molecular biology of potyviruses

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in general, and of PPV in particular, has increased signiﬁcantly (Riechmann et al., 1992; Shukla et al., 1994; Revers et al., 1999). The numerous PPV isolates differ in both biological and epidemiological properties such as aggressiveness, aphid transmissibility and symptomatology. Two main groups or types, Dideron (D) and Marcus (M), were distinguished serologically by Kerlan and Dunez (1976). With the advent of molecular techniques, complete or partial genomic sequences have been obtained for a large number of PPV isolates. Analysis of these sequences has conﬁrmed the existence of major groups of PPV isolates which correspond to the initial D and M groups. Two additional minor groups, represented by the geographically limited El Amar isolate from Egypt (PPV-EA; Wetzel et al., 1991a) and by the cherry-adapted isolates (PPV-C; Nemchinov and Hadidi, 1996; Nemchinov et al., 1996), have been identiﬁed. An unusual PPV isolate reported from Canada (PPV-W; James et al., 2003) probably represents a distinct ﬁfth PPV group. In addition, the wide distribution of natural recombinants between the D and M types of PPV has been recently demonstrated, leading to the suggestion to consider these recombinant isolates as constituting a new group (PPV-Rec; Glasa et al., 2004). Consequently, PPV isolates can currently be clustered into six clearly different groups. Given the variability of PPV, all techniques other than sequencing or some PCR-based assays (see below) may provide erroneous answers on the typing of a small percentage of isolates (Candresse et al., 1998a). However, the discrimination between D and M groups of PPV isolates is possible for most isolates using a variety of techniques. These include: (i) different serological pattern or reaction with D- or M-speciﬁc monoclonal antibodies (Cambra et al., 1994; Boscia et al., 1997); (ii) electrophoretic mobility of the viral coat protein as assessed by Western blot (Bousalem et al., 1994; Pasquini and Barba, 1994); (iii) sequence analysis of PCR fragments corresponding to the C-terminal region of the PPV coat protein gene or RsaI restriction fragment length polymorphism analysis of this region (Wetzel et al., 1991b; Bousalem et al., 1994; Candresse et al., 1994); and (iv) different variants of PCR, heminested-PCR, nested-PCR

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and cooperational PCR (Co-PCR), using speciﬁc primers (Candresse et al., 1994; Olmos et al., 1997, 1999, 2002, 2003) including colorimetric detection of the amplicons with D- or M-speciﬁc probes. In addition, real-time PCR (RT-PCR) assays using either SYBR Green or TaqMan chemistries have recently been developed that allow discrimination between D and M PPV types (Varga and James, 2005; Capote et al., 2006). Detection of all PPV isolates can be achieved by using either monoclonal antibody 5B-IVIA (Cambra et al., 1994) or polyclonal antibodies in a double-antibody sandwich indirect (DASI; also named triple-antibody sandwich, TAS) or a double-antibody sandwich (DAS) ELISA assay, respectively. Speciﬁc detection of PPV-D isolates (Cambra et al., 1994), PPV-M (Boscia et al., 1997), PPV-C (Myrta et al., 2000) and PPV-EA (Myrta et al., 1998) is possible by using available ELISA kits. Molecular hybridization techniques (Varveri et al., 1988) and different PCR-based assays have been developed for the detection (Korschineck et al., 1991; Wetzel et al., 1991b, 1992; Candresse et al., 1994, 1995; Levy et al., 1994; Olmos et al., 1996) or for the simultaneous detection and typing of PPV isolates (Olmos et al., 1997; Candresse et al., 1998a). Different systems of viral target preparation prior to PCR have been developed based on immunocapture (Wetzel et al., 1992) or, without the need for extract preparation, on print or squash capture (Olmos et al., 1996). The use of immobilized targets on paper (Cambra et al., 1997) allowed the detection of PPV in single aphids (Olmos et al., 1997) by squash capture-PCR. Nested-PCR in a single closed tube (Olmos et al., 1999) has been applied for the sensitive detection of PPV targets in plant material and in single aphids. A Co-PCR system using a universal probe for hybridization (Olmos et al., 2002) has been described, affording sensitivity similar to that of nested-PCR. Real-time RTPCR assays have been developed to detect and quantify PPV targets in plant material and individual aphids (Schneider et al., 2004; Olmos et al., 2005; Varga and James, 2005; Capote et al., 2006) with sensitivity higher than obtained by the previously described methods and, in some cases, without the need for RNA puriﬁcation (Olmos et al., 2005). Generally, serological and

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molecular characterization of PPV isolates correlate very well, although serological typing may prove in error for a few unusual isolates (Candresse et al., 1998a). A European protocol for the detection and characterization of PPV has been developed. The recommended methods include indexing (graft inoculation of ‘GF 305’ peach seedlings or Prunus tomentosa), serological and molecular tests (EPPO, 2004).

cause faster epidemics and more severe symptoms in peach ﬂowers, leaves and fruit than D isolates. The D isolates are able to spread naturally in apricot and plum orchards but spread much more rarely from these hosts to peach trees. These are, however, broad discriminations that may not apply to some individual isolates or under different epidemiological conditions. Control

Epidemiology The movement of infected plant propagation material is considered to be the most important means of long-distance spread of PPV. In addition, the virus is non-persistently transmitted by a number of aphid species existing in each region (Kunze and Krczal, 1971; Labonne et al., 1995). Non-aphid transmissible isolates have also been described (Maiss et al., 1989; López-Moya et al., 1995). Under natural conditions, PPV easily infects fruit tree species of the genus Prunus used as commercial varieties or rootstocks: apricot (Prunus armeniaca), European plum (Prunus domestica), Japanese plum (Prunus salicina), peach (Prunus persica), Myrobalan ﬂowering plum (Prunus cerasifera) and Mariana plum (Prunus mariana). Sour (Prunus cerasus) and sweet (Prunus avium) cherries and almond (Prunus dulcis) trees may be infected occasionally. The virus also infects most wild or ornamental Prunus species such as Western sand cherry (Prunus besseyi), purple-leaved sand cherry (Prunus cistena), damson plum (Prunus insititia), Nanking cherry (P. tomentosa), ﬂowering almond (Prunus triloba) and blackthorn (Prunus spinosa). The virus can be mechanically transmitted to numerous Prunus species, service tree (Sorbus domestica) and several herbaceous plants. Nicotiana benthamiana, Nicotiana glutinosa, Nicotiana clevelandii, garden pea (Pisum sativum) and Chenopodium foetidum are frequently used as experimental host plants. The PPV isolates belonging to the D or M groups appear to show different epidemiological behaviours, at least under western European conditions. Generally, the M isolates tend to be spread more readily by aphids to peach trees than the D isolates. M isolates

As is also the case for potyviruses infecting other host crops, fruit trees cannot be efﬁciently protected from PPV infection by the use of aphicides. Potyviruses are transmitted in a non-persistent manner; PPV can be inoculated by a viruliferous aphid during very short probes so that aphicides have no direct effect on the process. Aphid vector populations do not, for the most part, reside or develop on the fruit tree crops. Thus applications of insecticides to a growing orchard have only limited effects. In this context, control measures against PPV are of two kinds: (i) efforts at prophylaxis designed to reduce or eliminate the viral load in the environment (quarantine measures, eradication programmes, use of certiﬁed virus-tested planting material, etc.); and (ii) efforts at breeding for resistance. It should also be mentioned that in countries with endemic infection a third strategy, relying on the deployment of varieties with a reduced susceptibility (in particular with reduced symptoms on fruit), is widely used, despite the fact that it provides no real disease control (quite the contrary in fact) but allows instead for continued production under endemic infection conditions. In countries where infection levels are still low, strategies based on a strict control of the virus and on prophylaxis are generally used. PPV was recognized early as a major pathogen on stone fruit crops and was therefore included on quarantine lists. In Europe, for example, it was recognized as a quarantine pathogen in 1973 (Dosba, 1992). Currently, the European quarantine status of PPV is referred in the EPPO (European and Mediterranean Plant Protection Organization) Quarantine List A2

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and EU Annex designation IIAII. Similarly, in many countries plum pox is subject to strict control measures, including eradication schemes. In practice, there are, however, very few cases in which PPV was actually eradicated from a country (only Switzerland and the Netherlands). To be successful, these strategies must be undertaken early after the introduction of the disease in a country or region and must be very vigorously enforced. Generally, eradication schemes are labour-intensive and based on either visual inspection of symptoms or ELISA testing. Such approaches also necessitate a collective action which is often difﬁcult to obtain from fruit growers unless effective compensatory measures are implemented. Even if not completely successful, these eradication strategies have frequently allowed limitation of the rate of spread of the disease and of its impact to a low and manageable percentage of infection. Two different programmes are being conducted in the USA and Canada, since the year 2000, with the aim of eradicating PPV. The success of these programmes will be assessed in the near future. A complement to quarantine and eradication measures is the wide use of certiﬁed, virus-tested or virus-free planting material. Sanitation techniques, detection and sampling techniques, information on the protection of nurseries, etc. are available today, enabling many countries to develop efﬁcient certiﬁcation programmes. In parallel with these control measures, efforts aimed at the development of PPVresistant Prunus varieties have been undertaken in many countries. These programmes have explored both classical breeding approaches (screening of germplasm to identify resistance sources) and biotechnological approaches. In this respect, peach has so far proved a more complicated target than apricot and plum. Extensive screening of germplasm has failed to identify sources of resistance within the peach species, so that current efforts are aimed at the exploitation of resistance identiﬁed in the related Chinese wild peach (Prunus davidiana) by introgression of the trait through interspeciﬁc hybridization (Pascal et al., 1997; Escalettes et al., 1998; Bassi, 2006). By contrast, in apricot and plum, resistance sources have been identiﬁed within the target species, so breeding

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efforts are clearly more advanced (Dosba et al., 1989; 1991; Dicenta and Audergon, 1998; Karayiannis et al., 1999; Vilanova et al., 2003). Genetic transformation to create PPVresistant transgenic plants, through the use of coat protein-mediated protection, has been successful in both apricot and plum (Laimer da Camara Machado et al., 1992; Scorza et al., 1994, 2001; Ravelonandro et al., 1997). Efﬁcient genetic constructions are therefore available, some of which have been successfully validated in ﬁeld tests (Ravelonandro et al., 2000, 2002; Hily et al., 2004). In addition, novel approaches to immunomodulate host–PPV pathogen interactions by expression of antibody genes in plants have emerged (Esteban et al., 2003). All these possibilities have, however, not been transferred to peach because this species has so far largely remained refractory to genetic transformation. If a system for transformation/regeneration of peach was to become more broadly available, biotechnology could offer a new and innovative strategy to ﬁght the sharka disease.

17.3 Ilarviruses Economic importance and geographic distribution Ilarviruses that infect peach crops are Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV), Apple mosaic virus (ApMV) and American plum line pattern virus (APLPV). PNRSV, PDV and ApMV are found worldwide, infecting a wide range of Prunus species. Until very recently APLPV was only reported in North America in Japanese plum (P. salicina), peach (P. persica) and ﬂowering cherry (Prunus serrulata) (Fulton, 1982). APLPV is included in the EPPO Quarantine List A1 of plant pathogens (Smith et al., 1992) and was recently reported in Palestine, Italy, Albania and Tunisia (Myrta et al., 2002; Alayasa et al., 2003).

Symptoms Symptoms associated with PNRSV infection in peaches include foliar chlorotic rings

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(Fig. 17.8/Plate 174), necrotic spots (Fig. 17.9/ Plate 175) or deformation, and bark necrosis, pitting, splitting or girding. Infected trees tend to have smaller trunk diameter than uninfected ones and the yield of infected trees is usually reduced (Saunier, 1972; Pusey and Yadava, 1991; Scott et al., 2001). In addition, fruit maturity is affected depending on the rootstock. Besides necrotic leaf spot, colour break on ﬂower petals has been observed on the mature trees of some peach varieties (e.g. ‘Rio Oso Gem’). Some cultivars do not show overt symptoms. Symptoms caused by PDV in peach are less obvious and the virus produces only mild stunting in most peach cultivars and essentially no leaf symptoms. In some peach cultivars, however, PDV infection produces a dense canopy due to shortening of shoot

internodes (Fig. 17.10/Plate 176) and typical ring spots. Mixed infection with PNRSV plus PDV results in a disease known in Australia as peach rosette and decline (Smith and Challen, 1977) and in California as peach stunt disease (Asai and Uyemoto, 1991). Affected trees show premature defoliation at the end of the ﬁrst growing season following inoculation. Infected trees display bark splitting and increased water sprout (sucker) production, and yield is reduced by up to 60%. Reductions in shoot growth, trunk diameter and the number of leaves produced were observed and a delay in bloom date has also been noted (Uyemoto et al., 1992). ApMV is not very frequent in peach. The virus induces a bright yellow mosaic and/or spots (Fig. 17.11/Plate 177), so nurserymen

Fig. 17.8. Leaf symptoms (chlorotic rings and deformation) caused by Prunus necrotic ringspot virus in peach.

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Fig. 17.9.

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Necrotic spots caused by Prunus necrotic ringspot virus in peach leaves.

Fig. 17.10. Dense canopy due to shortening of shoot internodes caused by Prune dwarf virus in peach trees.

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Fig. 17.11. Leaf symptoms (bright yellow mosaic and spots) caused by Apple mosaic virus in peach.

generally avoid propagating the infected trees. Finally, in spring APLPV causes a thin reticulation or yellowing of the little veins on the leaves of the infected trees.

Causal agents and diagnosis PNRSV, PDV, ApMV and APLPV belong to the genus Ilarvirus, whose members are characterized by a tripartite genome and quasiisometric particles (van Regenmortel et al., 2000). Ilarviruses affecting stone fruit are closely related phylogenetically (Sánchez-Navarro and Pallás, 1997) and show at least 65% sequence similarity at the coat protein level. Historically, serological procedures have extensively used assays for the detection of these four viruses (e.g. Halk et al., 1984; Mink

and Aichele, 1984; Scott et al., 1989; Uyemoto et al., 1989). However, erratic ELISA results have been reported for shoot-leaf samples collected in early May when day temperatures exceeded 38°C over a 12-day period (Uyemoto et al., 1989). In addition, Scott et al. (1992) have described that when using ELISA, PNRSV was detectable in peach tissues only until stem elongation ceased. Molecular hybridization using radiolabelled probes allows the discrimination between healthy and virus-infected material throughout the growing season (Scott et al., 1992) and is suitable for detecting PNRSV serotypes that react poorly in ELISA (Crosslin et al., 1992). Nevertheless, the use of radiolabelling renders this approach unsuitable for routine diagnosis. Non-isotopic RNA probes have been used to monitor PNRSV infection after in vitro micrografting (Heuss-La Rosa

Viruses and Viroids

et al., 1995) and to detect these viruses in ﬁeld conditions (Pallás et al., 1998; Sánchez-Navarro et al., 1998; Saade et al., 2000). In addition, several variations of the PCR technique have been applied for the detection of these viruses (Parakh et al., 1995; Rowhani et al., 1995; Spiegel et al., 1996; Sánchez-Navarro et al., 1998; Helguera et al., 2001; Scott and Zimmerman, 2001). Both molecular hybridization-based methods and PCR-based methods detect these viruses even when they are only present in low concentration in the plant samples being tested. As a step towards the development of more rapid methods of detection, attempts have been made to simultaneously detect at least two of the ilarviruses. This has been easily achieved by using mixtures of several non-isotopic probes in molecular hybridization, for instance for the detection of PNRSV, PDV and ApMV (Saade et al., 2000). Detection of two ilarviruses or one ilarvirus together with other important stone fruit virus, e.g. PNRSV and PPV (Kölber et al., 1998), in a single multiplex RT-PCR with the same sensitivity as that observed during individual RT-PCR analyses has been reported. Additionally, a PCR-ELISA procedure has been described for the simultaneous detection of ApMV and PNRSV (Candresse et al., 1998b) but, in this case, an extra probe-capture step was required to differentiate between the two viruses. PNRSV, PDV and ApMV were simultaneously detected in a single assay by RT-PCR (Saade et al., 2000). More recently, a multiplex RT-PCR method has been developed to detect eight stone fruit viruses, including the four ilarviruses, in a single assay (Aparicio et al., 2003).

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as thrips or other ﬂower-dwelling arthropods may facilitate plant-to-plant transmission through pollen (Greber et al., 1992; Mink, 1992; Johansen et al., 1994). PNRSV has been detected in seedlings grown from seeds produced on healthy plants of several Prunus species after hand pollination with pollen from infected plants, strongly suggesting that fertilization could also be a contaminating event (reviewed by Mink, 1992). However, contradictory results have been reported concerning the location of PNRSV on or in pollen grains from infected cherry trees. Cole et al. (1982) showed that PNRSV antigens were easily removed from intact pollen by washing, indicating that most if not all the virus was on the pollen surface. Results obtained by Kelley and Cameron (1986) and Digiaro et al. (1992) suggested that PNRSV was located both externally and internally. In situ hybridization experiments conﬁrmed that the virus is located within the pollen grains (Aparicio et al., 1999).

Control The most important method for controlling the diseases caused by ilarviruses affecting peach crops is the use of virus-tested certiﬁed plants. Effective management requires prompt removal and destruction of diseased plants. Nurseries producing basic propagation material need to be separated from commercial orchards by an appropriate distance to prevent or limit contaminating pollen ﬂow. Thermotherapy (24–32 days at 38°C) and apical meristem culture have been used to eliminate these viruses. Cross-protection with mild PNRSV isolates has been used occasionally.

Epidemiology PNRSV and PDV are pollen- and seed-borne (Cole et al., 1982; Hamilton et al., 1984; Kelley and Cameron, 1986; Aparicio et al., 1999), which contributes to their rapid spread in stone fruit trees (Mink, 1992; Uyemoto et al., 1992). Infected pollen has been shown to play a key role in both seed and plant-to-plant transmission of these viruses. Recent evidence suggests, however, that certain biological agents such

17.4 Tomato Ringspot Virus Economic importance and geographic distribution First described in North America, where it is endemic, Tomato ringspot virus (ToRSV) has been associated with various diseases in different Prunus hosts. On peach, two diseases have

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been described: (i) the peach yellow bud mosaic disease, which is restricted to North America and is associated with the distribution of the nematode vector (Schlocker and Traylor, 1976); and (ii) the Prunus stem pitting disease, which is present in North America and Europe and is not associated with the vector distribution (Németh, 1986). Even though the virus is common on a wide range of ornamental and cultivated plants throughout the world, both diseases are rarely associated with severe losses in the peach industry. However, substantial losses due to infection with ToRSV still occur in orchards in Pennsylvania, USA.

ﬁrst stage of infection, chlorotic spots and rings or oak-leaf mottles are observed on leaves (mosaic phase). This is followed by the second phase, characterized by a severe reduction of leaf growth on buds, giving a rosette appearance (yellow bud phase) (Fig. 17.12/Plate 178). After a few years, infected trees display a denuded appearance and fruit production is reduced (Schlocker and Traylor, 1976). The most characteristic symptom for the Prunus stem pitting disease is an abnormal thickening of the bark, which shows a spongy aspect associated with pits and grooves in the wood (Barrat et al., 1968).

Causal agent and diagnosis Symptoms First described in 1936, the peach yellow bud mosaic disease shows two phases. During the

ToRSV is a member of the subgroup C of the genus Nepovirus (Mayo and Robinson, 1996) and has isometric particles about 28 nm in

Fig. 17.12. Severe reduction of leaf growth on buds, giving a rosette appearance, caused by Tomato ringspot virus in ‘GF 305’ peach seedlings.

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diameter, sedimenting as three components. It has a bipartite, single-stranded RNA genome characterized by an unusually large RNA-2 (7273 nucleotides) similar in size to the RNA-1 (8114 nucleotides) (Stace-Smith, 1984). For diagnosis purposes, the ToRSV can be detected after mechanical transmission to the herbaceous hosts Chenopodium quinoa or Chenopodium amaranticolor or, with greater sensitivity, by indexing on ‘GF 305’ peach seedlings following graft inoculation by chip budding (Desvignes, 1999). Owing to possible confusion with symptoms of other nepoviruses in particular, serological diagnosis by ELISA is, however, recommended for deﬁnitive identiﬁcation of ToRSV (Powell, 1984). In addition, PCR-based assays have been developed and are also available (Griesbach, 1995), including a colorimetric-PCR assay that allows quantiﬁcation of the virus in samples from woody hosts (Rowhani et al., 1998). Epidemiology On peach, ToRSV is naturally transmitted by the North American dagger nematodes, Xiphinema americanum Cobb, Xiphinema californicum Lamberti and Bleve-Zacheo and Xiphinema rivesi Dalmasso (Stace-Smith, 1984). In the ﬁeld, this mode of transmission is associated with typical tree to neighbouring tree spreading. Because of its wide host range, which includes common weeds such as dandelion (Taraxacum officinale) and sheep sorrel (Rumex acetosella), the virus can persist on a site for many years after removal of infected peach trees (Powell et al., 1984). Propagation of infected plants and grafting are also efﬁcient transmission and dissemination means of the virus.

Control The best way to control ToRSV is to prevent its introduction and therefore the implementation of quarantine measures and the use of planting material from a virus-free certiﬁcation programme are highly recommended. In addition, long crop rotations with non-host plants associated with a nematicide treatment of soil before planting is strongly recommended.

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In infected plots, diseased trees must be pulled out. ToRSV is associated with union necrosis in apples; thus replacing apple orchards with peach is inadvisable as severe and rapidly developing outbreaks of Prunus stem pitting may result.

17.5 Strawberry Latent Ringspot Virus Economic importance and geographic distribution Except for Canada, where this virus was described once but was not shown to spread naturally, Strawberry latent ringspot virus (SLRSV) has been mainly described under different names on peach trees in Europe. It was ﬁrst reported in 1962 in France as ‘court noué du pêcher’, then in Germany as ‘shoot dwarﬁng’, in Italy as ‘Rosetta a foglie saliciformi’ and in Hungary (Fortusini et al., 1983; Carles, 1984; Németh, 1986). In southern European countries it is quite widespread in the traditional production areas, where the virus can be naturally maintained in weeds or in wild-growing plants. Symptoms SLRSV is associated with mild symptoms on peach. During spring, particularly with cold weather, a delay in bud breaking, ﬂowering and leaf growth is observed. These early symptoms are usually conspicuous in the ﬁeld but later in the season they can be much less clear. Leaves become small, rolled and chlorotic and the internodes are shortened (Fig. 17.13/Plate 179), giving a stunted aspect of the trees. When the weather becomes warmer, new developing shoots are less affected and the symptoms tend to disappear. In mixed infections with PDV or PNRSV, symptoms are much more severe due to synergistic effects between the viruses. Causal agent and diagnosis SLRSV is a tentative member of the genus Nepovirus, displaying the typical 30 nm isometric

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Fig. 17.13. Internode shortening caused by Strawberry latent ringspot virus in peach trees.

particle morphology. The particles sediment as three components and encapsidate a bipartite, single-stranded RNA genome (Kreiah et al., 1994). Contrary to the majority of nepoviruses, which have only a single type of capsid subunit, SLRSV particles contain two different subunits (Mayo and Robinson, 1996). This virus is a good immunogen and is easily identiﬁed in serological tests such as ELISA. Being systemically distributed throughout the trees, it can also be detected by biological indexing on ‘GF 305’ peach seedlings (Desvignes, 1999). A PCR-based detection assay has also been developed (Bertolini et al., 2001), although it has not been tested extensively on stone fruit tree samples.

spp.) are susceptible, and natural latent infections occur in a number of other woody plants such as black locust (Robinia pseudoacacia) and elders (Sambuscus spp.), herbaceous plants and weeds (Murant, 1974). Thus, SLRSV has a potentially large number of reservoir hosts for a new orchard infection. In peach, its seed transmission has not been demonstrated. In strawberry, the type strain of the SLRSV is transmitted by the nematodes Xiphinema diversicaudatum and Xiphinema coxi (Murant, 1974). On peach its transmission by nematodes has been assumed (Desvignes, 1999). The virus can also easily be transmitted by grafting.

Epidemiology

Soil disinfections with nematicides and use of virus-tested material from a national certiﬁcation programme are good options to prevent introduction of the virus in a new orchard. In a contaminated orchard, often due

Many plant species are natural hosts for SLRSV. Cherry (P. avium), European plum (P. domestica), currants (Ribes spp.) and raspberries (Rubus

Control

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to the reduction/disappearance of the symptoms during the warmer months, growers tend to retain infected trees until they are no longer proﬁtable. In areas where ﬁeld transmission occurs, infected trees should be removed, and weed or shrub proliferation controlled.

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17.6 Peach Rosette Mosaic Virus

X. americanum has been demonstrated. The virus may also be transmitted by a Criconemoides species (Ramsdell and Myers, 1978). It naturally infects some weeds such as dandelion (T. officinale), which may constitute reservoirs for the virus in the environment, and it can be experimentally transmitted to several other herbaceous hosts (Chenopodium spp., Nicotiana spp.) (Dias, 1975).

Economic importance and geographic distribution

Control

The disease was ﬁrst observed in some peach orchards in North America (Michigan, USA and Ontario, Canada) and was also later associated with a disease on ‘Concord’ grape (Dias and Cation, 1976). It is not yet described in Europe, where it is considered a quarantine pathogen. With this limited distribution, the economic importance of this disease in peach is limited. Symptoms The foliation of infected trees is delayed. Leaves are small, curled and with chlorotic mottling along the main vein (mosaic symptoms). Later in the season, shortening of internodes gives a stunted aspect to infected trees and induces rosetting symptoms.

Causal agent and diagnosis The causal agent has been identiﬁed as Peach rosette mosaic virus (PRMV), a member of the subgroup C of the genus Nepovirus. It has isometric particles of 28 nm in diameter sedimenting as three components and possesses a bipartite, single-stranded RNA genome. Particles contain one single polypeptide subunit (Mayo and Robinson, 1996). PRMV can be detected using serological assays or by indexing on P. persica cv. Elberta (Klos, 1976).

Epidemiology PRMV is transmissible by grafting. It is described as soil-borne and transmission by

As for other nepoviruses, it is recommended to use certiﬁed virus-free peach trees, to remove and destroy diseased trees and to fumigate infected orchard sites against nematodes before replanting.

17.7 Peach Latent Mosaic Economic importance and geographic distribution Peach latent mosaic (PLM) disease is economically signiﬁcant because it affects fruit quality, reduces tree lifespan and causes peach trees to be more susceptible to other biotic and abiotic stresses. PLM disease, which is induced by Peach latent mosaic viroid (PLMVd), is present in most of the peach-growing areas of the world: the Mediterranean basin, North and South America, China, Japan and Australia, being particularly prevalent in those areas where varieties of American or Japanese origin predominate.

Symptoms PLM disease was initially described in France as a consequence of sanitary controls on imported peach material. It only affects peach and peach hybrids (Desvignes, 1976, 1986). The term ‘latent’ in the name of this disease refers to the fact that most natural infections occur without inducing leaf symptoms, with the ﬁrst pathological alterations being observed at least 2 years after planting. Early ﬁeld

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symptoms consist of delayed ﬂowering, foliation and ripening, accompanied by alterations of variable severity in different organs. Flowers present pink streaks on petals, and fruit show deformations and discolorations with cracked sutures (Fig. 17.14/Plate 180) and ﬂattened stones. Bud necrosis and stem pitting can also be observed. Leaf symptoms appear sporadically as chlorotic blotches (peach blotch), yellow-creamy mosaics (peach yellow mosaic) (Fig. 17.15/Plate 181) and, in the most severe cases, white patterns that may cover most or all of the leaf area (peach calico) (Fig. 17.16/Plate 182). The diseases with these names reported previously in the USA and Japan (Németh, 1986) are most likely manifestations of distinct PLMVd strains/ isolates. Generally, 5 years after planting, the trees present a reduced foliar density, a typical open growth habit and an increased susceptibility to biotic and abiotic stress, which ﬁnally causes their premature death. In the greenhouse, PLMVd isolates can be divided into severe strains and latent strains, depending on whether or not they induce leaf symptoms on seedlings of the peach indicator ‘GF 305’. Pre-inoculation with latent strains incite in ‘GF 305’ a cross-protection effect against

challenge inoculations with severe strains (see below). This effect is the basis of a bioassay for diagnosis (Desvignes, 1976, 1986).

Causal agent and diagnosis The search for the causal agent of the PLM disease, initially assumed to have a viral aetiology, was unsuccessful for some time. Later, a viroid RNA was isolated from plants exhibiting the typical PLM symptoms; this RNA, which was absent in healthy controls, could also be identiﬁed in asymptomatic ‘GF 305’ plants infected by a mild isolate of the aetiological agent (as revealed by the cross-protection assay) (Flores and Llácer, 1988). The involvement of a viroid was reinforced when the same RNA was found in naturally infected plants of 20 different peach varieties, but not in the plants resulting from sanitation by thermotherapy. A deﬁnitive causal relationship between PLM disease and the viroid RNA was established when, following inoculation of ‘GF 305’ with a puriﬁed preparation of the latter, the plants developed the typical symptoms and the same RNA could be recovered, which

Fig. 17.14. Fruit symptoms (deformations and discolorations with cracked sutures) caused by Peach latent mosaic viroid in peach.

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Fig. 17.15. Leaf symptoms (yellowcreamy mosaic) caused by Peach latent mosaic viroid in peach.

henceforth was termed Peach latent mosaic viroid (PLMVd) (Flores et al., 1990). Cloning and sequencing of PLMVd revealed a RNA genome of 337 nucleotides. Comparison of the motifs and structures present in this sequence with other previously described viroid sequences enable PLMVd to be grouped in the genus Pelamoviroid within the family Avsunviroidae (Flores et al., 2000). Under greenhouse conditions, PLMVd can be detected by a cross-protection bioassay in ‘GF 305’. Brieﬂy, ‘GF 305’ peach seedlings are graft-inoculated with material from the plants to be tested or from reference isolates. Most PLMVd natural isolates do not incite leaf symptoms in ‘GF 305’, whereas severe isolates induce a wide range of symptoms (see above) and are therefore detected in this ﬁrst phase of the assay. When challenge-inoculated with a severe isolate, ‘GF 305’ plants pre-inoculated

with a latent PLMVd isolate do not display the characteristic symptoms, allowing the identiﬁcation of latent PLMVd isolates in this second phase of the assay. This bioassay was very useful for the diagnosis and control of PLM in France even when the viroid aetiology of the disease was unknown (Desvignes, 1976, 1986). PLMVd can now be detected more quickly with different molecular approaches: (i) PAGE (Flores and Llácer, 1988; Flores et al., 1990); (ii) dot-blot hybridization with radioactive and non-radioactive probes (Flores et al., 1990; Ambrós et al., 1995; Loreti et al., 1995); and (iii) reverse transcription and PCR using speciﬁc primers (Shamloul et al., 1995). These tests have shown the presence of PLMVd in Japanese and Italian peach varieties displaying peach yellow mosaic and peach calico, respectively. Interestingly, in the latter case the symptoms have been demonstrated to result

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Fig. 17.16. White patterns (calico) covering most of the leaf area caused by Peach latent mosaic viroid in leaves of nectarine cultivar ‘Red-Gin’.

from the presence of an insertion of 12–13 nucleotides (Malﬁtano et al., 2003).

17.8 Peach Dapple Economic importance and geographic distribution

Epidemiology PLMVd is transmitted by grafting with infected material and mechanically as a result of agronomic practices, basically pruning (Hadidi et al., 1997), but not by pollen, seed or mites. The viroid might be also transmitted by aphids (Myzus persicae), although with a very low efﬁciency (Flores et al., 1992).

Control The only effective control measure is the use of viroid-free propagation material. PLMVdinfected peach material can be cured by thermotherapy, followed by tip grafting and subsequent propagation (Desvignes, 1986; Barba et al., 1995). The use of disinfested pruning tools is recommended.

Peach dapple (PD) disease, despite affecting fruit quality, is of limited economic signiﬁcance because it has been reported only in certain peach varieties grown in Japan (Sano, 2003). However, since its causal agent, Hop stunt viroid (HSVd), has been found infecting peach in other areas of the world (Flores and Llácer, 1988), the disease may have a wider geographic distribution but may have remained unnoticed because symptoms are expressed clearly only in some varieties.

Symptoms Symptoms consist of chlorotic blotches on the skin of the mature fruit, which can become crinkled depending on varietal sensitivity. Symptoms are not expressed in other organs.

Viruses and Viroids

Causal agent and diagnosis HSVd variants of 297 nucleotides, initially reported from dapple peach (and plum) (Sano et al., 1989), have been shown to be the causal agent of PD disease (Terai et al., 1990). This viroid, which has been found to naturally infect a wide range of plants, can be detected by bioassay in cucumber and other species of the family Cucurbitaceae (symptoms include leaf curling and stunting). PAGE can also be applied for diagnostic purposes, although the low titre of the viroid limits the reliability of this technique. For this reason, dot-blot hybridization or RT-PCR procedures are recommended.

Epidemiology The viroid is transmitted by grafting with infected material and, possibly, by mechanical inoculation with contaminated pruning tools.

Control Control is essentially the same as for PLMVd: use of viroid-free propagation material and decontamination of pruning instruments.

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have remained very high in at least some states (Larsen and Oldﬁeld, 1995; Oldﬁeld et al., 1995). There is currently no evidence for the presence of this disease outside North America (Desvignes, 1999).

Symptoms There has been quite a bit of confusion between the peach mosaic disease caused by the recently described Peach mosaic virus (PcMV) and that caused by PLMVd (see above). Since many of the early descriptions of symptoms were made at a time when PcMV and PLMVd were not known, the actual identity of the causal agents at that time is not clear. Symptoms are reported to be variable, depending on host cultivar, viral isolate, time of the year and the existence of co-infections with other agents. Flower breaking (discoloration of petals) may be seen in some varieties, as well as reduced petal size and petal deformation. On leaves, typical symptoms are chlorotic spots and streaks, together with reduced leaf size, leaf deformation and crinkling of the leaf margin. Chlorotic areas may become necrotic and abscise. Some growth reduction may be observed, together with rosetting or shoot proliferation. Fruit may become deformed and unmarketable (Larsen and Oldﬁeld, 1995). Other hosts, such as European and Japanese plums or apricot, may also show symptoms of similar type.

Economic importance and geographic distribution Causal agent and diagnosis The peach mosaic disease was ﬁrst described in Texas and Colorado, USA in the early 1930s and later surveys indicated its presence in other south-western states as well as in several states of Mexico (Cochran and Pine, 1958; Pine, 1976). Owing to its high transmissibility and the severity of the symptoms, extensive eradication efforts were carried out from 1930 to 1950 in the USA. This led to a very large reduction in the prevalence of the disease so that only a few cases were reported during the 1980s. In the absence of such eradication measures in Mexico, prevalence appears to

A member of the genus Trichovirus, PcMV, which is serologically related to Cherry mottle leaf virus (CMLV), has been associated with the peach mosaic disease (Gispert et al., 1998; James and Howell, 1998). The two viruses show similar genomic organizations. PcMV can be identiﬁed by: (i) indexing in susceptible peach varieties; (ii) serological detection using cross-reacting polyclonal or monoclonal antibodies reacting also to CMLV; or (iii) use of the RT-PCR assay developed by James and Upton (1999), which allows the

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simultaneous detection and differentiation of PcMV and CMLV.

Epidemiology PcMV is transmitted by the peach bud mite Eriophyes insidiosus (Keifer and Wilson, 1955; Oldﬁeld, 1970; Oldﬁeld et al., 1995). The virus has also been spread by this vector to other commercially grown Prunus spp. such as apricot and almond. Some American wild Prunus spp. are usually symptomless hosts but their potential as reservoirs for the virus is not precisely known.

Control The most effective control measures are: (i) quarantine in unaffected regions; and (ii) prompt removal and destruction of infected trees coupled with the use of certiﬁed virustested planting material. Such a strategy has been used with success in the USA, greatly reducing the incidence of the disease over a long period of time. Since the mite vectors have a strong association with the hosts (overwintering in buds), control of the disease has been attempted with some success through direct action against the vectors with pre-bloom and petalfall miticide applications (Jones et al., 1970).

17.10 Diseases of Unknown Aetiology and Experimental Infections in Peach The use of biological indexing on woody differential hosts is frequently a compulsory step in a certiﬁcation programme. Because many graft-transmissible diseases could be symptomless in the original host, this technique often uses pathogen-sensitive genotypes of the same genus or family as the indexing host. More than 100 virus-like diseases have been reported to affect Prunus spp. worldwide but for half of these diseases nothing is known about the causal agent except that it is graft-transmissible. Peach varieties

are frequently among the hosts used for indexing for Prunus diseases, with the objective of detecting graft-transmissible pathogens, validating the absence of pathogens and the elimination of such agents from propagative budwood. These indexing techniques are commonly performed on plants maintained in nurseries or in greenhouses. In nurseries, the main objective is to observe disease symptoms that develop after several years in fruit and/or bark. In greenhouses, the indexing is recommended to detect diseases with symptoms that develop rapidly, such as leaf symptoms or growth-modifying symptoms. Such indexing assays on peach varieties have led to the description of several diseases in peach that have never been observed in the ﬁeld. Among these, some are caused by known viruses while others are of unknown aetiology. Given the susceptibility of peach and the potential for transmission of viruses between Prunus spp. including peach, the potential for the natural occurrence of these diseases in peach cannot be ruled out.

Apricot latent virus, Peach sooty ringspot virus and Peach asteroid spot virus Apricot latent virus, Peach sooty ringspot virus and Peach asteroid spot virus are three related agents belonging to the genus Foveavirus that so far have only been reported in apricot. In this host, they have been observed both in symptomless plants and in plants displaying scattered foliar symptoms on new growth (Zemtchik et al., 1998; Gentit et al., 2001b). On peach trees, they induce characteristic symptoms in the form of chlorotic spots on young leaves that later develop into sooty green rings on a yellow background as the leaves mature and enter senescence (Figs 17.17 and 17.18/Plates 183 and 184).

Apple chlorotic leaf spot virus Apple chlorotic leaf spot virus (ACLSV), which is the type member of the genus Trichovirus, is common on many Prunus spp. hosts

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Fig. 17.17. Leaf symptoms (chlorotic spots) caused by Peach sooty ringspot virus in peach.

(Németh, 1986). In general, cultivars of plum, cherry, apricot or peach are scarcely affected by infection by ACLSV isolates (Hansen and Gilmer, 1976; Desvignes, 1999). However, some isolates of ACLSV, usually found on cherry or on apricot, are particularly severe. When experimentally transmitted to peach they can induce stem pitting on bark, yellowish line patterns or russet ring on leaves, as well as chlorotic rings or mosaic on fruit (Fig. 17.19/Plate 185).

peach by several nepoviruses, for which peach has not been reported to be a natural host, can result in disease symptoms. This includes reduced vigour with shortened internodes (rosetting) associated with chlorotic mottling and curling of leaves (i.e. Arabis mosaic virus, Myrobalan latent ringspot virus, Stocky prune virus, Apricot latent ringspot virus); xylem stem pitting (Myrobalan latent ringspot virus); and union necrosis (Apricot latent ringspot virus) (Dunez and Dupont, 1976; Desvignes, 1999; Gentit et al., 2001a).

Nepoviruses Nepoviruses generally have a wide host range and can be detected in artiﬁcially inoculated annual or perennial weeds, woody hosts, shrubs or trees. Artiﬁcial inoculation of

17.11 Concluding Remarks and Perspectives Many viruses and viroids of peach diseases can be spread naturally in the orchard, with

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Fig. 17.18. Sooty green rings on a yellow background in senescent leaves caused by Peach asteroid spot virus in peach.

different efﬁciencies, by vectors, through pollen or through agricultural practices. In addition, all viruses or virus-like agents are propagated together with their host during all vegetative multiplication practices. The initial planting of certiﬁed virus-tested plant material is therefore the ﬁrst step in maintaining a healthy and economically proﬁtable peach industry. Nurseries producing basic propagation material need to be separated from commercial orchards to prevent infections by viruliferous aphid species or pollen ﬂow from neighbouring diseased trees. Today, in vitro propagation and subsequent appropriate cultivation under screenhouse or in glasshouse facilities is, in many nurseries, a routine practice that considerably reduces the risks of infection.

Prophylaxis to eliminate or at least reduce the prevalence of graft-transmissible agents such as viruses and viroids in the environment is a second essential element of any control strategy. Quarantine measures, eradication programmes, efforts to limit the spread of the pathogens through the use of disinfestation measures for pruning tools and, when appropriate, the use of nematicides are strongly recommended to complement the use of certiﬁed virus-tested plant material. Thus, if a viral disease is detected in an established orchard, a prudent measure would be the prompt removal and destruction of the diseased trees and, if appropriate, treatment of the site prior to any replanting. In a globalized world, the emergence of new graft- and vector-transmitted diseases of

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Fig. 17.19. Leaf symptoms (yellowish line patterns and russet rings) and fruit symptoms (chlorotic rings and mosaic) caused by Apple chlorotic leaf spot virus in peach.

peach trees, but also the development of new detection methods and tools, is expected. In the near future, the detection of plant pathogens will probably be based on standardized and validated diagnosis protocols making use of more reliable and robust techniques and reagents. These techniques may gradually replace indexing, contributing to a more accurate control of viruses and viroids in propagative plant materials. However, it should be stressed that the development of more powerful detection techniques is only feasible once the agent to be detected has been characterized. For diseases of unknown aetiology, biological indexing will remain the sole diagnostic option as long as the pathogen responsible has not been identiﬁed and characterized, which stresses the importance of continued research in this area. In parallel with direct and indirect control measures, the development of peach trees resistant to different viruses and viroids needs to be more actively explored. Both conventional breeding and biotechnological-based programmes are already being developed for PPV resistance in some countries, but very

little work has been devoted to the development of resistance towards other agents. The screening of different available Prunus spp. or related germplasms (sexually compatible with peach or not) has great potential to identify resistance sources against viruses and viroids. Genetic transformation and the subsequent recovery of transgenic peach cultivars have so far stumbled on serious technical difﬁculties. Even for other Prunus spp. in which genetic transformation has been successfully developed, such as apricot and plum, the techniques still suffer from serious limitations, such as the obligate use of embryo tissues, with then ensuing loss of varietal genetic make-up. However, should the problems currently encountered with peach genetic transformation be lifted, the availability of ﬁeld-validated genetic constructions ensures that the development of resistant transgenic peach could be optimistically envisioned. The generation of new transformation vectors (some probably based on the viral genomes), the development of new strategies (expression of recombinant antibodies speciﬁc for key biological targets and addressed to

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the appropriate cell compartment), the search of genomic libraries for peach resistance genes or for other defence factors, and the identiﬁcation of substances with putative in

vivo antiviral or antimicrobial activities are likely, in time, to contribute to a better protection of peach trees or to the development of resistant or tolerant peach varieties.

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Journal of General Virology 70, 1311–1319. Saunier, R. (1972) Incidence d’un virus du type ringspot sur le comportement de deux cultivars du pêcher. La Pomologie Française 14(7), 175–185. Schlocker, A. and Traylor, J.A. (1976) Yellow bud mosaic. In: Virus Diseases and Non-Infectious Disorders of Stone Fruits in North America. USDA Handbook No. 437. US Department of Agriculture–Agricultural Research Service, Washington, DC, pp. 156–165. Schneider, W.L., Sherman, D.J., Stone, A.L., Damsteegt, V.D. and Frederick, R.D. (2004) Specific detection and quantification of plum pox virus by real-time fluorescent reverse transcription-PCR. Journal of Virological Methods 120, 97–105. Scorza, R., Ravelonandro, M., Callahan, A.M., Cordts, J.M., Fuchs, M., Dunez, J. and Gonsalves, D. (1994) Transgenic plums (Prunus domestica L.) express the plum pox virus coat protein gene. Plant Cell Reports 14, 18–22. Scorza, R., Callahan, A., Levy, L., Damsteegt, V., Webb, K. and Ravelonandro, M. (2001) Post-transcriptional gene silencing in plum pox virus resistant transgenic European plum containing the plum pox potyvirus coat protein gene. Transgenic Research 10, 201–209. Scott, S.W. and Zimmerman, M.T. (2001) American plum line pattern virus is a distinct ilarvirus. Acta Horticulturae 550, 221–227. Scott, S.W., Barnett, O.W. and Burrows, P.M. (1989) Incidence of prunus necrotic ringspot virus in selected peach orchards of South Carolina. Plant Disease 73, 913–916. Scott, S.W., Bowman-Vance, V. and Bachman, E.J. (1992) The use of nucleic acid probes for the detection of prunus necrotic ringspot virus and prune dwarf virus. Acta Horticulturae 309, 79–83. Scott, S.W., Zimmerman, M.T., Yilmaz, S., Zehr, E.I. and Bachman, E. (2001) The interaction between prunus necrotic ringspot virus and prune dwarf virus in peach stunt disease. Acta Horticulturae 550, 229–236. Shamloul, A.M., Minafra, A., Hadidi, A., Giunchedi, L., Waterworth, H.E. and Allam, E.K. (1995) Peach latent mosaic viroid: nucleotide sequence of an Italian isolate, sensitive detection using RT-PCR and geographic distribution. Acta Horticulturae 386, 522–530. Shukla, D.D., Ward, C.W. and Brunt, A.A. (1994) Genome structure, variation and function. In: Shukla, D.D., Ward, C.W. and Brunt, A.A. (eds) The Potyviridae. CAB International, Wallingford, UK, pp. 74–112. Smith, I.M., McNamara, D.G., Scott, P.R. and Harris, K.M. (eds) (1992) Quarantine Pests for Europe. Data sheets on Quarantine Pests for the European Communities and for the European and Mediterranean Plant Protection Organization. CAB International, Wallingford, UK and European and Mediterranean Plant Protection Organization, Paris. Smith, P.R. and Challen, D.K. (1977) Initial and subsequent yield reduction of peach trees affected by peach rosette and decline disease. Australian Journal of Agricultural Research 28, 441–444. Spiegel, S., Scott, S.W., Bowman-Vance, V., Tam, V., Galiakparov, N.N. and Rosner, A. (1996) Improved detection of prunus necrotic ringspot virus by the polymerase chain reaction. European Journal of Plant Pathology 102, 681–685.

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Spiegel, S., Kovalenko, E., Varga, A. and James, D. (2004) Detection and partial molecular characterization of two plum pox virus isolates from plum and wild apricot in Southeast Kazakhstan. Plant Disease 88, 973–979. Stace-Smith, R. (1984) Tomato ringspot virus. In: Harrison, B.D. and Murant, A.F. (eds) CMI/AAB Descriptions of Plant Viruses. Commonwealth Agricultural Bureaux Press, Slough, UK, No. 290 (No. 18 revised). Terai, Y., Sano, T. and Shikata, E. (1990) Back inoculation of plum dapple fruit disease and graft transmission of peach dapple fruit disease. Annals of the Phytopathology Society of Japan 56, 428. Thompson, D., McCann, M., McLeod, M., Iue, D., Green, M. and James, D. (2001) First report of plum pox potyvirus in Canada. Plant Disease 85, 97 (Report). Uyemoto, J.K., Luhn, C.F., Asai, W.K., Beede, R., Beutel, J.A. and Fenton, R. (1989) Incidence of ilarviruses in young peach trees in California. Plant Disease 73, 217–220. Uyemoto, J.K., Asai, W.K. and Luhn, F. (1992) Ilarviruses: evidence for rapid spread and effects on vegetative growth and fruit yields of peach trees. Plant Disease 76, 71–74. van Regenmortel, M.H.V., Fauquet, C.M., Bishop, D.H.L., Carstens, E.B., Estes, M.K., Lemon, S.M., McGeoch, D.J., Maniloff, J., Mayo, M.A., Pringle, C.R. and Wickner, R.B. (eds) (2000) Virus Taxonomy. Classification and Nomenclature of Viruses. Seventh ICTV Report. Academic Press, New York. Varga, A. and James, D. (2005) Detection and differentiation of plum pox virus using real-time multiplex PCR with SYBR green and melting curve analysis: a rapid method for strain typing. Journal of Virological Methods 123, 213–220. Varveri, C., Candresse, T., Cugusi, M., Ravelonandro, M. and Dunez, J. (1988) Use of a 32P labelled transcribed RNA probe for dot hybridization detection of plum pox virus. Phytopathology 78, 1280–1283. Vilanova, S., Romero, C., Abbott, A.G., Llácer, G. and Badenes, M.L. (2003) An apricot (Prunus armeniaca L.) F2 progeny linkage map based on SSR and AFLP markers, mapping plum pox virus resistance and selfincompatibility traits. Theoretical and Applied Genetics 107, 239–247. Wetzel, T., Candresse, T., Ravelonandro, M., Delbos, R.P., Mazyad, H., Aboul-Ata, A.E. and Dunez, J. (1991a) Nucleotide sequence of the 3′-terminal region of the RNA of the El Amar strain of plum pox potyvirus. Journal of General Virology 72, 1741–1746. Wetzel, T., Candresse, T., Ravelonandro, M. and Dunez, J. (1991b) A polymerase chain reaction assay adapted to plum pox potyvirus detection. Journal of Virological Methods 33, 355–365. Wetzel, T., Candresse, T., Macquaire, G., Ravelonandro, M. and Dunez, J. (1992) A highly sensitive immunocapture polymerase chain reaction method for plum pox potyvirus detection. Journal of Virological Methods 39, 27–37. Zemtchik, E.Z., Verderevskaya, T.D. and Kalashian Yu, A. (1998) Apricot latent ringspot virus: transmission, purification and serology. Acta Horticulturae 472, 153–158.

18

Insects and Mites

D.L. Horton,1 J. Fuest1 and P. Cravedi2 1Department 2Instituto

of Entomology, University of Georgia, Athens, Georgia, USA di Entomologia e Patologia Vegetale, Università del Sacro Cuore, Piacenza, Italy

18.1 Introduction 18.2 Direct Insect Pests Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae) Codling moth, Cydia pomonella Linnaeus (Lepidoptera: Tortricidae) Peach twig borer, Anarsia lineatella Zeller (Lepidoptera: Gelechiidae) Tufted apple bud moth, Platynota idaeusalis (Walker) (Lepidoptera: Tortricidae) Plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) Scarab beetles (Coleoptera: Scarabaeidae) Plant bugs (Hemiptera: Miridae), stink bugs (Hemiptera: Pentatomidae) and leaf-footed bugs (Hemiptera: Coreidae) Thrips (Thysanoptera) Mediterranean fruit ﬂy, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) 18.3 Indirect Insect Pests Peachtree borers, Synanthedon spp. (Lepidoptera: Sesiidae) Armoured scale (Hemiptera: Diaspididae) Aphids (Hemiptera: Aphididae) 18.4 Mite Pests Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae)

18.1 Introduction Insects and, to a more modest extent, mites are important pests of peaches and nectarines worldwide. Peaches in commercial culture today are derived from selections of Prunus spp. ecotypes native to south-eastern China (Rieger, 2006). In most of the world’s production areas, peaches are an introduced species. Accordingly, peach arthropod pest complexes

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vary with production area and are normally an assortment of insect and mite species native to the region and exotic species that have adapted to peach. As is typical for orchard crops, peaches have a complement of cosmopolitan pests that are injurious across numerous production areas. China is the world’s leading peach producer. Although southern China and the southeastern USA are climatically similar, many of

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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the world’s signiﬁcant peach production areas are in arid to semi-arid production areas of Italy, Spain, Greece, France, Iran, Chile and the western USA (Rieger, 2006). Orchard pest management is a pragmatic discipline that strives to protect fruit while mitigating tree-attacking pests to sustain yield potential and enhance tree longevity. Peaches are a relatively short-lived (Brittain and Miller, 1978) but high-value crop. Growers must be mindful of direct, fruit-attacking pests and they must also diligently address complexes of indirect or tree-attacking insects and mites. Unless managed properly, tree-attacking pests can reduce vigour, longevity and proﬁtability. The grower adage ‘take care of the trees, the trees will take care of you’ is particularly appropriate for peaches. Nectarine fruits are particularly sensitive to damage by insects with piercing–sucking mouthparts like aphids and thrips. This chapter’s review of peach arthropod pests and current management options is an effort to address the current status of peach entomology while highlighting the crop’s important entomological research needs.

18.2 Direct Insect Pests Fruit-attacking insect pests, species that feed on and/or lay eggs in the fruit, may be referred to as direct pests. Orchardists aim to produce fruit of a quality that competes well in the marketplace while protecting tree health and longevity. Management decisions must cater to market expectations. Fruit quality expectations are often on a sliding quality scale, which shifts with the overall availability of that day’s premium grade. Sound fruit with minor cosmetic insect injury may be discounted or fail to sell. The grower’s best option is to produce peaches as free from insect-related blemishes as possible, because other fruit quality variables, such as cold injury or low sugar from excessive rainfall at harvest, are beyond his/her control. Accordingly, peach growers often opt for insecticideintensive pest management programmes, because optimizing the percentage of fruit that make top grades is frequently rewarded with better price, lower grading costs, and in

some cases, better control of indirect treeattacking pests. Fortunately, newer management strategies (insect growth regulator (IGR) insecticides and mating disruption) are less disruptive to beneﬁcial insects and allow greater integration of parasitoids. Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae) Oriental fruit moth, Grapholita molesta (Busck) (OFM), is a serious pest of peaches, nectarines and quince worldwide. In California, prune, cherry, almond and apricot are occasional OFM hosts, and pear and plum suffer vegetative shoot strikes (Strand, 1999). OFM is increasingly important as a pest of apples in many regions (Reis et al., 1988). OFM larvae feed on succulent terminal growth during the initial spring and subsequent autumn vegetative growth ﬂushes. Stem feeding by OFM larvae produces withered or dead shoots, which are referred to as ‘ﬂagged’ (Fig. 18.1/Plate 186). Vegetative shoot feeding typically destroys the shoot’s distal or terminal bud, increasing lateral branching as multiple lateral buds break to vie for dominance. Larvae may continue to burrow in the original shoot or enter other shoots before they reach maturity (Hogmire, 1995). Injury from OFM terminal feeding is more important in young trees, because rapid growth of young trees is sought to quickly ﬁll each tree’s space, which optimizes early yields. Conversely, OFM terminal feeding on mature trees is of little consequence. In young trees, the inﬂuence of OFM on terminal growth varies according to tree training style. OFM injury to terminals in trees trained to decidedly ﬂat, open-vase systems is seldom signiﬁcant. Open-vase training systems emphasize heading cuts to scaffold limbs (Lockwood and Myers, 2005). These cuts systematically prune out terminal growth to stimulate development of secondary and tertiary scaffold limbs. These prescribed heading cuts remove the terminals of most scaffolds, rendering OFM injury to them irrelevant. Conversely, upright-vase or V-tree systems require unbranched scaffold limbs, because loss of terminal dominance in

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Fig. 18.1. Oriental fruit moth injury to peach terminal growth. (Courtesy of the University of Georgia, Bugwood Network.)

a scaffold limb slows growth, decreases limb ﬂexibility under fruit load and reduces early yields (Marini and Rossi, 1985). Accordingly, OFM feeding on terminals is intuitively detrimental in trees trained to upright systems. The importance of OFM as a fruit-feeding pest varies with region; however, it is a key fruit-feeding pest in most major peach production areas. Although it was thought to have originated in Asia, OFM is now cosmopolitan. In the USA, OFM is the key direct pest of peach in the western states, the midAtlantic region, where it produces four or ﬁve generations per year, and the upper Midwest (Hogmire, 1995; Horton et al., 2005). In the USA’s largest production area, California’s Central Valley, it completes up to six generations per year and is a dominant pest (Pickel et al., 2006). OFM’s status is less deﬁned in the south-eastern USA, particularly in the warmer production areas of South Carolina, Georgia and Alabama. Cochran et al. (1955) observed that OFM was an occasionally injurious, but erratic, pest that seldom merited chemical control on varieties ripening before ‘Hiley’ (early July in South Carolina’s Ridge production area). The senior author’s on-farm observations in Georgia and South Carolina support Cochran’s characterization of OFM’s modest pest status in the south-eastern USA.

In production areas with diverse fruitattacking pest complexes, such as the southeastern and mid-Atlantic regions of the USA, where plum curculio rivals or exceeds OFM in importance, standard management practice relies on broad-spectrum insecticides which simultaneously control OFM, plum curculio and fruit-feeding hemipterans (plant bugs, stink bugs, leaf-footed bugs). In California, and in processing peach production scattered across eastern North America, pheromone mating disruption is more often the management option of choice for OFM. In Europe, OFM was ﬁrst reported in 1920 in Italy. Since then it has distributed itself into all production areas, becoming one of their most dangerous pests. OFM is a polyphagous pest which in recent years has become increasingly injurious to pear and apple, creating a new and complex situation owing to the proximity of fruit orchards of mixed species and the possibility of seasonal migration of the populations (Sciarretta and Trematerra, 2006). OFM adults are 6–7 mm long, herringbone grey moths with dark bands that may be seen across the wings when at rest (Fig. 18.2/ Plate 187). Adult OFM have a wingspan of approximately 12 mm (Strand, 1999). Larvae are pinkish-white caterpillars with three pairs

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of thoracic legs and ﬂeshy abdominal prolegs. OFM larvae have brown heads and a black anal comb on the last body segment, which is a key diagnostic characteristic for differentiating

Fig. 18.2.

OFM larvae (Fig. 18.3/Plate 188) from codling moth larvae, which are otherwise quite similar in appearance but lacking anal plates (Hogmire, 1995).

Oriental fruit moth adult. (Courtesy of the University of California IPM Program.)

Fig. 18.3. Anal plate of oriental fruit moth larva. (Courtesy of the University of California IPM Program.)

Insects and Mites

OFM overwinter as mature larvae in silken hibernacula on the tree, in dried fruits, on leaves or twigs beneath trees, or other protected areas such as ﬁeld bins. Pupation takes place in late winter. Adult emergence is frequently initiated a few days before peaches begin to bloom. Egg laying begins a few days after adult emergence. Females lay up to 200 white, ﬂattish eggs, most often on twigs or leaves near the distal ends of shoots (Howitt, 1993). Depending on fruit phenology, newly hatched OFM larvae burrow into either the tender, succulent tissue at the distal end of shoots or ripening fruits. Newly hatched, neonate OFM larvae are known for quickly tunnelling beneath the surface and into the fruit (Fig. 18.4/Plate 189). OFM injury to harvested peaches typically falls into two classes (Howitt, 1993). ‘Old injury’ occurs when larvae move into green fruit after abandoning twigs, leaves or tight places where fruit touch. As fruit matures, gum often extrudes from the entrance wounds; this exudate darkens with time and may be seen as a blackish blotch at harvest. Larval entrances for many of these green fruit infestations are through the sides of fruit,

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which makes them more visible than infestations to more mature fruit. ‘New injury’ predominates as the season progresses and fruit ripens. Larval infestations in maturing fruit are often difﬁcult to discern. Many are associated with the stem cavity, leaving very modest frass accumulation adjacent to the stem. OFM larvae also enter the peach through the stem, leaving no visible entrance wounds and very little indication of infestation until mature larvae exit the fruit (Hogmire, 1995). As the season progresses into mid- and late-season cultivars, OFM females will increasingly oviposit directly on fruits, preferring fruit that are at least halfway through their development (Myers et al., 2006). Once inside the fruit, OFM larvae may wander about or conﬁne themselves to small areas. Very often they do much of their injury near the pit, where they leave considerable amounts of sawdust-like frass. These accumulations of frass differentiate OFM injury from that of plum curculio, which leave cleaner cavities with far less accumulation of frass (Howitt, 1993). In summer OFM pupate on the tree itself, while overwintering pupae more often form hibernacula in cracks of tree

Fig. 18.4. Oriental fruit moth larva tunnelling in peach. (Courtesy of the University of California IPM Program.)

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bark, on refuse or weeds on the orchard ﬂoor, or in degraded fruits (Hogmire, 1995). Efﬁcient OFM management requires timely initiation of controls. Pest management efforts for OFM begin with pheromone monitoring of adult male OFM. Capture patterns indicate generational start-up dates, known as bioﬁxes, which trigger accumulation of heat units in the OFM degree-day (°D) developmental model. These tactics accurately predict the timing of various life stages (Croft et al., 1980). Resistance of OFM to conventional insecticides – organophosphates, carbamates and pyrethroids – has been observed in at least two North American production areas (Ontario and New Jersey) (Kanga et al., 1999; Shearer and Usmani, 2001). A 4-year study by Kanga et al. (2003) suggests that resistance is at least somewhat unstable, and that rotation of insecticides may reduce and stabilize resistance levels. Because the OFM neonate is the primary surface-feeding life stage, the window for insecticidal control of larvae is quite narrow. Effective insecticide-based OFM programmes rely on precise timing of applications to optimize control, while alternating classes of chemistry to moderate selective pressure for pest resistance. Pheromone mating disruption is an adaptation of traditional pheromone use that saturates the orchard atmosphere with pheromone at levels that confuse, delay and impede the ability of male moths to locate receptive females. Mating disruption is non-toxic and species-speciﬁc, which conveys obvious advantages for integrated pest management (IPM). However, the narrow spectrum of activity for mating disruption requires the use of additional controls to address other insect pests, which adds to the cost of pest control. Most often, pheromone mating disruption is used to control key pest species in systems with relatively narrow pest complexes or pesticide resistance issues. Though utilization of pheromone mating disruption varies considerably by pest species and region, disruption of OFM typically performs well. Mating disruption is commonly the OFM management tool of choice in regions where the technique is economically competitive. For example, OFM mating disruption

has been widely used with good success on stone fruit in California (Pickel et al., 2006), Australia (Il’ichev et al., 2006) and Europe (Rouzet et al., 1995; Cravedi and Molinari, 1996; Cravedi et al., 2001). Codling moth, Cydia pomonella Linnaeus (Lepidoptera: Tortricidae) Codling moth, Cydia pomonella L. (CM), is widely distributed as a pest of temperatezone fruit production areas worldwide, including all of the USA, southern Canada, Europe, south-eastern Australia, New Zealand, the southernmost and northernmost limits of Africa, the western and eastern portions of Asia, as well as the South American countries Argentina, Bolivia, Brazil, Chile, Colombia, Peru and Uruguay. CM is a serious, direct pest worldwide on pome fruits, primarily apples and pears (Epstein et al., 2006). The importance of CM as a pest of peaches varies by region. In California, CM is an occasional, but serious, pest of peach (Neven et al., 2006). CM infestations of peaches in California are often associated with pheromone mating disruption for CM in adjacent pome fruits or walnuts (Strand, 1999). CM is also of import as a quarantine pest restricting export of American-grown pome fruit, walnuts and peaches (Neven et al., 2006). In eastern North America, CM is seldom seen as a peach pest; in Europe CM is of little consequence as a peach pest. CM overwinters as mature larvae in debris on the orchard ﬂoor or under bark on trees, and pupates there in early spring. Adults are mottled grey moths with brownish ﬂecking and tented wings (Fig. 18.5/Plate 190). They emerge, mate and oviposit on fruit and adjacent leaves, often preferring to remain on the host species in which they developed as larvae (Myers et al., 2006). Upon hatching, ﬁrst instar CM larvae tunnel into available stages of fruit development, leaving characteristic piles of frass at the entry site. Three generations per year are common in Central Valley locations in California, with a possible fourth generation when very mild winters are followed by temperate springs (Strand, 1999).

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Fig. 18.5.

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Adult codling moth. (Courtesy of the University of California IPM Program.)

Pheromone monitoring and use of degree-day developmental models are very important tools for optimizing the timing of IPM interventions. In Californian peaches, large-scale monitoring efforts for CM are normally reserved for orchards with a history of CM injury (Strand, 1999). These programmes use the CM sex pheromone ((E,E)-8,10-dodecadien-1-ol) (Epstein et al., 2006) and degreeday accumulations to optimize the timing of IPM responses. In CM-prone peach orchards, it is recommended that a single insecticide application be applied at 250–300°D or 400– 500°D, depending on whether light or heavy damage is expected (Strand, 1999). Pheromone mating disruption is a very reliable technique when used for managing OFM in arid peach production areas with relatively narrow complexes of direct pests. However, mating disruption of CM is a more challenging and problematic proposition. The technique is seldom viewed as a reliable stand-alone technology when employed against CM, especially where CM abundance is high (Knight, 2000). CM control is primarily insecticide-based. However, in apples, insecticide resistance and

greater inherent challenges with pheromone mating disruption frequently require use of multiple IPM tactics to ensure control and slow the development of resistance. Multiple insecticide classes, organophosphates, IGRs and CM granulosis virus, as well as pheromone mating disruption, must sometimes be used in concert to manage resistant CM populations.

Peach twig borer, Anarsia lineatella (Zeller) (Lepidoptera: Gelechiidae) Peach twig borer, Anarsia lineatella (Zeller), is a pest of peaches and other stone fruit, particularly almond (Hathaway et al., 1985) and apricot. Peach twig borer is present in temperate regions worldwide, occurring throughout Europe, coastal North Africa, Israel, Lebanon, Pakistan, Persia, Syria, Turkey, Iraq and China. It is common throughout the USA and southern British Columbia (Schlamp et al., 2006). Peach twig borer is a frequently encountered pest of almonds, peaches and most other stone fruits in the western USA

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(Strand, 1999). Although widely distributed across North America, peach twig borer is seldom injurious to peaches in production areas east of the Rocky Mountains (Horton et al., 2005). In Europe, peach twig borer is widely distributed, and its importance as a pest of peach and apricot is thought to be on the rise. In areas where peach twig borer is a perennial peach pest, its management focuses on prevention of early-season vegetative injury, which minimizes subsequent risk of direct injury to ripening fruit. Peach twig borer adults are small, mottled grey moths with distinct snout-like projections from the head (Fig. 18.6/Plate 191). Larvae are initially white with black heads and brown rings. Mature larvae are distinctly ringed by brown body segments separated by whitish intersegmental membranes, which readily distinguish them from other caterpillars feeding on stone fruit (Pickel et al., 2006) (Fig. 18.7/Plate 192). Peach twig borer overwinters as a ﬁrst or second instar larva within a silken chamber or hibernaculum, which is usually tucked into the crotches of 2- or 3-year-old wood, pruning wounds, etc. Chimney-like mounds of frass are often seen at the entrance of the hibernaculum, although winter rains can easily wash the frass away. Peach twig borer larvae normally emerge from their hibernacula as peaches come into bloom. Larvae feed

initially on opening vegetative and ﬂower buds. As terminal growth reaches sufﬁcient size, peach twig borer larvae tunnel into terminals. A single larva may injure several stems. As with vegetative feeding by OFM larvae, the peach twig borer’s indirect injury to terminal growth is most injurious in tree training systems that emphasize upright-vase or V-tree forms, which feature unbranched scaffold limbs. Later in the season, as fruit begin to colour, peach twig borer larvae feed shallowly on the fruit, which results in offgrade or cull fruit (Strand, 1999). Peach twig borer is an important, but easily managed, pest in California. Preventive controls are commonly used prior to fruit set. Dormant or delayed dormant applications of oil plus an organophosphate insecticide will provide very reliable control of peach twig borer. Oil alone does not control peach twig borer. Alternatively, two bloom sprays of the entomopathogenic bacterium Bacillus thuringiensis also provide very reliable control of peach twig borer. While B. thuringiensis treatments lack efﬁcacy against scale or mites, they preserve natural enemies and eliminate the environmental risks of dormant organophosphate applications (Pickel et al., 2006). In-season management options for peach twig borer are based on observation of shoot strikes and use of pheromone trapping to initiate accumulation of degree-day heat units.

Fig. 18.6. Adult of the peach twig borer moth. (Courtesy of the Catholic University, Piacenza, Italy.)

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Fig. 18.7.

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Mature peach twig borer larva. (Courtesy of the University of California IPM Program.)

An average of three to four shoot strikes per tree is sufﬁcient to warrant insecticide application. Each peach twig borer generation requires about 950–1080°D using a lower threshold of 10°C and upper threshold of 31°C. Shoot strike monitoring should begin as degree-day accumulations approach 400. Asneeded insecticides are applied at 400–500°D. Twice-weekly monitoring for the bioﬁxes of each subsequent generation should begin as degree-days reach 900. Treatments to protect ripening fruit are more commonly required late in the season (Pickel et al., 2006). Pheromone mating disruption of peach twig borer has also worked effectively in California (Pickel et al., 2006). Some European researchers have observed an inconsistent attractiveness of the peach twig borer pheromone, which results in monitoring that is less reliable than for OFM. Cases of mating disruption failure have been reported for pheromone dispensers that combine peach twig borer and OFM pheromones, with damage produced mainly by peach twig borer. Research is ongoing on the complex of natural enemies affecting peach twig borer (Molinari et al.,

2005a), as well as on the development of forecasting models (Molinari et al., 2005b).

Tufted apple bud moth, Platynota idaeusalis (Walker) (Lepidoptera: Tortricidae) Tufted apple bud moth, Platynota idaeusalis (Walker) (TABM), is a bivoltine pest of both peach (Hogmire, 1995) and apple (Myers and Hull, 2003) in the eastern USA (Fig. 18.8/Plate 193). On peach, larval feeding produces a succession of injury types as the maturing larvae feed on fruit surfaces, gumming and later feeding internally (Fig. 18.9/Plate 194). As areas of damage develop, rolled leaves and leaf shelters may be seen over protected areas where larvae are actively feeding (Hogmire, 1995). The second generation, as with many other fruit-feeding lepidopteran pests, is the most damaging, owing to the potential for greater pest abundance and the presence of maturing fruit. Mature fruit wounded by split pits, cold injury or TABM infestation are

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Fig. 18.8.

Tufted bud moth adult. (Courtesy of G. Krawczyk, University Park, Pennsylvania, USA.)

Fig. 18.9. USA.)

Tufted bud moth larva on fruit. (Courtesy of G. Krawczyk, University Park, Pennsylvania,

more susceptible to brown rot and other fungal diseases. Such fruits may serve as a source inoculum for fungal diseases in the orchard (Hogmire, 1995).

Control measures for TABM have relied heavily on organophosphate pesticides, but the development of resistance has forced growers to use pyrethroids and carbamates,

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to which the moths have also developed resistance in Pennsylvania, USA. First tebufenozide and then methoxyfenozide, a growth regulator that induces moulting, were registered in some measure as a response to TABM resistance and concerns over the susceptibility of coccinellid predators to pyrethroids (Biddinger et al., 2006). The application of insecticides for TABM controls early larval instars. The TABM degree-day model developed for use in apples has been used as a decision-making aid in peaches as well. Plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) Plum curculio, Conotrachelus nenuphar (Herbst) (PC), is a key fruit-feeding pest of North American peach (Quaintance and Jenne, 1912) and apple (Racette et al., 1992) production areas east of the Rocky Mountains. This weevil is found across the eastern half of North

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America, with small populations occurring as far west as Montana and Utah. Particularly in the south-eastern USA, where PC is multivoltine (multiple generations per year), it is the key fruit-feeding pest of peaches (Horton et al., 2005). PC is a native pest of indigenous plum and crabapple species that has adapted well to peach, nectarine and plum (Maier, 1990; Jenkins et al., 2006). PC adults are brownish-grey weevils with four pairs of bumps on the wing covers. They are approximately 5 mm long (Quaintance and Jenne, 1912) (Fig. 18.10/Plate 195). North of Virginia, most populations exhibit an obligate diapause and thus are univoltine (one generation per year). However, in the south-east, a facultative diapause produces a bivoltine cycle (two generations per year) (Padula and Smith, 1971). Overwintering adults emerge from orchard debris and ground cover to feed on buds, ﬂowers and developing fruits (Hogmire, 1995). PC produce feeding injury which is seen as round, puncture wounds and

Fig. 18.10. Plum curculio adult. (Courtesy of the University of Georgia, Bugwood Network.)

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D-shaped oviposition wounds (Fig. 18.11/ Plate 196). In young peaches, the abundant fuzz makes attacks by overwintered adults difﬁcult to discern. Successful oviposition produces yellowish-white, legless larvae that tunnel through fruit and feed near the pit (Hogmire, 1995). Larval infestations from overwintered adults normally cause peach fruitlets to abort, while ﬁeld or second-generation larvae produce wormy, unmarketable fruit (Quaintance and Jenne, 1912). Throughout eastern North America, PC utilizes a range of native fruits, primarily rosaceous and ericaceous species (Quaintance and Jenne, 1912; Mampe and Neunzig, 1967). Maier (1990) found that 19 species of native and exotic (primarily cultivated) rosaceous hosts were acceptable PC hosts in Connecticut. In that region of eastern North America, PC is univoltine, favouring Crataegus spp. as hosts, while readily feeding on apples. Fur-

ther south in Georgia, where PC is multivoltine, the Chickasaw plum (Prunus angustifolia) is a preferred early host, while peach has become a very signiﬁcant host for PC’s ﬁeld generation (Jenkins et al., 2006). The abundance of native PC hosts in adjacent woodland and roadside habitats across much of eastern North America confounds management of PC. Especially in the south-eastern USA, where PC from wild hosts move to peach during their ﬁeld generation (Jenkins et al., 2006), the prolonged threat of PC attack is a major concern which forces employment of very conservative management strategies. Monitoring options for PC remain rudimentary. Leskey and Wright’s (2004) work on apples in the north-eastern USA showed that traps baited with the aggregation pheromone (grandisoic acid and benzaldehyde) are not reliable enough to direct as-needed insecticide

Fig. 18.11. Plum curculio oviposition wound. (Courtesy of J.A. Payne, University of Georgia, Bugwood Network.)

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applications for PC in commercial orchards. Subsequent work suggests that more competitive attractants will likely require complex, multiple-component blends of tree volatiles (Leskey et al., 2005). Owing to the lack of commercially reliable sampling technologies to direct as-needed insecticide application, PC control is insecticide-based and preventive. In production areas where PC is univoltine, early-season preventive insecticide applications, applied in part for OFM, plant bugs and scale crawlers, provide very reliable control of PC. In the southeastern USA, insecticide applications for PC are initiated at petal fall. The absence of reliable sampling technologies forces most growers, certainly those who are wholesale shippers of peaches, to spray preventively for PC season-long, normally on a 14-day schedule (Horton et al., 2007). Prevailing market standards for control of internal fruit-feeding insects are stringent, and in wholesale shipping are market-driven. In essence, fruit must be totally free of internal fruit feeders such as OFM or PC. This rigorous market standard has perpetuated highly reliable but risk-aversive and insecticide-intensive control programmes. In the eastern USA, the organophosphate insecticide phosmet and, to a lesser degree, high-rate applications of pyrethroids form the basis of control for PC and other fruit-attacking pests. Alternative, reducedrisk insecticides, the application of entomopathogenic nematodes (Shapiro-Ilan et al., 2004), the use of cellulose sheeting to limit overwintering populations (Benoit et al., 2006) and the application of ﬁnely ground kaolin particle ﬁlms (Lalancette et al., 2005) have all shown promise, but are not in wide commercial utilization for PC control.

Scarab beetles (Coleoptera: Scarabaeidae) Scarab beetles are large, elongate to oval, heavy-bodied, convex beetles typically bearing ﬁve-segmented tarsi and eight- to 11segmented, lamellate antennae. Scarabs are plant feeders (Triplehorn and Johnson, 2005b) that are primarily direct fruit feeders in peach, although Japanese beetles are also foliage

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feeders. Scarab larvae are soil-dwelling, most often feeding on organic matter or roots. They are white, C-shaped grubs. Green June beetles (Subfamily Cetoniinae), rose chafers (Mycrodactylus subspinosus (Fabricius)) (Subfamily Melonlonthinae) and Japanese beetles (Subfamily Rutelinae) are the common scarab pests of peaches in eastern North America. Japanese beetle, Popillia japonica Newman Japanese beetle, Popillia japonica (Newman) (JB), is known for its exceptionally broad host range, which encompasses more than 275 plant species. On peach, JB feeds on foliage, producing a characteristic lace-like defoliation, and as fruit matures, JB feeds heavily on fruit (Hogmire, 1995). JB is native to Japan, where natural enemies typically keep its populations in check. The life history of JB is typical of many white beetle grub species that feed on the roots of grass. Eggs laid in the soil in summer produce larvae (white grubs) which may be diagnosed by their raster pattern, i.e. a series of V-shaped bristles found at the tip of the abdomen on the underside. The larvae overwinter in the soil, pupate and emerge as adults from mid-May to July (Shetlar and Johnson, 2005). The adults are characterized by the presence of ﬁve white tufts of hairs on each side of their copper-coloured wing covers (Shetlar and Johnson, 2005) (Fig. 18.12/Plate 197). JB is largely univoltine, and the presence of large, synchronized, adult populations in summer can pose signiﬁcant problems for growers. Adults are long-lived; they feed voraciously throughout their 30–45-day lifespan (Hogmire, 1995). Adult beetles are attracted both to the aggregation pheromone produced by feeding adults (Shetlar and Johnson, 2005) and by olfactory cues and kairomonal signals emitted from damaged fruit (Loughrin et al., 1995). Furthermore, the emission of sex pheromone by females may attract more beetles to damaged fruit and increase the localized concentrations of beetles seen in orchards (Potter and Held, 2002). Orchards can easily be monitored by visual observation, or trapping with a combination of the sex pheromone (japonilure) and fruit volatiles is also feasible (Potter and Held, 2002).

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Fig. 18.12. Japanese beetle adult. (Courtesy of the University of Georgia, Bugwood Network.)

Control of JB is based on as-needed use of insecticides. Especially in orchards near pastures, controls should be implemented before signiﬁcant defoliation occurs and certainly before JB begins to attack fruit. In North America, attempts at classical biological control have been made by importation of natural enemies (Jackson and Klein, 2006). Despite successful establishment of some parasitoid species, suppression or control of JB is sporadic. JB is a quarantine pest in Europe. Although a single occurrence of JB in the Portuguese Azores Islands (Atlantic Ocean) has been observed, no further observations of this serious scarabeid pest have been reported in Europe (Tremblay, 2000). Green June beetle, Cotinis nitida (Linnaeus) The green June beetle, Cotinis nitida (Linnaeus) (GJB), is native to much of the eastern half of the USA. GJB is seasonally abundant in peaches, especially in the south-eastern USA. It can be a very important fruit-feeding pest on late varieties (Flanders and Johnson, 2005). GJB is a large, metallic green- and bronze-coloured scarab beetle (Fig. 18.13/ Plate 198) which emerges and often moves to

ripening peaches in late June to July (Flanders and Johnson, 2005). Females attract males with sex pheromone, mate and lay their eggs in tightly packed masses in moist soils, preferring those rich with organic matter (Brandhorst-Hubbard et al., 2001). Each female continues a cycle of feeding, mating and egg laying that lasts approximately 2 weeks (Brandhorst-Hubbard et al., 2001). Regular orchard monitoring, which may be augmented by the use of fermenting fruit trays to detect adults, readily identiﬁes developing GJB infestations. Initiation of fruit feeding very often warrants application of insecticides with short preharvest intervals (Flanders and Johnson, 2005).

Plant bugs (Hemiptera: Miridae), stink bugs (Hemiptera: Pentatomidae) and leaf-footed bugs (Hemiptera: Coreidae) Plant bugs (Hemiptera: Miridae), stink bugs (Hemiptera: Pentatomidae) and leaf-footed bugs (Hemiptera: Coreidae) are fruit-feeding pests of peaches and nectarines. As a group, they are polyphagous; most feed successively through the growing season on ﬂower buds,

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Fig. 18.13. Green June beetle adult. (Courtesy of the University of Georgia, Bugwood Network.)

blooms, fruitlets and mature fruits of numerous broadleaved hosts. Many of their preferred hosts are herbaceous. They have stylet-like mouthparts that inject saliva which breaks down host tissues, allowing the bugs to suck in the liqueﬁed cellular contents. Plant bugs are small, soft-bodied true bugs. The antennae and beak are four-segmented (Triplehorn and Johnson, 2005a). The most important plant bug pest of peach in eastern North America is the tarnished plant bug, Lygus lineolarius (Palisot de Beauvois) (TPB) (Horton et al., 2005), which is a variable, mottled brass-brown colour with a red thorax (Sanderson and Peairs, 1921) (Fig. 18.14/Plate 199). In California, Lygus hesperus (Knight) and Lygus elisus (Van Duzee) are the key plant bug pests of stone fruit (Strand, 1999). L. hesperus adults are yellowish to reddish-brown, while L. elisus adults are a pale green. In Europe, damage has been reported for Lygus rugulipennis (Poppius) (Tavella et al., 1996). In peach, TPB are most abundant from bloom to shuck off, although they may be injurious through harvest. Rings (1958) thoroughly characterized TPB injury. He showed that TPB feeding typically aborted peach blossoms and small fruitlets from bloom to shuck off. TPB-induced fruit deformation or scarring,

often called ‘cat-facing’, typically occurred from shuck off to 35 days after bloom. Bluishgrey scarring and shallow pitting of the fruit predominated from 35 days post-bloom to harvest. TPB also produced gumming and water soaking, both of which were more common later in the season. Stink bugs, and to a lesser degree leaffooted bugs, feed on green and ripening peaches. Stink bugs, often green or brown (Fig. 18.15/Plate 200) in colour, are large, round to oval, true bugs with ﬁve-segmented antennae. As the name implies, many stink bugs have an unpleasant odour. Leaf-footed bugs are elongate, often brown, with the head narrower and shorter than the ﬁrst thoracic segment, and expanded, leaf-like hind tibiae (Triplehorn and Johnson, 2005a) (Fig. 18.16/ Plate 201). The brown stink bug (Euschistus servus (Say)), the dusky stink bug (Euschistus tristigmus (Say)), the southern green stink bug (Nezara viridula (Linnaeus)), the green stink bug (Acrosternum hilare (Say)) and Thyanta spp. are peach pests in the eastern USA (Johnson et al., 2005). In the arid peach production areas of the western USA, Euschistus conspersus (Uhler), A. hilare and Thyanta pallidovirens (Stål) are signiﬁcant fruit feeders (Strand, 1999). The leaf-footed bug, Leptoglosus phyllopus

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Fig. 18.14. Tarnished plant bug adult. (Courtesy of S. Bauer, USDA.)

Fig. 18.15. Brown stink bug adult. (Courtesy of J. Greene, Clemson University, South Carolina, USA.)

(Linnaeus), is also a pest of peaches in the south-eastern USA (Johnson et al., 2005). Stink bug injury to peaches parallels the injuries produced by plant bugs. Rings (1957) showed that fruit phenology at the time of feeding dramatically inﬂuenced the type of injury produced. Early-season feeding, from bloom to fruitlets of 13 mm diameter, produced fruit abortion, ‘cat-facing’ or fruit

deformation (Fig. 18.17/Plate 202) and normally took place from bloom to 49 days postbloom. Scarring, characterized by brown, corky scars, and some loss of fuzz in the affected areas took place 42–56 days after bloom. Gumming, the most common injury, took place from 42 to 115 days after bloom. Water-soaked injury also developed during the same time interval. All common stink

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Fig. 18.16. Leaf-footed bug adult. (Courtesy of D. Cappaert, University of Georgia, Bugwood Network.)

Fig. 18.17.

Cat-facing injury on peach. (Courtesy of University of Georgia, Bugwood Network.)

bug species produce similar injury to peaches. The hemipteran pests of peaches are highly mobile and are difﬁcult to monitor (Legrand and Los, 2003). Close visual monitoring for bugs and injury, emphasizing the vulnerable orchard edges, should be integral in any orchard monitoring plan (Johnson et al., 2005). Bug populations often build up on herbaceous

hosts, particularly when moisture is abundant. Movement to peaches, a deep-rooted perennial, is most evident when herbaceous hosts dry down and senesce. Trap-based monitoring techniques for plant bugs and stink bugs are available and, in some peach production areas, trapping is utilized as an adjunct to observation. Pink and, to a lesser extent, white sticky traps are used to monitor for TPB (Legrand

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and Los, 2003). Yellow pyramid traps baited with the Euschistus spp. (Hemiptera: Pentatomidae) aggregation pheromone have shown promise for monitoring stink bugs in pecans (Cottrell, 2001) and apples (Hogmire and Leskey, 2006). However, additional work deﬁning the relationship between injury and capture remains to be done before this system can be fully incorporated as a commercial IPM decisionmaking tool (Hogmire and Leskey, 2006). Cultural control, in the form of selective use of herbicides, is a basic tenet of managing the plant bug and stink bug pests of peaches. Orchard ﬂoor management does not eliminate the need for insecticides, but it consistently reduces pest pressure, thus improving the performance of insecticide applications and occasionally diminishing the need for sprays (Horton et al., 2005). The prescribed orchard ﬂoor management practices minimize in-orchard populations of late-winter and spring broadleaved annual weeds. Removal of these preferred hosts renders the orchard less attractive to heteropteran ﬂower and fruit feeders, consistently reducing injury (Killian and Meyer, 1984; Atanassov et al., 2002).

Thrips (Thysanoptera) Thrips are occasional, but sometimes quite injurious, pests of peach. Thrips are typically more injurious to stone fruit grown in arid production areas. However, even in production areas with abundant rainfall, thrips can be problematic, especially when dry weather prevails just before and during bloom. Thrips are typically more important as pests of nectarines. Western ﬂower thrips, Frankliniella occidentalis (Pergande), is a well-documented pest of nectarine and, to a less signiﬁcant extent, peaches in California (Weldon, 1921). In the south-eastern USA thrips are less commonly pests of peach, but when abundant, western ﬂower thrips are injurious (Yonce et al., 1990). Other western ﬂower thrips, Thrips meridionalis (Priesner) and Thrips major (Uzel), are pests of nectarines and peach in various Italian peach-producing regions (Cravedi et al., 2001).

Adult thrips are slender, cigar-shaped and quite small; western ﬂower thrips, one of the key pest species of peach, is about 1 mm in length (Fig. 18.18/Plate 203). Adult thrips have long, narrow, fringed wings which are folded along the back when at rest. The mouthparts of thrips scar plant tissues by piercing the surface, releasing cellular ﬂuids which are then consumed. Oviposition injury occurs when females insert their ovipositors into tender ﬂower parts. Thrips produce two distinct types of injury to stone fruit (Weldon, 1921). Russeting, the more severe injury, is seen as a roughened, corky brownish scar on the surface of fruit (Fig. 18.19/Plate 204). Russeting is produced early in the season when ﬂower thrips, which overwinter on weed species, move to peach as bloom is initiated. Adult thrips may enter ﬂower buds soon after the buds begin to swell signiﬁcantly. Adults feed inside buds and in open blooms; females further injure the nascent fruit by inserting their eggs into succulent ﬂower parts. Feeding by the resultant nymphs adds their injury to that of the adults. Silvering occurs as maturing fruit begin to colour. Injury at this time produces numerous small, clear blemishes where the pigment has been evacuated with the cellular contents. In hand, silvering is seen as a silver sheen (Fig. 18.20/Plate 205). Light to moderate silvering is sometimes ignored, especially when demand for fruit is high. Fresh market peaches should be monitored by shaking or ﬂailing ﬂowers over a cigar box or a stiff piece of paper. Unopened blooms can be sampled by removing soon-toopen buds and placing them into small, sealed plastic bags. Adult and immature thrips will leave the buds if the bags are allowed to warm on a window sill, which drives them out of hiding. Formal treatment thresholds for ﬂower thrips do not exist in peaches. High thrips numbers are required to damage peach. However, pest management practitioners must consider the limited availability of insecticides for thrips control and the difﬁculty of obtaining spray coverage thorough enough to reach thrips inside of soon-to-open ﬂowers. Cultural control in the form of orchard ﬂoor management to minimize the abundance of

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Fig. 18.18. Western flower thrips on peach leaf. (Courtesy of J.A. Payne, University of Georgia, Bugwood Network.)

Fig. 18.19. Western flower thrips russeting on fruit. (Courtesy of J.A. Payne, University of Georgia, Bugwood Network.)

weed hosts in and adjacent to the orchard has been shown to be of value (Cravedi et al., 2001). Similarly, California growers are cau-

tioned to avoid cutting lucerne as nearby peaches mature to minimize movement from lucerne to peach (Strand, 1999).

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Fig. 18.20. Western flower thrips silvering on fruit. (Courtesy of J.A. Payne, University of Georgia, Bugwood Network.)

Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) Mediterranean fruit ﬂy, Ceratitis capitata (Wiedemann), which is thought to have originated in Africa, is a serious pest of numerous fruit and vegetable species. It is well adapted to diverse climates and has in excess of 350 host fruit species (Liquido et al., 1991). Mediterranean fruit ﬂy is well established in Central America, South Africa, Israel, much of the Mediterranean and Australia (Peck and McQuate, 2000). In general, it is found in most tropical and subtropical areas of the world. Numerous temporary populations have been established in the continental USA but, to date, eradication efforts have prevented the establishment of permanent or adventive populations. Mediterranean fruit ﬂy was introduced in the state of Hawaii, USA, in 1910, where it became established (Anon., 2006). The adult Mediterranean fruit ﬂy is slightly smaller than a house ﬂy (Fig. 18.21, Plate 206). It has dark blue eyes and a shiny thorax of glistening black overlain with a mosaic of yellowish white. The abdomen is yellowish with two silvery cross bands. Its wings, which are normally drooping, are banded and blotched with yellow, brown and black. As with other fruit ﬂy species, the adult diet is exclusively liquids. Females insert their

eggs into the ﬂesh of suitable fruits. Larvae complete development inside fruit, at which time the mature larvae exit fruit and move into the soil to pupate. Under the most favourable of conditions the life cycle may be completed in as little as 17 days. In various parts of the world Mediterranean fruit ﬂy completes from 1 to 12 generations per year (Anon., 2006). The economic impacts of fruit ﬂy species are twofold: (i) larval feeding directly injures fruit, rendering it unmarketable; and (ii) fruit ﬂy infestations limit access to markets which impose quarantine restrictions (Malavasi et al., 1994). Management of Mediterranean fruit ﬂy in production areas with persistent infestations varies according to the intensity of infestation and the type of markets utilized to sell fruit. In regions where export of produce to uninfested regions is not pursued, a variety of traditional pest management approaches are employed to mitigate losses. Control relies primarily on broad-spectrum insecticides applied in baits or as cover sprays (Roessler, 1989). The sterile insect technique is an alternative approach for suppressing or eradicating fruit ﬂies on an area-wide scale (Hendrichs, 1996). Large numbers of males, which have been irradiated to render them sterile, are released to dramatically reduce the probability of virgin females successfully mating with viable males. Sterile male releases are normally preceded by use of insecticidal

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Fig. 18.21. Mediterranean fruit fly mating. (Courtesy of Catholic University, Piacenza, Italy.)

baits and/or cover sprays to reduce the ambient population of ﬂies. Use of insecticides to ensure a relative paucity of viable males increases the probability of females laying infertile eggs. Quarantine restrictions often prompt creation of area-wide management protocols which prescribe aggressive, region-wide trapping for adults. Trapping of even very low numbers of fruit ﬂy adults will trigger prompt area-wide use of insecticidal baits, as-needed foliar insecticide and, in some cases, release of sterile male fruit ﬂies.

although except for occasional stunting of young trees, they are seldom truly injurious. However, aphids are important vectors of plant diseases, including Plum pox virus. Management of indirect peach insect pests should focus on tree health, productivity and orchard longevity. Proﬁts are returned to the grower from the time trees generate sufﬁcient income to pay for themselves until the orchard’s eventual demise. Productivity or longevity lost to borers or scale very quickly eats into an orchard’s lifetime income potential. Cultural and pest management efforts should focus on maintaining tree health and vigour to optimize economic returns.

18.3 Indirect Insect Pests Indirect pests of peaches are the tree-attacking pests, those which feed on the foliage, bark, inner bark or the roots. They are indirect in that their injury impacts the tree itself before exacting costs from the fruit. Scale species are key indirect pests of peaches wherever they are grown. Borers of various sorts are regionally important, as is the case with the peach tree borer and lesser peach tree borer in eastern North America. Aphids and leafhoppers are frequently present in peaches,

Peachtree borers, Synanthedon spp. (Lepidoptera: Sesiidae) Peachtree borer, Synanthedon exitiosa (Say) (PTB), and lesser peachtree borer, Synanthedon pictipes (Grote & Robinson) (LPTB), are key tree-attacking pests of peach in eastern North America. Native Prunus spp. are their seminal hosts, but both PTB and LPTB have adapted quite well to peaches. The larvae (Fig. 18.22/Plate 207) of both species feed

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Fig. 18.22. Peachtree borer larva. (Courtesy of University of Georgia, Bugwood Network.)

beneath the bark on phloem tissue. As subsurface vascular feeders, they are initially difﬁcult to diagnose and often do substantial damage before infestations are evident. Both species are quite injurious; if uncontrolled, they debilitate fruiting wood, scaffold limbs and entire trees, often leading to premature orchard decline (Fig. 18.23/Plate 208). PTB is generally univoltine; the white larvae (Fig. 18.22/Plate 207) construct pupal cases below ground, pupate and produce adults that mate and oviposit on tree trunks and exposed roots shortly after emergence. After 10 days the neonates hatch, gain access to cambial tissue through cracks or wounds in the bark, and overwinter in various stages of development. This sexually dimorphic diurnal PTB moth is also an effective wasp mimic; its shining clear wings, metallic blue-black body and, particularly in the males, superb ﬂight capabilities make it easily mistaken for a wasp (Hogmire, 1995) (female – Fig. 18.24/ Plate 209; and male – Fig. 18.25/Plate 210). LPTB is a similar species; however, it is less sexually dimorphic: both males and females are similar to PTB males, while lacking the triangular shape of the terminal abdominal segments and yellow scales between the

antennae. The LPTB lays its eggs on aboveground structural wood. The larvae tunnel through cambial tissues, producing a gum– frass mixture that is highly diagnostic of infestation (Fig. 18.26/Plate 211). Remnants of previously eclosed pupae that extrude out of the damaged, sticky bark are also diagnostic. LPTB is bivoltine in the south-eastern USA (Hogmire, 1995). Control options for PTB and LPTB vary with production area. Barrier insecticide applications and pheromone mating disruption are the commercial standards for management of these pests. Both methods are preventive in nature. Nematode-based control of PTB (Cossentine et al., 1990; Cottrell and Shapiro-Ilan, 2006) and LPTB (ShapiroIlan and Cottrell, 2006) has shown promise. In eastern North America diverse fruitfeeding pest complexes necessitate at least some measure of repetitive, in-season cover spray. Cover spray insecticide applications are thought to diminish the levels of biological control of PTB and LPTB which would otherwise be provided by natural enemies. However, history suggests that both barrier insecticides and mating disruption may have been augmented by cover spray suppression

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Fig. 18.23. Branches damaged by lesser peachtree borer. (Photo by J. Fuest, University of Georgia.)

Fig. 18.24.

Adult female peachtree borer. (Photo by J. Fuest, University of Georgia.)

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Fig. 18.25. Adult male peachtree borer. (Courtesy of University of Georgia, Bugwood Network.)

Fig. 18.26.

Lesser peachtree borer wounding. (Photo by J. Fuest, University of Georgia.)

of the borer species. Organophosphate insecticides have been the peach insecticides of choice in eastern North America since the mid-1950s. In the early 1990s, regulatory mandate transitioned growers in the eastern USA from encapsulated methyl parathion to phosmet. Phosmet has performed quite well as a fruit protectant. However, after a few

years of widespread reliance on phosmet, borer control in the south-eastern USA began to deteriorate. LPTB, which is multivoltine, and to a lesser degree PTB have asserted themselves as aggressive, often debilitating tree pests and led to premature decline and removal of heavily infested orchards (Horton et al., 2005).

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Chlorpyrifos, also an organophosphate, is the most effective barrier insecticide treatment for borers. As a protective barrier, it provides excellent control of PTB (Yonce, 1980), and at least a measure of LPTB suppression. Chlorpyrifos barrier sprays target neonate and ﬁrst instar larvae, with some measure of ovicidal and adulticide activity. In much of the eastern USA, chlorpyrifos barrier sprays are the commercial standard. While targeted primarily at PTB, barrier sprays at least suppress LPTB. Chlorpyrifos barrier insecticides are applied either postharvest or a minimum of 14 days preharvest. Application is by handgun-directed coarse sprays to optimize coverage and, in the mid-Atlantic states, where preharvest sprays are needed, to allow applicators to scrupulously minimize residue deposition on the fruit. In eastern North America, pheromone mating disruption of borer species in peaches is in common use in the mid-Atlantic production area, Ontario and Michigan. Acreages using mating disruption in these areas are now similar to those receiving the more conventional barrier insecticide treatment with chlorpyrifos. Rates required for efﬁcacious pheromone mating disruption of the borer species in the south-eastern USA, where the growing season is substantially longer than in the above areas, are signiﬁcantly higher and hence more costly.

Armoured scale (Hemiptera: Diaspididae) White peach scale, Pseudaulacaspis pentagona (Targioni-Tozzetti) White peach scale, Pseudaulacaspis pentagona (Targioni-Tozzetti) (WPS), is an important cosmopolitan pest of peaches. WPS has an extremely wide host range, including nearly all non-coniferous plants (Nalepa and Meyer, 1990). Although native to south-eastern Asia, WPS has become a pest with a worldwide distribution (Erkiliç and Uygun, 1997). Since its introduction to the USA in the late 1800s, WPS has been most notable as a peach pest in the south-eastern states (Van Duyn and Murphey, 1971; Yonce and Jacklin, 1974). The range of WPS in the eastern USA extends west

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to Texas and northwards to Maryland and Tennessee (Hanks and Denno, 1993). This insect also causes economic damage in Turkey, where it is a dominant pest of peach (Erkiliç and Uygun, 1997), Italy (Pedata et al., 1995), Asia, Australia, Africa, the Caribbean and the Paciﬁc Islands (Hanks and Denno, 1993). Female WPS are creamy white to reddish-orange, sac-like, sessile insects that are covered in waxy, brownish coverings approximately 1 mm in diameter (Hodges, 2005) (Fig. 18.27/Plate 212). Female WPS overwinter beneath their scale covers, becoming active pre-bloom. Adult females emit sex pheromone in a rhythm that matches the daily egg hatching cycles of males, which are, in turn, controlled by light and temperature (McLaughlin et al., 1990). The tiny, yellowish, winged males are attracted to calling females and can inseminate multiple females in each aggregation (McLaughlin et al., 1990). Crawlers, or nymphs, disperse from beneath the females to seek unoccupied feeding sites on the tree bark (Hodges, 2005). In as little as a week crawlers have begun to settle, at which time they become sessile and lay down scale covers. WPS infestations of peach result in loss of tree vigour, with reduced fruit production and ultimately death of fruiting wood, scaffolds and trees. In the absence of management steps speciﬁcally for scale, heavy WPS infestations can kill portions of a tree or even the entire tree in as few as 2 or 3 years (Kuitert, 1967). WPS is a multivoltine pest, having three generations in central Virginia (Bobb et al., 1973) and four generations in north Florida, where it is a major pest of peaches (Kuitert, 1967). In Europe, WPS is present in that continent’s central and southern production areas, where two or three generations per year can develop (Kozar et al., 1997). In addition to peach and cherry, WPS is an important pest of kiwifruit (Paloukis and Navrozidis, 1997). In the USA, WPS is most injurious in the south-east’s warmer, coastal plain production areas. Peaches are quite susceptible to injury from WPS. Kuitert (1967) observed that peaches were severely debilitated by WPS infestations when visually similar infestations did not appear to be detrimental to chinaberry, privet, black walnut or mulberry. WPS is,

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Fig. 18.27. White peach scale: adult females and crawlers. (Courtesy of Catholic University, Piacenza, Italy.)

however, widely noted as a pest of mulberry (Hanks and Denno, 1993). Control of WPS in the south-eastern USA is reliably obtained by annual application of two dormant-season horticultural oil sprays (Bobb et al., 1973). Control of WPS via cover sprays can occur if applications coincide with crawler emergence. However, determination of the optimal timing for spray applications is difﬁcult to obtain and, thus, good WPS control via cover sprays seldom occurs. Biological control of WPS, primarily from parasitoids such as Encarsia berlesei (Howard), can be quite effective in the south-eastern USA; unfortunately natural control is severely impeded by the necessary in-season insecticide applications to control the region’s diverse complexes of fruit-feeding pests (Nalepa and Meyer, 1990). Insecticides applied to control other peach pests have been shown to exacerbate WPS infestation levels by reducing parasitoid abundance in Italy (Pedata et al., 1995), Turkey (Erkiliç and Uygun, 1997) and Florida (Collins and Whitcomb, 1975). San Jose scale, Quadraspidiotus perniciosus (Comstock) San Jose scale, Quadraspidiotus perniciosus (Comstock), is a cosmopolitan species which is a

key pest of peach worldwide. San Jose scale was inadvertently introduced to the USA via San Jose, California, in 1873, which explains how an insect thought to be native to northern China, eastern Siberia and Korea (Rosen and DeBach, 1978) came to have such a decidedly inappropriate common name (Flanders, 1960). San Jose scale is difﬁcult to see and readily spread on infested fruit, bud wood or young trees, accounting for its global distribution. San Jose scale has a broad host range, attacking at least 34 host families and over 700 plant species. San Jose scale is often particularly problematic in stone fruit (Vasseur and Schvester, 1957; Gentile and Summer, 1958). San Jose scale is a major pest of peach which beneﬁts from annual management inputs in virtually all production areas (Rice et al., 1979; Kyparissoudas, 1987a,b; Masoodi et al., 1989). San Jose scale is an armoured scale and, except for the ﬁrst nymphal stage and the adult males, all life stages live under hard, protective scale coverings. The scales of adult female San Jose scale are round, about 1.6–2 mm across, grey and ﬂattened, with a raised projection or nipple in the centre (Fig. 18.28/ Plate 213). Beneath her scale covering, the adult female is yellow, ﬂattened, somewhat pear-shaped and immobile. Immature male

Insects and Mites

Fig. 18.28.

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San Jose scale: adult females and crawlers. (Courtesy of Catholic University, Piacenza, Italy.)

San Jose scales are similarly coloured, but found beneath elongated scale coverings. The adult male is a tiny, yellow, winged insect which seeks out and mates with virgin females. San Jose scale males can be differentiated from other small, yellow, gnat-like insects by a dark band across the back, their prominent beaded antennae and small black eyes (Strand, 1999). Fertilized females produce eggs which are deposited under the mother’s protective scale. Eggs very quickly hatch and the small, yellow, mite-like crawlers disperse to search for a suitable site to feed and mature. Shortly after settling, the crawler inserts its stylet-like mouthparts into the host plant to feed, loses its antennae, eyes and legs, and secretes a greyish-white protective scale called a white cap. Females remain immobile throughout their lives, while the males regain their mobility as adults to seek out and mate with the immobile females. After only a few days, the white cap scale secretes a series of dark rings, which indicates attainment of the immature scale’s next stage, which is called a black cap. After a subsequent moult, the immature scale takes on its dark grey adult colour, and the elongate males can be distinguished from the round females (Strand, 1999).

San Jose scale is very proliﬁc, each female being able to produce up to 400 crawlers per season (Quaintance, 1960). When abundant, San Jose scale can kill fruiting wood, scaffold limbs and trees within 3 years (Marlatt, 1953). Although biocontrol can be impressive, natural enemies are seldom able to hold scale populations in peach below damaging levels (Rice et al., 1979). Heavily infested trees will have scale on the fruit, producing inﬂamed red lesions around the scale, which will still have its characteristic nipple. Fruit infestations are an indicator of very high San Jose scale populations, which should be expected to reduce vigour and fruit size, and ultimately kill limbs and trees. Management of San Jose scale, and other armoured scale species which attack peach, requires annual inputs in order to prevent injury and loss of productivity. Insecticidal applications for San Jose scale target either the sessile overwintering stages or the crawlers (Downing and Logan, 1977). Dormant oil applications should be the foundation of scale control in peach. The concentration of oil applied may be varied, with lower concentrations being appropriate early in the dormant season and again shortly before bud break.

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Higher concentrations are somewhat more effective, but they should be reserved for the cooler months when trees are more fully dormant. As a general rule, two dormant oil applications each winter will consistently provide better control than a single application. This is especially so in regions with heavy scale pressure and mixed populations of San Jose scale and WPS (Cochran et al., 1953). Oil applications may be made 10–14 days apart or several months apart. IGR chemistries are valuable, though expensive, corrective materials that are best reserved for problematic blocks which experienced heavy scale build-up in the previous season, but did not receive two dormant oil applications. Growth regulators may be applied pre-bloom as buds break or they may be applied as the ﬁrst crawlers appear. In like fashion, where pest resistance is not a problem, high-rate application of a broad-spectrum, organophosphate insecticide cover spray, applied as crawler movement is initiated, is also very effective. As with growth regulator applications, this management approach is dependent on timing the applications to coincide with the onset of crawlers. The cryptic nature of scale and the high attention to detail required to successfully time spray application to crawler movement make this approach challenging. However, reliable techniques are available for monitoring San Jose scale life stages. San Jose crawlers may be monitored by placing transparent, double-sided Scotch™ tape around selected, scale-infested branches of a consistent size (2 cm diameter) on several trees per block (Badenes-Perez et al., 2002). Tapes should be hung well before bud break. Old tapes should be removed and new ones put in place, with a 2-week schedule working well. Tapes should be examined for the presence of crawlers using a dissecting microscope. The San Jose scale phenology model of Jorgensen et al. (1981) may be used with meteorological data to predict scale life cycle events. A bioﬁx, consisting of the season’s ﬁrst capture of male San Jose scale in pheromone traps, is necessary to properly time initiation of heat unit accumulation. Pheromone traps are the most practical means to monitor adult male emergence.

Aphids (Hemiptera: Aphididae) Aphids are soft-bodied, teardrop-shaped insects which use their piercing and sucking mouthparts to imbibe a liquid diet of plant juices (Fig. 18.29/Plate 214). Most aphid species have very high reproductive rates, and it is common to see dense aggregations of these slow-moving insects on succulent plant terminals. In peach, the impact of direct aphid injury, the result of aphid feeding, is typically modest, and many peach growers regard aphids as minor, or even inconsequential, pests. Aphids of several species are known to utilize peach as a host. In the USA, surveys by Stoetzel and Miller (1998), Gildow et al. (2004) and Wallis et al. (2005) overviewed the peach aphids of North America, with particular emphasis on their potential as viral vectors. Blackman and Eastop (1985) included peach aphids in their survey of crop-feeding aphids. Naturally occurring biological control is normally effective in mitigating aphid abundance in peach. Even in productions systems that must utilize regular application of broadspectrum insecticides to control key fruit or tree pests, a robust complement of predacious and parasitic insects is commonly successful in bringing even the occasional high aphid population down to low or moderate abundances. Aphids are, however, important vectors of plant viruses. Numerous aphid species feed on peach and many of them are vectors. The virus vector potential of these aphid species is far more signiﬁcant to the health and performance of peaches than direct feeding injury. The vectors of Plum pox virus (PPV) in peach in the eastern USA have been surveyed (Stoetzel and Miller, 1998; Gildow et al., 2004). However, the detailed biology and behaviour of these aphids, which at least in the USA were regarded as minor peach pests, is inadequately understood. PPV, which causes plum pox, also known as sharka disease, is perhaps the most serious of the viruses of peach. Plum pox-infected trees suffer dramatic reductions in fruit quality and yield (Kölber et al., 2001). PPV is spread over long distances by human activities, primarily movement of asymptomatic virus-infested bud wood or young trees and

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Fig. 18.29. Green peach aphid: parthenogenetic female and nymphs. (Courtesy of Catholic University, Piacenza, Italy.)

rootstocks. Movement within and among adjacent orchards is by aphid transmission (Shukla et al., 1994). PPV was ﬁrst observed in the Balkans, but it has since spread throughout most key peach production areas in Europe, the Middle East, China and South America. For many years plum pox was successfully excluded from North America. However, in 1999 the disease was conﬁrmed in the north-eastern USA, in Adams County, Pennsylvania. A second PPV infestation was subsequently conﬁrmed in south-eastern Canada, on the Niagara Peninsula in 2000 (Levy et al., 2000). This infestation has since spread across the Saint Lawrence River to stone fruit orchards in neighbouring New York State, USA. Orchard destruction programmes have been implemented in each of these areas in an effort to eradicate the disease. In eastern Europe Hyalopterous pruni (Geoffroy) and Phorodon humuli (Schrank) are felt to be key PPV vectors. In western Europe and Pennsylvania, USA, the green peach aphid, Myzus persicae (Sulzer), and the spirea aphid, Aphis spiraecola (Patch), are considered to be the more important vectors of PPV (Wallis et al., 2005). Plum pox is not easy to detect,

and infected trees may be visually asymptomatic. Aphid transmission of PPV is nonpersistent, meaning the virus can be acquired by aphids which either feed or brieﬂy probe infested material to determine host suitability. It is generally accepted that potyviruses such as PPV are seldom carried long distances because the vector’s infectivity is short-lived (Wallis et al., 2005). Green peach aphid is a cosmopolitan species which is important as a pest of numerous vegetable, ornamental and fruit crops around the world (Blackman and Eastop, 1985). Green peach aphid is discussed here because of its widespread distribution as both a direct pest of stone fruit and its importance as a virus vector of peach. In southern Europe, green peach aphid is a major direct pest of peaches, owing to its injury of succulent terminal growth and leaves and feeding on the fruit, which can reduce fruit quality (Pascal et al., 2002). Green peach aphid is also regarded as one of the key European vectors of PPV (Pascal et al., 2002). Management of green peach aphid in southern Europe is complicated to some degree by the aphid’s resistance to insecticides (Devonshire et al., 1998). In the

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USA peach aphids, including the green peach aphid and spirea aphid, have not been regarded as important pests. Control, when needed, has been insecticidal. In warmer production areas such as California (Strand, 1999) and the southeastern USA (Baker, 1994), green peach aphid moves from one crop or weed host to the next. In these regions, they show no dramatic preference for peach and there is no egg stage. Both green peach aphid and spirea aphid are more commonly seen on peach in these regions during the early spring. In cooler production areas, such as Michigan, green peach aphid overwinters on peach as either eggs or mated females. In the spring, as peach foliage emerges, female green peach aphids give birth parthogenetically to wingless offspring (Fig. 18.29/ Plate 214). By June winged adults develop and disperse, leaving peach for summer hosts. They return to peach in the autumn (Howitt, 1993).

18.4 Mite Pests Two-spotted spider mite (TSM), European red mite (ERM) and other foliage-feeding mites are indirect pests of peaches. Relative to other deciduous fruits, peaches are very tolerant of mite feeding. It is generally accepted that mites are more problematic in drier production areas and that peaches with adequate moisture are more tolerant of mites. It is also believed that mite outbreaks in many orchard systems are at least partially an unintended consequence of broad-spectrum insecticide use for fruit- or tree-attacking pests (Croft et al., 1987). Kovach and Gorsuch (1986) asserted that pyrethroid insecticides should have only a modest role on south-eastern peaches because of their tendency to encourage TSM populations. Multiple studies indicate that peach yield and/or fruit quality were not reduced until mite numbers were quite high. Kovach and Gorsuch (1985) reported that more than 48 TSM/leaf were required to reduce the percentage of fruits that reached the more desirable, large size categories. In like fashion, Bailey (1979) showed that TSM densities of 40–50 mites/leaf did not reduce peach yield in South Australia. Working with ERM on

peaches, McClernan and Marini (1986) showed no reduction of yield, fruit quality or tree growth parameters at mite densities of less than 100 per leaf. In Europe, IPM strategies in northern Italy signiﬁcantly reduced the damage produced by tetranychid mites, whose importance still remains high in more arid climates. Problematic situations have been reported in Greece. Peach’s ability to tolerate mite infestations with very modest risk of yield loss must be balanced with tree health issues. Defoliation from heavy mite infestations exposes scaffold limbs and ripening fruit to sunburn. Miticides should be applied in advance of defoliation to protect the scaffold limbs and fruit from sun injury. Hogmire (1995) advocated conservative provisional mite thresholds for peaches, suggesting treatment for >10 mites/leaf during mid-season and >20 mites/leaf as fruit approach maturity. These values are approximately twice those used in apples at similar points in crop development. Hogmire (1995) also noted, as have others, that it is often necessary to treat peaches for mites preharvest to lessen the dermal irritation experienced by pickers. Resistance management is a logical consideration in formulating pest management plans. While miticide use in peach is modest, it is well to be aware that various TSM populations have shown themselves to be resistant to chlorpyrifos, dicofol, cyhexatin, abamectin and two ovicides, clofentezine and hexythiazox, which have a common mode of action (Stumpf and Nauen, 2001). Overuse of the ‘best’ miticides, and use of least-cost cover spray insecticides (pyrethroids) which may adversely impact natural enemy populations and enemies, can work in concert to increase the selective pressures favouring resistance (Croft et al., 1987). The most practical means of managing miticide resistance is the alternation of miticides with differing modes of action and the incorporation of horticultural mineral oils into a management programme. Resistance management plans should be standard for mites and other resistance-prone pests. Pest management advisors should help growers develop plans by describing use patterns to ensure rotation between unlike modes of action. Such plans can easily be developed

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Plate 164. Leaves on branch infected with European stone fruit yellows phytoplasma (left) are small in size, rolled upward longitudinally, and have a pale yellow colour compared with leaves on a non-infected branch (right) (from A. Ragozzino). Plate 165. Peach tree infected with European stone fruit yellows phytoplasma with leaf midrib and lateral veins enlarged and necrotic (from L. Giunchedi). Plate 166. Two trees of the same age of cultivar ‘Babygold 7’. The tree in foreground is infected with the European stone fruit yellows phytoplasma (exhibiting reduced vigour) compared with the non-infected tree in the background (from A. Ragozzino). Plate 167. Discoloration symptoms of Plum pox virus type M on peach cv. ‘Baby Gold 6’ flowers (courtesy of J.C. Desvignes, La Force, France). Plate 168. Colour break symptoms of Plum pox virus type M on petals of peach cv. ‘Gladys’ flowers (courtesy of M.A. Cambra, Zaragoza, Spain). Plate 169. Leaf symptoms of Plum pox virus on ‘GF 305’ peach seedlings used as indicator plant.

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Plate 170. Leaf symptoms of Plum pox virus type M on peach cv. ‘Royal Gem’. Plate 171. Fruit symptoms (under-pigmented yellow rings) caused by Plum pox virus in peach cv. ‘Springcrest’. Plate 172. Chlorotic rings and line pattern caused by Plum pox virus in nectarine cv. ‘Arm King’ fruits. Plate 173. Chlorotic spots and under-pigmented yellow rings caused by Plum pox virus in peach cv. ‘Catherine’ fruits (courtesy of M.A. Cambra, Zaragoza, Spain). Plate 174. Leaf symptoms (chlorotic rings and deformation) caused by Prune necrotic ring spot virus in peach. Plate 175. Necrotic spots caused by Prunus necrotic ring spot virus in peach leaves.

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Plate 176. Dense canopy due to shortening of shoot internodes caused by Prune dwarf virus in peach trees. Plate 177. Leaf symptoms (bright yellow mosaic and spots) caused by Apple mosaic virus in peach. Plate 178. Severe reduction of leaf growth on buds giving a rosette appearance caused by Tomato ringspot virus in ‘GF 305’ peach seedlings. Plate 179. Internode shortening caused by Strawberry latent ringspot virus in peach trees. Plate 180. Fruit symptoms (deformations and discolorations with cracked sutures) caused by Peach latent mosaic viroid in peach.

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Plate 181. Leaf symptoms (yellow-creamy mosaic) caused by Peach latent mosaic viroid in peach. Plate 182. White patterns (calico) covering most of the leaf area caused by Peach latent mosaic viroid in nectarine cv. ‘Red-Gin’ leaves. Plate 183. Leaf symptoms (chlorotic spots) caused by Peach sooty ringspot virus in peach. Plate 184. Sooty green rings on a yellow background in senescent leaves caused by Peach asteroid spot virus in peach. Plate 185. Leaf symptoms (yellowish line patterns and russet rings) and fruit symptoms (chlorotic rings and mosaic) caused by Apple chlorotic leaf spot virus in peach. Plate 186. Oriental fruit moth injury to peach terminal (University of Georgia, Bugwood).

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Plate 187. Oriental fruit moth adult (University of California, IPM). Plate 188. Anal plate of oriental fruit moth larva (University of California, IPM). Plate 189. Oriental fruit moth larva tunnelling in peach (University of California, IPM). Plate 190. Adult codling moth (University of California, IPM). Plate 191. Adult of the peach twig borer moth (Catholic University, Piacenza). Plate 192. Mature peach twig borer larva (University of California, IPM).

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Plate 193. Tufted bud moth adult (courtesy of G. Krawczyk, University Park, Pennsylvania, USA). Plate 194. Tufted bud moth larva on fruit (courtesy of G. Krawczyk, University Park, Pennsylvania, USA). Plate 195. Plum curculio adult (University of Georgia, Bugwood). Plate 196. Plum curculio oviposition wound (courtesy of J.A. Payne, University of Georgia). Plate 197. Japanese beetle adult (University of Georgia, Bugwood). Plate 198. Green June beetle adult (University of Georgia, Bugwood).

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Plate 199. Tarnished plant bug adult (courtesy of S. Bauer, USDA). Plate 200. Brown stink bug adult (courtesy of J. Greene, Clemson University, South Carolina, USA). Plate 201. Leaffooted bug adult (courtesy of D. Cappaert, University of Georgia, Bugwood). Plate 202. Cat-facing injury on peach (University of Georgia, Bugwood). Plate 203. Western flower thrips on peach leaf (courtesy of J.A. Payne, University of Georgia, Bugwood). Plate 204. Western flower thrips russeting on fruit (courtesy of J.A. Payne, University of Georgia, Bugwood).

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Plate 205. Western flower thrips silvering on fruit (courtesy of J.A. Payne, University of Georgia, Bugwood). Plate 206. Mediterranean fruit fly mating (Catholic University, Piacenza). Plate 207. Peachtree borer larva (University of Georgia, Bugwood). Plate 208. Branches damaged by lesser peachtree borer (courtesy of J. Fuest, University of Georgia). Plate 209. Adult female peachtree borer (courtesy of J. Fuest, University of Georgia). Plate 210. Adult male peachtree borer (University of Georgia, Bugwood).

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Plate 211. Lesser peachtree borer wounding (courtesy of J. Fuest, University of Georgia). Plate 212. White peach scale. Adult females and crawlers (Catholic University, Piacenza). Plate 213. San José scale. Adult females and crawlers (Catholic University, Piacenza). Plate 214. Green peach aphid. Parthenogenetic female and nymphs (Catholic University, Piacenza). Plate 215. Twospotted spider mite with egg (University of Georgia, Bugwood). Plate 216. European red mite adult (INRA Montepellier).

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Plate 217. Galls on ‘Okinawa’ (A) and ‘Nemaguard’ (B) peach roots caused by Meloidogyne floridensis (courtesy of W.B. Sherman, Gainesville, Florida, USA). Plate 218. Galls on peach (A and B) and Myrobalan plum (C) roots caused by root-knot nematode (RKN), Meloidogyne sp. Severe early symptoms (A); root decay following an attack (B); two Myrobalan plum individuals from a progeny segregating for the Ma RKN resistance gene (left = host; right = resistant) (C) (photos by A.P. Nyczepir (A) and D. Esmenjaud (B, C)).

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Plate 219. Reproductive life cycle of Meloidogyne spp. (N = female nematode; * = giant cells) (courtesy of INRA, Sophia-Antipolis, France). Plate 220. Galls on Myrobalan plum root caused by the association of Meloidogyne spp. and Agrobacterium tumefaciens (crown gall) (photo by D. Esmenjaud, INRA). Plate 221. Influence of Mesocriconema xenoplax (Mx) on ‘Nemaguard’ peach feeder root growth after 6 months ((–)Mx, uninoculated; (+)Mx, inoculated; Pi = 14,000 nematodes/1500 cm3 soil, where Pi is initial nematode population density) (photo by A.P. Nyczepir).

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Plate 222. Dead peach tree with suckers at the crown during summer in the presence of Mesocriconema xenoplax and the peach tree short life disease complex (photo by A.P. Nyczepir). Plate 223. Typical cambial tissue damage of the trunk above the soil line and healthy viable tissue below the soil line in tree dying from peach tree short life disease (photo by A.P. Nyczepir). Plate 224. Eight dead 3-year-old peach trees on ‘Nemaguard’ rootstock (foreground) and live trees on all ‘Guardian®’ rootstock (background, same row) in the presence of Mesocriconema xenoplax and the peach tree short life disease complex (photo by A.P. Nyczepir). Plate 225. Influence of Pratylenchus vulnus on ‘G × N No. 15’ almond–peach hybrid root growth after 24 months (left, uninoculated; right, inoculated; Pi = 1000 nematodes/plant where Pi is initial nematode population density) (courtesy of J. Pinochet, Agromillora Catalana SA, Barcelona, Spain). Plate 226. Peaches picked at different maturity levels.

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Plate 227. The influence of increased nitrogen fertilization (kg/ha) on red skin coloration of 'Fantasia' nectarine. Plate 228. Water stress late in the summer causes fruit defects such as deep sutures and double-fruit formation. Plate 229. Canopy position affects fruit size, red colour development and storage potential. Plate 230. Leaf removal around the fruit improves red colour but may decrease fruit size. Plate 231. Peach girdling (removal of a strip of scaffold bark) at the main scaffolds advances maturity and increases fruit size. Plate 232. Internal breakdown symptoms in peaches (top of image) include flesh mealiness, flesh browning and loss of flavour.

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Plate 233. Peach inking or staining as a consequence of abrasion combined with heavy metal contamination during harvesting and hauling operations. Plate 234. Bin of peaches being pre-cooled on conveyor-type hydro-cooler prior to packing. Plate 235. Packaged fruit in unitized pallet loads are stacked to form a forced-air cooling tunnel. Plate 236. Storage temperature influences incidence and severity of internal breakdown in susceptible cultivars. Plate 237. Peaches for fresh market are hand picked. Harvesters work on ladders using picking bags or baskets.

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Plate 238. Harvesters transfer peaches to field bins which are moved through the field on low trailers. Plate 239. View of a shaded loading area to protect fruit from excess heating while awaiting transportation to the packing house. Plate 240. Dry bin dumping of fruit on to a commercial packing line. Plate 241. Sorting peaches by skin colour and removing blemished fruit.

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Plate 242. Packers sizing, sorting and packing fruit by hand into two-layer tray packs. Plate 243. Fruit moving on to an electronic weight sizer. Plate 244. Cull removal and disposal can be a major problem and expense in peach packing. Plate 245. Peach fruit display at a retail store.

Insects and Mites

by referring to the Insecticide Resistance Action Committee’s eClassiﬁcation site (http:// www.irac-online.org/eClassiﬁcation/), which facilitates this process by assigning numbers to classes of toxins. Alternating among miticides of differing numbers substantially reduces selective pressure for resistance. Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) Two-spotted spider mite, Tetranychus urticae Koch, is a cosmopolitan, indirect, foliage-feeding pest of fruits, vegetables and nursery crops worldwide, and is well known as a pest of peach (Unwin, 1971) (Fig. 18.30/ Plate 215). TSM is the most commonly injurious phytophagous mite of peaches. In California, TSM and Paciﬁc spider mite, Tetranychus pacificus (McGregor), are the key mite pests of peaches and other stone fruits. Paciﬁc spider mite feeds on both the upper and lower sides of leaves, while TSM feeds primarily on the undersides. The biology and management of these web-spinning mites are quite similar; hence the discussion that follows will focus on the more widely problematic TSM. In Europe,

Fig. 18.30. Network.)

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TSM is more problematic as a peach pest in warmer and drier areas like southern Italy and Greece. In most peach-producing areas, TSM overwinters as adult females on the orchard ﬂoor or at the base of trees. The overwintering females are reddish-orange and their namesake spots are less visible. In North Carolina, TSM continues to reproduce on hosts such as henbit during mild winters, though at a reduced rate (Meagher and Meyer, 1990). As peaches leaf out in spring, TSM moves ﬁrst to foliage in the lower part of trees. Eggs, which are spherical and translucent, are laid primarily on the underside of leaves. Eggs hatch into six-legged larvae, which subsequently pass through two eight-legged nymphal stages before reaching the eight-legged adult stage. TSM adults are small, about 0.4 mm long, pale green, greenish-amber or yellowish, with two, sometimes four, spots on their sides. TSM development is rapid and temperaturedependent, with generation times as short as 5 days being seen under optimal conditions. Mite injury within an orchard is often clumped; however, when densities are high, air-borne dispersal of mites occurs with even gentle breezes.

Two-spotted spider mite with egg. (Courtesy of University of Georgia, Bugwood

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TSM feeds by piercing the epidermis of leaves, releasing sap which the mite ingests. Injured mesophyll cells collapse and produce a small chlorotic spot at each feeding site. A delicate stippling develops and, as infestations progress, the leaves become off-colour, often turning yellow or bronze (Meagher and Meyer, 1990). Leaf discoloration, webbing and defoliation can develop quickly. TSM development is favoured by hot, dry conditions, which lends more signiﬁcant pest status to TSM in California and other arid production areas. European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae) European red mite, Panonychus ulmi (Koch), is an occasional pest of peaches (Fig. 18.31/ Plate 216) that is generally considered to be less important than TSM. However, ERM is abundant on peaches, producing stippling and bronzing of leaves and defoliation. Population growth of ERM is favoured by humid, shady conditions, which may partially explain its greater importance as a mite pest of peaches in the more humid production areas of eastern North America and northern Italy in Europe. McClernan and Marini (1986)

observed that ERM was the most prevalent phytophagous mite of peaches in New Jersey, and that its numbers often increase dramatically in mid-summer after orchards are treated with carbamate insecticide for scarab beetle infestations. Similar observations by Croft et al. (1987) from work with apples underscore the potential consequences of inadvertently shifting the predator/phytophagous mite balance to favour the plant-feeding mites. ERM overwinters in the egg stage on host trees. Eggs are dark red in colour, slightly ﬂattened, with a hair-like spine that projects up from the centre (Hogmire, 1995). The eggs begin to hatch as peaches leaf out, and the resultant nymphal mites move directly to foliage. As is the case with TSM, ERM passes through a six-legged larval stage, followed by two eight-legged nymphal stages before moulting to an eight-legged adult. ERM adults are similar in size to TSM, but are a dark brick-red colour, with long curved dorsal hairs projecting from whitish spots on the mites’ back (Hogmire, 1995). As is the case with TSM and silver mite, the presence of stable, low numbers of ERM populations should be viewed positively, because non-injurious, low-level infestations provide a food source for predacious complexes that

Fig. 18.31. European red mite adult. (Courtesy of INRA, Montepellier, France.)

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normally provide biological control of these species in peaches (Strand, 1999). Management of ERM in many peach orchards is aided by one to two dormant oil applications made for scale control. Infestations can normally be monitored by being alert for foliage that is off-colour or stippled. The work of McClernan and Marini (1986)

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noted that outbreaks of ERM do occur on peach, but that ERM is a minor pest that should be dealt with as needed using curative miticide treatments. Treatments, particularly those made late in the season, are often made for the comfort of harvesters who sometimes suffer dermal irritation from disoriented mites that crawl over their skin.

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Nematodes

A.P. Nyczepir1 and D. Esmenjaud2 1USDA-ARS,

Southeastern Fruit and Tree Nut Research Laboratory, Byron, Georgia, USA 2INRA, UMR ‘Interactions Biotiques et Santé Végétale’ (IBSV), 400 Route des Chappes, F-06560 Sophia-Antipolis Cedex, France

19.1 Introduction 19.2 Root-knot Nematodes Species Speciﬁc identiﬁcation and polymorphism Symptoms Biology Survival and dissemination Economic importance Environmental factors Host range Control 19.3 Ring Nematodes Species Symptoms Biology Survival and dissemination Economic importance Disease complexes Host range Control 19.4 Root-lesion Nematodes Species Symptoms Biology Survival and dissemination Economic importance Disease complexes Host range Control 19.5 Dagger Nematodes Species Symptoms

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© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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Biology Nepovirus diseases Survival, dissemination and host range Economic importance Methods of diagnosis Control 19.6 Other Nematodes 19.7 Outlook

19.1 Introduction Nematodes are microscopic, true roundworms that are non-segmented and have bilateral symmetry and no appendages (Hirschmann, 1971). Most plant-parasitic nematodes are generally thread-like in shape (at least during one of their life stages) and range from 0.4 mm (e.g. Meloidogyne, Mesocriconema and Pratylenchus spp.) to 5 mm in length (e.g. Xiphinema spp.). Plant-parasitic nematodes are associated with many forms of plant life including orchard crops such as peach (Prunus persica (L.) Batsch). Due to their soil localization and their non-speciﬁc above-ground symptoms, the presence of nematodes and their economic importance to the fruit industry are frequently ignored and underestimated. Nematodes, if not managed, can cause some of the most important rootstock diseases of peach, contributing to reduced yield and vigour and even tree death. Successful nematode management in peach begins with site selection. A preferred site is one which is suitable for peach culture and does not have a history of stone fruit or nematode problems. If nematode-free sites are not available, then nematode problems need to be identiﬁed and proper management practices implemented. Recommended control practices include preplant and post-plant nematicide application, resistant rootstocks, cultural practices and biological control agents, when available. Additionally, proper sanitation is recommended to prevent reinfestation of treated sites and nematode-free and certiﬁed virus-free rootstocks should be planted to circumvent any future problems. There are several nematode genera known to be associated with causing severe losses in peach orchards worldwide. This chapter

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focuses on four major nematode pests of peach: root-knot (Meloidogyne spp.), ring (Mesocriconema spp.), root-lesion (Pratylenchus spp.) and dagger (Xiphinema spp.) nematodes.

19.2 Root-knot Nematodes Root-knot nematodes, Meloidogyne spp., are considered to be the most damaging nematodes in the world and are distributed in the temperate, tropical and equatorial areas (Lamberti, 1979; Sasser, 1979; Sasser and Freckman, 1987). Root-knot nematodes reduce fruit production in several economically important Prunus species, including peach.

Species The three predominant root-knot nematode species affecting Prunus species are Meloidogyne arenaria, Meloidogyne incognita and Meloidogyne javanica, all of which feed on many hosts (polyphagous) and reproduce asexually via parthenogenesis. The northern root-knot nematode, Meloidogyne hapla, develops poorly on Prunus spp. (Esmenjaud et al., 1994). A more recently described species, Meloidogyne hispanica (Hirschmann, 1986; Esmenjaud et al., 1994), appears to be restricted to the southern part of the Iberian Peninsula, but is destructive when present (C. Scotto La Massèse, France, 1992, personal communication). As with other plant species, host suitability tests performed on Prunus rootstocks in different countries show high variations in aggressivity among the populations (Pinochet et al., 1989, 1992; Marull and Pinochet, 1991; Esmenjaud et al., 1994; Fernández et al., 1994a).

Nematodes

A less prominent Meloidogyne sp. was reported on peach in Florida in the 1960s (Sharpe and Perry, 1967; Sharpe et al., 1969) as overcoming the resistance of ‘Nemaguard’ and ‘Okinawa’ rootstocks (Fig. 19.1/Plate 217). This nematode had initially been identiﬁed as M. incognita race 3 (Sherman et al., 1981; Sherman and Lyrene, 1983) and produces smaller galls that do not coincide and are more aligned on the rootlets than those of the parthenogenetic species. Recently this isolate was described as a new species and named the ‘peach root-knot nematode’, Meloidogyne floridensis Handoo (Handoo et al., 2004). From phylogenetic analysis, M. floridensis was intermediate between two distinct and individualized groups: M. arenaria, M. incognita and M. javanica, on the one hand and M. hapla on the other. Although the distribution of this new species is unknown (Nyczepir et al., 1998b), M. floridensis has been detected in several areas in Florida (W. Sherman, Florida, 2004, personal communication).

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galling symptoms. Therefore, integrated tools were developed for nematode identiﬁcation such as morphological and morphometrical characters (Golden, 1976; Eisenback et al., 1981) in conjunction with electrophoresis (i.e. esterases) (Janati et al., 1982; Esbenshade and Triantaphyllou, 1985, 1990). The study of the nucleus has shown high variations in the number of chromosomes due to polyploidy and aneuploidy (Triantaphyllou, 1971, 1985), suggesting that each species is composed of clones. Moreover, a low genetic polymorphism was observed among these species, which is related to their parthenogenetic reproduction (Dalmasso and Berge, 1975, 1978). Molecular data have conﬁrmed the previous separation of species (Piotte et al., 1992; Castagnone-Sereno et al., 1993; Powers and Harris, 1993; Petersen et al., 1997; Randig et al., 2001) and simpliﬁed molecular diagnosis is now possible by PCR using speciﬁc primers from ribosomal genes (Zijlstra, 1997; Zijlstra et al., 2000) that allows direct identiﬁcation of M. arenaria, M. incognita and M. javanica from a single juvenile nematode (i.e. J2).

Specific identification and polymorphism Symptoms Species identiﬁcation among the parthenogenetic root-knot nematodes cannot be differentiated on the basis of below-ground root

The nematodes belonging to this genus have a sedentary endoparasitic feeding habit.

Fig. 19.1. Galls on ‘Okinawa’ (A) and ‘Nemaguard’ (B) peach roots caused by Meloidogyne floridensis. (Courtesy of W.B. Sherman, Gainesville, Florida, USA.)

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Attacks by root-knot nematodes on peach often cause typical below-ground root galls (Fig. 19.2/ Plate 218) and the associated above-ground stunted growth of young peach trees. Attacks during early root development may lead to extensive tree death across an orchard. Additional above-ground symptoms include a reduction in tree vigour and early defoliation, which ultimately results in yield reduction. Symptom expression is enhanced in sandy soils, especially when trees are exposed to drought conditions. Extensive galling has sometimes been observed without associated reductions in tree vigour or stunted growth (Bertrand, 1985). In such cases, it is believed that the orchard was established on a site with low initial soil population levels of Meloidogyne, thus allowing the tree to develop a more extensive root system. Biology Meloidogyne spp. are extremely polyphagous and can parasitize hundreds of plant species

(a)

(c)

from numerous botanical families (de Guiran and Netscher, 1970; Sasser, 1979). M. arenaria, M. incognita and M. javanica are mitotic and reproduce exclusively by parthenogenesis (Triantaphyllou, 1971, 1985), and have thus been designated as the parthenogenetic Meloidogyne complex. The reproductive life cycle is summarized in Fig. 19.3/Plate 219. Eggs are deposited in gelatinous egg masses and can survive in the soil or on plant residues. The mobile second-stage juveniles (J2) hatch directly from the egg and move to root tips, where they penetrate and migrate intercellularly within root tissues. The J2 initiate feeding cells in the region of what will become the vascular area, where they develop into swollen third- and fourth-stage juveniles. They ﬁnally develop into sedentary adult females which can each lay several hundred eggs in a single egg mass, usually positioned exterior to the root surface. Adult females feed with their protruded stylet, which perforates the cell wall but not the cell plasma membrane. Feeding juveniles and adults induce the formation of a few ‘giant cells’ (‘feeding sites’)

(b)

Fig. 19.2. Galls on peach (a and b) and Myrobalan plum (c) roots caused by root-knot nematode (RKN), Meloidogyne sp. Severe early symptoms (a); root decay following an attack (b); two Myrobalan plum individuals from a progeny segregating for the Ma RKN resistance gene (left, host; right, resistant) (c). (Photos by A.P. Nyczepir (a) and D. Esmenjaud (b,c).)

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Fig. 19.3. Reproductive life cycle of Meloidogyne spp. (N = female nematode; *= giant cells). (Courtesy of INRA, Sophia-Antipolis, France.)

around the nematode head along with the multiplication of cells surrounding cortical and vascular parenchyma. Nutrient uptake by root-knot nematodes suppresses plant development. The parasitism of the plant by the rootknot nematode described above is a compatible interaction. In certain plant species, Meloidogyne do not develop on all accessions and an incompatible interaction results. In Prunus, resistant rootstocks have been detected but few studies have been conducted on the characterization of the resistance mechanisms involved. For instance, in Myrobalan plum, M. arenaria J2 penetrated resistant and host accessions (carrying or lacking, respectively, the Ma gene for resistance to Meloidogyne spp.) (see section on ‘Resistance’ below) and showed an equivalent early penetration of the nematodes into the roots during the 48 h after their inoculation into the soil. The J2 numbers increased rapidly in the host accession, but decreased slowly in the resistant accessions (Voisin et al., 1999). The results substantiate the hypothesis that parasitized cells of the resistant accessions express a hypersensitive reaction to the juveniles. In contrast, a more delayed resistance reaction termed ‘walling off’ allows the J2 to penetrate

roots and form small galls, but prevents maturation and reproduction. Such a phenomenon was observed with M. javanica in the resistant peach stocks of ‘Nemared’ and ‘Okinawa’ (Malo, 1967; Marull et al., 1994) and with M. incognita in ‘Guardian®’ (Nyczepir et al., 1999).

Survival and dissemination Root-knot nematodes survive as eggs grouped in egg masses. At this stage, they may survive for several years in the soil under Mediterranean and temperate conditions. This persistence during unfavourable conditions is attributed to an egg diapause (de Guiran, 1979; de Guiran and Villemain, 1980). These polyphagous nematodes can also develop on numerous annual crops including weed species associated with the orchard ﬂoor (de Guiran and Netscher, 1970; Sasser, 1979). Nematodes are readily disseminated by the use of nematodeinfected nursery stock. Seedlings or rooted cuttings constitute the most effective longdistance way of disseminating these pests. Because of the increasing exchange of plant material at national and international levels,

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populations originating from distant geographic origins are expected to be extensively mixed. Nevertheless, such dissemination should be limited by the increased use of certiﬁed nematode-free plant material. Economic importance Peach production is negatively inﬂuenced by the presence of Meloidogyne spp. In South Carolina, USA the use of either a pre-plant fumigant or ‘S-37’ resistant rootstock increased peach yields in Meloidogyne-infested soil compared with the untreated check (Foster et al., 1972). In Georgia, USA, pre-plant fumigation with methyl bromide to control Meloidogyne spp. increased yield in the third to ﬁfth growing seasons of ‘Redhaven’ on ‘Lovell’ rootstock by 2535 kg/ha (Sharpe et al., 1993). In Spain as well as in North Africa, root-knot nematodes are involved in replant disease and tend to be a serious problem in warm, well-drained sandy soils. The development of speciﬁc replant problems caused by root-knot nematodes in these regions has been attributed to the high degree of rootstock susceptibility to Meloidogyne spp. (Calvet et al., 2000). Environmental factors Meloidogyne spp. are very damaging pests of stone fruits especially when cultivated on sandy soils (Stirling, 1975). Plant damage is increased under drought conditions and high soil temperature favours nematode parasitism of the rootstock (Canals et al., 1992; Fernández et al., 1994b). In water-saturated soils, hatching of juveniles is inhibited (Baxter and Blake, 1969). Nematodes have been shown to facilitate penetration of the bacterium Agrobacterium tumefaciens into the root tissues and the subsequent development of symptoms of crown gall in almond (Orion and Zutra, 1971), peach (Dhanvantari et al., 1975) and plum (RubioCabetas et al., 2001) (Fig. 19.4/Plate 220). M. incognita in combination with Fusarium oxysporum has been shown to reduce growth of peach seedlings more than either organism alone (Wehunt and Weaver, 1972).

Host range Root-knot nematodes parasitize a wide range of plant species that are either crop plants (annuals or perennials) or weeds. Among Prunus, rootstocks may express differing host susceptibilities such as those summarized in Table 19.1.

Control Control measures must be applied against root-knot nematodes in both the plant and soil. After their introduction into the orchard, eradication of nematodes from soil is difﬁcult. Therefore, management strategies rely on the combination of different methods to keep the nematode density below economic damage levels (Bernhard et al., 1985). Pre- and postplant chemical nematicides have been shown to be effective tools in managing root-knot nematodes in peach. However, because most of the nematicides are being progressively removed from the market, alternatives to chemical control methods are encouraged (Batchelor, 2002). For example, methyl bromide has been associated with atmospheric ozone depletion, which has resulted in a ban (according to the 1992 Montreal Protocol) on its importation and manufacture in the USA and Western Europe since January 2005 (Clean Air Act, 1990). Additionally, the manufacturer of fenamiphos, the one remaining recommended post-plant nematicide on peach in the south-eastern USA, was voluntarily cancelled of all product registrations effective from 31 May 2007 (Anon., 2003). Nematicides Root-knot nematodes can be controlled by preplant soil fumigation plus post-plant application of non-fumigant nematicides. Because state/country recommendations for nematicide use are not the same and change frequently, current local sources of information need to be consulted for updated recommendations. Rotation It is recommended to plant a non-host such as cereal grains or leave the soil fallow prior to

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Fig. 19.4. Galls on Myrobalan plum root caused by the association of Meloidogyne spp. and Agrobacterium tumefaciens (crown gall). (Photo by D. Esmenjaud.)

planting a peach orchard in order to suppress nematode populations to undetectable levels (McKenry, 1985). However, weeds also must be controlled because many of them are good hosts for root-knot nematodes, thus allowing them to survive between successive orchards (McKenry, 1985; Nyczepir and Halbrendt, 1993). Resistance The most economic and environmentally sound method for managing Meloidogyne in Prunus species is the use of resistant rootstocks (Cook and Evans, 1987; Layne, 1987). The search for peach rootstock resistance began in the USA (Tufts, 1929; Day and Tufts, 1939; Weinberger et al., 1943) but has since been investigated and documented in other countries (Kochba and Spiegel-Roy, 1976; Scotto La Massèse et al., 1984; Fernández et al.,

1994a; Pinochet et al., 1999). A summary of Prunus rootstock reactions to Meloidogyne spp. is reported in Table 19.1. The impact of root-knot nematodes on peach has justiﬁed speciﬁc breeding efforts. In the USA, breeding programmes have focused mainly on the creation of peach or peach– almond rootstocks using peach germplasm (such as ‘Nemaguard’ and ‘Okinawa’) as the resistance sources. For example, ‘Nemared’ (Ramming and Tanner, 1983) used ‘Nemaguard’ as its source of resistance, whereas ‘Hansen 2168’ and ‘Hansen 536’ (Kester and Asay, 1986) and ‘Flordaguard’ (Sherman et al., 1991) both relied on ‘Okinawa’ and Prunus davidiana. The source of root-knot nematode resistance in ‘Guardian®’ comes from ‘Nemaguard’ and ‘S-37’ (Okie et al., 1994a). In Europe, an extensive evaluation of known or new germplasm sources that include many new selections of peach-based hybrids has been

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Table 19.1. Reaction of rootstocks used for peach to root-knot (Meloidogyne spp.), root-lesion (Pratylenchus spp.) and ring (Mesocriconema xenoplax) nematodes. (From Westcott and Zehr, 1991; Pinochet et al., 1992; Nyczepir and Halbrendt, 1993; Okie et al., 1994b; Alcaniz et al., 1996; Esmenjaud et al., 1997; Nyczepir et al., 1999; Nyczepir and Beckman, 2000; Nyczepir and Pinochet, 2001; D. Esmenjaud, France, 2007, personal communication.) Nematodesa Species/accession Peach Prunus persica ‘Bokhara’ ‘B-S6’ ‘Cadaman’ ‘Elberta’ ‘Flordaguard’ ‘GF 305’ ‘Guardian®’ ‘Harrow Blood’ ‘Lovell’ ‘Missour’ ‘Montclar’ ‘Nemaguard’ ‘Nemared’ ‘Okinawa’ ‘Rancho Resistant’ ‘Rubira’ ‘Rutgers Red Leaf’ ‘S-37’ ‘Shalil’ ‘Siberian C’ ‘Yunnan’ Almond–peach hybrids Prunus dulcis × P. persica ‘Adafuel’ ‘Alcaniz’ ‘Bergasa’ ‘Cachirulo’ ‘Felinem’ ‘Fermoselle’ ‘Garnem’ ‘GF 557’ ‘GF 677’ ‘Hansen 2168’ ‘Hansen 536’ ‘Titan’ (hybrids) P. persica × Prunus belsiana ‘Citation’ Plums Prunus cerasifera ‘Myrabi’ ‘Myrobalan P-2175’

Origin

Propagation

MA

MI

MJ

USA Italy France Australia USA France USA Canada USA Tunisia/ Morocco France USA USA USA USA France USA USA USA Canada USA

Seedling Seedling Seedling Seedling Seedling Seedling Seedling Seedling Seedling Seedling

Rb

R MR? R H

H

Spain Spain Spain Spain Spain Spain Spain France France USA USA USA

Cutting Cutting Cutting Seedling Cutting Cutting Cutting Cutting Cutting Cutting Cutting Seedling

USA

Cutting

France France

Cutting Cutting

Seedling Seedling Seedling Seedling Seedling Seedling Seedling Seedling Seedling Seedling Seedling

R

R/H

R R R H

R/H R H H

H R R R R H H R R

MF

R H H R/H

Pp

Pv

Mx

H T H H

H H H H H H H

H T H H

H

H H

H R H H

H H

H

R/H R/H R H

H H H

H H/T

H

H H H

R

H

H H H

H H H

H H

R H R R H R R R

R H R R H R R R

R R/H H R/H H H R R R

H

H R

H H H H H H

H

H H H H H

H

H

R

H R

H H H H

H

H R

H R (Continued)

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Table 19.1.

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continued Nematodesa

Species/accession

Origin

Propagation

MA

MI

MJ

MF

R

R R H H MR

R R H

R

‘Myrobalan P-2980’ ‘Myrobalan 29C’ ‘Myrobalan franc’ ‘Myrobalan 605’ ‘Myrobalan B’ P. cerasifera × Prunus salicina ‘GF 31’ P. cerasifera × Prunus munsoniana ‘GF 8-1’ ‘Marianna 2624’ ‘Redglow’ Prunus domestica ‘Brompton’ ‘Damas’ ‘GF 43’ ‘Torinel’ P. domestica × Prunus spinosa ‘GF 1869’ Prunus insititia ‘Montizo’ ‘PSM 101’ ‘Saint Julien 655-2’

France USA France Spain UK

Cutting Cutting Seedling Cutting Cutting

France

Cutting

France USA USA

Seedling Cutting Cutting

R R

R R

R R

UK France France France

Cutting Cutting Cutting Cutting

R R H R

R R H R

R R H R

MR

France

Cutting

Spain Spain France

Cutting In vitro Cutting

R

H H H

H

Pp

Pv

Mx

H H H

R

H

H MR

R R R R

R R R

aMA,

Meloidogyne arenaria; MI, Meloidogyne incognita; MJ, Meloidogyne javanica; MF, Meloidogyne floridensis; Pp, Pratylenchus penetrans; Pv, Pratylenchus vulnus; Mx, Mesocriconema xenoplax. bR, resistant; MR, moderately resistant; H, host; T, tolerant.

performed to characterize resistance in parent material according to their: (i) spectrum of activity (Marull et al., 1994; Pinochet et al., 1996a); (ii) tolerance to high population levels (Esmenjaud et al., 1996a,b, 1997); (iii) heat stability (Canals et al., 1992; Fernández et al., 1994b); and (iv) inﬂuence of age of the plant on resistance expression (Fernández et al., 1995). Resistance in tested peach and almond cultivars is not complete and does not control M. floridensis (Esmenjaud et al., 1997) (Table 19.2). However, ‘Flordaguard’ has been reported to be tolerant to this nematode, but its spectrum of genetic resistance is currently unknown (Sherman et al., 1991). In contrast, Myrobalan plum (Prunus cerasifera from the subgenus Prunophora, grouping plums and apricot) comprises certain clones that also resist M. floridensis and carry a complete spectrum and high level of resistance to other Meloidogyne

spp. (Esmenjaud et al., 1996a, 1997). Some of these clones impart favourable agronomic features for peach scions such as broad graft compatibility and high adaptation to waterlogged soils (Kester and Grasselly, 1987; Layne, 1987; Salesses et al., 1992). In Myrobalan plum, resistance to M. arenaria, M. incognita, M. javanica and M. floridensis is conferred by the single major gene Ma, which behaves as completely dominant in the accessions ‘P-2175’ (allele Ma1, heterozygous) (Esmenjaud et al., 1996b; Lecouls et al., 1997) and ‘P-2980’ (allele Ma3, heterozygous) (Rubio-Cabetas et al., 1998) (Table 19.2). This gene also controls Meloidogyne mayaguensis (Rubio-Cabetas et al., 1999), a species of tropical origin that overcomes the resistance conferred by the Mi gene from tomato (Rammah and Hirschmann, 1988; Fargette et al., 1996), and M. hispanica (Stalin et al., 1998).

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Table 19.2. breeding.

Spectrum of resistance of main sources to root-knot nematodes used in Prunus rootstock

Resistance status toa Accession

MA

MI

MJ

MF

Amygdalus Peach (Prunus persica) ‘Shalil’ ‘GF 557’ (= almond × ‘Shalil’) ‘GF 557’

Rc

R

H

H

‘Nemaguard’

Resistance gene and genotype

References

RMia557 gene controlling MA and MI

Esmenjaud et al. (1994, 1997)

(RMia557/rMia557)

Claverie et al. (2004)

RMiaNem gene controlling MA and MI

‘Nemaguard’

R

R

R/Hd

H

(RMiaNem/RMiaNem)

Esmenjaud et al. (1997)

‘Nemared’

R

R

R/H

H

(RMiaNem/RMiaNem)

Claverie et al. (2004)

‘Rubira’b

H

H

H

H

(rMiaNem/rMiaNem)

R R H

Ma gene controlling MA, MI, MJ and MF (Ma1/ma) (Ma3/ma) (ma/ma)

Prunophora Myrobalan plum (Prunus cerasifera) ‘P-2175’ ‘P-2980’ ‘P-2032’b

R R H

R R H

R R H

Esmenjaud et al. (1994; 1996b, 1997); Lecouls et al. (1997); Rubio-Cabetas et al. (1999)

aMA,

Meloidogyne arenaria; MI, Meloidogyne incognita; MJ, Meloidogyne javanica; MF, Meloidogyne floridensis. bHost control accession. cR, resistant; H, host. dR/H, variable behaviour in function of M. javanica isolates.

In ‘Shalil’ and ‘Nemared’ peach, the genetics of resistance is still not clear and at least one major gene for resistance to both M. arenaria and M. incognita, designated RMia, has been reported and shown to be independent from the Ma gene (Claverie et al., 2004). Yamamoto and Hayashi (2002) have also reported two tightly linked genes controlling either M. incognita alone (Mia) or M. javanica (Mja) in the Japanese accession ‘Juseitou’. The SCAR (sequence characterized ampliﬁed regions) markers designed by these authors for Mia were closely linked to the RMia gene (Claverie et al., 2004). Consequently, the RMia and Mia genes from peach are presumably the same. In contrast, the corresponding Mi (for M. incognita) and Mij genes (for both M. incognita and M. javanica) obtained by Lu et al. (1999, 2000) in ‘Nemared’ were only found distantly linked to RMia (Claverie et al., 2004).

Based on the Ma and RMia genes, a breeding programme for new Meloidogyne-resistant rootstocks for stone fruits is being developed in France in collaboration with Spain and Italy. Interspeciﬁc rootstocks of the type Myrobalan × peach, Myrobalan × almond or Myrobalan × almond–peach have been created in order to pyramid at least one Ma allele and one resistance gene from peach. Their selection is in progress for complementary adaptative characteristics putatively inherited from their parents (tolerance to waterlogging, drought and chlorosis). Several SCAR markers co-segregate with the Ma gene and are available for marker-assisted selection for all interspeciﬁc crosses carrying this gene (Lecouls et al., 1999, 2004; Dirlewanger et al., 2004). This development can enable highly efﬁcient procedures for evaluating woody plants for Meloidogyne spp. resistance. The Ma

Nematodes

gene has also been demonstrated to have a protective effect against A. tumefaciens when its expression follows root-knot nematode attacks (Rubio-Cabetas et al., 2001). This protective effect of Ma and presumably of other root-knot nematode resistance genes against Meloidogyne-transmitted crown gall is an additional argument for their introgression into Prunus rootstocks. Additional peach rootstock programmes that evaluate germplasm for resistance to root-knot nematodes using different selection criteria are currently under way in other countries (Reighard, 2002).

19.3 Ring Nematodes Species Ring nematodes are widely distributed throughout the world with certain species considered to be economically important to the peach industry. The two most important ring nematode species associated with peach decline diseases are Mesocriconema xenoplax (Raski) Loof & de Grisse and Mesocriconema curvatum (Raski) Loof & de Grisse (Nyczepir, 2001; Nyczepir and Becker, 1998). Of less importance is Mesocriconema rusticum (Micoletzky) Loof & De Grisse, which Jaffee et al. (1987b) reported on peach in Pennsylvania, USA.

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Symptoms Ring nematodes are ectoparasites. ‘Nemaguard’ peach parasitized by M. xenoplax was characterized by a lack of feeder roots (Fig. 19.5/Plate 221) (Nyczepir et al., 1987). Extensive pits and lesions were observed on cultured peach seedling roots parasitized by M. curvatum (Hung and Jenkins, 1969). In the south-eastern USA, peach trees parasitized by M. xenoplax are predisposed to cold injury and bacterial canker infection (Pseudomonas syringae pv. syringae van Hall) or a combination of both. This disease complex is termed peach tree short life (PTSL) (Brittain and Miller, 1978; Nyczepir, 1990). Late winter/early spring temperature ﬂuctuations are associated with PTSL. In California, M. xenoplax also predisposes peach trees to bacterial canker infection, a disease complex termed bacterial canker complex (BCC) (McKenry, 1989) (see section on ‘Disease complexes’ below). Typical above-ground PTSL symptoms commonly occur when trees are 3–6 years of age, although younger or older trees have been reported to be affected. Symptoms occur suddenly in the spring with developing leaves collapsing as if deprived of water, ultimately resulting in premature death of the tree. One or two branches may be stricken,

Fig. 19.5. Influence of Mesocriconema xenoplax (Mx) on ‘Nemaguard’ peach feeder root growth after 6 months ((–) Mx, uninoculated; (+) Mx, inoculated, Pi = 14,000 nematodes/1500 cm3 soil, where Pi is initial nematode population density). (Photo by A.P. Nyczepir.)

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but frequently the entire tree collapses (Brittain and Miller, 1978). In severe cases, neither ﬂower nor leaf buds open at all. Bacterial canker infection is generally linked with delay of bloom or foliation of individual limbs, which usually die during the summer. If infection is severe, entire trees may collapse with branches exhibiting alternate zones of darkened and healthy tissue with the presence of a sour sap odour (Fig. 19.6/ Plate 222). Since the soil buffers low temperature ﬂuctuations, dead trunk tissue usually does not extend below the soil line, thus leaving the primary root system alive (Fig. 19.7/ Plate 223). Suckers are usually produced at the tree crown during summer, resulting from the live primary root system (Fig. 19.6/Plate 222). In BCC, limbs and entire trees infected by P. syringae die in the spring. With the presence of cold injury, trees begin to leaf out until additional water is required by the tree. It is at that time the leaves collapse and the bark may crack and separate from the scaffold limbs and tree trunk. Shepard et al. (1999) reported that M. xenoplax also was responsible for predisposing

peach trees (cv. ‘Suwanee’) to bacterial spot (Xanthomonas arboricola pv. pruni) (see Chapter 16). Trees growing in M. xenoplax-infested soil exhibited more severe bacterial spot damage than trees in soil where the nematode populations had been suppressed.

Biology M. xenoplax completes its life cycle in 25–34 days at 22–26°C, under laboratory conditions (Seshadri, 1964). Nematode life stage development requires 11–13 days for egg, 3–5 days for J2, 4–7 days for J3, 5–6 days for J4, and 2–3 days for adult. Gravid females lay 8 to 15 eggs over a 2–3-day period. Eggs are deposited in close proximity to host roots or on the root surface. Sixty-six per cent of M. xenoplax eggs were observed to hatch between 13°C and 32°C, and aborted at temperatures above 32.5°C (Westcott and Burrows, 1991). Reproduction is presumed to be primarily by parthenogenesis, since males are rarely found. Feeding is required for juveniles to moult and

Fig. 19.6. Dead peach tree with suckers at the crown during summer in the presence of Mesocriconema xenoplax and the peach tree short life disease complex. (Photo by A.P. Nyczepir.)

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Fig. 19.7. Typical cambial tissue damage of the trunk above the soil line and healthy viable tissue below the soil line in tree dying from peach tree short life disease. (Photo by A.P. Nyczepir.)

for oocyte maturation in adult females. Feeding activity of M. xenoplax occurs along peach roots and root tips (Thomas, 1959). Unlike other ectoparasitic feeders, this ring nematode was reported to feed from a single root cortical cell for up to 8 days with no necrotic tissue development at the feeding site (Westcott and Hussey, 1992). Individual cortical cells were modiﬁed by M. xenoplax into discrete ‘food cells’ in order to sustain ingestion of food for long periods of time (Hussey et al., 1992). M. xenoplax reproduces faster in sandy soils than in loam or silty loam soils and prefers soil temperatures ranging from 22°C to 26°C (Seshadri, 1964; Stirling, 1975). Ring nematode populations also were reported to be higher in wetter soils (i.e. 15.5% moisture) than in soils that were drier (i.e. 11.6% and 7.8% moisture) (Seshadri, 1964).

to transplants. M. xenoplax generally prefers woody perennials, but this nematode can also survive on weeds found in peach orchards in the south-eastern USA (Seshadri, 1964; Zehr et al., 1990).

Economic importance Tree loss due to PTSL varies among years. Miller (1994) estimated losses during 1980– 1992 as over $6 million per year in South Carolina alone. Managing M. xenoplax on a known PTSL site, following pre-plant methyl bromide fumigation, in a test orchard during its third to ﬁfth year of production resulted in 20% greater yields in fumigated compared with unfumigated soil (Sharpe et al., 1993).

Survival and dissemination Disease complexes Unlike root-knot nematode, dissemination of ring nematodes occurs primarily via infested soil transported on farm equipment and the feet of animals, in water, and in soil clinging

Since the late 1600s, the unsatisfactory performance of trees grown on sites where peach trees were previously removed, commonly

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referred to as replant sites, has plagued peach growers (Brittain and Miller, 1978). In the south-eastern USA a speciﬁc type of disease complex problem exists which has been termed PTSL (see above). It has been clearly demonstrated through long-term research that the ring nematode, M. xenoplax, is a key biotic component of the PTSL disease complex (Nyczepir et al., 1983). Equally important was the discovery that other plant-parasitic nematodes such as the root-knot nematode, M. incognita, do not play a role in PTSL tree death (Nyczepir et al., 1997). Furthermore, it was established that a reduction in tree growth was more severe with trees growing in the presence of both of these nematode species. M. incognita appears to be the more dominant nematode species in this interaction and is a stronger competitor than M. xenoplax for food on ‘Lovell’ peach roots. Severity of PTSL in orchards infested with M. xenoplax increases and orchard lifespan decreases with each successive peach planting (Nyczepir and Okie, 1996). In a follow-up study, Nyczepir et al. (2004a) were able to create a PTSL site on land with no known history of peach production, 3 years after M. xenoplax introduction. It appears that development of PTSL varies with exposure of trees to the cumulative population of M. xenoplax. In South Africa, peach trees parasitized by a concomitant infestation of M. xenoplax and M. javanica defoliated 3 to 4 months before natural leaf drop (Hugo and Meyer, 1995). In California, M. xenoplax has been associated with increasing the susceptibility of peach trees to BCC (McKenry, 1989). An important distinction between PTSL and BCC is that cold injury is not typically associated with bacterial canker tree death in California, even though BCC is more likely to occur in cold spots within an orchard. It is also important to note that the California ‘replant problem’ as described by McKenry (1999) is not the same as the PTSL or BCC disease complexes described above. This ‘replant problem’, which is known to occur worldwide, is associated with leaf yellowing and tree stunting following the replanting of a site within several years of removing the previous orchard (http://www.uckac.edu/nematode/).

Host range M. xenoplax prefers woody perennials to annuals, with some exceptions (Seshadri, 1964; Zehr et al., 1986, 1990). Peach rootstock reaction to M. xenoplax is summarized in Table 19.1. All tested materials are hosts to the nematode, except ‘Guardian®’ peach, which is tolerant.

Control Nematicides Ring nematodes can be controlled by pre-plant soil fumigation and post-plant application of non-fumigant nematicides. Because state/ country recommendations for nematicide use are not the same and change frequently, current local sources of information need to be consulted for updated recommendations. Under South Carolina, USA ﬁeld conditions, a nematicide treatment threshold of >50 M. xenoplax/100 cm3 soil is recommended in peach orchards for prolonging tree life on PTSL sites (E.I. Zehr, South Carolina, 2005, personal communication). In Georgia, the nematicide treatment threshold is ≥1 M. xenoplax/100 cm3 soil (Nyczepir and Halbrendt, 1993; Davis et al., 1996). In North Carolina, it was estimated that PTSL tree death was likely at average cumulative population densities of 38–83 M. xenoplax/100 cm3 soil (Ritchie, 1988). It is important to note that extraction efﬁciency of M. xenoplax from sandy soils can be improved if the dry soil is ﬁrst moistened and allowed to stand for up to 7 days before extracting the nematode (Lawrence and Zehr, 1978). Cultural practices In the early 1970s, a 10-Point Management Program was developed and recommended to peach growers in the south-eastern USA to help reduce tree losses from PTSL (Brittain and Miller, 1978; Ritchie and Zehr, 1995). It is important to note that this programme is not a cure for PTSL, but rather a management scheme for the disease complex. One of the major points to this programme is pre- and

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post-plant soil fumigation as a management strategy for M. xenoplax. However, a continued reduction in the availability of chemical nematicides as a result of apprehension associated with potential environmental problems is leaving growers with fewer nematode management options (e.g. methyl bromide and fenamiphos – see control of root-knot nematodes above). Therefore, ﬁnding a cost-effective and environmentally safe alternative to chemical control of ring nematodes is warranted. Alternatives to chemical control for nematode management have been explored over the past 14 years with some promising results. Several ground covers appear promising as either pre-plant or post-plant management strategies for M. xenoplax. Nimblewill (Muhlenbergia schreberi J. Gmelin) planted around peach trees suppressed populations of M. xenoplax without being highly competitive for nutrients and water (Meyer et al., 1992; Nyczepir and Bertrand, 2000). Two disadvantages in using nimblewill are that: (i) it supports reproduction by M. javanica and M. arenaria, and to a lesser extent M. incognita (McKenry, 1990; A.P. Nyczepir, 1995, personal observation); and (ii) since it is a cool-season grass, nimblewill establishment in the south-eastern USA peach orchards (i.e. Georgia and South Carolina) has proved difﬁcult (Olien et al., 1994; A.P. Nyczepir, 2004, personal observation). In Georgia, chemically mowed bahiagrass (Paspalum notatum Flugge) sod previously grown in orchard row middles infested with M. xenoplax suppressed the nematode population density after 3 years (Nyczepir and Bertrand, 2000). When peach trees were planted into the killed-sod row middles they generally grew better in the killed bahiagrass sod, but tree survival was no different from that in unfumigated weed ground cover soil on a PTSL site. Additionally, wheat alone or double-cropping wheat (Triticum aestivum L. emend. Thell cv. ‘Stacy’) and sorghum (Sorghum vulgare Pers. cv. ‘NK2660’) for 3 years was as effective as pre-plant methyl bromide fumigation in suppressing M. xenoplax populations and prolonging tree survival on a PTSL site (Nyczepir and Bertrand, 2000; Nyczepir, 2003a). In southern Brazil, selected double-crop rotation schemes which include

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alternating summer and winter non-host plants have also shown promise in managing M. xenoplax and Meloidogyne spp. in peach orchards and nurseries (Carneiro et al., 1998). Interplanting wheat (i.e. after orchard establishment) around newly planted or 4-year-old well-established peach trees did not suppress M. xenoplax populations after 3 years (Nyczepir et al., 1998a). Besides ‘Stacy’ there are other wheat varieties that suppress ring nematode populations (Nyczepir, 2003b). Integration of a 3-year pre-plant wheat rotation in conjunction with the improved ‘Guardian®’ rootstock are the basis for developing a non-chemical pre- and post-plant recommendation for M. xenoplax management on PTSL sites in the south-eastern USA. Biofumigation is a non-chemical approach of planting various crops which produce breakdown products upon decomposition that are toxic to nematodes, weeds and various soil diseases. Some potential green manure crops include rapeseed, barley, sudangrass and velvetbean. When sorghum was used as a green manure with and without a plastic tarp, it suppressed M. xenoplax populations in the early stages of a 5-year experiment. This suppression, however, did not last as long as pre-plant methyl bromide fumigation (i.e. 19 versus 24 months, respectively) (Nyczepir and Rodriguez-Kabana, 2007). On the other hand, double-cropping rapeseed (Brassica napus L. ‘Humus’) as a green manure and sorghum for 3 years was as effective as pre-plant methyl bromide fumigation in suppressing M. xenoplax populations and prolonging tree survival on a PTSL site (Nyczepir, 2003a). One matter that every grower must decide upon when considering utilizing any pre-plant cultural practice is whether or not that particular practice can be incorporated into their farm operation. For the grower with much available land for peach production this may not be an issue. However, for the growers who have limited land suitable for peach production, this may not be an economically feasible nematode management approach. Resistance ‘Lovell’ and ‘Nemaguard’ are two commonly used peach rootstocks in the USA. Trees on

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‘Lovell’ generally outlive those on ‘Nemaguard’ in the south-east, particularly where M. xenoplax is prevalent; however, both are subject to cold injury, bacterial canker infection and eventual PTSL tree death (Sharpe et al., 1989). ‘Nemaguard’ has been shown to be a better host to M. xenoplax than ‘Lovell’, and this may explain why ‘Lovell’ trees survive longer on PTSL sites (Table 19.1) (Nyczepir, 1990; Beckman et al., 1993). ‘Lovell’ rootstock was the recommended rootstock for south-eastern USA stone fruit growers for over 20 years (1973–1994). ‘Guardian®’, a new commercially available rootstock that tolerates M. xenoplax parasitism, increases scion longevity on PTSL sites compared with ‘Nemaguard’ or ‘Lovell’ rootstocks (Fig. 19.8/Plate 224) (Okie et al., 1994a,b). ‘Guardian®’ has also been reported to be a poor host to some Meloidogyne spp., but not all (Nyczepir et al., 1999, 2006; Nyczepir and Beckman, 2000). Although M. incognita J2 penetrated ‘Guardian®’ roots and formed galls, the majority of the nematodes failed to mature and reproduce (Nyczepir et al., 1999).

Molecular DNA studies are currently under investigation to determine the genetic basis of tolerance in ‘Guardian®’ to M. xenoplax and how this may relate to prolonged tree life on PTSL sites (Blenda et al., 2002, 2006). Biological The endoparasitic fungus, Hirsutella rhossiliensis Minter & Brady, suppressed populations of M. xenoplax in ﬁve of nine controlled experiments (Eayre et al., 1987). Furthermore, amending the soil with KCl did not appear to stimulate fungal parasitism or affect the level of nematode suppression in most tests. Kluepfel et al. (2002) reported that a Pseudomonas sp. (BG33R) isolated from a PTSL suppressive site in South Carolina suppressed M. xenoplax reproduction. Under orchard conditions, ring nematode populations on newly established peach seedlings inoculated with BG33R and planted into solarized soil remained at or below the nematicide treatment threshold for South Carolina for up to

Fig. 19.8. Eight dead 3-year-old peach trees on ‘Nemaguard’ rootstock (foreground) and live trees on all ‘Guardian®’ rootstock (background, same row) in the presence of Mesocriconema xenoplax and the peach tree short life disease complex. (Photo by A.P. Nyczepir.)

Nematodes

2 years (Nyczepir et al., 1998c). Furthermore, it was observed that signiﬁcant and stable qualitative changes in the microbial community induced by soil solarization were correlated with this reduction in M. xenoplax population. In fact, solarization plus BG33R applications and solarization alone were shown to provide effective long-term nematode suppression. In a second orchard trial (D.A. Kluepfel, California, 2004, personal communication), BG33R was delivered to trees through a microsprinkler irrigation system and similar M. xenoplax control was achieved. Nyczepir et al. (2004b) also demonstrated that multiple applications of the entomopathogenic nematodes, Steinernema riobrave Cabanillas, Poinar, & Raulston and Heterorhabditis bacteriophora Poinar, were not effective in suppressing populations of M. xenoplax under controlled conditions for peach in replicated tests. Results with other Mesocriconema spp. have been inconsistent. Smitley et al. (1992) reported that applications of H. bacteriophora did not reduce M. rusticum populations on turf, whereas S. riobrave applications reduced recovery of a Mesocriconema sp. on turf in Georgia (Grewal et al., 1997). One explanation as to why there was a lack of M. xenoplax suppression may be the result of parasitic behaviour. The entomopathogenic nematodes (i.e. Steinernema glaseri) are known to be attracted to root tips, whereas M. xenoplax does not have a partiality towards feeding at any speciﬁc root region other than the root cortex tissue (Thomas, 1959; Bird and Bird, 1986).

19.4 Root-lesion Nematodes Species At least nine root-lesion nematode species have been reported on peach throughout the world, they include: Pratylenchus penetrans (Cobb) Chitwood & Oteifa, Pratylenchus vulnus Allen & Jensen, Pratylenchus pratensis (de Man) Filipjev, Pratylenchus brachyurus (Godfrey) Goodey, Pratylenchus zeae Graham, Pratylenchus convallariae Seinhorst, Pratylenchus neglectus (Rensch) Filipjev & Schuurmans Stekhoven,

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Pratylenchus thornei Sher & Allen and Pratylenchus sefaensis Fortuner from Turkey (Nyczepir and Becker, 1998; Kepenekci, 2001).

Symptoms These nematodes are migratory endoparasites that cause extensive root damage resulting from their intra- and intercellular movement while feeding on cortical cells. Above-ground symptoms can resemble nutrient deﬁciency and include reduced shoot growth and general tree vigour, and a reduction in fruit size. In Georgia USA, Fliegel (1969) reported P. vulnus being associated with reduced peach tree vigour. In Canada, P. penetrans was afﬁliated with peach tree decline (Mountain and Patrick, 1959). Below-ground symptoms of Pratylenchus spp. damage include a reduction in feeder root number, root darkening and necrotic lesions (McKenry, 1989) (Fig. 19.9/Plate 225). Pitcher et al. (1960) related root tissue necrosis following nematode injury to phenol content or the ability of damaged plant cells to synthesize phenols.

Biology Unlike the adult stage of root-knot nematode, Pratylenchus spp. have the capability of both entering and exiting the root. Histological studies of the peach–almond hybrid, ‘G × N No. 1’, revealed that all life stages of P. vulnus were observed in ‘large pockets’ and cavities of living root cortical parenchyma cells (Marull and Pinochet, 1991). Both P. penetrans (Corbett, 1973) and P. vulnus (Corbett, 1974) reproduce sexually. Generally, adult females lay eggs singly within individual living root cells. However, some eggs can be found in necrotic tissue resulting from nematode feeding and movement. The ﬁrst moult occurs in the egg with the second-stage juvenile emerging at hatch. Developing juveniles moult three more times between feeding intervals before becoming adults. Generally, the complete life cycle for P. penetrans is temperature-dependent and varies between 30 and 86 days at 30°C or 20/24°C, respectively.

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Fig. 19.9. Influence of Pratylenchus vulnus on ‘G × N No. 15’ almond–peach hybrid root growth after 24 months (left, uninoculated; right, inoculated, Pi = 1000 nematodes/plant, where Pi is initial nematode population density). (Courtesy of J. Pinochet, Agromillora Catalana SA, Barcelona, Spain.)

Both P. penetrans and P. vulnus are more damaging to plants growing in sandy loam (coarse) than in ﬁner-textured soils (Corbett, 1973, 1974). In Georgia, USA, P. vulnus soil populations were highest from August to December (Fliegel, 1969). Corbett (1973) reported that P. penetrans populations on most crops were highest in late summer and early autumn and lowest in late spring and early summer.

Survival and dissemination P. vulnus is typically found in warmer climates, whereas P. penetrans is usually associated with cooler climates and higher elevations (McKenry, 1989). Nematode-infested nursery stock and transport of infested soil on machinery account for most of Pratylenchus spp. movement to uninfested areas.

Economic importance P. penetrans in Canada (Mountain and Patrick, 1959) and P. vulnus in the USA (McKenry, 1989), Spain (Pinochet et al., 2000) and France

(Scotto La Massèse, 1975) are economically important pests of peach. In California, P. vulnus damage to peach rootstocks is estimated to cause a reduction of about 16% in marketable fruit size and yield (McKenry, 1989). In ﬁeld microplots, P. vulnus was associated with reduced peach tree growth of ‘Guardian®’, ‘Lovell’ and ‘Nemaguard’ rootstocks (Nyczepir and Pinochet, 2001). Furthermore, tree growth suppression in the same study was greatest in the P. vulnus (GA-peach isolate) infested plots than in the P. vulnus (ID-apple isolate) plots. In Spain, damage to ‘Nemared’ peach and ‘Garnem’ and ‘Monegro’ peach–almond hybrids was evidenced at the end of the second growing season in P. vulnus-infested microplots. All tested rootstocks were good hosts for P. vulnus, which reached a high population density in the roots (Pinochet et al., 1996b). In another study also conducted in Spain, ‘Cadaman’ peach rootstock growth was suppressed in the presence of P. vulnus (Spain-plum isolate) (Hernandez-Dorrego et al., 1999). Pathogenic diversity among P. vulnus isolates attacking Prunus rootstocks appears to be high (Pinochet et al., 2000). P. penetrans is also associated with the peach replant problem in Canada (see following section).

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Disease complexes P. penetrans is associated with the peach replant problem in Canada (Mountain and Patrick, 1959). The invading nematode causes peach root necrosis in the absence of bacteria and fungi. It is believed that P. penetrans initiates root degeneration, thereby providing sites for secondary infection by other soil microbes. P. vulnus is associated with peach replant problems in Italy (Ricciardi et al., 1975) and the USA (Fliegel, 1969). In the south-eastern USA, P. vulnus was the primary root-lesion nematode species most often associated with extensive feeder root damage/loss and reduced tree vigour. After 6 years in a ﬁeld microplot study, ‘Nemaguard’ peach trees growing in soil infested solely with P. vulnus lived while trees growing in soil infested solely with M. xenoplax died from PTSL (A.P. Nyczepir, 2004, personal observation).

Host range The host range of P. vulnus and P. penetrans includes over 80 and 350 plant species, respectively; most hosts of P. vulnus are woody perennials (Corbett, 1973, 1974; Pinochet et al., 1992). Peach rootstocks (i.e. ‘Cadaman’, ‘Flordaguard’, ‘Guardian®’, ‘Lovell’, ‘Montclar’, ‘Nemaguard’ and ‘Rutgers Red Leaf’) tested under controlled conditions were all hosts to P. vulnus and/or P. penetrans (Table 19.1) (Mountain and Patrick, 1959; Pinochet et al., 2000; Nyczepir and Pinochet, 2001). Control Nematicides Pre-plant soil fumigation and post-plant application of recommended nematicides provided adequate control of Pratylenchus spp. in peach (Nyczepir, 1991). In Canada, tree growth was improved and P. penetrans populations suppressed for up to 4 years following soil fumigation with Vorlex (Olthof et al., 1989). In Georgia, USA, the nematicide treatment threshold is ≥1 P. vulnus/100 cm3

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soil (Davis et al., 1996). Because state/country recommendations for nematicide use are not the same and change frequently, current local sources of information need to be consulted for updated recommendations. Cultural practices McFadden-Smith et al. (1993) noted that byproducts (i.e. allyl glucosinolate) of Brassica green manure were toxic to P. penetrans. However, under ﬁeld conditions, no root-lesion nematode suppression was observed using this green manure. Resistance Little progress has been made in identifying sources of resistance to P. vulnus in commercial peach rootstocks (McKenry, 1989; Pinochet, 1997; Pinochet et al., 2000; Nyczepir and Pinochet, 2001). Resistance to root-lesion nematodes has been difﬁcult to detect and it is also difﬁcult to transmit from wild Prunus or existing germplasm (e.g. obsolete plum rootstocks of American origin) into commercial rootstocks. Sources of resistance have been identiﬁed in two wild Prunus species (i.e. Prunus fremonti and Prunus tomentosa) (Scotto La Massèse, 1975) and recently in ‘Redglow’ plum. Unfortunately, these sources are non-viable from a breeding standpoint since they do not graft or cross with existing commercial rootstocks (Pinochet et al., 2000). Findings in the last decade also indicate differences in pathogenicity among P. vulnus isolates, which further complicates the evaluation of plant material (Pinochet et al., 1994, 1996a, 2000). Despite all these constraints, a few commercial rootstocks have been found to be moderately resistant to some P. vulnus isolates. Since only partial sources of resistance have been found to individual nematode isolates, pooling genes from different sources appears to be the only long-term effective breeding strategy for now (Pinochet, 1997). Resistance mechanisms to P. vulnus are unknown. Tolerance to P. penetrans was identiﬁed in ‘Rutgers Red Leaf’, ‘Tzim Pee Tao’, ‘Bailey’, ‘BY520-8’, ‘Higama’ and ‘Guardian®’ peach rootstocks (Table 19.1) (Potter et al., 1984; McFadden-Smith et al., 1998).

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19.5 Dagger Nematodes Dagger nematodes (Xiphinema spp.) are ectoparasites of Prunus that also transmit nepoviruses (i.e. nematode-transmitted polyhedral viruses) which are lethal to stone fruits (see section on ‘Nepovirus diseases’ below).

Species There are more than 280 Xiphinema spp., but only seven have been associated with stone fruit disease. Two species, Xiphinema diversicaudatum and Xiphinema vuittenezi, originated from Europe and ﬁve species including Xiphinema americanum, Xiphinema brevicolle, Xiphinema californicum, Xiphinema pachtaicum and Xiphinema rivesi are from the X. americanum group (Table 19.3). The species of the latter group were considered as a single species until 1979 and are found mainly in North America. Since that date, X. americanum (today referred to as X. americanum sensu lato) has been redeﬁned by Lamberti and BleveZacheo (1979) into several distinct species (mainly X. americanum sensu stricto, X. californicum, Xiphinema bricolensis and X. rivesi). Nevertheless, the current status of those species is not clear. Separation of the predominant species from North America can be conﬁrmed by molecular analysis using ISTRFLP (internal transcribed spacer–restriction fragment length polymorphism) markers

(Vrain, 1993; Vrain et al., 1992) and those species will be discussed in more detail within this chapter. More recently, a complete listing of the putative species from the X. americanum group, their geographical occurrence and distribution was published (Lamberti et al., 2000, 2002). The authors have reclassiﬁed all species into three categories: (i) the widespread species (i.e. those previously mentioned); (ii) the localized species; and (iii) the rare species. For example, one of the rare species, Xiphinema pacificum, was recently reported for the ﬁrst time in peach in Georgia, USA (Nyczepir and Lamberti, 2001). X. diversicaudatum is widely dispersed in the temperate climates of Europe (Dalmasso, 1969, 1970; Scotto La Massèse, 1985) and is occasionally found in North America, where it was introduced on woody plants (Robbins and Brown, 1991). X. vuittenezi is commonly found in soils from stone fruit orchards in Central and Eastern Europe (Taylor and Brown, 1997), whereas X. pachtaicum, a European species of X. americanum sensu lato, is often found on Prunus in France (C. Scotto La Massèse, France, 1990, personal communication). X. americanum sensu stricto is common in North and South America but has also been reported in South Africa (Lamberti and Golden, 1984; Loots and Heyns, 1984; Luc and Doucet, 1990; Robbins and Brown, 1991), whereas X. rivesi is present in north-eastern USA, eastern Canada, the former USSR, France, Germany and Spain (Romanenko and Stegarescu, 1985; Luc and Doucet, 1990; Robbins

Table 19.3. Dagger nematode species and their associated nepoviruses in peach rootstocks. Nematode

Nepovirus

Xiphinema diversicaudatum

Strawberry latent ringspot virus (SLRV) Arabis mosaic virus (ArMV) – – Peach rosette mosaic virus (PRMV) Cherry rasp leaf virus (CRLV) Tomato ringspot virus (ToRSV) Tobacco ringspot virus (TRSV) ToRSV ToRSV ToRSV

Xiphinema vuittenezi Xiphinema pachtaicum Xiphinema americanum sensu stricto

Xiphinema californicum Xiphinema rivesi Xiphinema bricolensis

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and Brown, 1991). X. rivesi is suspected to have been introduced to Europe (Taylor and Brown, 1997). X. californicum has frequently been detected along the western seaboard of the Americas, but it has also been reported in the eastern USA (Lamberti et al., 1988; Robbins and Brown, 1991). X. bricolensis is present in British Columbia, Canada and also in Washington State and California, USA, where it is more frequent in vineyards than in orchards (Brown et al., 1994b).

Symptoms Some species of Xiphinema induce gall formation at feeder root tips, which may appear swollen and curled.

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and detailed information can be found elsewhere (Nyczepir and Halbrendt, 1993). The most economically important nepovirus is the Tomato ringspot virus (ToRSV) affecting stone fruit in North and South America (Brown et al., 1994a). The established vectors of ToRSV are nematodes from the X. americanum sensu lato group, including X. americanum sensu stricto, X. bricolensis, X. californicum and X. rivesi. This virus causes Prunus stem pitting in peach (Mircetich and Fogle, 1976). Other peach virus diseases include tobacco ringspot caused by Tobacco ringspot virus (TRSV) and peach rosette mosaic caused by Peach rosette mosaic virus (PRMV), both vectored by X. americanum sensu stricto (Klos, 1976), and strawberry latent ringspot caused by Strawberry latent ringspot virus (SLRV), vectored by X. diversicaudatum (Crossa-Reynaud and Audergon, 1987). Strawberry latent ringspot is the most economically important nepovirus disease in Europe.

Biology Little is known about the biology and life cycle of most Xiphinema spp. X. diversicaudatum reproduces by amphimixis (i.e. true sexual reproduction with fusion of sperm and egg nuclei) and males are abundant. X. diversicaudatum has a long life cycle (up to 3 years) and showed no comparable annual cycle (Flegg, 1968; Jaffee et al., 1987a). The life cycle may take from several months to several years depending on the environmental conditions (temperature, soil moisture, soil type) (D. Esmenjaud, unpublished results). Other Xiphinema spp. reproduce by parthenogenesis and the male stage is uncommon. Halbrendt and Brown (1992) have shown that X. americanum sensu stricto, X. californicum and X. rivesi have only three juvenile stages and not four as usually encountered with European species such as X. diversicaudatum.

Nepovirus diseases Most nepoviruses associated with Prunus have been observed and described in North America. A list of the nepoviruses and their corresponding vectors is reported in Table 19.3

Survival, dissemination and host range All stone fruits and many other woody plant species are hosts of Xiphinema spp. Nepoviruses that are vectored by Xiphinema spp. are naturally found in common broadleaved weeds, which serve as natural reservoirs of latent infections. Nematodes acquire the virus by feeding on infected plants and subsequently transmit it when feeding on the peach tree (Taylor and Robertson, 1970). Soil moisture, temperature and texture affect nematode survival and virus-vectoring efﬁciency (Nyczepir and Becker, 1998).

Economic importance The total economic impact of Xiphinema spp. and nepoviruses to the European and US peach industries has been difﬁcult to estimate (Nyczepir and Halbrendt, 1993). This is because many factors impact orchard life and productivity and it is difﬁcult to attribute loss to a single factor. Crop losses of 10% due to X. americanum and P. penetrans damage have been estimated by Klonsky and Bird (1981)

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for the Michigan tree fruit industry. Nematodes or weeds putatively harbouring ToRSV as a primary causal agent for peach tree death in Pennsylvania have been found in 90% of the locations sampled (Greene et al., 1988).

Methods of diagnosis Characteristic symptoms such as stem pitting, constriction, brown line, rasp leaf and rosette symptoms are the primary indicators of a virus disease. Identiﬁcation of ToRSV can be conﬁrmed by ELISA or dot-blot hybridization (Powell et al., 1991). Subsequently, detection of the vector nematode can be attempted, but sampling for Xiphinema vectors is difﬁcult on the established crop. The occurrence of X. diversicaudatum and X. vuittenezi can be conﬁrmed using multiplexed PCR primers designed from ribosomal genes, which permit a direct identiﬁcation from a single nematode (Wang et al., 2002), but molecular tools for the identiﬁcation of species from the X. americanum group are lacking.

Control Since X. diversicaudatum and SLRV share many common hosts in the Rosaceae family, the risk of virus transmission by the nematode between different plant species is high. Therefore, ﬁelds where rosaceous species have been previously cultivated should be avoided. In situations where soil transmission by dagger nematodes is clearly established, pre-plant fumigation is an effective means of managing virus diseases (Bernhard et al., 1985). Applications of post-plant nematicides and broadleaf herbicides to control spread of nepoviruses are highly recommended. Because state/country recommendations for nematicide and herbicide use are not the same and change frequently, current local sources of information need to be consulted for updated recommendations. Rootstock resistance to ToRSV exists in Prunus (Hoy and Mircetich, 1984), but is of limited commercial interest for peach because of graft union incompatibility problems.

19.6 Other Nematodes Paratylenchus prunii Sharma, Sharma & Khan suppressed peach growth under controlled conditions and its reproduction rate was inversely proportional to the initial population density (Sharma and Sharma, 1987, 1988; Nyczepir and Becker, 1998). A single species of Longidorus, Longidorus diadecturus, appears to be involved with transmitting PRMV, is widespread in the central USA and extends northwards to Ontario, Canada (Allen et al., 1982; Halbrendt, 1993). Molecular identiﬁcation of certain Longidorus spp. found in Germany and Western Europe has been developed (Hubschen et al., 2004). Lists of nematodes found in association with, but not necessarily causing economic damage to, peach are recorded elsewhere (Wehunt and Nyczepir, 1988).

19.7 Outlook Utilization of nematicides for nematode control in commercial nursery and orchard systems is still heavily relied upon. In the south-eastern USA alone, present management practices include: (i) pre-plant fumigation (i.e. Telone II), which gets the trees off to a good start and gives control for up to 2 years, depending on the quality of the fumigation and the nematode involved; and (ii) resistant rootstocks (when available). However, with the continued scrutiny and removal of the various nematicides by the regulatory agencies, fewer and fewer chemical management options are available to the grower. As a result, current research efforts have shifted towards various forms of alternative (non-chemical) nematode control. Emphasis on non-chemical control is partly due to the apprehension about the environmental problems associated with soil fumigation with methyl bromide and most recently the voluntary removal in registration of the post-plant nematicide, fenamiphos. As a result of methyl bromide’s reputed role in ozone depletion, the importation and manufacture of methyl bromide in the USA have been banned since January 2005 (Clean Air Act, 1990), with certain exceptions (i.e. Critical Use Exemption,

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quarantine and pre-shipment exemptions, and emergency exemptions). Therefore, ﬁnding an alternative to chemical control of nematodes is warranted. Alternative non-chemical research areas under investigation include the search for biological control agent(s), biofumigation, rotation/cover crops, rootstock resistance and soil solarization, which could be used in an integrated nematode management system. We think that the key phrase here is integrated

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pest management system (i.e. IPM). The term IPM is not new, but it appears to be evident that a combined nematode management system approach for nematode control is what needs to be developed and/or improved upon for growers in the near future. Development of such nematode management systems through fundamental and applied research will provide the basis for nematode control that is more effective, economical, and less hazardous to man and the environment.

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20

Preharvest Factors Affecting Peach Quality C.H. Crisosto1 and G. Costa2

1University

of California, Davis, Department of Plant Sciences; located at Kearney Agricultural Center, Parlier, California, USA 2Department of Fruit Trees and Woody Plant Sciences, University of Bologna, Bologna, Italy

20.1 Introduction 20.2 Quality Deﬁnition 20.3 Maturity and Quality 20.4 Genotype 20.5 Mineral Nutrition Nitrogen Calcium Potassium Iron 20.6 Irrigation 20.7 Canopy Manipulation

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20.1 Introduction This chapter describes and discusses exclusively the impact of preharvest factors on peach fruit ﬂavour and postharvest life (storage and shelf-life). It does not include the role of environmental factors and the use of plant growth regulators on peach quality; these topics are covered well in other chapters in this book. The present chapter begins by emphasizing quality deﬁnitions from the consumer point of view and follows with a series of short sections that update knowledge on preharvest orchard factors. The relationship between maturity and quality is covered, and the role of genotype (cultivar and rootstock) 536

on fruit ﬂavour and postharvest life potential is described. Then the effect of mineral nutrition on peach quality is discussed with detailed attention on N and Ca as the most studied nutrients. Updated information on the effect of foliar nutrient application on fruit quality including foliar Ca sprays is also reported. Detailed practical information on the effect of different irrigation regimes on fruit quality is described next, followed by a section on canopy management. The canopy management section describes practical information on leaf removal, girdling techniques, and the use of reﬂective materials to improve fruit size and enhance red skin colour. Examples that illustrate the inﬂuence of crop load

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

Preharvest Factors Affecting Quality

and canopy position on fruit quality and postharvest storage potential are presented.

20.2 Quality Definition Fruit ‘quality’ is a concept encompassing sensory properties (appearance, texture, taste and aroma), nutritive value, mechanical properties, safety and defects. Altogether, these attributes give the fruit a degree of excellence and an economic value (Abbott, 1999). Everyone in the peach production and marketing chain from the grower to the consumer looks for fruit with no or few defects. However, in each step of this chain, the term ‘quality’ takes on different meanings and the economic relevance of the various quality traits is largely variable. For example, the grower is interested in high yield, in fruit with large size and high disease resistance, and in the opportunity to reduce the number of pickings. The deﬁnition of ‘quality’ for packers, shippers, distributors and wholesalers is mainly based on ﬂesh ﬁrmness, which is considered a good indication to predict fruit potential storage and market life. Peaches and nectarines ripen and deteriorate quickly at ambient temperature and cold storage is required to slow down these processes, especially for some cultivars and/or long-distance market situations. However, ﬁrmness is an erroneous and incomplete way to estimate peach postharvest potential for domestic distribution. In fact, in some production areas such as California and Chile, the development of internal breakdown symptoms such as lack of ﬂavour, ﬂesh mealiness and ﬂesh browning limits the storage life and the postharvest quality of tasty cultivars. For retailers, red colour, size and ﬁrmness have historically represented the main components of fruit quality, as they need fruit that are attractive to the consumer, resistant to handling and have a long shelflife. From the consumer’s point of view, in general peach fruit quality has declined, mainly because of premature harvesting, chilling injury and lack of ripening prior to consumption, resulting in consumer dissatisfaction. In addition, quality is badly deﬁned and the only parameters being considered are fruit size and skin colour. Other characters

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such as ﬂesh ﬁrmness, sugar content, acidity and aroma, which are perceived by the consumer as fruit quality, are completely disregarded by the grower and other individuals along the chain. In fact, the grower, identifying fruit quality almost exclusively with the fruit size, does not consider that these are only the ﬁrst characters perceived by the consumer and they orient him just in his very ﬁrst choice. As soon as he realizes that the fruit, even with good size and attractive colour, is tasteless, with low sugar content, poor aroma and rapidly perishable, he redirects his interest towards other types of fruit. As a consequence, it is imperative for the grower and other individuals in the delivery chain to direct their attention to fruit quality from the consumer’s perspective in order to regain the conﬁdence of the consumer. In addition, there is now an increasing appreciation that ‘quality’ of fruit also includes nutritional properties (e.g. vitamins, minerals, dietary ﬁbre) and health beneﬁts (e.g. antioxidants); and these are becoming important factors in consumer preferences. Experimental, epidemiological and clinical studies provide evidence that diet has an important role in the prevention of the chronic degenerative diseases such as tumours, cardiovascular diseases and atherosclerosis. It is supposed, in fact, that the consumption of fresh fruit and vegetables exerts a protective role against the development of such pathologies (Doll, 1990; Ames et al., 1993; Dragsted et al., 1993; Anderson et al., 2000). Changes in quality deﬁnition that are focusing more on consumer demand can increase peach consumption if marketing promotion and education programmes are well executed. Because the consumer quality of peaches cannot be improved after harvest, it is important to understand the role of preharvest factors in consumer acceptance and market life (Kader, 1988; Crisosto et al., 1997).

20.3 Maturity and Quality Peaches and nectarines are climacteric fruit characterized by a sharp rise in ethylene biosynthesis at the onset of ripening, which is associated with changes in sensitivity to the hormone itself and changes in colour, texture, aroma and other biochemical features (Fig. 20.1/Plate 226).

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Ethylene plays a key role in peach fruit ripening by coordinating the expression of ripening-related genes responsible for ﬂesh softening, colour development and sugar accumulation, as well as other processes such as abscission (Ruperti et al., 2002; Trainotti et al., 2003, 2006). The deﬁnition of the proper harvest time is essential, as fruit maturity at harvest greatly inﬂuences peach fruit market life potential and quality. Recently, the most important peach-producing countries in Europe have lost considerable market share mainly due to excessive early harvesting. A delayed harvest could lead to a better fruit organoleptic quality but also to faster softening and a shorter shelf-life. In fact, different from other species, in peach fruit there is a close link between ‘on-tree physiological maturity’ and evolution of key traits responsible for peach quality during the postharvest phase. On the other hand, melting ﬂesh peaches and nectarines undergo a rapid softening after harvest, which leads to dramatic losses in the marketing chain, as soft fruit are easily bruised during handling and more susceptible to decay. Therefore, they are often picked at an early

Fig. 20.1.

stage of ripening, and they never reach their full ﬂavour and aroma potential. Modulation of pre- and postharvest peach fruit ripening by the means of chemicals that interfere with ethylene biosynthesis and/or perception, such as aminoethoxyvinylglycine and 1-methylcyclopropene, has already been reported (Mathooko et al., 2001; Bregoli et al., 2002, 2005; Ziosi et al., 2006). A better understanding of the physiological basis of the peach fruit ripening process should make it possible to develop further strategies to regulate ripening. Such strategies need objective parameters able to accurately describe fruit ripeness stages and internal quality changes occurring in pre- and postharvest conditions. Until recently, few studies have been carried out on this topic, and mainly by using traditional fruit quality traits (ﬂesh ﬁrmness, soluble solids concentration (SSC) and titratable acidity (TA)) which are assessed with simple devices such as penetrometers, refractometers and titrators. Early studies carried out in Europe and the USA have associated peach fruit consumer acceptance with high SSC (Mitchell et al., 1990; Parker et al., 1991; Ravaglia et al., 1996; Anon., 1999). In California,

Peaches picked at different maturity levels.

Preharvest Factors Affecting Quality

a minimum of 10% SSC for yellow-ﬂeshed peaches and nectarines was proposed as a quality standard (Kader, 1995). In France, a minimum of 10% SSC for low-acidity (TA <0.9%) and 11% SSC for high-acidity (TA ≥0.9%) peaches was proposed as part of their quality standard (Hilaire, 2003). In Italy, a minimum of 10% SSC for early-season, 11% for mid-season and 12% for late-season cultivars was suggested for yellow-ﬂeshed peaches (Testoni, 1995; Ventura et al., 2000). In preliminary studies carried out in California by using trained panels and ‘in-store’ consumer acceptance tests on ‘Ivory Princess’ (white ﬂesh/low TA), ‘Elegant Lady’, ‘O’Henry’ and ‘Spring Bright’ (yellow ﬂesh/high TA) peaches and ‘Honey Kist’ (yellow ﬂesh/low TA) nectarine, it was shown that acceptance correlated well with ripe soluble solids concentration or the ratio of ripe soluble solids concentration to ripe titratable acidity; it was also shown that the relationship was strictly dependent on cultivar and/or maturity and that consumer acceptance was not a linear relationship (Crisosto and Crisosto, 2005). The analyses of traditional fruit quality traits are cheap and fast, but they do not consider other fundamental aspects of quality, such as antioxidant capacity, aroma volatile emission, soluble sugars and organic acids content. A more accurate deﬁnition of fruit quality would require sophisticated analyses (high-performance liquid chromatography, gas chromatography or mass spectrometry) that are not usually run because they should be carried out only in well-equipped laboratories with trained personnel. In any case, simple or more complex destructive analyses can be performed only on samples of a limited number of fruit, often not fully representative of the entire lot (Costa et al., 2002, 2003b). In recent years, extensive research has been focused on the development of non-destructive techniques for assessing internal fruit quality attributes. These techniques offer a number of advantages, including: the possibility to extend the assessments on a large number of, or even on all, the fruit in a lot; to repeat the analysis on the same samples, monitoring their physiological evolution; and to achieve real-time information on several fruit quality parameters at the same time (Abbott, 1999). Among the

539

non-destructive techniques, near infrared spectroscopy can be used efﬁciently for determining traditional peach fruit quality traits and concentrations of the main organic acids and simple sugars. In addition, this technique allowed deﬁnition of a new maturity index strictly related to the fruit ethylene emission and ripening stage. This index, called ‘absorbance difference’ (AD), can be effectively used for determining harvest date and for grouping harvested fruit into homogeneous classes which show different ripening rates during shelf-life (Costa et al., 2006). As a ﬁnal consideration, as new plantings are based on new cultivars with different organoleptic characteristics (low- and highacid, high SSC, highly aromatic, non-melting, etc.) and since new markets and consumer groups with different ethnic backgrounds are being reached (Liverani et al., 2002; Crisosto, 2003), it is important to understand which characters are determining consumer acceptance and segregate cultivars into different organoleptic categories prior to proposing any quality index (Crisosto, 2002, 2003). As a long-term solution, it is expected that breeding programmes will include quality characteristics in their screening process. The creation of peach categories with their own quality indices according to an organoleptic description may help marketing and promotion.

20.4 Genotype Genotype (cultivar and/or rootstock) has an important role in ﬂavour quality, nutrient composition and postharvest life potential. SSC and acidity are determined by several factors such as cultivar (Crisosto et al., 1995, 1997; Frecon et al., 2002; Liverani et al., 2002; Byrne, 2003) and rootstock (Reighard, 2002). Reduction of physiological disorders and even decay and insect losses can be achieved by choosing the correct genotype for given environmental conditions. Extensive harvest quality and postharvest storage potential evaluations have been carried out since 1970 by several researchers in all the main important peach cultivation areas, such as the USA,

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Italy, Spain, France, Chile and South Africa. Brown rot and grey mould resistance have not been successfully included in recently released cultivars. These are the main diseases, although other ones have been investigated (Frecon et al., 2002; Reighard, 2002), but current breeding programmes are constantly creating new cultivars with improved production and visual appearance attributes. Unfortunately, an ideal cultivar(s) with all of the current consumer quality attributes for domestic and long-distance shipping has (have) not been developed yet.

20.5 Mineral Nutrition Nutritional status is an important factor of quality and postharvest life potential. Deﬁciencies, excesses or imbalances of various nutrients may result in disorders that can limit storage life. Fertilization rates vary widely among growers, locations and cultivars, and generally depend upon soil type, cropping history and ﬁeld testing results.

Nitrogen This is the nutrient that has been studied the most. N has the single greatest effect on peach quality. Detailed and extensive research performed since the early 1990s at the Kearney Agricultural Center (Parlier, California, USA) has evaluated the role of N in peach and nectarine production and quality under California conditions (Daane et al., 1995). Based on

this work, in California, N should be kept between 2.6 and 3.0% leaf N for best fruit quality without reduction in production or size (Table 20.1). Similarly, optimal fruit quality in nectarines in the Eastern Po Valley area (Italy) was obtained in trials having 3.0% leaf N concentration (Tagliavini et al., 1997; Scudellari et al., 1999). Response of peach and nectarine trees to N fertilization is dramatic; high N levels stimulate vigorous vegetative growth, causing shading out and death of lower fruiting wood. Although high-N trees may look healthy and lush, excess N does not increase fruit size, production or SSC. Furthermore, excessive N delays peach maturity because it induces poor visual red colour development (Fig. 20.2/Plate 227) and inhibits ground colour change from green to yellow. As growers delay harvest waiting for fruit colour changes from green to yellow and red colour development, high-N fruit are picked soft especially when measured on the softest position on the fruit such as tips, which generally ripen faster than the rest of the fruit in warm production areas. These fruits then have fast softening rates during postharvest handling and are more susceptible to bruising and decay development. N deﬁciency leads to small fruit with poor ﬂavour and unproductive trees. Fruit water loss from fruit with the highest N rate (3.6% leaf N) was greater than that from the lowest rate (2.6% leaf N). The relationship between fruit N concentration and fruit susceptibility to decay produced by brown rot (Monilinia fructicola (Wint.) Honey) has been studied extensively on stored fruit (Daane et al., 1995). Wounded and brown rotinoculated fruit from ‘Fantasia’ and ‘Flavortop’

Table 20.1. Relationship between leaf nitrogen and per cent of fruit surface that is red, yield and fruit size (mean for 3 years) on ‘Fantasia’ nectarine. (Adapted from Daane et al., 1995.) N-fertilization treatment (kg N/ha) 0 112 196 280 364

Leaf N (%)

Fruit visual redness (%)

Yield (kg/tree)

Fruit weight (g)

2.7a

92a

132a

3.0b

80b

207b

3.1c 3.5d 3.5d

72c 69c 70c

193b 222b 197b

131a 166b 168b 169b 167b

a,b,cValues within columns with unlike superscript letters were significantly different by the Least Significant Difference test (P < 0.05).

Preharvest Factors Affecting Quality

541

Fig. 20.2. Influence of increased nitrogen fertilization (kg/ha) on red skin coloration of ‘Fantasia’ nectarine.

trees having more than 2.6% leaf N were more susceptible to brown rot than fruit from trees with 2.6% leaf N or less. Fruit anatomical observations and cuticle density measurements indicated differences in cuticle thickness among ‘Fantasia’ fruit from the low, middle and high N treatments. These changes in cuticle and epidermis anatomy can partially explain the differences in fruit susceptibility to this disease and water loss.

Calcium The nutrient Ca is involved in numerous biochemical and morphological processes in plants and has been implicated in many disorders of considerable economic importance to production and postharvest quality. While Ca accumulation in apple, kiwifruit and grape occurs predominantly in the ﬁrst stages of

fruit development, in peaches, owing to their ability to maintain signiﬁcant transpiration rates, Ca continues to accumulate until harvest (Tagliavini et al., 2000). Foliar Ca sprays have not been successful and are not used commercially to maintain peach fruit quality. Over the last decade, trials carried out in California using several commercial Ca foliar sprays on peach and nectarine (applied every 14 days, starting 2 weeks after full bloom and continuing until 1 week before harvest) showed no effect on fruit quality of mid- or late-season cultivars (Crisosto et al., 2000). These foliar spray formulations and new formulations did not affect fruit SSC, ﬁrmness, decay incidence, fruit ﬂesh Ca concentration or postharvest disorders. Fruit ﬂesh Ca concentration measured at harvest varied among cultivars from 200 to 300 µg/g dry weight basis. A lack of decay control was also reported on ‘Jerseyland’ peaches, grown in Pennsylvania, treated with ten weekly preharvest Ca sprays of CaCl2 at 0,

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34, 67 or 101 kg/ha (Conwall, 1987). Even fruit treated at a rate of 101 kg/ha, which had 70% more ﬂesh Ca (490 versus 287 µg/g dry weight basis) than untreated fruit, showed no reduction in decay severity. Our recent research suggests that any Ca spray formulations and timing on peaches and nectarines should be treated with caution because their heavy metal content (Fe, Al, Cu, etc.) may contribute to peach and nectarine skin discoloration (Crisosto et al., 1999). A moderate and cultivar-dependent effect of Ca sprays on the reduction of skin russeting development has been reported for nectarines in Italy (Scudellari et al., 1995).

Potassium K is the major nutrient present in peaches (about 2–2.5 kg/t fresh weight basis), where it accumulates progressively as fruit approach maturity (Tagliavini et al., 2000). Optimal K nutrition usually leads to high photosynthetic rates and reallocation of sugars and organic acids that will enhance fruit quality.

Iron Fe, as a micronutrient, is taken up by fruit trees in relatively small amounts; however, its deﬁciency not only affects fruit yields but also peach fruit quality (Álvarez-Fernández et al., 2003). In a study carried out in Spain, only 47% of fruits from Fe-deﬁcient trees had optimal fruit size compared with 95% from green trees (Álvarez-Fernández et al., 2003). Peach fruit colour could also be affected by Fe deﬁciency: in a red-skin peach cultivar (‘Babygold’) Fe deﬁciency caused decreases in the mean ‘a’ colour coordinate and increases in the mean ‘L’ and ‘b’ colour coordinates (ÁlvarezFernández et al., 2003).

20.6 Irrigation Despite the important role of water in fruit growth and development, few speciﬁc studies

have been done on the inﬂuence of the amount and the timing of water applications on peach quality at harvest and postharvest performance (Prashar et al., 1976). An early report indicated that when trees were allowed to grow without irrigation during the growing season on a shallow soil under California conditions, yield and fruit size were reduced, SSC increased and fruit developed an abnormal texture (Uriu et al., 1964). Reducing the amount of applied water after harvest of earlyseason peaches (postharvest stress) has shown no negative effects on yield in California; however, timing of the water deﬁcit interval is important. An increase in fruit defects such as deep suture and double-fruit formation has been reported for early-season ‘Regina’ peaches as a consequence of imposing a postharvest water stress (50% evapotranspiration; ET) in mid- and late summer during the previous season (Fig. 20.3/Plate 228). These defects reduced the ﬁnal packout for the next season’s crop (Johnson et al., 1992). The regulated irrigation deﬁcit (RID) technique has been evaluated for peach performance in different production areas (Chalmers et al., 1981; Ben Mechlia et al., 2002; Girona, 2002; Goldhamer et al., 2002). In general, this technique imposes a moderate stress (30–50% ET) to reduce vegetative growth and save water use (4–30%) at a given physiological stage without affecting yield. Researchers agree that the water stress-tolerant phases in peach, which has a double-sigmoid fruit development pattern, have been identiﬁed as stage II, the lag phase of fruit growth and the postharvest period (Goldhamer et al., 2002). In some situations, besides saving water, the RID technique also increased fruit size and SSC. Researchers claim that consistency of the beneﬁts of the RID technology will depend on the understanding of local climatic conditions, soil depth and composition, identiﬁcation of the fruit growth stages and fruit crop load (Berman and DeJong, 1996; Girona, 2002). In California, during three seasons, the inﬂuence of three different irrigation regimes applied 4 weeks before harvest on ‘O’Henry’ peach quality and postharvest performance was evaluated: (i) normal irrigation (100% evapotranspiration); (ii) overirrigation (150% ET); and (iii) RID irrigation (50% ET) (Crisosto et al., 1994; Johnson and

Preharvest Factors Affecting Quality

543

Fig. 20.3. Water stress late in the summer causes fruit defects such as deep sutures and double-fruit formation.

Handley, 2000). Yield, ﬂesh ﬁrmness, per cent red surface, acidity and pH were not altered at harvest by any of these irrigation regimes in any season. Average fruit size, measured as fruit weight, was lower but SSC was higher for fruit from 50% ET than from the other treatments. Ripe yellow-ﬂeshed peaches and nectarines with 10% SSC or higher with low to moderate TA (<0.7%) are highly acceptable to consumers. Although fruit from the 50% ET treatment were smaller, they had higher SSC and consumers would probably prefer their eating quality over fruit from the other two treatments. An economic study showed that peaches with a higher SSC may have a higher retail value (Parker et al., 1991). The irrigation regimes (100%, 50% and 150% ET applied 4 weeks before harvest) did not affect ‘O’Henry’ peach postharvest storage potential based on internal breakdown development during 2, 4 and 6 weeks in cold storage at 0°C or 5°C. Fruit from 50% ET had a lower water loss rate than fruit from 150% ET or 100% ET. Fruit from 150% ET lost nearly 35%

more water than fruit from 50% ET or 100% ET after 24 h. Light microscopy studies indicated that fruits from 50% ET and 100% ET had a continuous and much thicker cuticle and a higher density of trichomes than fruits from the 150% ET. These differences in exodermis structure may explain the higher percentage of water loss from fruit from 150% ET compared with the others (Crisosto et al., 1994). Recently, RID and partial root zone drying (PRD) were evaluated on white-ﬂeshed peach growing under California conditions (Goldhamer et al., 2002). PRD involves inducing partial stomatal closure by exposing some part of the root zone to continual soil drying. After 2 years of evaluations, yield and fruit quality were affected equally by the PRD and the RID treatments. Except for a few studies which have comprehensively tested a broad range of water management practices and conditions and their impacts on postharvest quality, it is often difﬁcult to generalize about the effects of water management from the

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site-speciﬁc irrigation regimes that have been reported.

14

20.7 Canopy Manipulation

12

O’Henry

r2 = 0.72

May Glo

r2 = 0.67

O’Henry

r2 = 0.82

May Glo

r2 = 0.64

SSC (%)

11 10 9 8 300 (b)

Fruit weight (g)

In most cultivars, fruitlet thinning increases fruit size while also reducing total yield, thus a balance between yield and fruit size must be achieved. Some cultivars must not be thinned too much because their fruit will crack easily. In some cases, fruit size, SSC and TA are modiﬁed without affecting fruit cracking. In other cultivars the fruit do not ripen properly when trees are carrying too high a fruit load. In general, the number of fruit that can ripen on a tree will depend on the cultivar and orchard conditions. Thus detailed information about cultivar response to crop load adjustment and potential beneﬁts should be developed for each speciﬁc situation. Historically, maximum proﬁt does not occur at maximum marketable yield since larger fruit bring a higher market price. Furthermore, new market trends for highly tasty fruit may force a review of this topic. The crop load and fruit quality relationship has been studied by researchers in various countries (Forlani et al., 2002; Giacalone et al., 2002; Luchsinger et al., 2002; Costa et al., 2003a). Leaving too many fruit on a tree reduces fruit size and SSC in the early-season ‘May Glo’ nectarine and late-season ‘O’Henry’ peach (Fig. 20.4). Crop load on ‘O’Henry’ peach trees affected the incidence of internal breakdown. In general, the overall incidence of mealiness and ﬂesh browning in fruit from the high crop load was low, intermediate in fruit from the commercial crop load, and the highest in fruit from the low crop load (Crisosto et al., 1997). Fruit quality measured at harvest and during storage for several peach and nectarine cultivars varied according to fruit canopy position in different production areas (Marini et al., 1991; Crisosto et al., 1997; Iannini et al., 2002). Large differences in SSC, acidity and fruit size were detected between fruit obtained from the outside and inside canopy positions of open-vase trained trees (Marini et al., 1991; Crisosto et al., 1997). During the last decade, we have observed that fruit grown under a high light environment (outside canopy) has

(a) 13

250 200 150 100 50 0

400 100 200 300 Crop load (1000s fruit/ha)

500

Fig. 20.4. Relationship between (a) crop load and soluble solids concentration (SSC) and (b) crop load and fruit weight for ‘O’Henry’ peach and ‘May Glo’ nectarine. (Adapted from Crisosto et al., 1997.)

a longer shelf-life (storage and market) than fruit grown under a low light environment (inside canopy). During our work, we found that fruit that developed in the more shaded inner canopy positions have a greater incidence of internal breakdown than fruit from the high light, outer canopy positions (Fig. 20.5/ Plate 229). Thus, fruit from the outer canopy have a longer potential market life, especially for cultivars susceptible to internal breakdown. The use of more efﬁcient training systems which allow more sunlight penetration into the centre and lower canopy areas is recommended to reduce the number of shaded fruit, thus extending postharvest life (Crisosto et al., 1997). Summer pruning and leaf removal around the fruit increase fruit light exposure and, when performed properly, can increase fruit colour without affecting fruit size and

Preharvest Factors Affecting Quality

545

Fig. 20.5. Canopy position affects fruit size, red colour development and storage potential.

SSC (Fig. 20.6/Plate 230). Excessive leaf pulling or leaf removal executed too close to harvest can reduce both fruit size and SSC in peaches and nectarines (Crisosto et al., 1997; Day, 1997). Girdling (removal of bark) 4–6 weeks before harvest is performed to increase peach and nectarine fruit size (Fig. 20.7/Plate 231) and to advance and synchronize maturity (Day, 1997). Girdling increases fruit SSC in some cases but also increases fruit acidity and phenolics, so the ﬂavour resulting from the additional SSC may be masked. Girdling can also cause the pits of peaches and nectarines to split, especially if it is done too early during pit hardening. Fruit with split pits soften more quickly than intact fruits and are more susceptible to decay. Reports on the beneﬁts of using different reﬂective materials to improve peach red

colour and fruit size and speed up maturation varied according to cultivar, orchard situation and location (Layne et al., 2001; Fiori et al., 2002). Under California’s long and hot growing season, canopy manipulations including water sprout removal and leaf removal around fruit become necessary to achieve the beneﬁt of red colour development in vigorous orchards. Also, even when reﬂected light was reaching fruit in the canopy, but temperatures remained high during that maturation period, improvement in red colour development was not observed. In spite of the limited literature available on the role of preharvest factors in consumer quality, there is strong evidence that fruit ﬂavour quality, market life and physiological disorders are related to preharvest factors. We therefore encourage more detailed work on

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Fig. 20.6.

C.H. Crisosto and G. Costa

Leaf removal around the fruit improves red colour but may decrease fruit size.

Fig. 20.7. Peach girdling (removal of a strip of scaffold bark) at the main scaffolds advances maturity and increases fruit size.

Preharvest Factors Affecting Quality

this subject with an emphasis on consumer satisfaction. In order to maximize ‘orchard quality potential’, all of the preharvest factors inﬂuencing quality must be investigated by physiologists and understood by pomologists.

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Detailed information on how these factors are controlling peach consumer quality combined with an effective marketing programme will help to increase peach consumption (Crisosto, 2002).

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Crisosto, C.H., Johnson, R.S., Luza, J.G. and Crisosto, G.M. (1994) Irrigation regimes affect fruit soluble solids content and the rate of water loss of ‘O’Henry’ peaches. HortScience 29, 1169–1171. Crisosto, C.H., Mitchell, F.G. and Johnson, R.S. (1995) Factors in fresh market stone fruit quality. Postharvest News and Information 6, 17–21. Crisosto, C.H., Johnson, R.S., Day, K.R. and DeJong, T. (1997) Orchard factors affecting postharvest stone fruit quality. HortScience 32, 820–823. Crisosto, C.H., Johnson, R.S., Day, K.R., Beede, B. and Andris, H. (1999) Contaminants and injury induce inking on peaches and nectarines. California Agriculture 53, 19–23. Crisosto, C.H., Day, K.R., Johnson, R.S. and Garner, D. (2000) Influence of in-season foliar calcium sprays on fruit quality and surface discoloration incidence of peaches and nectarines. Journal of the American Pomological Society 54, 118–122. Daane, K.M., Johnson, R.S., Michailides, T.J., Crisosto, C.H., Dlott, J.W., Ramirez, H.T., Yokota, G.T. and Morgan, D.P. (1995) Excess nitrogen raises nectarine susceptibility to disease and insects. California Agriculture 49, 13–17. Day, K.R. (1997) Production practices for quality peaches. Proceedings of Florida State Horticultural Association 77, 59–61. Doll, R. (1990) An overview of the epidemiological evidence linking diet and cancer. Proceedings of the Nutrition Society 49, 119–131. Dragsted, L.O., Strube, M. and Larsen, J.C. (1993) Cancer-protective factors in fruit and vegetables: biochemical and biological background. Pharmacology and Toxicology 72, 116–135. Fiori, G., Bucchi, F., Corelli Grappadelli, L. and Costa, G. (2002) Effetto dteli riflettenti a terra sugli scambi gassosi e la qualità delle produzioni in pesco. In: Atti VI Giornate Scientifiche SOI, Spoleto, Italy, 23–25 April, pp. 157–158. Forlani, M., Basile, B., Cirillo, C. and Iannini, C. (2002) Effects of harvest date and fruit position along the tree canopy on peach fruit quality. Acta Horticulturae 592, 459–466. Frecon, J.L., Belding, R. and Lokaj, G. (2002) Evaluation of white-fleshed peach and nectarine varieties in New Jersey. Acta Horticulturae 592, 467–478. Giacalone, G., Peano, C. and Bounous, G. (2002) Correlation between thinning amount and fruit quality in peaches and nectarines. Acta Horticulturae 592, 479–484. Girona, J. (2002) Regulated deficit irrigation in peach. A global analysis. Acta Horticulturae 592, 335–342. Goldhamer, D.A., Salinas, M., Crisosto, C., Day, K.R., Soler, M. and Moriana, A. (2002) Effects of regulated deficit irrigation and partial root zone drying on late harvest peach tree performance. Acta Horticulturae 592, 343–350. Hilaire, C. (2003) The peach industry in France: state of art, research and development. In: Marra, F. and Sottile, F. (eds) Proceedings of the First Mediterranean Peach Symposium, Agrigento, Italy, 10 September, pp. 27–34. Iannini, C., Cirillo, C., Basile, B. and Forlani, M. (2002) Estimation of peach yield efficiency and light interception by the canopy in different training systems. Acta Horticulturae 592, 357–366. Johnson, R.S. and Handley, D.F. (2000) Using water stress to control vegetative growth and productivity of temperate fruit trees. HortScience 35, 1048–1050. Johnson, R.S., Handley, D.F. and DeJong, T. (1992) Long-term response of early maturing peach trees to postharvest water deficit. Journal of the American Society for Horticultural Science 69, 1035–1041. Kader, A.A. (1988) Influence of preharvest and postharvest environment on nutritional composition of fruits and vegetables. In: Quebedeaux, B. and Bliss, F.A. (eds) Horticulture and Human Health Contributions of Fruits and Vegetables. Prentice-Hall, Englewood Cliffs, New Jersey, pp. 18–22. Kader, A.A. (1995) Fruit maturity, ripening, and quality relationships. Perishables Handling Newsletter 80, 2. Layne, D.R., Jiang, Z.W. and Rushing, J.W. (2001) Tree fruit reflective film improves red skin coloration and advances maturity in peach. HortTechnology 11, 234–242. Liverani, A., Giovannini, D. and Brandi, F. (2002) Increasing fruit quality of peaches and nectarines: the main goals of ISF-FO (Italy). Acta Horticulturae 592, 507–514. Luchsinger, L., Ortin, P., Reginato, G. and Infante, R. (2002) Influence of canopy fruit position on the maturity and quality of ‘Angelus’ peaches. Acta Horticulturae 592, 515–522. Marini, R.P., Sowers, D. and Marini, M.C. (1991) Peach fruit quality is affected by shade during final swell of fruit growth. Journal of the American Society for Horticultural Science 116, 383–389. Mathooko, F.M., Tsunashima, Y., Owino, W.Z.O., Kubo, Y. and Inaba, A. (2001) Regulation of genes encoding ethylene biosynthetic enzymes in peach (Prunus persica L.) fruit by carbon dioxide and 1-methylcyclopropene. Postharvest Biology and Technology 21, 265–281.

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Mitchell, F.G., Mayer, G., Biasi, W., Gulli, D. and Faubian, D. (1990) Selecting and handling high quality stone fruit. California Tree Fruit Agreement 1989 Research Report. California Tree Fruit Agreement, Sacramento, California. Parker, D., Ziberman, D. and Moulton, K. (1991) How quality relates to price in California fresh peaches. California Agriculture 45, 14–16. Prashar, C.R.K., Pearl, R. and Hagan, R.M. (1976) Review on water and crop quality. Scientia Horticulturae 5, 193–205. Ravaglia, G., Sansavini, S., Ventura, M. and Tabanelli, D. (1996) Indici di maturazione e miglioramento qualitativo delle pesche. Frutticoltura 3, 61–66. Reighard, G.L. (2002) Current directions of peach rootstock programs worldwide. Acta Horticulturae 592, 421–428. Ruperti, B., Cattivelli, L., Pagni, S. and Ramina, A. (2002) Ethylene-responsive genes are differentially regulated during abscission, organ senescence and wounding in peach (Prunus persica). Journal of Experimental Botany 53, 429–437. Scudellari, D., Tagliavini, M. and Pelliconi, F. (1995) Aspetti teorici ed applicativi del calcio nelle colture arboree. L’Informatore Agrario LI 15, 45–49. Scudellari, D., Toselli, M., Marangoni, B. and Tagliavini, M. (1999) La diagnostica fogliare nelle piante arboree da frutto a foglia caduca. Bollettino della Società Italiana di Scienza del Suolo 48, 829–842. Tagliavini, M., Scudellari, D., Corelli Grappadelli, L. and Pelliconi, F. (1997) Valutazione di metodi rapidi per stimare il livello azotato del pescheto. In: Atti XXII Convegno Peschicolo, Cesena, Italy, 5–7 October 1995, pp. 141–150. Tagliavini, M., Zavalloni, C., Rombolà, A.D., Quartieri, M., Malaguti, D., Mazzanti, F., Millard, P. and Marangoni, B. (2000) Mineral nutrient partitioning to fruits of deciduous trees. Acta Horticulturae 512, 131–140. Testoni, A. (1995) Momento di racolta, qualita, condizionamento e confezionamento delle pesche. In: Proceedings of the Symposium ‘La peschicoltura Veronesa alle soglie del 2000’, Verona, Italy, 25 February, pp. 327–354. Trainotti, L., Zanin, D. and Casadoro, G. (2003) A cell-oriented genomic approach reveals a new and unexpected complexity of the softening in peaches. Journal of Experimental Botany 54, 1821–1832. Trainotti, L., Bonghi, C., Ziliotto, F., Zanin, D., Rasori, A., Casadoro, G., Ramina, A. and Tonutti, P. (2006) The use of microarray µPEACH1.0 to investigate transcriptome changes during transition from pre-climacteric to climacteric phase in peach fruit. Plant Science 170, 606–613. Uriu, K., Wereniels, P.G., Retan, A. and Fox, D. (1964) Cling peach irrigation. California Agriculture 18, 10–11. Ventura, M., Sama, A., Minguzzi, A., Lanzón, S. and Sansavini, S. (2000) Ottimizzazione del carico di fruti per migliorare la produzione e la qualita delle nectarine Supercrimson e Venus. In: Proceedings of XXIV Convengo Peschiolo, Cesena, Italy, 24–25 February, pp. 173–176. Ziosi, V., Bregoli, A.M., Borghi, C., Fossati, T., Biondi, S., Costa, G. and Torrigiani, P. (2006) Transcript levels of ethylene perception and biosynthesis genes as altered by putrescine, spermidine and aminoethoxyvinylglycine (AVG) during the course of ripening in peach fruit (Prunus persica L. Batsch). New Phytologist 172, 229–238.

21

Ripening, Nutrition and Postharvest Physiology A. Ramina,1 P. Tonutti2 and W. McGlasson3

1Department

of Environmental Agronomy and Crop Science, University of Padova, Legnaro, Italy 2Sant’Anna School of Advanced Studies, Pisa, Italy 3Centre for Plant and Food Science, University of Western Sydney, Sydney, New South Wales, Australia

21.1 Introduction 21.2 The Main Processes Deﬁning the Ripening Syndrome Respiration Ethylene biosynthesis and perception Flesh softening and melting Organic acid and sugar metabolism Colour and aroma development 21.3 Nutritional Value and Healthiness 21.4 Postharvest Physiology Genetic differences among cultivars Effect of low temperature Effect of controlled atmosphere and modiﬁed atmosphere packaging 21.5 Future Perspectives and Conclusions

21.1 Introduction Peach fruits ripen rapidly and have a short postharvest life, usually limited to 3–4 weeks depending on storage conditions. They are climacteric fruit that ripen on the tree or after harvest if picked mature. Crop maturity at harvest strongly inﬂuences quality and shelflife. Determination of ideal harvest maturity is critical to maximize yield, fruit size and consumer acceptability. Generally, early-harvested fruits have good storability but they are of lower quality than late-harvested fruits, 550

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which have higher quality but shorter storage life. Immature peaches will not ripen to dessert quality, whereas those harvested too late will be too soft to withstand commercial handling. Early picking results in poor ﬂavour and a bitter acid taste, which is due to relatively low sugar concentrations and a high content of organic acids, polyphenolics and aldehydes (Robertson et al., 1988; Horvat et al., 1990). Typical peach ﬂavour compounds such as d-decalactone, g-decalactone, linalool and benzaldehyde that contribute to fruit fragrance are low or absent in fruit harvested

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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immature (Horvat et al., 1990; Visai et al., 1993). Change in ground colour is a useful maturity index (Eccher Zerbini et al., 1991), because it changes along with other important parameters such as soluble solids, ﬂesh ﬁrmness and volatile compounds. Ground colour can be estimated by comparison with colour charts (Meredith et al., 1989) or it can be measured with an electronic colorimeter according to the CIE system (McGuire, 1992). Neri and Brigati (1994) proposed several minimal instrumental parameters that peach fruits should possess at harvest in order to meet quality standards. These parameters include ﬁrmness no more than 45 N, positive ‘a’ values and soluble solids content not less than 12%. The relationship between changes in ground colour and ﬁrmness of fruit ripening on the tree is affected by the light environment in which a fruit develops (Lewallen and Marini, 2003). Newer technologies that use time-resolved reﬂectance spectroscopy offer the prospect of machine grading of fruit maturity (Eccher Zerbini et al., 2006; Tijskens et al., 2007). These technologies are based on the relationship between degreening and softening of the ﬂesh during ripening. In practice, compromises among fruit maturity, yield and possible higher prices for early-picked fruit are often adopted. An immunological assay of ripening-related proteins is feasible for establishing the physiological age of the fruit (Abdi et al., 2002). The changes in the ripening-related proteins would be related to changes in external appearance to assist pickers to select mature fruit. Although perishability is the limiting factor in postharvest handling and marketing of peaches, ﬁnal quality and consumer acceptance and some postharvest responses are also affected by preharvest factors, such as growing conditions, cultural practices and genetic potential. Various preharvest stresses may have signiﬁcant impact on fruit ﬂavour, weight, overall appearance and storage potential (Crisosto et al., 1997). Peach fruit ripening can be slowed by application of postharvest technologies that reduce metabolic activity. These technologies include cooling the fruit and/or establishing controlled and/or modiﬁed atmosphere conditions (low concentration of oxygen and elevated concentration of carbon dioxide). Application

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of these technologies reduces respiration rate, ethylene biosynthesis and action as well as other biochemical processes. However, these technologies may negatively affect speciﬁc quality parameters and induce the development of physiological disorders (Lill et al., 1989). Thus, the knowledge of ripening physiology and the postharvest behaviour of peach fruits provides the basis for improving quality and maintaining high eating quality along the marketing chain. In the last decade many biochemical and molecular processes that operate during peach fruit ripening have been elucidated and ways to optimize postharvest practices to maintain shelf-life have been proposed.

21.2 The Main Processes Defining the Ripening Syndrome Respiration Peach is classiﬁed as a climacteric fruit because respiration increases during ripening. Compared with other species the average respiration rates of peaches are classiﬁed as moderate (Wills et al., 2007). According to the growth stages deﬁned by Tonutti et al. (1991), respiration rates are high (about 150 cm3 CO2/kg per h) during stage I of fruit development, when growth occurs predominantly by cell division, decreasing through stage II (pit hardening) and part of stage III (second exponential growth), rising gradually at the end of stage III and ﬁnally reaching the climacteric peak at stage IV (ripening). However, climacteric peaks are highly variable and range from 15 to 80 cm3 CO2/kg per h according to genotype, including yellow versus white ﬂesh, melting versus non-melting (Brady, 1993; Ventura et al., 1998; Brovelli et al., 1999). In some genotypes, the increase in respiration at ripening is so moderate that the typical climacteric behaviour is not readily apparent. Marked differences have also been observed in relation to the duration of the fruit developmental cycle, which dictates the harvest time: the shorter the developmental cycle (and the earlier the harvest date), the higher and more pronounced the respiration rate at the climacteric (Ventura et al., 1998).

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Ethylene biosynthesis and perception Ethylene plays a crucial role in the initiation and continuation of ripening of climacteric fruit. An increase of ethylene biosynthesis is associated with several plant developmental events. Internal ethylene concentrations are less than 1 µl/l during fruit growth and development up to the onset of ripening. This basal level refers to ‘system 1’ of ethylene biosynthesis. At stage IV ethylene evolution begins to increase, reaching a peak usually associated with the last stage of ripening (Tonutti et al., 1991). This constitutes the ‘system 2’ of ethylene biosynthesis, characterized by the autocatalytic action of the hormone (McMurchie et al., 1972). As a consequence of this autocatalytic action, the application of exogenous ethylene or one of its analogues, such as propylene, to mature fruit at 10 µl/l for 24–48 h at 20–25°C is sufﬁcient to enhance ripening, although less mature fruits need continuous exposure to the hormone for longer periods. Also in peach fruit, the biosynthesis of ethylene requires the action of two key enzymes, 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO), responsible for the formation of ACC and the oxidation of ACC to ethylene, respectively, as demonstrated in early works (Miller et al., 1988; Amoros et al., 1989; Tonutti et al., 1991). At ripening, peach whole fruit and mesocarp tissue show a temporal difference in ethylene biosynthesis. A gradient in biosynthesis between mesocarp and epicarp has been detected. The epicarp is more efﬁcient in converting ACC to ethylene (Tonutti et al., 1991). In several peach cultivars (‘Springcrest’, ‘Redhaven’, ‘Fayette’, ‘Bailey’, ‘Suncrest’) ethylene evolution begins to increase when fruits have already started to soften and the highest biosynthetic rates occur in the latest stage of ripening (Fig. 21.1a). Thus, peaches should be listed among those fruit species in which the ethylene climacteric coincides with or follows eating ripeness. In peach this stage corresponds to ﬂesh ﬁrmness values of about 30–40 N. Huge variation exists among cultivars in terms of ethylene evolution rates at ripening (Ventura et al., 1998). Low levels of ethylene biosynthesis are not necessarily related to slower rates of loss of ﬁrmness or to the non-melting trait (Brovelli et al., 1999).

Stony hard (hd) peaches are characterized by the absence of both ethylene production at ripening and postharvest softening. However, melting and non-melting hd genotypes have been distinguished by the degree of softening following exogenous ethylene treatments (Haji et al., 2003, 2005). In the ‘Fantasia’ nectarine cultivar and in some of its progenies a correlation between ethylene evolution and softening rate has been observed (Brecht and Kader, 1984). Within these progenies an interesting ripening mutation was found (see Chapter 1, ‘Time of ripening’ section) called ‘slow ripening’. This mutant does not show a characteristic pattern of ripening in terms of ethylene evolution and respiration: in fact, it remains ﬁrm and green and does not exhibit a rise in carbon dioxide or ethylene production for at least 4 weeks after harvest at 20°C. Ethylene production remains at a low basal level for 4 weeks and begins to increase before the respiratory rise, reaching only 15–33% of that detected in the wild type. When exposed to exogenous ethylene during the pre-climacteric stage the response of these fruits is similar to that of non-climacterics. Short exposure to ethylene provokes a respiratory rise but does not affect the rate of ethylene production (Brecht and Kader, 1984). The accumulation of high levels of conjugated ACC in peaches is a curiosity. Amoros et al. (1989) and Uthairatanakij et al. (2005) reported conjugated ACC concentrations ten times greater or more than those of ACC. Three ACS isogenes (Pp-ACS1, Pp-ACS2 and Pp-ACS3) have been reported in peach but only Pp-ACS1 is associated with ripening (Mathooko et al., 2001; Tatsuki et al., 2006). Ethylene production at ripening is strictly related to increases in ACC content and ACS activity and related transcripts. Analysis of the accumulation pattern of speciﬁc mRNA indicates that, in peach, Pp-ACS1 is developmentally controlled. Southern blot analysis revealed that, as in other species, ACS is encoded by a multigene family. In tomato these members are differently regulated and the polymorphism of ACS has been claimed to be involved in the transition from system 1 to system 2 of ethylene biosynthesis (Nakatsuka et al., 1998; Barry et al., 2000). Preharvest application of aminoethoxyvinylglycine (AVG) has been shown to delay ripening and to

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Fig. 21.1. Firmness and ethylene evolution (a), 1-aminocyclopropane-1-carboxylate oxidase (ACO) activity and Pp-ACO1 transcript accumulation (b) and Pp-ETR1 and Pp-ERS1 expression (c) during the final stages of fruit development of cultivar ‘Springcrest’. (Parts a and b modified from Tonutti et al., 1997; part c modified from Rasori et al., 2002.)

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allow further increase in fruit size (Rath and Prentice, 2004). AVG is a strong inhibitor of ACS activity (Boller et al., 1979). Work with nectarines suggested that AVG may act on other enzyme systems in addition to ACS. Softening was retarded in AVG-treated fruit ripened at 20°C soon after harvest, whereas AVG-treated fruit ripened after 1 week of storage at 1.0–1.5°C softened at the same rate as untreated fruit (McGlasson, et al., 2005). Recently it has been shown that the reduced level of ethylene production in stony-hard peaches, causing a lack of softening, is due to a suppression of Pp-ACS1 transcription at ripening (Hayama et al., 2006; Tatsuki et al., 2006) (for ﬂesh texture phenotypes, see Chapter 1, ‘Flesh texture’ section). Interestingly, the same gene appeared to be transcribed in wounded immature, pre-climacteric and climacteric fruits. This would indicate that one possible mechanism of repression of Pp-ACS1 mRNA is the interruption of the ripening-related transcriptional activity by some insertion or deletion in the 5′-ﬂanking region of Pp-ACS1, which contains a cis-regulatory domain of the ripening-related sequences. Another possible reason is the disruption of a transcriptional factor speciﬁcally activated to induce PpACS1 mRNA at ripening (Tatsuki et al., 2006). Callahan et al. (1992, 1993) and Lester et al. (1994) were the ﬁrst to isolate ACO cDNA clones. They demonstrated that ACO transcripts strongly accumulated during the late stages of ripening, consistent with the patterns of ethylene evolution and ACO activity (Fig. 21.1b) (Tonutti et al., 1991). In mature peach fruit, the ﬁrst detectable increase in ACOrelated transcripts takes place when ethylene biosynthesis is still at a basal level and before textural changes occur (Lester et al., 1996). This pattern indicates that peach ACO gene expression is under developmental control and that it is ethylene-regulated. This has been conﬁrmed by Ruperti et al. (2001), who isolated and characterized two members of the peach ACO gene family, named Pp-ACO1 and Pp-ACO2. Pp-ACO1 is organized in four exons interrupted by three introns whereas Pp-ACO2 has only two of the three introns of Pp-ACO1. Comparison of deduced amino acid sequences of the two genes revealed 77.7% identity. Pp-ACO1 transcripts accumu-

late strongly in ripe mesocarp as well as in abscising fruitlets and senescing leaves, and are enhanced by ethylene. Pp-ACO2 mRNA is detected in fruits only during early development and is unaffected by ethylene. Functional analysis (Rasori et al., 2003) showed that, within the promoter region of the gene, ethylene-responsive elements are present in Pp-ACO1 but not in Pp-ACO2. This may account for the different responsiveness to exogenous ethylene of the two genes. In addition, two auxin-responsive elements, probably responsible for the auxin suppression of the ethylene induction of Pp-ACO1 gene expression are present upstream of the ethylene-responsive elements. Speciﬁc regulatory elements affecting transcription in a tissue-speciﬁc manner as well as a region controlling the temporal expression of the gene have been identiﬁed in the promoter of PpACO1 (Moon and Callahan, 2004). There have been tremendous advances in elucidation of the mechanisms of ethylene perception and signal transduction in Arabidopsis (Chang et al., 1993; Hua et al., 1995). Recently, two peach genes, Pp-ETR1 and PpERS1, showing a similar organization to that of the corresponding genes in Arabidopsis have been isolated (Rasori et al., 2002). As observed in other species (Bleeker, 1999), these two genes belong to a multigene family. Southern blot analysis carried out with the speciﬁc probe for Pp-ERS1 suggests that, in peach, at least one other gene related to PpERS1 exists. The presence of two genes encoding ERS type protein has only been reported in Arabidopsis (Hua et al., 1998). The deduced proteins of the two genes contain a sensor domain and a hystidine kinase domain, in which residues thought to be important for the normal function of ETR and ERS type protein as ethylene receptors are conserved. These results indicate that Pp-ETR1 and PpERS1 could be putative ethylene receptors with the ability to bind ethylene in peach. Quantitative RT-PCR data showed that PpETR1 and Pp-ERS1 transcripts are differentially expressed in immature and ripe fruit (Fig. 21.1c). Pp-ETR1 appears to be constitutive and ethylene-independent during fruit development and ripening, whereas Pp-ERS1 transcripts increase during fruit ripening and its expression appears to be upregulated by

Ripening, Nutrition and Postharvest Physiology

ethylene (Rasori et al., 2002). The correlation between ripening and expression of Pp-ERS1 has been conﬁrmed by experiments with 1-methylcyclopropene (1-MCP), a competitor of ethylene for the binding sites. The continuous application of the chemical delayed fruit ripening, evaluated in terms of softening, decay and ethylene evolution, and concurrently downregulated Pp-ERS1 while Pp-ETR1 transcription was unaffected. 1-MCP action was rapidly abolished after moving fruits to air, when a stimulation of ethylene evolution and a concurrent increase in Pp-ERS1 mRNAs were observed. Recent investigations pointed out that the ethylene biosynthetic and signal transduction pathways are differently affected by 1-MCP in apple and peach (Dal Cin et al., 2006). The chemical is effective in delaying ripening in apples while in peaches it has only a limited effect. This different behaviour has been attributed to differences in terms of ratio, expression patterns and/or turnover of the ethylene receptors.

Flesh softening and melting Most fruit soften during ripening and this is the major quality attribute that often dictates shelf-life. Fruit softening could arise from different processes: loss of turgor, degradation of starch and breakdown of the fruit cell walls. Loss of turgor is largely a non-physiological process associated with postharvest dehydration of the fruit. Degradation of starch probably results in a pronounced textural change, especially in fruits like banana, where starch accounts for a high percentage of the fresh weight. Changes in texture occurring during the ripening of most fruit are thought to be largely the result of cell wall degradation. Carbohydrate polymers make up 90–95% of the structural components of the wall, the remaining 5–10% being largely hydroxyprolinerich glycoproteins. The carbohydrate polymers can be grouped together as cellulose, hemicelluloses and pectins. In melting peaches ﬂesh ﬁrmness decreases slowly at the beginning of ripening (softening stage). During the later stage of ripening the loss of ﬁrmness is rapid (melting stage). Also in the peach, ﬂesh softening has been related to the modiﬁcation of

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pectic polymers which undergo solubilization and depolymerization, particularly during the melting stage (Dawson et al., 1992). Besides pectins, hemicelluloses also change their apparent molecular mass during peach softening, resulting in decreased tissue cohesion (Hedge and Maness, 1998). Cell wall enzymes are responsible for these changes and a number of cell wall hydrolases have been identiﬁed in fruit tissue. The most important enzymes include pectinmethylesterase (PME) (EC 3.1.1.15), polygalacturonase (PG) (EC 3.2.1.15), b-(1,4)-glucanase (EG) (EC 3.2.1.4) and b-galactosidase (b-GAL) (EC 3.2.1.23). These are either constitutive throughout development and ripening, or present in very low amounts and exist as several isoforms within the fruit tissue. In general, PME and b-GAL activities are present during the development of the fruit. Both PG and EG tend to be absent in mature green fruit but their activities become measurable only with the onset of ripening and increase dramatically afterwards. Both of these enzymes tend to be predominantly endo-acting hydrolases, although exo-acting PG activity is also found during ripening in several fruits. Considering the complexity of both wall structure and enzyme proﬁles it is unlikely that a single enzyme is responsible for textural change. This process probably involves a complex interaction of enzyme activity with physicochemical changes in the cell wall. In melting peaches, PG activity increases during ripening (Pressey et al., 1971) and exoand endo-acting PG have been identiﬁed in ripe peaches (Pressey and Avants, 1973). The endo-acting enzyme (EC 3.2.1.15; endoPG) is found in signiﬁcant amounts only in melting peaches; the exo-enzyme (EC 3.2.1.67; exoPG) has comparable activity in the mesocarp of both melting and non-melting fruit (Pressey and Avants, 1978). Downs and Brady (1990) found two forms of exoPG that increase during ripening. EndoPG and exoPG activity increase gradually as fruit soften, but the rate of increase in activity accelerates when the fruit are very soft (<20 N) (Downs et al., 1992; Orr and Brady, 1993). These ﬁndings suggest that initiation of softening is not associated with exo- and endoPG activity. In the earlyripening nectarine cultivar ‘Armking’, PME activity appeared to be more closely related

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with the decrease in ﬂesh ﬁrmness than PG, even though the increase in enzyme activity measured throughout ripening was higher for PG than for PME (Artes et al., 1996). The approach to study PG at the molecular level in peach started from the evidence that tomato and peach endoPG are immunologically related. Using a tomato PG cDNA, a 3.5 kb fragment of peach DNA was isolated and 3.25 kb was subcloned and sequenced. The 3′ ends of tomato and peach PG showed extensive homology in the coding region but some differences in part of the gene structures. The presence of several bands in Southern blot analyses suggests that endoPG in peach is encoded by a multigene family with more than three genes (Lester et al., 1994). Expression analyses carried out with the partial PG cDNA conﬁrmed that the accumulation of speciﬁc mRNA in ‘Flavorcrest’ (melting) fruit occurred in a pattern similar to that of increases in endoPG activity (Lester et al., 1994). Thus, no hybridization was detected in fruits with ﬂesh ﬁrmness values ranging from 120 to 40 N, but only when the ﬁrmness value dropped below 5 N did a strong signal appear. These data conﬁrm the role played by endoPG during the melting stage in peach fruit. A cDNA, PRF5, was identiﬁed as a fruit-related endoPG that may be involved with the texture differences (Lester et al., 1996). Callahan et al. (2004) and Morgutti et al. (2006) found a relationship between the non-melting trait and a deletion in at least one of the PRF5related PG genes. Recent ﬁndings revealed the existence of a single locus containing at least one gene encoding an endoPG controlling both freestone and melting ﬂesh traits with at least three effective alleles (Peace et al., 2005). As far as EG (also known as cellulase) is concerned, it hydrolyses the b-1,4-glucan linkages of plant cell wall polymers that contribute to weakening of the wall structure during processes (such as ripening) characterized by cell separation phenomena. Hinton and Pressey (1974) found during ripening that EG activity increases before any signiﬁcant change in fruit ﬁrmness. Similar results have been obtained by Bonghi et al. (1998), who found that the increase of EG activity, occurring at early softening and stimulated by propylene, was due to a pronounced increase in the basic

isoform. These data conﬁrm that there is a relationship between ethylene and EG and show that EG is mainly involved in the initial phase of peach fruit softening, before the action of PME and PG. The presence of different EG isoforms suggests that a multigene family is present in peach as observed in other plant species. Three cDNA clones (pCel10, pCel20 and pCel30) have been isolated from peach leaf and fruit abscission zone RNA: the three clones showed a high degree of divergence and different expression patterns (Trainotti et al., 1997). Only transcripts related to pCel10 have been detected with a Northern blot analysis in leaf and, to lesser extent, in ﬂower abscission zones. RNase protection assay (RPA) conﬁrmed that pCel20- and pCel30-related mRNAs scarcely accumulate during abscission and ripening and that pCel10-related transcripts are barely detectable during fruit softening. The screening of a genomic library with the cDNA clone pCel10 allowed the isolation of a peach EG gene named PpEG1, which encodes a polypeptide of 497 amino acids with a predicted molecular mass of 54.3 kDa that shares the highest similarity (76.3%) to the avocado ripening EG. PpEG1, a member of the small peach EG family, is present in the peach genome as a single-copy gene. Using a 753 bp PCR product, identical to the corresponding sequence of PpEG1, Bonghi et al. (1998) were unable to detect related transcripts when Northern blot analysis was performed on poly(A) + RNA extracted from peach mesocarp during early and late climacteric stages. A lack of signal in these tissues was also observed when RPA was performed, indicating the low abundance of EG transcripts in peach fruit tissues. EG transcripts were detected in fruits at all stages of fruit development only following RT-PCR. The highest accumulation of EG-speciﬁc transcript corresponded to the onset of the ethylene climacteric and the early phase of ﬂesh softening. Treating pre-climacteric peach fruits with propylene, besides enhancing EG activity, strongly accelerated speciﬁc transcript accumulation and the loss of ﬁrmness within 24 h. In the same experiments the use of a speciﬁc inhibitor of ethylene action (2,5-norbornadiene) reduced these parameters. Differently from PpEG1, PpEG4,

Ripening, Nutrition and Postharvest Physiology

another member of the peach EG family, shows a decreasing expression pattern through ripening (Trainotti et al., 2006b), being downregulated by ethylene (Begheldo et al., 2008). Expansins are proteins that have been shown to contribute to tomato fruit softening. Recently, some expansins have been related to a loss of fruit ﬁrmness in peach (Hayama et al., 2003). Three expansins, named Pp-Exp1, Pp-Exp2 and Pp-Exp3, have been isolated from ripe peach fruit: all three expansins were detected in the fruit and not in other tissue, although each showed a different pattern of expression during fruit development. Pp-Exp2 RNA was expressed constitutively throughout fruit development but was more abundant in stage III, during exponential growth and maturation. Pp-Exp1 and Pp-Exp3 were upregulated at the onset of ripening but Pp-Exp1 was induced at an earlier stage. However, by comparing cultivars with different rates of softening, Pp-Exp3 shows a closer association with softening. A cell wall-oriented genomic approach revealed a new and unexpected complexity in the softening of peaches (Trainotti et al., 2003). The genes analysed encode proteins involved in the main metabolic aspects of a primary cell wall (degradation, synthesis, structure) (Fig. 21.2). In addition, some genes encoding cell wall-related proteins with an unknown function have been found. The gene expression proﬁles showed that softening begins well before the ethylene climacteric rise and continues thereafter. Genes whose expression begins before the climacteric rise are mostly downregulated by ethylene, while those that are ripening-speciﬁc are mostly upregulated by the hormone. A few other genes are apparently insensitive to ethylene. According to the expression analysis of the genes involved in cell wall degradation, pectatelyase seems to play an interesting role. Speciﬁc transcripts for this enzyme are downregulated by ethylene but they increase markedly during the early stage of softening and before the highest accumulation of PG transcripts. Besides the expected partial degradation, softening processes include some repair of the cell walls performed by enzymes involved in the synthesis of cell wall polysaccharides, especially by proteins with structural functions. The newly

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synthesized polysaccharides and structural proteins would thus help to maintain cell wall integrity while not preventing softening (Trainotti et al., 2003).

Organic acid and sugar metabolism Peach organoleptic quality depends on colour, texture and ﬂavour attributes that are mostly determined during ripening (Brady, 1993). In contrast, acidity, which is an essential component of the fruit taste, is thought to be determined during the early stages of fruit development. In peach, as in most fruits, the two major organic anions are malate and citrate (amounting to 140 and 120 mM H+, respectively), which account for most of the titratable acidity and, as a general trend in high-acid cultivars, tend to decrease during ripening. Major differences exist between high- and low-acid (sub-acid) cultivars: for example, in ripe fruit of ‘Fantasia’, which is an acidic cultivar, juice titrable acidity is about 400 mmol l−1 H+, while in ‘Jalousia’ (low-acid) it is around 40 mmol l−1 H+ (Moing et al., 1998) (Fig. 21.3). Low acidity is a quantitative trait regulated by a single dominant gene (Yoshida, 1970; Monet, 1979; see Chapter 1, ‘Flesh compounds’ section). In acidic cultivars, malate accumulates mainly in early fruit development, slows down during stage II and increases moderately in stage III, while citrate increases mainly during late stage III. In lowacid cultivars a reduced accumulation of malate at early growth stage and citrate at late stage III has been observed (Moing et al., 2000). It was proposed that phosphoenolcarboxylase (PEPC) plays a major role in controlling the fruit organic acid metabolism (Moing et al., 1999). PEPC has been regarded as the key enzyme because it catalyses the b-carboxylation of phosphoenolpyruvate to yield oxaloacetate and inorganic phosphate. The oxaloacetate is reduced by NAD-dependent malate dehydrogenase to produce malate. Oxaloacetate and malate can enter the tricarboxylic acid cycle to produce citrate and other metabolites. PEPC mRNA and speciﬁc protein levels peaked at early development and late stage III in ‘Fantasia’. In ‘Jalousia’, both

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Fig. 21.2. Using a genomic approach, expression patterns of cDNA clones throughout fruit development and ripening (stage I to stage IV, S1 to S4) were grouped according to three different functions as cell wall weakening (a), cell wall synthesis (b), cell wall structure (c) and unknown (d). Among the previous clones assessed for sensitivity to ethylene at pre-climacteric and climacteric stages, 11 (ctg 219, 404, 167, 364, 874, 254, 10, 152, 187, 418, 839) are upregulated, and nine (ctg 257, 251, 124, 125, 95, 393, 6, 153, 188) are downregulated by ethylene. Five (ctg 190, 285, 907, 528, 821) are apparently insensitive to ethylene. Values on the ordinate axis are expressed as the ratio of the subtracted volumes of the indicated expressed sequence tags and ubiquitin. Arrows indicate ethylene climacteric. (Modified from Trainotti et al., 2003.)

parameters were very low at early fruit development and reached levels similar to ‘Fantasia’ at late stage III. For both cultivars in vitro PEPC activity was maximal at early fruit development, decreased from 24 to 60 days after bloom and then remained constant. The activity of fruit PEPC appears to be extremely sensitive to malate and low pH. PEPC may participate in the control of organic acid accumulation through fruit development in highacid cultivars. However, mechanisms other than organic acid synthesis may account for differences in acidity between acidic and low-acid

fruits. Six peach cDNAs encoding key proteins in organic acid metabolism and solute accumulation have been isolated and characterized (Etienne et al., 2002). The genes involved in organic acid metabolism (mitochondrial citrate synthase, cytosolic NAD-dependent malate dehydrogenase and cytosolic NADP-dependent isocitrate dehydrogenase) showed a stronger expression in ripening fruit than during the earlier phase of development, although their expression patterns were not necessarily correlated with changes in organic acid content. Concerning genes involved in

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storage, the tonoplast proton pump showed a biphasic expression pattern more consistent with the pattern of organic acid accumulation and the tonoplast pyrophosphatases were more highly expressed in the fruit of low-acid cultivar during the second rapid growth phase. Sweetness is the most important factor affecting consumer acceptability of peaches. Sucrose, glucose and fructose in proportion of about 3:1:1 are the main sugars in peaches (Genard et al., 2003). Peaches with high eating quality are considered to have relatively large amounts of fructose and low quantities of glucose and sorbitol (Brooks et al., 1993) because fructose is considered to be 3.0, 2.3 and 1.7 times sweeter than sorbitol, glucose and sucrose, respectively (Kulp et al., 1991). The sugars comprise more than 60% of the soluble solids concentration (SSC) as measured with

120

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Fig. 21.3. pH and titratable acidity of ‘Jalousia’ and ‘Fantasia’ peaches during growth and development. Values are means, with their standard deviation represented by vertical bars (n = 5 fruit). (From Moing et al., 1998.)

a refractometer. There is a general consensus that an SSC reading of at least 12% is required to ensure that peaches are acceptable to most consumers. However, acidity can modify ﬂavour perception. Cultivars have been bred with low, medium or high acidity (Moing et al., 1998). In practice, SSC among fruit of similar size harvested at similar maturity from the same group of trees can vary by 8%. This variation among a population of fruit has serious implications for retailers wishing to provide peaches with guaranteed sweetness, especially in seasons when assimilation rates are low. Genard et al. (2003) developed models to describe the relationships between sugar concentrations in fruit and assimilate supply, metabolism and dilution. The SUGAR model (Fig. 21.4; Genard and Souty, 1996) has been used to relate the ﬂuxes in carbon among

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k1(t)

Sucrose λph

CO2

k1(t)

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Glucose

Carbon supply

k4(t) k2(t) Other compounds

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k3(t) Fig. 21.4. Diagram of the SUGAR model. The arrows and boxes represent carbon fluxes and carbon components, respectively. The two ellipses represent carbon supply and losses by respiration. The proportion of sucrose in the phloem-sourced sugar pool (lph) and the relative rates of sugar transformation k1(t), k2(t), k3(t) and k4(t) for each arrow are indicated. The model predicts the partitioning of carbon into sucrose, sorbitol, glucose and fructose into the mesocarp of peach fruit. The model can be used to simulate the effects of changing assimilate supply and fruit volume on sugar concentrations. (From Genard et al., 2003.)

sugars, sorbitol, other compounds and respiration. Glucose and fructose are accumulated at a nearly constant rate throughout development and ripening (Souty et al., 1998). The glucose:fructose ratio decreases during maturation: being nearly 1 during stage III, it falls to 0.8 at ripening, showing that glucose is preferentially used for respiration. Sucrose accounts for the major part of the increase in dry weight, and its concentration at ripening represents more than 50% of the dry weight. There is a good correlation between sucrose accumulation and the increase in fruit dry weight. Sucrose accumulates rapidly during the last few days of maturation on the tree, reaching a plateau at the ethylene climacteric. These data suggest a negative role for ethylene in sucrose accumulation since pre-climacteric applications of AVG and polyamines delay the ethylene climacteric and SSC increase at harvest (Bregoli et al., 2002; Vizzotto et al., 2002). Although sorbitol is generally low in peach fruit, this sugar alcohol and sucrose account for most of the carbon translocated in the phloem from leaves to the fruit. After unloading in the fruit, sorbitol is rapidly

metabolized to glucose and fructose by sorbitol oxidase and sorbitol dehydrogenase, respectively. It has been shown that the mesocarp exhibits a capacity to actively accumulate sugars and that this tissue has different sucrose synthesis and cleavage activities, including sorbitol dehydrogenases, sucrose synthases and invertases (Vizzotto et al., 1996). A full-length cDNA for NAD-dependent sorbitol dehydrogenase (NAD-SDH) from peach has been isolated and characterized (Yamada et al., 2001). Peach NAD-SDH activity on a fresh weight basis was very strong in immature fruit, declined temporarily and then increased again with fruit maturation. Protein level and enzyme activity paralleled transcript accumulation. The authors concluded that NAD-SDH plays an important role in sorbitol metabolism during peach fruit development, and that the increase in NAD-SDH activity as fruit matures is regulated by gene transcription. More recently RT-PCR gene expression analyses carried out with speciﬁc primers have allowed grouping of genes according to their differential regulation (Nonis et al., 2003). Three genes encoding,

Ripening, Nutrition and Postharvest Physiology

respectively, a putative sucrose synthase (SuSy2), a hexose transporter and a vacuolar invertase showed higher levels of transcription at the early stages of fruit development (stage I), when fruit growth was characterized by active cell division. Subsequently, the transcripts of these genes gradually decreased towards stage II, when endocarp (pit) hardening and seed development primarily take place. Genes for a hexose transporter and SuSy2, together with a gene encoding a putative sucrose phosphate synthase, were clearly upregulated during fruit ripening (stage IV), a phase characterized by cell expansion. Three genes, encoding respectively a cell wall invertase, a cytoplasmic invertase and a sucrose transporter, also appeared to be transcribed to some extent during early fruit development. In addition, there was a transient increase in their mRNAs coincident with the onset of the second phase of exponential fruit growth (stage III) and of sucrose accumulation in mesocarp cells. The transcription of a neutral invertase (Pp-NT1) appeared to be regulated in response to sugar signals only in the phase of fruit expansion coincident with the onset of sucrose accumulation (Nonis et al., 2007). A gene encoding an additional sucrose synthase (SuSy1) was expressed at low levels in fruits. Expression data obtained for genes related to sugar metabolism may point to a role for these genes during peach fruit growth. In fact, an association was found between the expression of some of these genes and the stages of fruit development during which growth is powered by cell division. A relationship was also evident between the transient upregulation of a different group of genes and the developmental switch leading to sucrose accumulation and to growth processes driven by cell enlargement.

Colour and aroma development Colour changes that are associated with ripening strongly inﬂuence visual and eating quality of peaches. Genotypical differences markedly affect colour and intensity; for example, non-melting peaches have signiﬁcantly higher total carotenes and xanthophylls

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than melting-ﬂesh peaches (Karakurt et al., 2000). Colour changes are associated with degradation of chlorophyll, which in turn, in the yellow-ﬂeshed cultivars, unmasks other pigments such as carotenoids. The loss of chlorophyll is accompanied by the biosynthesis of anthocyanins in the epicarp and deep mesocarp. Lessertois and Moneger (1978), working on fruits of ‘Earlyglo’ (yellow ﬂesh), showed that fruit pigments of the mesocarp are of the foliar type, i.e. chlorophylls, a- and b-carotene, lutein, epoxylutein, violaxanthin and neoxanthin. The transformation of the ovary into the green adult fruit is accompanied by a decline in the content of chlorophylls; total carotenoids decrease to levels as low as 55% of the initial content and subsequently transitorily accumulate. In mature fruits, 42% of the carotenoids are oxidized and all carotenoids are of the b-conﬁguration. Later on, the carotenoids disappear but the chlorophylls remain in traces. More recent data from ‘Red Star’ (yellow ﬂesh, late ripening) showed that carotenoid content increases throughout fruit ripening and this occurs concurrently with an accumulation of phytoene synthase, z-carotene desaturase, lycopene b-cyclase and b-carotene hydroxylase transcripts, as reported, in ‘Fantasia’, by Trainotti et al. (2006a). However, carotenoid content decreases during the postharvest phase. Ethylene biosynthesis and action might be involved in the regulation of carotenoid biosynthesis during ripening, since anoxia or 1-MCP treatments applied at a pre-climacteric stage reduce the level of pigments. 1-MCP treatment performed in a conﬁned environment on the tree at early ripening maintains carotenoid content while it is totally ineffective if applied during the postharvest phase (Mencarelli et al., 1998). Aroma is determined by volatile components produced by peaches in concentrations that can be perceived by the human nose. Aroma compounds arise from several different substrates including fatty acids, amino acids, phenolics and terpenoids. Aldehydes, esters, ketones, terpenoids and sulfur-containing compounds account for most of the important ﬂavour volatiles in fruits. Takeoka et al. (1988) emphasized the important role of lactones and other products of the peroxidation

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of unsaturated fatty acids by lipoxygenase (LOX) in nectarines. In unripe peaches most of the compounds that impart green aroma are aldehydes and C6 alcohols (hexanal, trans2-hexanal, hexanol, trans-2-hexanol), while in ripe fruit the main components are lactones (g-decalactone and d-decalactone). Signiﬁcant increases in benzaldehyde and linalool have also been detected. A good marker for peach aroma is cis-3-hexenylacetate (De Santis and Mencarelli, 2001). At least some part of the development of peach aroma is controlled by ethylene. Application of 1-MCP results in higher levels of C6 compounds (hexenals and hexanols) and lower amounts of esters (Mencarelli et al., 2003). Similarly, it has been shown in banana fruit that initiation of volatile production occurs at a later stage in ripening and 1-MCP stimulates production of aldehydes and alcohols and suppresses ester production (Golding et al., 1999).

21.3 Nutritional Value and Healthiness Fruits are an important part of our daily diet, given the protective role played by some fruit components against serious human diseases. Recent experimental evidence has shown that fruit have higher ‘global’ antioxidant activity than either isolated natural single components or conventional synthetic antioxidants used as food additives (Eberhardt et al., 2000). From a dietary point of view, the most important fruit constituents are carotenoids, phenolics and ﬁbre. Carotenoids, besides being an important component of fruit colour, are a good source of vitamin A, which is essential for normal growth, reproduction and resistance to infections in man. Carotenoids are converted to vitamin A after ingestion. Yellow-ﬂeshed peaches are considered a good source of provitamin A carotenoids, mainly b-carotene and b-cryptoxanthin (Gross, 1987). Carotenoids are unstable when exposed to low pH, oxygen and light (Klein, 1987). Wounding, by triggering ethylene production and senescence, provokes the oxidation of fatty acids by LOX and may cause degradation of carotenoids by co-oxidation (Thompson et al., 1987).

Antioxidant activity of phenolic compounds is closely related to their chemical structure (Robards et al., 1999), particularly the hydroxylation level of the B-ring (Dziedzie and Hudson, 1983) and the extent of glycosylation. Glycosylated forms are normally characterized by a lower antioxidant activity compared with the aglycones. Flavonols, which are glycosylated forms of quercetin and kaempferol, are the most abundant phenolics in peach and other stone fruits (Henning and Herrmann, 1980; Young et al., 1989, Bengoechea et al., 1997). Myricetin has been proposed as a phenolic marker for peaches since this ﬂavonol is not present in other fruit species (Fernandez de Simon et al., 1990, 1992). Recent work by Costa and co-workers (G. Costa, Italy, 2007, personal communication) showed that the chromatographic proﬁle of phenolics in peaches is characterized by 17 main peaks, identiﬁed on the basis of their retention times and ultraviolet absorbance, and by co-chromatography with commercial standards. The phenolic proﬁle appears to be consistent among cultivars, although the concentration of each compound may vary within cultivars and tissue. Cyanidin and glycosylated quercetin are present mainly in the epicarp, while the cinnamic acids including chlorogenic and neochlorogenic acids are the most abundant and widely distributed in the mesocarp and epicarp (1.27 and 0.5 mg/g dry weight, respectively). In fruits and vegetables complex carbohydrates such as cellulose, hemicellulose and pectins, which are not digested by humans, comprise dietary ﬁbre (Salunkhe et al., 1991; Kader and Barret, 1996; Kader, 2002). It has been shown that ﬁbre consumption, mainly the soluble forms, decreases plasma cholesterol (Ebihara et al., 1979) and glycaemic response (Sharaftedinov et al., 1999; Southon, 2000). Recent studies have shown that dietary ﬁbre concentrates from by-products of processed fruit and vegetables have total ﬁbre content (35–58%) higher than cereal brans and a better insoluble:soluble ratio (Holloway, 1983; Grigelmo and Martin-Belloso, 1999). Grigelmo et al. (1999) reported that total dietary ﬁbre constitutes about 31–36% of dry matter in peach concentrates, with insoluble ﬁbre being the major fraction (20–24%). The dietary

Ripening, Nutrition and Postharvest Physiology

ﬁbre content of peach baby foods is higher than that found in other types of baby foods (Torija Isasa et al., 1985). Melting and nonmelting ﬂesh peach types differ in pectin content and solubility, and this inﬂuences fruit softening (Pressey and Avants, 1978; Maness et al., 1993; Karakurt et al., 2000). These differences may be of interest from a nutritional point of view because of the well-recognized role of ﬁbre in regulating intestine function, peristaltic movement and, as a consequence, the hunger and/or satiety sensation. Chemoprotective activity of peach fruit is under evaluation in rats and man. Preliminary results showed that a diet enriched with peach fruit downregulates several isoforms of the cytochrome P450-dependent monooxygenases which are involved in the onset of degenerative diseases. The haematic residual antioxidant activity varies among cultivars. According to these preliminary data, cultivars with high dietary values can be identiﬁed (S. Ciapellano, Italy, 2007, personal communication). According to recent epidemiological studies food allergies are increasing in many Western countries. Allergies to fruits are an important problem and research should be aimed at selection of hypoallergenic fruits. The major allergens in Rosaceae fruits are lipid-transfer proteins (LTPs). LTPs are abundant and widespread in nature and form a broad family of proteins whose role is not clearly deﬁned. Besides their biological functions, LTPs have been recently identiﬁed as the major allergen of peach (Pastorello et al., 1999; Sanchez-Monge et al., 1999) and other stone fruits (Pastorello et al., 2000, 2001). They cause an allergy syndrome usually restricted to the oral cavity (oral allergy syndrome), although systemic reactions, including anaphylactic shock, have also been reported (Ortolani et al., 1988). Recently, Asero et al. (2000) showed that immunoglobulin E (IgE) antibodies to stone and pome fruit LTPs react to a broad range of extracts of different plant species such as groundnut, walnut, pistachio, broccoli, carrot, tomato, melon and kiwifruit, indicating that LTPs represent a genuine panallergen. The 9 kDa peach LTP has been puriﬁed and sequence analysis of the protein (named Pru p 1) shows a high degree of homology (average of 65%) with LTPs from

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other plant species (Pastorello et al., 1999). The protein extracted from peach fruit skin, where most LTPs are found (Lleonart et al., 1992), retains its IgE-binding capacity and demonstrates a high stability following heat treatment (Brenna et al., 2000) and pepsin digestion (Asero et al., 2000). Two LTP-related cDNAs have been identiﬁed. As observed in several plant species (Kader, 1996), it has been shown that a multigene family encoding LTPs is present in peach. Southern blot analysis clearly demonstrates the presence of at least four or ﬁve genes. The two isolated peach LTP clones, PpLTP1 and Pp-LTP2, share the common features of plant LTPs (positions of cysteine residues, lipid-binding motifs) but show only 49.6% identity of deduced amino acid sequences (Botton et al., 2002). Low similarity values and phylogenetic analysis, which grouped PpLTP1 and Pp-LTP2 in two distinct clusters, show that these are not duplicated genes, as observed for some members of the LTP family in other species (Pelese-Siebenbourg et al., 1994; Pyee and Kolattukudy, 1995; Arondel et al., 2000), but they have evolved independently from a common ancestor. Like PpLTP1, Pp-LTP2 appears to encode a type-1 (9 kDa) LTP but it lacks the conserved proline and tyrosine residues that characterize the type 2 (7 kDa) LTPs (Monnet et al., 2001) and differs signiﬁcantly from the 7 kDa LTP sequenced by Conti et al. (2001) in apricot. The differential expression patterns of the two isolated clones reinforce the hypothesis of multiple roles for LTPs (Fig. 21.5). In contrast to Pp-LTP1, Pp-LTP2 transcripts have been strongly detected in non-pollinated ovaries and their level declined during a 4-week period after pollination. The absence of PpLTP2 transcripts in petals, sepals, stamens and fruit tissues supports the hypothesis that the role of this gene is highly speciﬁc and conﬁned to pistils, in which it may have different functions (Botton et al., 2002). In fruits only Pp-LTP1 is expressed and its transcripts and related protein abundantly accumulate in epicarp but not in mesocarp, with different patterns according to the genotype (Botton et al., 2006). Since peach allergenic activity is largely concentrated in the skin, it is likely that Pp-LTP1 encodes the

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in Pp-LTP1 transcripts and related protein accumulation indicate that it is possible to select hypoallergenic cultivars (A. Botton, G. Pasini and P. Tonutti, Italy, 2007, personal communication).

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21.4 Postharvest Physiology Genetic differences among cultivars

Pp-LTP2

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Fig. 21.5. Northern blot analysis carried out with Pp-LTP1 and Pp-LTP2 cDNA probes on total RNA (10 µg) extracted from (a) petals (Ptl), sepals (Spl), stamens (Stm), ovaries at different developmental stages (Np-Ov, non-pollinated ovary; P-Ov, pollinated ovary; P-Ov-7DAB, P-Ov-14DAB, P-Ov-21DAB and P-Ov-28DAB, pollinated ovary 7, 14, 21 and 28 days after full bloom, respectively) and (b) epicarp collected at stage I (SI, first exponential growth phase), stage II (SII, endocarp lignification), stage III (SIII, second exponential growth phase), pre-climacteric (PC), climacteric rise (CR) and climacteric peak (CP). (Modified from Botton et al., 2002.)

major allergen of peach, although it cannot be ruled out that also other members of the peach LTP family (or other proteins) may account for allergenicity. These results conﬁrm that peeling is essential for the production of hypoallergenic peach foods. The similar transcript levels detected throughout ripening suggests that the allergenicity due to LTP does not change during the last developmental stage (Botton et al., 2002). Moreover, it has been shown that postharvest storage at low temperature does not affect Pp-LTP1 transcript accumulation. In addition, preliminary assays showing a large variation within genotypes

In addition to differences in ﬂesh colour, sugar levels and acidity, peaches display differences in duration of fruit development, ﬂesh texture, fruit shape and strength of attachment of ﬂesh to the pit. Worldwide, most cultivars are mid- to high-chill, which mature fruit in early summer to autumn. These cultivars have a fruit development period (FDP) in excess of 100 days. More than 30 years ago low-chill cultivars that ﬂower after less than 250 chill units were introduced on to the market. In countries with a wide range of climatic conditions such as Australia, the introduction of low-chill cultivars has extended the peach season to about 6 months. The FDP for low-chill peaches can be as short as 70 days, but even in mediumchill cultivars very early-ripening peaches are available. The slow second phase of fruit growth is absent in these fruit and their growth in size follows essentially a sigmoidal pattern. Early-ripening cultivars may receive high prices when they ﬁrst arrive on the market but frequently consumers are disappointed because the fruit rarely accumulate more than 10% SSC. A disappointing experience early in the season can deter consumers from buying peaches until much later, even though SSC has reached acceptable levels. Breeders are continuously seeking ways to improve SSC levels in early-maturing cultivars by selection, use of rootstocks that grow well when soil temperatures are still low and enclosures to create microclimates that improve peach tree growth (Nissen et al., 2005a,b).

Effect of low temperature Storage at low temperatures is the most practical way to slow metabolism and extend the

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commercial life of fruits (see also Chapter 22). Both respiration and ethylene biosynthesis are decreased when peach fruits are exposed to low temperatures, which also reduce the activity of cell wall hydrolases, thus delaying softening. Therefore, cold storage is used to slow ripening and decay development even though chilling injury may limit the storage life of peaches and nectarines under low temperature (Lurie and Crisosto, 2005). Considering ethylene physiology, no increase in ACC accumulation has been reported in peaches or nectarines stored at low temperatures either before physiological disorders had begun or after their appearance (Uthairatanakij et al., 2005). It must be noticed that, in prolonged cold storage, maintaining the ability of the fruit to produce ethylene may be crucial to prevent chilling-related physiological disorders (Dong et al., 2001; Zhou et al., 2001). These disorders include a loss of the ability to soften normally when the fruit are returned to normal temperatures, ﬂesh browning, spread of anthocyanin pigments through the ﬂesh (bleeding) and gel breakdown. The most common symptom is a loss of juiciness and the development of a mealy texture. This disorder is called mealiness or woolliness. Mealiness develops in fruit stored at less than 8°C. These disorders are not typical of chilling injury in tropical fruit because best storage life of 2–4 weeks depending on cultivar is achieved near 0°C, but symptoms may also develop following a week of storage at about 5°C (Anderson, 1979). Conditioning at about 20°C for up to 48 h before refrigerated storage or delayed storage sometimes improves the cold storage life of peaches (Zhou et al., 2001; Crisosto et al., 2004). Mealy peaches have a dry texture (cork-like), lack ﬂavour, become brown and less juice can be extracted from affected fruit. Ben-Arie and Sonego (1980) reported that pectin metabolism was abnormal in chilled peaches, leading to the formation of a gel when the soluble pectins were mixed with water. The viscosity of the soluble pectin from chilled peaches was higher than from peaches ripened normally. The binding of water in pectin gels may explain the reduction of extractable juice in mealy fruit. Higher PME activity during cold storage of peach fruit may account for this increase in viscosity

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of soluble pectin. PME produces de-esteriﬁed pectins of high molecular mass that incorporate water in a gel. Normally endoPG breaks down de-esteriﬁed pectins into small fragments but low-temperature storage reduces PG activity, resulting in the accumulation of larger-sized pectin polymers and high juice viscosity in mealy fruits (Zhou et al., 1999). The incidence of mealiness depends on genetic factors and maturity stage; Fernandez-Trujillo et al. (1998) found that less mature fruit were more susceptible to mealiness. Generally, susceptibility to mealiness is less in early-season cultivars than for those that mature late in the season. According to this pattern slow-ripening genotypes are supposed to be more susceptible to mealiness (Brecht et al., 1984; Kader and Chordas, 1984).

Effect of controlled atmosphere and modified atmosphere packaging Reduction in oxygen concentration and an increase in carbon dioxide concentration may retard ripening of peaches and, in some cases, delay or prevent the appearance of chilling symptoms (Lill et al., 1989). With the decreasing availability of molecular oxygen a decline in the general metabolism of the cells occurs. However, large changes do not take place until oxygen falls below about 5%. The critical factor is the actual concentration of oxygen within the cells. Internal oxygen concentration is controlled by resistance of the ﬂesh to oxygen diffusion and the rate of respiration. Changes in these parameters lead to variations in the optimum external oxygen concentration required for various products. Large, dense products generally have a higher external oxygen requirement than smaller and/or less dense products. Due to their sensitivity to chilling injuries some products must be stored at higher temperatures than others, thus increasing their oxygen utilization rate. When low oxygen (1–5% O2) and/or enhanced carbon dioxide concentrations are applied to peaches, softening and colour development may be retarded and the rates of respiration and ethylene production reduced (Smilanick and Fouse, 1989). Oxygen at

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0.25% reduces respiration by 45%, ethylene production rates by more than 90% (Ke et al., 1991) and delays the increase in PG activity (Lurie and Pesis, 1992). Carbon dioxide concentrations are important during storage at low temperature. An atmosphere containing 5% CO2 may delay the appearance of physiological disorders caused by low temperature (Lill et al., 1989). However, there are no speciﬁc recommendations for the composition of the controlled atmosphere because relatively few cultivars give a beneﬁcial response. Wade (1981) found that 20% CO2 (without reduction of O2) effectively decreased the incidence of physiological disorders in ‘J.H. Hale’ peaches during 6 weeks’ storage at 0°C. Subsequent research has shown that only a few cultivars respond to high carbon dioxide levels (Uthairatanakij, 2004). The storage of peaches under controlled atmosphere for longer periods may cause the development of off-ﬂavours and excessive accumulation of acetaldehyde and ethanol (Kader, 1986; Smilanick and Fouse, 1989). The development of off-ﬂavours is a result of prolonged storage in atmospheres particularly rich in carbon dioxide. Considering the effects of low oxygen or high carbon dioxide concentration on ripening physiology, short treatments (a few hours to a few days) may be beneﬁcial to prolong the storage life. Lurie and Pesis (1992) showed that short exposure of fruit to anaerobic conditions (24 h) retards the softening of peach in successive 6-day storage without changing other quality parameters, such as soluble solids and acidity. Gaseous shocks such as ultra-low oxygen (ULO) and 30% CO2 applied for up to 24 and 48 h at 20°C have been shown to maintain ﬂesh ﬁrmness during the post-treatment phase (in air) (Bonghi et al., 1999). This effect is accompanied by a strong inhibition of ethylene evolution, particularly in those fruits harvested at an early stage of ripening when endogenous ethylene production is low. The effect of these treatments on the softening process has been related to the temporary inhibition of EG activity. Levels of O2 below 1% or CO2 levels above 20% induce acetaldehyde and ethanol accumulation in several fruit species including peaches. Prolonged anaerobiosis results in excessive accumulation of

acetaldehyde and ethanol in peach mesocarp (Tonutti et al., 1998). Short-term treatments with low oxygen, besides reducing the softening rate, induce a prompt accumulation of acetaldehyde and ethanol. However, their concentrations in fruit tissue decline gradually when the fruit are transferred to air. Acetaldehyde accumulates naturally during normal ripening, although its concentration does not exceed that in anaerobically stored fruit. The decrease in acetaldehyde is a result of its metabolism to other compounds (Ke et al., 1995) or diffusion out of the fruit tissue. At 4°C much less acetaldehyde and ethanol accumulate than at 20°C. Fruit stored at lower temperature are apparently less sensitive to anaerobic conditions compared with higher temperature. Induction of alcohol dehydrogenase (ADH) is regarded as one of the reasons for anaerobic fermentation and accumulation of ethanol (Kennedy et al., 1992). Extractable ADH activity depends on oxygen or carbon dioxide concentration as well as on the duration of anaerobic treatment and temperature. Bonghi et al. (1999) detected the presence of a multigene ADH family in ‘Springcrest’ and showed that anaerobic metabolism is rapidly activated following exposure to ULO and high CO2 concentrations.

21.5 Future Perspectives and Conclusions Challenges for peach physiologists include ﬁnding ways to reduce the variability in SSC among fruit within trees and to ensure accumulation of levels that are acceptable to consumers. This is particularly important in low-chill cultivars that have a short FDP. Advances in portable near infra-red technology that permit measurements of sugar levels in developing fruit should greatly assist development of tree management strategies that will reduce within-tree variability (Golding et al., 2006). Peach growers are in the ‘fashion business’ because customers are constantly seeking products with different appearance and ﬂavours. Since the generation time is only about 3 years for peaches, an enormous number of new cultivars are released

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each year. However, breeders must keep uppermost the need to maximize the yield of marketable fruit with high eating quality that will withstand the many transfer points along the distribution chain from orchard to consumer. A challenge for geneticists and breeders is to improve the cool storage life of peaches. Although the seasonality of peaches is one of their attractions to consumers, there is increasing interest in global trading arrangements. The short storage life of peaches restricts the time and distance the fruit can be shipped. An increase in cool storage life of 50% would enable peaches to be shipped by cheaper sea freight to many markets and at the same time achieve in-transit non-chemical quarantine disinfestation treatment of some insect pests. It is an academic challenge to understand why peaches suffer physiological disorders when stored below about 8°C yet maximum storage life is achieved at near freezing temperatures. Findings at the molecular and biochemical levels of the observation that only some cultivars respond beneﬁcially to atmospheres containing up to 20% CO2 could open up new insights into ways to improve cool storage life. Recent advances have shed light on the molecular basis of peach fruit ripening and postharvest physiology. Examination of some aspects of ethylene biosynthesis and perception has demonstrated homology with the basic model deﬁned in Arabidopsis and tomato. Research focused on fruit softening showed that cell wall metabolism during peach ripening is complex and involves the sequential action of different cell wall hydrolases and ethylene, and is developmentally regulated.

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Genetic and molecular characterization of sugar metabolism, pigmentation, aroma, dietary and allergenic properties of peach fruit are proceeding in several laboratories. Each one of these physiological aspects may represent a target for practical manipulation that aims to improve peach fruit quality. The continuing development of genomic tools, including expressed sequence tags (ESTs) and cDNA microarrays, will rapidly advance knowledge of fruit development and ripening in peach as well as other species. In this context, a signiﬁcant contribution has been made by the ESTree Consortium (http://linuxbox.itb.cnr. it/estree_mar2004/, accessed August 2007), which developed the ﬁrst oligo-based microarray (µPEACH 1.0), corresponding to 4806 unigenes expressed in peach fruit (ESTree Consortium, 2005). This array has been used to investigate transcriptome changes during the transition from the pre-climacteric to climacteric phases (Trainotti et al., 2006a). Largescale analysis showed that 267 and 109 genes are up- and downregulated, respectively, during this transition. These genes have been classiﬁed according to the TAIR gene ontology, allowing the identiﬁcation of a new member of the ETR family in peach and a number of transcription factors belonging to several families, putatively involved in the regulation of peach ripening. The number of peach fruit ESTs is expected to increase along with the availability of genomics tools since several research programmes around the world are moving in this direction, and peach is a candidate model for genetic studies among Rosaceae species because of the small size of its genome (see also Chapter 4).

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Lewallen, K.S. and Marini, R.P. (2003) Relationship between flesh firmness and ground colour in peach as influenced by light and canopy position. Journal of the American Society for Horticultural Science 128, 163–170. Lill, R.E., O’Donoghue, E.M. and King, G.A. (1989) Postharvest physiology of peaches and nectarines. Horticultural Reviews 11, 413–452. Lleonart, R., Cistero, A., Carriera, J., Batista, A. and Moscoso del Prado, J. (1992) Food allergy: identification of the major IgE-binding component of peach (Prunus persica). Annals of Allergy 69, 128–130. Lurie, S. and Crisosto, C. (2005) Chilling injury in peach and nectarine. Postharvest Biology and Technology 37, 195–208. Lurie, S. and Pesis, E. (1992) Effect of acetaldehyde and anaerobiosis as postharvest treatments on the quality of peaches and nectarines. Postharvest Biology and Technology 1, 317–326. McGlasson, W.B., Rath, A.C. and Legendre, L. (2005) Preharvest application of aminovinylglycine (AVG) modifies harvest maturity and cool storage life of ‘Arctic Snow’ nectarines. Postharvest Biology and Technology 36, 93–102. McGuire, R.G. (1992) Reporting of objective color measurements. HortScience 27, 1254–1255. McMurchie, E.J., McGlasson, W.B. and Eaks, I.L. (1972) Treatment of fruit with propylene gives information about the biogenesis of ethylene. Nature 237, 235–236. Maness, N.O., Chrz, D., Hedge, S. and Goffreda, J.C. (1993) Cell wall changes in ripening peach fruit from cultivars differing in softening rate. Acta Horticulturae 343, 200–203. Mathooko, F.M., Tsunashima, Y., Owino, W.Z.O., Kubo, Y. and Inaba, A. (2001) Regulation of genes encoding ethylene biosynthetic enzymes in peach (Prunus persica L.) fruit by carbon dioxide and 1-methylcyclopropene. Postharvest Biology and Technology 21, 265–281. Mencarelli, F., Garosi, F. and Tonutti, P. (1998) Postharvest physiology of peaches and nectarines slices. Acta Horticulturae 465, 462–470. Mencarelli, F., Cecchi, F., De Santis, D., Aquilani, R., Giuliano, G. and Rotondi, R. (2003) Influence of ethylene on volatiles and carotenoids biosynthesis of peach. In: Vendrell, M., Klee, H., Pech, J.C. and Romojaro, F. (eds) Biology and Biotechnology of the Plant Hormone Ethylene III. NATO Science Series 348. IOS Press, Amsterdam, pp. 222–226. Meredith, F.I., Robertson, J.A. and Horvath, R.J. (1989) Changes in physical and chemical parameters associated with quality and post harvest ripening of harvested peaches. Journal of Agricultural and Food Chemistry 37, 1210–1214. Miller, A.N., Krizek, B.A. and Walsh, C.S. (1988) Whole-fruit ethylene evolution and ACC content of peach pericarp and seeds during development. Journal of the American Society for Horticultural Science 113, 119–124. Moing, A., Svanella, L., Rolin, D., Gaudillere, M., Gaudillere, J.P. and Monet, R. (1998) Compositional changes during the fruit development of two peach cultivars differing in juice acidity. Journal of the American Society for Horticultural Science 123, 770–775. Moing, A., Svanella, L., Gaudillere, M., Gaudillere, J.P. and Monet, R. (1999) Organic acid concentration is little controlled by phosphoenolpryruvate carboxylase activity in peach fruit. Australian Journal of Plant Physiology 26, 579–585. Moing, A., Rothan, C., Svanella, L., Just, D., Diakou, P., Raymond, P., Gaudillere, J.P. and Monet, R. (2000) Role of phosphoenolpyruvate carboxylase in organic acid accumulation during peach fruit development. Physiologia Plantarum 108, 1–10. Monet, R. (1979) Transmission génétique du caractère ‘fruit doux’ chez le pêcher. Incidence sur la sélection pour la qualité. In: Proceedings of the EUCARPIA ‘Tree Fruit Breeding’ Symposium. INRA, Angers, France, pp. 273–276. Monnet, F.P., Dieryck, W., Boutron, F., Jourdier, P. and Gautier, M.F. (2001) Purification, characterisation and cDNA cloning of a type 2 (7 kDa) lipid transfer protein from Triticum durum. Plant Science 16, 747–755. Moon, H.S. and Callahan, A.M. (2004) Developmental regulation of peach ACC oxidase promoter–GUS fusion in transgenic tomato fruits. Journal of Experimental Botany 55, 1519–1528. Morgutti, S., Negrini, N., Nocito, F.F., Ghiani, A., Bassi, D. and Cocucci, M. (2006) Changes in endopolygalacturonase levels and characterization of putative endo-PG gene during fruit softening in peach genotypes with nomelting and melting flesh fruit phenotypes. New Phytologist 171, 315–328. Nakatsuka, A., Murachi, S., Okunishi, H., Shiomi, S., Nakano, R., Kubo, Y. and Inaba, A. (1998) Differential expression and internal feedback regulation of 1-aminocyclopropane-1-carboxylate synthase, and ethylene receptor genes in tomato fruit during development and ripening. Plant Physiology 118, 1295–1305.

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Neri, F. and Brigati, S. (1994) Sensory and objective evaluation of peaches. In: De Jager, A., Jhonson, A. and Hohn, E. (eds) COST 94: The postharvest treatment of fruit and vegetables. European Commission, Brussels, pp. 107–115. Nissen, R.J., George, A.P. and Topp, B.L. (2005a) Producing super sweet and firm peaches and nectarines. Acta Horticulturae 694, 311–314. Nissen, R.J., George, A.P., Waite, G., Lloyd, A. and Hamacek, E. (2005b) Innovative new production systems for low-chill stonefruit in Australia and South-East Asia: a review. Acta Horticulturae 694, 247–251. Nonis, A., Ruperti, B., Casatta, E. and Vizzotto, G. (2003) Expression of sugar metabolism-related genes during peach fruit and leaf development. In: Proceedings of ‘Phloem 2003’ Symposium. University of Bayreuth, Bayreuth, Germany, p. 214. Nonis, A., Ruperti, B., Falchi, R., Casatta, E., Enferadi, S.T. and Vizzotto, G. (2007) Differential expression and regulation of a natural invertase encoding gene from peach (Prunus persica): evidence for a role in fruit development. Physiologia Plantarum 129, 436–446. Orr, G. and Brady, C. (1993) Relationship of endopolygalacturonase activity to fruit softening in a freestone peach. Postharvest Biology and Technology 3, 121–130. Ortolani, C., Ispano, M., Pastorello, E.A., Bigi, A. and Ansaloni, R. (1988) The oral allergy syndrome. Annals of Allergy 61, 47–52. Pastorello, E.A., Farioli, L., Pravettoni, V., Ortolani, C., Ispano, M., Monza, M., Broglio, C., Scibola, E., Ansaloni, R., Incorvaia, C. and Conti, A. (1999) The major allergen of peach (Prunus persica) is a lipid transfer protein. Journal of Allergy and Clinical Immunology 103, 520–526. Pastorello, E.A., D’Ambrosio, F., Pravettoni, V., Farioli, L., Giuffrida, G., Monza, M., Ansaloni, R., Fortunato, D., Scibola, E., Rivolta, F., Incorvaia, C., Bengtsson, A., Conti, A. and Ortolani, C. (2000) Evidence for a lipid transfer protein as the major allergen of apricot. Journal of Allergy and Clinical Immunology 105, 371–377. Pastorello, E.A., Farioli, L., Pravettoni, V., Giuffrida, M.G., Ortolani, C., Fortunato, D., Trambaioli, C., Scibola, E., Calamari, A.M., Robino, A.M. and Conti, A. (2001) Characterization of the major allergen of plum as a lipid transfer protein. Journal of Chromatography B: Biomedical Sciences and Applications 756, 95–103. Peace, C.P., Crisosto, C.H. and Gradziel, T.M. (2005) Endopolygalacturonase: a candidate gene for freestone and melting flesh in peach. Molecular Breeding 16, 21–31. Pelese-Siebenbourg, J., Caellas, C., Kader, J.K., Delseny, M. and Puigdomenech, P. (1994) A pair of genes coding for lipid-transfer protein in Sorghum vulgare. Gene 148, 305–308. Pressey, R. and Avants, J.K. (1973) Two forms of polygalacturonase in tomatoes. Biochimica et Biophysica Acta 309, 363–369. Pressey, R. and Avants, J.K. (1978) Difference in polygalacturonase composition of clingstone and freestone peaches. Journal of Food Science 43, 1415–1417. Pressey, R., Hinton, D.M. and Avants, K. (1971) Polygalacturonase activity and solubilization of pectin in peaches during ripening. Journal of Food Science 36, 1070–1073. Pyee, J. and Kolattukudy, P.E. (1995) The gene for the major cuticular wax associated protein and three homologous genes from broccoli (Brassica oleracea) and their expression patterns. The Plant Journal 7, 49–59. Rasori, A., Ruperti, B., Bonghi, C., Tonutti, P. and Ramina, A. (2002) Characterization of two putative ethylene receptor genes expressed during peach fruit development and abscission. Journal of Experimental Botany 53, 2333–2339. Rasori, A., Bertolasi, B., Furini, A., Bonghi, C., Tonutti, P. and Ramina, A. (2003) Functional analysis of peach ACC oxidase promoters in transgenic tomato and in ripening peach fruit. Plant Science 165, 523–530. Rath, A.C. and Prentice, A.J. (2004) Application of Retain plant growth regulator increases the yield and fresh firmness of ‘Arctic Snow’ nectarines both at harvest in Australia and after export to Taiwan. Australian Journal of Experimental Agriculture 44, 343–351. Robards, K., Prenzler, P., Tucker, G., Swatsitang, P. and Glover, W. (1999) Phenolic compounds and their role in oxidative processes in fruits. Food Chemistry 66, 401–436. Robertson, J.A., Meredith, F.I. and Scorza, R. (1988) Characteristics of fruit from high and low quality peach cultivars. HortScience 23, 1032–1034. Ruperti, B., Bonghi, C., Rasori, A., Ramina, A. and Tonutti, P. (2001) Characterization and expression of two members of the peach 1-aminocyclopropane-1-carboxylate oxidase gene family. Physiologia Plantarum 111, 336–344. Salunkhe, D.K., Bolin, H.R. and Reddy, N.R. (1991) Storage, Processing and Nutritional Quality of Fruits and Vegetables, 2nd edn, Vol. 1. CRC Press, Boca Raton, Florida. Sanchez-Monge, R., Lombardero, M., Garcia-Selles, F.J., Barber, D. and Salcedo, G. (1999) Lipid-transfer proteins are relevant allergens in fruit allergy. Journal of Allergy and Clinical Immunology 103, 514–519.

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Sharaftedinov, K.K., Mescheryakova, V.A., Plotnikova, O.A., Nikolskaya, G.V. and Pavlova, Y.V. (1999) The influence of drinks with fructose on glycemic parameters of patient with type II diabetes. Voprosy Pitaniya 1, 42–45. Smilanick, J.L. and Fouse, D.C. (1989) Quality of nectarines in insecticidal low O2 atmospheres at 5°C. Journal of the American Society for Horticultural Science 114, 431–436. Southon, S. (2000) Increased fruit and vegetable consumption within the EU. Potential health benefits. Food Research International 33, 211–217. Souty, M., Reich, M., Albagnac, G. and Génard, M. (1998) Quality of peach fruit in relation to carbon supply. Acta Horticulturae 465, 481–490. Takeoka, G.R., Flath, R.A., Gunter, M. and Jennings, W. (1988) Nectarine volatiles: vacuum steam distillation versus headspace sampling. Journal of Agricultural and Food Chemistry 36, 553–560. Tatsuki, M., Takashi, H. and Yamaguchi, M. (2006) The involvement of 1-aminocyclopropane-1-carboxylic acid synthase isogene, Pp-ACS1, in peach fruit softening. Journal of Experimental Botany 57, 1281–1289. Thompson, J.E., Legge, R.J. and Barber, R.F. (1987) The role of free radicals in senescence and wounding. New Phytology 105, 317–324. Tijskens, T.M.M., Eccher-Zerbini, P., Schouten, R.E., Vanoli, M., Jacob, S., Grassi, M., Cubbedu, R., Spinelli, L. and Torricelli, A. (2007) Assessing harvest maturity in nectarines. Postharvest Biology and Technology 45, 204–213. Tonutti, P., Casson, P. and Ramina, A. (1991) Ethylene biosynthesis during peach fruit development. Journal of the American Society for Horticultural Science 116, 274–279. Tonutti, P., Bonghi, C., Ruperti, B., Tornielli, G.B. and Ramina, A. (1997) Ethylene evolution and 1-aminocyclopropane-1-carboxylate oxidase gene expression during early development and ripening of peach fruit. Journal of the American Society for Horticultural Science 122, 642–647. Tonutti, P., Bonghi, C., Ramina, A. and Vidrih, R. (1998) Molecular and biochemical effects of anoxia, hypoxia and CO2-enriched atmosphere on Springcrest peaches. Acta Horticulturae 465, 439–446. Torija Isasa, M.E., Carballido, A. and Barragan Ruiz, M.R. (1985) Bromatological study of baby foods. 6. Contents of crude and dietary fibre. Anales de Bromatologia 36, 137–149. Trainotti, L., Spolaore, S., Ferrarese, L. and Casadoro, G. (1997) Characterization of ppEG1, a member of a multigene family which encodes endo-b,1,4-glucanase in peach. Plant Molecular Biology 34, 791–802. Trainotti, L., Zanin, D. and Casadoro, G. (2003) A cell wall-oriented genomic approach reveals a new and unexpected complexity of the softening in peaches. Journal of Experimental Botany 54, 1821–1832. Trainotti, L., Bonghi, C., Ziliotto, F., Zanin, D., Rasori, A., Csadoro, G., Ramina, A. and Tonutti, P. (2006a) The use of microarray µPEACH 1.0 to investigate transcriptome changes during transition from pre-climacteric to climacteric phase in peach fruit. Plant Science 170, 606–613. Trainotti, L., Pavanello, A. and Zanin, B. (2006b) PpEG4 is a peach endo-b-1,4-glucanase gene whose expression in climacteric peaches does not follow a climacteric pattern. Journal of Experimental Botany 57, 589–598. Uthairatanakij, A. (2004) Responses of nectarines to atmospheres containing high carbon dioxide concentrations. PhD thesis, The University of Western Sydney, New South Wales, Australia. Uthairatanakij, A., Penchaiya, P., McGlasson, B. and Holford, P. (2005) Changes in ACC and conjugated ACC following CA storage of nectarines. Australian Journal of Experimental Agriculture 45, 1635–1641. Ventura, M., Magnanimi, E. and Sansavini, S. (1998) Sistema automatico di misurazione dei gas nella maturazione dei frutti. Rivista di Frutticoltura e di Ortofloricoltura 60, 63–67. Visai, C., Vanoli, M. and Rizzolo, A. (1993) Caratteristiche aromatiche durante l’accrescimento e la maturazione di frutti di pesco. In: Proceedings of ‘XXI Convegno peschicolo’. Camera di Commercio di Ravenna e Forlì, Ravenna, Italy, pp. 295–304. Vizzotto, G., Pinton, R., Varanini, Z. and Costa, G. (1996) Sucrose accumulation in developing peach fruit. Physiologia Plantarum 96, 225–230. Vizzotto, G., Casatta, E., Bomben, C., Bregoli, A.M., Sabatini, E. and Costa, G. (2002) Peach ripening as affected by AVG. Acta Horticulturae 592, 561–566. Wade, N.L. (1981) Effects of storage atmosphere and calcium on low-temperature injury of peach fruit. Scientia Horticulturae 15, 145–154. Wills, R., McGlasson, B., Graham, D. and Joyce, D. (2007) Physiology and biochemistry. In: Wills, R., McGlasson, B., Graham, D. and Joyce, D. (eds) Postharvest: An Introduction to the Physiology and Handling of Fruit, Vegetables and Ornamentals, 5th edn. CABI, Wallingford, UK, p. 202. Yamada, K., Niwa, N., Shiratake, K. and Yamaki, S. (2001) cDNA cloning of NAD-dependent sorbitol dehydrogenase from peach fruit and its expression during fruit development. Journal of Horticultural Science and Biotechnology 76, 581–587.

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22

Harvesting and Postharvest Handling of Peaches for the Fresh Market C.H. Crisosto1 and D. Valero2

1University

of California, Davis, Department of Plant Sciences; located at Kearney Agricultural Center, Parlier, California, USA 2University Miguel Hernández, Department of Food Technology, Alicante, Spain

22.1 Origin 22.2 Fruit Consumption and Antioxidant Capacity Fruit composition Ascorbic acid, carotenoids and phenolic composition Antioxidant capacity 22.3 Deterioration Problems Internal breakdown Mechanical injury Inking 22.4 Peach Maturity Maturity and quality Maturity deﬁnition Maturity indices Field application of maturity indices 22.5 Temperature Requirements and Management Ideal storage conditions Temperature management Water loss control New temperature management approach 22.6 Field Harvesting, Hauling and Packaging Harvesting Fruit hauling Fruit packaging Sorting and sizing operation Shipping and transportation 22.7 Cull Utilization Potential uses Situation in California Other uses 22.8 Fruit Handling at Retail Distribution Fruit preparation for consumers

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Fruit buyer handling Peach handling at retail stores

22.1 Origin Peach (Prunus persica (L.) Batsch) is native to China; at one time it was called ‘Persian apple’. Chinese literature dates its cultivation in China to 1000 BC. Probably carried from China to Persia (Iran), the peach quickly spread from there to Europe. In the 16th century, peaches were established in Mexico, probably by the Spaniards. In the 18th century Spanish missionaries introduced the peach to California, which turned out to be the most important production area after China and Italy (LaRue, 1989). In recent years, an important development of fruit with high soluble solids concentration (SSC), high aromatic white ﬂesh, and low-acidity white and yellow cultivars has occurred in all the production areas (Okie, 1998; Sansavini et al., 2000; Crisosto et al., 2001a; Crisosto, 2002).

22.2 Fruit Composition and Antioxidant Capacity Fruit composition Peaches are characteristically soft-ﬂeshed and highly perishable fruit, with a limited market life potential. A peach fruit is approximately 87% water with 180 kJ (43 kcal) and contains carbohydrates, organic acids, pigments, phenolics, vitamins, volatiles, antioxidants and trace amounts of proteins and lipids, which make it very attractive to consumers (Kader and Mitchell, 1989b; USDA, 2003). Immature peach fruit contain very low or no starch grains and these starch grains are rapidly converted into soluble sugars as the fruit mature and ripen. Consequently, there is no signiﬁcant increase in soluble sugars during storage and ripening (Romani and Jennings, 1971). Soluble sugars contribute approximately 7–18% of total weight and ﬁbre contributes approximately 0.3% of fresh weight (FW) of total fruit. Sucrose, glucose and fructose represent about 75% of peach fruit soluble sugars. Malic acid

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is the predominant organic acid in mature peach fruit followed by citric acid. These organic acids (0.4–1.2% FW) are important because it has been reported that the ratio of soluble solids to titratable acidity determines consumer perception in most ripe peach cultivars. In most peach cultivars, we found that acidity decreased about 30% during ripening. Peach fruit has low protein content (0.5 to 0.8% FW) but these small-size proteins have an important function as enzymes catalysing the various chemical reactions responsible for compositional changes. Despite lipids constituting only 0.1 to 0.2% FW, they are important because they make up surface wax that contributes to fruit cosmetic appearance and cuticle that protects fruit against water loss and pathogens. Lipids are also important constituents of cell membranes, which inﬂuence physiological activities of fruits. Minerals in fruits include base-forming elements (Ca, Mg, K, Na) and acid-forming elements (P, Cl, S). Ca associated with cell wall structure is important in fruit softening and Ca in the apoplast has been related to senescence. Postharvest changes in mineral content in fruits are small. Volatile compounds in very low concentrations include esters, alcohols, aldehydes, ketones and acids, and these are responsible for the characteristic fruit aroma. Lactones may be organoleptically important in peach ﬂavour but more detailed studies are needed on this topic.

Ascorbic acid, carotenoids and phenolic composition Peach fruit has ascorbic acid (vitamin C), carotenoids (provitamin A) and phenolic compounds which are good sources of antioxidants (Tomás-Barberán et al., 2001; Byrne, 2002). Since these compounds are located in a high concentration in the fruit peel, which constitutes only about 15% of total fruit FW, most of the antioxidant potential is restricted to the peel; thus, it is recommended to eat

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peaches with the peel to ensure intake of most of the antioxidant compounds. The total ascorbic acid (vitamin C) content in a survey of ten cultivars of California peach ranged from 6 to 9 mg/100 g in white ﬂesh and from 4 to 13 mg/100 g in yellow ﬂesh (Gil et al., 2002). Accordingly, similar concentrations of ascorbic acid (5–6 mg/100 g) have been found in European peach cultivars (Carbonaro et al., 2002; Proteggente et al., 2002). Total carotenoids concentration was in the range of 71–210 mg/100 g FW for yellow-ﬂeshed and 7–20 mg/100 g FW for white-ﬂeshed peach cultivars (Gil et al., 2002). Thus, there were about ten times more carotenoids in yellowﬂeshed than in white-ﬂeshed peach cultivars. The main carotenoid detected was b-carotene (provitamin A), but also small quantities of a-carotene and b-cryptoxanthin are present in some peach cultivars. The total phenolics concentration expressed as mg/100 g FW varied from 28 to 111 for white-ﬂeshed and from 21 to 61 for yellow-ﬂeshed California cultivars (Gil et al., 2002). Other European cultivars had values of 38 mg/100 g (Proteggente et al., 2002), while the Spanish cultivar ‘Caterina’ showed values of 240 and 470 mg/100 g for pulp and peel, respectively (Goristein, et al., 2002). Fruit phenolics have a role in fruit visual appearance (colour), taste (astringency) and health antioxidant property (Tomás-Barberán et al., 2001). The predominant hydrocinnamic acid is chlorogenic acid. Catechin and epicatechin are the main procyanidins identiﬁed and their concentrations are higher in white-ﬂeshed than in yellow-ﬂeshed peaches. Cyanidin-3-glucoside is the predominant anthocyanin, which, along with other anthocyanins, is present mainly in the skin. Concentrations of ﬂavonols (including quercetin and kaempferol) are higher in yellow-ﬂeshed than in white-ﬂeshed peaches (Gil et al., 2002).

capacities than yellow-ﬂeshed peaches. The total antioxidants ranged from 13 to 107.3 mg of ascorbic acid equivalents when evaluated by the DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical method and from 19 to 119.6 mg of ascorbic acid equivalents when evaluated by the FRAP (ferric reducing ability plasma) method (Tomás-Barberán et al., 2001). When these values are compared with the amount of ascorbic acid equivalents provided by 100 ml of red wine, 100 g of ‘Snow Skin’ (white ﬂesh) or ‘September Sun’ (yellow ﬂesh) will provide the same amount, while approximately 1000 g of ‘Summer Sweet’ (white ﬂesh) or ‘Flavorcrest’ (yellow ﬂesh) would have to be consumed to match the same amount of antioxidant capacity in 100 ml of red wine. In fact, the total antioxidant activity of peach is similar to that reported for pear, apple and tomato; and signiﬁcantly lower than those observed in strawberry, raspberry and red plum (Proteggente et al., 2002).

Antioxidant capacity

Internal breakdown

The antioxidant capacity per peach fruit serving based on the intake of a fruit serving of 100 g (peel + ﬂesh) varied widely according to cultivar. In general, white-ﬂeshed peaches were slightly higher in total antioxidant

This phenomenon (IB or CI) is genetically controlled and triggered by storage temperature. It manifests itself as dry, mealy, woolly or hardtextured fruit (not juicy), ﬂesh or pit cavity browning, and ﬂesh translucency usually

22.3 Deterioration Problems Commercial postharvest losses are mainly due to decay and internal breakdown (IB) or chilling injury (CI) (Ceponis et al., 1987; Mitchell and Kader, 1989a). Postharvest loss of stone fruits to decay-causing fungi is considered the greatest deterioration problem. Worldwide, the most important pathogen of fresh stone fruits is grey mould or Botrytis rot, caused by the fungus Botrytis cinerea. In California, an even greater cause of loss due to decay is caused by the fungus Monilinia fructicola (brown rot). Details on the fungi life cycle, epidemiology, orchard sanitation practices, fungicide applications and pre-/postharvest management to reduce these problems are presented in Chapter 15 of this book.

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radiating through the ﬂesh from the pit (Fig. 22.1/Plate 232). An intense red colour development of the ﬂesh (‘bleeding’) usually radiating from the pit may be associated with this problem in some peach cultivars. Recently released cultivars rich in skin red pigment showed ﬂesh bleeding that is not affecting fruit taste. The development of this symptom has been associated with fruit maturity rather than storage temperature. In all of the cases, in susceptible cultivars ﬂavour is lost before visual CI symptoms are evident (Crisosto and Labavitch, 2002). There is large variability in IB susceptibility among peach cultivars (Mitchell and Kader, 1989a; Crisosto et al., 1999c). In general, most of the mid-season and late-season peach cultivars are more susceptible to CI than early-season cultivars (Mitchell and Kader, 1989a), although as new cultivars are being released from a new genetic pool, the susceptibility to CI is becoming random in the new

cultivar population (Crisosto et al., 1999c; Crisosto, 2002). It has been widely reported that the expression of CI symptoms develops faster and more intensely when susceptible fruit are stored at temperatures between about 2.2°C and 7.6°C (‘killing zone’ temperature) than when stored at 0°C or below but above their freezing point (Harding and Haller, 1934; Smith, 1934; Mitchell and Kader, 1989a). Therefore, market life is dramatically reduced when fruit are exposed to the ‘killing zone’ temperature (Crisosto et al., 1999c). In addition, the severity of CI depends on the ripening stage at harvest since higher incidence was reported for ‘Maycrest’ cultivar picked at more advanced ripening stage (Valero et al., 1997), although the opposite has been found in other cultivars (Von Mollendorff et al., 1992). Several treatments to delay and limit development of this disorder have been tested, such as controlled atmosphere (CA) environment,

Fig. 22.1. Internal breakdown symptoms in peaches (top of image) include flesh mealiness, flesh browning and loss of flavour.

Harvesting and Postharvest Handling

calcium applications, warming cold storage interruptions (Anderson, 1979; Nanos and Mitchell, 1991; Garner et al., 2001), plant growth regulators and controlled delayed cooling. The major beneﬁts of CA during storage/shipment are retention of fruit ﬁrmness and ground colour. CA conditions of 6% O2+17% CO2 at 0°C have shown a limited beneﬁt for reduction of IB during shipments for yellow-ﬂeshed cultivars (Crisosto et al., 1999a) and white-ﬂeshed cultivars (Garner et al., 2001). The CA efﬁcacy is related to cultivar (Mitchell and Kader, 1989a), preharvest factors (Von Mollendorff, 1987; Crisosto et al., 1997), temperature, fruit size (Crisosto et al., 1999a), marketing period and shipping time (Crisosto et al., 1999c). Another tool that reduced CI in peach was modiﬁed atmosphere packaging (MAP). Thus, ‘Paraguayo’ cultivar (ﬂat type) showed reductions in CI severity using polypropylene standard ﬁlm with steady-state atmosphere of 12% CO2 and 4% O2, or oriented polypropylene (23% CO2 and 2% O2) (Fernández-Trujillo et al., 1998). The preconditioning treatment (Crisosto et al., 2004) prior to storage/shipment has shown to be effective in delaying IB symptoms and is successfully being used commercially on Californian and Chilean fruit shipped to the USA and England (Crisosto et al., 2004). The ‘Paraguayo’ cultivar subjected to intermittent warming cycles of 1 day at 20°C every 6 days of storage at 2°C was also effective in reducing CI symptoms although scald and translucency occurred (Fernández-Trujillo and Artés, 1998).

Mechanical injury Peaches are susceptible to mechanical injuries including impact, compression, abrasion (or vibration), bruising, and wounds or cuts, which can occur during harvest and transport (Mitchell and Kader, 1989a). Impact bruising is the result of dropping, bouncing or jarring. Compression bruising occurs primarily when bins are overﬁlled and stacked, and fruits are ‘crushed’ against each other. Abrasion bruising results from fruit rubbing against each other or against container surfaces. Proper fruit handling and transport will reduce these

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types of injury and contribute to the production of a high-quality ﬁnal product. Careful handling during harvesting, hauling and packing operations to minimize such injuries is important because the injuries result in reduced appearance quality, accelerated physiological activity, potentially more entry points for and inoculation by fruit decay organisms, and greater water loss. Incidence of impact and compression bruising has become a greater concern as a large part of the peach industry is harvesting fruit at more advanced maturity (softer) to maximize fruit ﬂavour quality. Our observations indicate that most impact bruising damage occurs during long hauling from orchard to packinghouse and during the packinghouse operation. Critical impact bruising thresholds (the minimum fruit ﬁrmness measured at the weakest point to tolerate impact abuse) have been developed for many peach and nectarine cultivars (Crisosto et al., 2001b). Physical wounding or cuts on peaches can occur at any time from harvest until consumption. Good worker supervision assures adequate protection against impact bruising during picking, handling and transport of fruit. Abrasion damage can occur at any time during postharvest handling. Protection against abrasion damage involves procedures to reduce vibrations during transport and handling by immobilizing the fruit. These procedures include: installing air-suspension systems on axles of ﬁeld and highway trucks, plastic ﬁlm liners inside ﬁeld bins, the use of plastic bins, installing special bin top pads before transport, avoiding abrasion on the packing line, and using packing procedures that immobilize the fruit within the shipping container before they are transported to market. It is also helpful to grade farm roads to reduce roughness, avoid rough roads during transport, and establish strict speed limits for trucks operating between orchards and packinghouses. Some research indicates that treatment of peaches with plant growth regulators (i.e. polyamines and gibberellic acid) before handling and storage is also effective in reducing the fruit susceptibility to mechanical damage by increasing fruit ﬁrmness and thus inducing resistance to compression forces (MartínezRomero et al., 2000). Additionally, preharvest

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application of Ca+Mg+Ti spray led to ﬁrmer fruits (Serrano et al., 2004), which would be another way to increase the fruit resistance to mechanical damage.

Inking In situations when abrasion damage occurs during harvesting on fruit that have heavy metal contaminants on their skin (i.e. Fe, Cu and/or Al), a dark discoloration referred to as inking, staining or peach skin discoloration occurs on the skin (Cheng and Crisosto, 1997). These dark or brown spots or stripes on the fruit surface are a cosmetic problem that is limited to the skin but they lead to market rejection and ﬁnancial loss to the grower (Fig. 22.2/Plate 233). Light brown spots or stripes are also produced on the surface of whiteﬂeshed peaches and nectarines as a consequence of abrasion occurring mainly during harvesting and hauling operations. These symptoms appear generally 24–48 h after harvest. This problem is usually triggered during

the harvesting and hauling operations, but it may also occur later during postharvest handling (packaging). Heavy metal contaminants on the surface of the fruit can occur as a consequence of foliar nutrients and/or fungicides sprayed within 15 or 7 days before harvest, respectively. Gentle fruit handling, shortdistance hauling, avoiding any foliar nutrient sprays within 15 days of harvest, and following the suggested preharvest fungicide spray interval guidelines are our recommendations to reduce inking incidence (Crisosto et al., 1999b).

22.4 Peach Maturity Maturity and quality The maturity at which peaches are harvested greatly inﬂuences their ultimate ﬂavour, market life and quality potential (Von Mollendorff, 1987; Lill et al., 1989; Kader and Mitchell, 1989a; Crisosto et al., 1995). Peach maturity controls the fruit’s ﬂavour components, physiological deterioration problems, susceptibility

Fig. 22.2. Peach inking or staining as a consequence of abrasion combined with heavy metal contamination during harvesting and hauling operations.

Harvesting and Postharvest Handling

to mechanical injuries, resistance to moisture loss, susceptibility to invasion by rot organisms, market life and ability to ripen (Shewfelt et al., 1987; Crisosto, 1994). Peaches that are harvested too soon (immature) may fail to ripen properly or may ripen abnormally. Immature fruit typically soften slowly and irregularly, never reaching the desired melting texture of fully matured fruit. Green ground colour of fruit picked immature may never fully disappear. Because immature fruit lack a fully developed surface cuticle, they are more susceptible to water loss than properly matured fruit. Immature and low-maturity fruit have lower SSC and higher acids than harvested matured fruit, all of which contribute to inadequate ﬂavour development and low consumer acceptance. Over-mature fruit have a shortened postharvest life, primarily because of rapid softening and they are already approaching a senescent stage at harvest. Such fruit have partially ripened, and the resulting ﬂesh softening renders them highly susceptible to mechanical injury and fungus invasion. By the time such fruit reach the consumer they may have become overripe (senescent), with poor eating quality including off-ﬂavours and irregular or mushy texture.

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(Crisosto, 1994). Based on this information, maturity indices based on skin background colour and ﬁrmness are being used to determine and supervise harvesting operations. In California and other places, harvest date is determined by skin background colour changes from green to yellow in most cultivars. A colour chip guide is used to determine maturity of most cultivars except for white-ﬂeshed cultivars. Fruit skin background colour is a useful, non-destructive method of estimating fruit maturity, and is most easily employed and understood by ﬁeld workers during harvesting operations. Since the proper background colour for estimating optimum harvest maturity varies by cultivar, experience with a particular cultivar is helpful in making the correct decision. In California, for new cultivar releases where skin ground colour is masked by full red colour development prior to maturation, fruit ﬁrmness is being used to determine how long fruit can be left on the tree before harvest. In Europe, fruit ﬁrmness on fresh market peach is not very reliable, so maximum maturity index is recommended. Maximum maturity is deﬁned as the minimum ﬂesh ﬁrmness at which fruits can be handled without bruising damage. Maximum maturity varies among peach cultivars and handling situations (Crisosto et al., 2001b).

Maturity definition Field application of maturity indices Optimum maturity must be deﬁned for each peach cultivar to assure maximum taste and storage quality but in all cases it should assure that the fruit has the ability to ripen satisfactorily (Kader and Mitchell, 1989a). Peach quality was discussed in detail in Chapter 20 of this book. The ideal maturity varies according to markets; for example, a more advanced maturity is recommended for near-distance markets than for long-distance markets. Maturity indices Several information sources from different production areas have reported that ﬂesh colour, ﬁrmness and background colour changes are well correlated to chemical and physical fruit changes during maturation and ripening

In applying either one of these two maturity indices (background colour and ﬂesh ﬁrmness) at the start of a block or cultivar, proper, easily understood directions for estimating maturity should be given to the workers. By selecting a few fruit of varying maturity and demonstrating what maturity level is acceptable and unacceptable, many mistakes can be avoided. It is recommended to leave these samples with the crew leader as a reference throughout the day. When a maturity index based on fruit ﬁrmness is used, the instructions to the harvesters will also imply minimum size and location of the fruit in the tree canopy. The value of a good and expert crew leader cannot be overemphasized. This person should be considered essential and integral in the harvesting process. He should be instructed

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to continually monitor the fruit being picked and the fruit remaining on the tree to determine if the correct balance is achieved. Orchard managers should involve the crew leader in all stages of the decision-making process when determining optimum harvest maturity. Doing so will give him greater understanding and experience in the process. More importantly, it will solidify in his mind the importance of his role in harvesting fruit at the proper maturity. A number of factors can affect how quickly fruits ripen. Trees tend to ripen from top to bottom and periphery to interior. This is probably related to the amount of sunlight they receive. Consequently, fruit of a given cultivar on weak trees tend to ripen earlier than on strong trees, as do fruit on summerpruned trees. Fruit of a given cultivar on girdled trees or trees in sandy areas ripen earlier than fruit on non-girdled trees or in loamy soils. These fruit also tend to ripen more uniformly within the tree from top to bottom. A skilful manager will consider these factors, as well as others, and judge when and how often an orchard should be harvested, and how much fruit can be removed in any one picking. Because of the complexity of these factors, there is no substitute for experience in making these decisions. Strategies that are effective for one grower may be ineffective for another because of different organizational and marketing situations and tactics. An example of differing strategies is demonstrated by grower A, who prefers to harvest ﬁve to eight times for each cultivar where each harvest is 2 to 3 days apart. This is in contrast to grower B, who prefers to pick only two or three times with a longer interval in between harvests. Grower A may decide that he does not mind spending the extra money on increased labour because he is achieving a higher packout percentage (less cullage). Grower B may not mind a reduced packout percentage (more cullage) because he is saving money on labour. In Spain, the indigenous cultivar ‘Calanda’ is much appreciated by European consumers and it dominates the late fresh market because of its special characteristics. Fruit is individually wrapped in a paper bag, is free of pesticides, and during the development on the tree reaches a uniform cream or straw

colour (Ferrer et al., 2005). For marketing purposes, only slight blush is accepted, but green or orange-yellowish colours are refused. In this cultivar, ﬁrmness and skin colour charts have been proposed to estimate the optimal harvest point.

22.5 Temperature Requirements and Management Ideal storage conditions The ideal peach storage temperature is −1°C to 0°C. The ﬂesh freezing point varies depending on SSC. Storage-room relative humidity should be maintained at 90–95% and air velocity of approximately 0.0236 m3/s is suggested during storage (Lill et al., 1989; Thompson et al., 1998).

Temperature management The application of the ideal cooling requirements will depend on the speciﬁc operation and the way to apply these requirements depends on the scheduling of the packing operation (Mitchell, 1987). Fruit can be cooled in ﬁeld bins by hydro-cooling or pre-cooling (Fig. 22.3/Plate 234). Hydro-cooling is normally done by a conveyor-type hydro-cooler. Fruit in ﬁeld bins can be cooled to intermediate temperatures (5–10°C) provided packing will occur the next day. If packing is to be delayed beyond the next day, then fruit should be thoroughly cooled in the bins to near 0°C. In IB-susceptible cultivars fast cooling within 8 h and maintaining fruit temperature near 0°C are traditionally recommended (Mitchell, 1987). Fruit in packed containers should be cooled to near 0°C. Even fruit that were thoroughly cooled in the bins will warm substantially during packing and should be thoroughly re-cooled after packing. Forcedair cooling is normally indicated after packing (Fig. 22.4/Plate 235). A rare exception to the need for cooling after packing would be a system that handles completely cold fruit and provides protection against warming during packing.

Harvesting and Postharvest Handling

Fig. 22.3.

Bin of peaches being pre-cooled on a conveyor-type hydro-cooler prior to packing.

Fig. 22.4.

Packaged fruit in unitized pallet loads are stacked to form a forced-air cooling tunnel.

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Water loss control Economic loss to the grower can result when as little as 8% of the fruit fresh weight is lost (Crisosto et al., 1994). The economic loss is due to both decreased weight of the fruit and the unsightly shrivelling that occurs. While there is a large variability in susceptibility to water loss among cultivars, all cultivars must be protected to ensure the best postharvest life. Fruit waxes or coatings that are commonly used as carriers for postharvest fungicides can reduce the rate of water loss when excess surface brushing has not occurred. Mineral oil waxes can potentially control water loss better than vegetable oil and edible coatings, although the use of waxes or coatings is regulated according to destination point requirements. The main ways to limit fruit water loss include short cooling delays, efﬁcient waxing with gentle brushing, fast cooling followed by storage under constant low temperature and high relative humidity. New temperature management approach A new technique to delay IB symptoms and preripen fruit has been successfully introduced

to the California and Chilean industries. This technique, described above, consists of a ~48 h controlled cooling delay (Crisosto et al., 2004). A preconditioning protocol has been developed and promoted among packers/shippers (Crisosto et al., 2004). In this delivery system, preconditioned peaches should be arriving at the distribution centre at ~2.3–3.6 kgf ﬁrmness, measured at the weakest point on the cheeks. This new fruit delivery system is one more approach to limit IB and enhance the fruit-eating experience for consumers. Due to physical and chemical changes occurring in the fruit during a well-controlled preconditioning treatment, peaches undergo fruit softening to the ‘ready to buy’ stage (~2.7–3.6 kgf). Thus, fruit become tastier, more aromatic and juicier, resulting in high consumer acceptance. Generally, all peach cultivars should be kept out of the ‘killing zone’ temperature range of 2.2–10°C (Fig. 22.5/Plate 236). The ideal storage temperature is from 0°C to 1.7°C. Keeping fruit at this temperature will slow softening and reduce shrivelling, decay and the incidence of IB or mealy fruit. The exact temperature management will be part of a broader fruit preparation for consumers that takes into account the ﬁrmness on arrival of fruit and the fruit turning schedule (time that

Fig. 22.5. Storage temperature influences incidence and severity of internal breakdown in susceptible cultivars.

Harvesting and Postharvest Handling

fruit remain on display tables). This needs to be coordinated with the store-level demand and it will depend on a particular company’s anticipated sales/consumption schedule (fruit turning schedule). Cheek ﬁrmness is a good tool to determine ripening stage (transfer point, ready to buy, ready to eat, etc.), while ﬁrmness measured at the weakest position (shoulder, tips or suture) is well related to potential impact and transportation damages. Fruit ﬁrmness does not accurately certify the quality of the preconditioning execution, however.

22.6 Field Harvesting, Hauling and Packaging The goals of fruit harvesting should be to pick fruit at optimum maturity and transport fruit to the packing facility with no deterioration in fruit quality. To do this requires proper coordination between human resources, fruit

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maturity, environmental factors, technical resources and equipment. An understanding of these factors and their relationship is essential to making the proper management decisions for a given orchard situation. Harvesting Peach fruit are hand picked using bags (Fig. 22.6/Plate 237), baskets or totes. Most commercial peach fruit operations use picking bags and bins in their harvest operations (Corelli Grappadelli, 2001). Peaches are dumped in bins (Fig. 22.7/Plate 238) that are on the top of trailers between rows in the orchard. If totes are being used, they are placed directly inside the bins. Baskets are placed on top of modiﬁed trailers. Fruit picked at advanced maturity stages and white-ﬂeshed peaches are generally picked and placed into baskets or totes. Because of the availability of new cultivars that adapt well to harvesting more mature (softer), the increase in popularity of

Fig. 22.6. Peaches for fresh market are hand picked. Harvesters work on ladders using picking bags or baskets.

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Fig. 22.7. Harvesters transfer peaches to field bins which are moved through the field on low trailers.

high-quality, less ﬁrm fruit (more mature) and use of more sophisticated packinghouse equipment, a large proportion of stone fruits are being picked at a more advanced maturity stage than historically. Regardless of maturity, a number of precautions should be taken with any harvest operation (Mitchell and Kader, 1989b). Harvesters should be instructed to treat the fruit as gently as possible at every stage of the harvest process. When emptying bags into the transport bins, care should be taken to ensure that the fruit are not dumped into the bin from a high height. Again, this is where the crew leader is helpful in reducing problems. Picking bags and buckets should be kept clean. There appears to be a relationship between inking, surface abrasion and dirty containers. Washing picking bags at regular intervals may be helpful in reducing this problem. After harvest, but while still in the ﬁeld, fruit should be protected from exposure to direct sunlight and excess heating (Fig. 22.8/

Plate 239). Insulated bin covers are the most beneﬁcial shading technique. Some growers use cloth coverings to protect the fruit. On very hot days these should be supported above the fruit because direct contact can allow enough heat to pass through to cause fruit scald. After harvest fruit should be hauled to a cooling facility as quickly as possible. If there is a delay in transportation, fruit should be stored in a cool, shaded area. Temporary structures near the harvest location are often constructed from shade cloth material. Care should be taken as the harvested fruit are being loaded for transport to the packing facility. Forklift drivers should be informed of the importance of treating fruit gently when loading and unloading bins of fruit. Fruit hauling Fruit are hauled for short distances by trailer, but if the distance is longer than 10 km, bins

Harvesting and Postharvest Handling

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Fig. 22.8. View of a shaded loading area to protect fruit from excess heating while awaiting transportation to the packinghouse.

are loaded on trucks for transportation to packinghouses. Peaches are transported from orchard to packinghouse and cooler as soon as possible after harvest. Fruit should be shaded during any delay between harvest and transport. Tractor drivers should be instructed to drive slowly and smoothly. Severe fruit damage can result from poor driving practices, especially on turns and starts. There appears to be a beneﬁt to using ‘suspensiontype’ bin trailers instead of solid axle trailers. These trailers tend to ride more smoothly. Similar results can be obtained to a lesser degree by lowering tyre air pressure. Both of these procedures are probably more helpful for road transport conditions than ﬁeld transport. Unloading of trailers should also be performed as gently as possible. Care should be taken to educate workers as to the importance of this process. It is helpful if the unloading area is smooth and spacious to eliminate bumping and jarring. During hauling, drivers should reduce and eliminate jarring and bouncing. By choosing proper transportation routes and avoiding rough, bumpy roads fruit injury can be minimized. Position of fruit on the trailer is also important. Within-bin vibration

levels are highest at the front of the trailer, intermediate in the rear, and lowest in the middle of the trailer. The addition of air-suspension systems to trailers has been shown to be of tremendous value in reducing this type of fruit damage. Plastic bin liners and padded bin covers have also been demonstrated to reduce transport injury. Research has shown that thick bubble padding is more beneﬁcial than thin, and that larger bubbles are preferred to small (Mitchell and Kader, 1989b).

Fruit packaging At the packinghouse the fruit are dumped (mostly using dry bin dumps, Fig. 22.9/Plate 240) and cleaned (Mitchell and Kader, 1989b). Here debris is removed and fruit may be washed with chlorinated water. Peaches are normally wet-brushed to remove the trichomes (fuzz), which are single-cell extensions of epidermal cells and protect fruit from new inoculations. Waxing and fungicide treatment may follow, depending on country regulations (http://www.fas.usda.gov/htp/MRL.asp).

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Fig. 22.9. Dry bin dumping of fruit on to a commercial packing line.

Water-emulsiﬁable waxes are normally used, and fungicides may be incorporated into the wax. Sorting and sizing operation Sorting is carried out to eliminate fruit with visual defects, cuts and wounded areas and sometimes to divert fruit of high surface colour to a high-maturity pack (Fig. 22.10/Plate 241). Attention to details of sorting line efﬁciency is especially important with peaches, where a range of fruit colours, sizes and shapes can be encountered. Sizing segregates fruit by either weight or dimension. Sorting and sizing equipment must be ﬂexible to efﬁciently handle large volumes of small fruit or smaller volumes of larger fruit. In California, most yellow-ﬂeshed peaches are packed into twolayer (trays) boxes (Fig. 22.11/Plate 242). In the eastern USA, most are volume-ﬁll packed.

Electronic weight sizers are used to automatically ﬁll shipping containers (Fig. 22.12/Plate 243). Most of the white-ﬂeshed peaches and ‘tree ripe’ peaches are packed into one-layer (tray) boxes (ﬂat). In some cases, peaches are also packed in small-size plastic bags or clamshell plastic containers. In some operations, mechanical place-packing units use hand-assisted ﬁllers where the operator can control the belt speed to match the ﬂow of fruit into plastic trays. Limited volumes of high-maturity peaches are ‘ranch’ or ‘ﬁeld’ packed at the point of production. In a typical ‘ranch’ or ‘ﬁeld’ packed operation, fruit of high maturity and quality are picked into buckets or totes that are carried by trailer to the packing area. These packers work directly from the buckets to sort, grade, size, and pack fruit into plastic trays. In these cases, the fruit are not washed, brushed, waxed or fungicide-treated. In other cases, fruit are picked into buckets or totes but then dumped into a smooth-operating,

Harvesting and Postharvest Handling

Fig. 22.10.

Sorting peaches by skin colour and removing blemished fruit.

Fig. 22.11.

Packers sizing, sorting and packing fruit by hand into two-layer tray packs.

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Fig. 22.12. Fruit moving on to an electronic weight sizer.

low-volume packing line for washing, brushing, waxing, sorting and packaging. Because of less handling of the fruit, a higher maturity can be used, and growers can beneﬁt from increased fruit size, red colour and greater yield. High-quality fruit can also be produced by managing orchard factors properly and picking fruit that are ﬁrm. But in this latter case, ripening at the retailer will be essential to ensure good ﬂavour quality for consumers.

the fruit, the temperature ﬂuctuations in the storage system and equipment performance (Thompson et al., 1998; Thompson, 2002). Holding peaches at these low temperatures minimizes both the losses associated with rotting organisms, excessive softening and water losses, and the deterioration resulting from IB in susceptible cultivars, therefore optimizing their postharvest life (Mitchell, 1987).

22.7 Cull Utilization Shipping and transportation Potential uses At the shipping point, fruit should be cooled and held near or below 0°C according to their freezing point. During transportation, if IBsusceptible cultivars are exposed to 5°C their postharvest life can be signiﬁcantly reduced (Mitchell and Kader, 1989a). Peach storage and overseas shipments should be at or below 0°C. Maintaining these low pulp temperatures requires knowledge of the freezing point of

The main use of peach culls is for cattle feed because culled peach is palatable and a good source of energy (Fig. 22.13/Plate 244), but it is low in protein and has other characteristics that make it different from other feed sources (Thompson, 2002). For example, peaches contain ~85% water, 9% digestible dry matter, 5% pits and 2% indigestible dry matter. The high

Harvesting and Postharvest Handling

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Fig. 22.13. Cull removal and disposal can be a major problem and expense in peach packing.

water content diminishes the real value as feed because it makes culls expensive to transport, requires large trough volumes, and allows the feed to spoil quickly. If fed in large proportions, culled fruit causes almost continuous urination and consequently the animals require a high amount of salt. The only potential advantage to the high water content is that animals in a remote, dry location will not need extra water hauled to them. Low protein levels in culled fruit limit the quantity that can be fed where rapid weight gain is important, such as in feed lots. For example, only about 20% of the ration can be composed of culls (Thompson, 2002). The use of culls for fuel alcohol production is limited mainly by the low sugar content; thus peach is not included in this group (Thompson, 2002). The 8 to 12% sugar content of most culled peaches results in an alcohol yield of about 42 l/t (10 gal/t) of fruit, which is too low compared with potatoes (83 to 104 l/t) or maize (375 l/t). This low yield makes it uneconomical in addition to the waste management problem. Unfortunately, the limits to the use of culls often result in large portions of them being discarded. Improper disposal can cause sanitary and pollution problems (Thompson, 2002). Flies and odour problems can be prevented by ensuring rapid drying.

Fly maggots hatch into adults within 7 to 10 days, and odour problems can develop before ﬂies appear. The culls should be crushed and spread no more than one or two layers deep; sometimes this is done on orchard roads or fallow ﬁelds. Culls can be disked into the soil, although this tends to cover the fruit with soil and slows drying; also, insects or diseases that may have caused the fruit to be culled in the ﬁrst place may infect a future crop. Disposal sites should be as far away from neighbours as possible. Flies can travel up to 8 km (5 miles) from the place where they hatch. Culls should not be dumped near streambeds. Fruit cull piles can attract the dumping of many other kinds of refuse. If culls are deposited away from the point of production, use municipal solid waste disposal sites if available. Some culls can be turned into dried fruit for human consumption. However, good-quality dried fruit is made only from good-quality fresh fruit. Only undersized or slightly overripe fruit should be considered for drying. Situation in California In general, peach culls are going for frozen or canned peaches or juice, dried for charity donation, or used for livestock feed. When fruit have

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worms and decay they are utilized as green waste for compost. The amount of culls varies according to season, cultivar and other conditions from ~10 to 30% of total production. The decision on the cull utilization is made based on returns. In general, when the reason for disposal has been small sizes and mainly cosmetic blemishes, fruit still have value for human consumption and can be frozen, canned or used for making juice or other value-added products.

Other uses A very limited peach fresh-cut business has been developed because of the short market life of this produce (Gorny et al., 1999). The optimal ripeness for preparing fresh-cut peach slices is when the ﬂesh ﬁrmness reaches 1.4–2.7 kgf, and these slices can retain good eating quality for 2–8 days (depending on cultivar) while kept at 5°C and 90–95% relative humidity. Post-slice dips in ascorbic acid and calcium lactate or use of MAP may slightly prolong the shelf-life of peach slices. Recently, mild heat pre-treatments (40°C for 70 min) before minimal processing and packing under passive MAP conditions were effective in inducing ﬁrmness (Steiner et al., 2006), while preserving nutritional quality (organic acids and vitamins).

22.8 Fruit Handling at Retail Distribution Fruit preparation for consumers Because peaches are a climacteric fruit they are usually harvested when they reach a minimum or higher maturity, but are not completely ripe (‘ready to eat’). Initiation of the ripening process must occur before consumption to satisfy consumers. It has been demonstrated that most consumers are satisﬁed after eating ripe peaches. A ripe or ‘ready to eat’ peach is deﬁned when ﬂesh ﬁrmness is approximately 0.9–1.4 kgf. Peaches with ﬁrmness below 2.7– 3.6 kgf (‘ready to buy’) are becoming attractive to consumers while still tolerating retail

handling. For this reason, this range is also called the transfer point. Thus, a delivery system should target store displays of peaches with ﬁrmness below 2.7–3.6 kgf and ensure that consumers are eating peaches that are ‘ready to eat’. Promotional programmes should be established to educate consumers on ripening issues. As the market for fresh produce is growing steadily, the need for assuring quality is increasing in European markets. In this sense, the market splits into two classes of produce: commodity (low price) and high-quality fruits, which are in demand from the new export markets. Accordingly, the combination of colour measurements using two wavelengths (450 and 680 nm) with non-destructive ﬁrmness testing gave a good procedure for classifying peaches for ripeness (Ruiz-Altisent et al., 2006). It has been reported that the presence of g-decalactone, d-octalactone and g-octalactone can be used to indicate the maturity stage for harvesting peaches (Lavilla et al., 2002). Two sensors based on solid-state detection of gas concentration of g- and d-decalactone (which increase signiﬁcantly during the ﬁnal stages of ripeness) were able to grade peaches by ripening stages. Moreover, the sensors were capable of detecting skin breakage produced by mechanical or pathological causes and showed a good correlation with ﬁrmness measurements (Moltó et al., 1999).

Fruit buyer handling If retailers are receiving mature peaches (4.5– 7.3 kgf), the ripening process can be initiated at the distribution centres (receivers). Detailed ripening protocols for retail handlers, warehouse and produce managers have been developed and well promoted (Crisosto and Parker, 1997). In general, peach cultivars harvested commercially will ripen properly without exogenous ethylene application. Temperature conditions for peaches during and after ripening should be adjusted according to the desired sales/consumption schedule. We encourage that further fruit ripening, if necessary, be done at the distribution level. The rate of fruit softening (pressure loss (kgf)

Harvesting and Postharvest Handling

per day) varies among peach cultivars and can be controlled by the storage temperature used. Fruit stored at 2.2°C will soften slower than fruit stored at 20°C. When the fruit reaches the transfer ﬁrmness mentioned above, the rate of softening slows. However, rate of softening also varies according to orchard and season, so ﬁrmness measurements should be taken to protect fruit integrity during the ripening process. These fruit will reach their ‘ready to eat’ ﬁrmness of 0.9–1.8 kgf after 2–3 days at room temperature (15–20°C dry retail display). Firmness is measured mid-cheek, perpendicular to the fruit suture. When kept at 2.2°C or below, peaches should be shipped out of the distribution centre within 4–5 days (ideally within 2–3 days). To the extent that the distribution centre does not have rooms that can maintain temperatures at this 2.2°C and below range, it might make more sense to set up two shipments per week from the shipper to ensure better temperature control and extend the market life of the product. In general, soft fruit are more susceptible to bruising than hard fruit. To reduce potential physical damage occurring during transportation from the distribution centres to retail stores and handling at the retail stores, we suggest transferring fruit to

Fig. 22.14.

Peach fruit display at a retail store.

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the retail store before fruit reaches no lower than 1.8–2.3 kgf measured on the weakest position for tray-packed peaches and nectarines. In general, the shoulder position is the weakest point on mid- or late-season fruit. As bruising incidence varies among cultivars, and bruising potential is related to each speciﬁc operation, producers should ﬁne-tune their transfer points for their handling situation. These are general handling guidelines but they need to be modiﬁed and assessed in light of one’s particular company facilities, logistics and customer requirements.

Peach handling at retail stores Ideally, peaches should be transported at 0–1.7°C from the distribution centre and kept at 0–1.7°C prior to transfer to dry/warm table for display. In situations where fruit temperature cannot be maintained out of the ‘killing zone’, it would be preferable to move fruit fast. Firmness measurements need to be considered in the decision-making process (Crisosto and Mitchell, 2002). Peaches should ideally be arriving from the distribution centre to the retail stores with

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ﬁrmness in the range of 1.8–2.7 kgf (weakest position) or 2.7–3.6 kgf (cheeks). This fruit is at the ‘ready to buy’ or ‘transfer point’ stage of ripening and within ~48–72 h at 20°C should be ‘ready to eat’ in the 0.9–1.8 kgf ﬁrmness range. This is the ﬁrmness range at which most consumers claim the highest satisfaction when eating peaches. Produce managers need to be educated about this new ‘ready to buy’ type of fruit (preconditioned) to minimize mechanical damage and expedite an effective rotation (ﬁrst in, ﬁrst out). Peaches should be displayed on dry tables and labelled well as ‘ready to buy/eat’, and consumers should understand that this

fruit is riper than conventionally packed tree fruit (Fig. 22.14/Plate 245). In order to protect these fruit, the display should be no more than two layers deep and in-box display should be attempted. As tree fruit will continue to ripen on the display warm/dry table, they should be checked often and the softest fruit be placed at the front of the display. Fruit that reach the ‘ready to eat’ ripeness of 0.9–1.4 kgf cheek ﬁrmness need to be sold quickly or refrigerated to extend their shelf-life. It is essential that consumers be instructed that this type of fruit should be refrigerated if it is not going to be consumed within 3 days of purchase.

References Anderson, R.E. (1979) The influence of storage temperatures and warming during storage on peach and nectarine fruit quality. Journal of the American Society for Horticultural Science 104, 459–461. Byrne, D.H. (2002) Peach breeding trends. Acta Horticulturae 592, 49–59. Carbonaro, M., Mattera, M., Nicoli, S., Bergamo, P. and Cappelloni, M. (2002) Modulation of antioxidant compounds in organic vs conventional fruit (peach, Prunus persica L., and pear, Pyrus communis L.). Journal of Agricultural and Food Chemistry 50, 5458–5462. Ceponis, M.J., Cappellini, R.A., Wells, J.M. and Lightner, G.W. (1987) Disorders in plum, peach and nectarine shipments to the New York market, 1972–1985. Plant Disease 71, 947–952. Cheng, G.W. and Crisosto, C.H. (1997) Iron–polyphenol complex formation and skin discoloration in peaches and nectarines. Journal of the American Society for Horticultural Science 122, 95–99. Corelli Grappadelli, L. (2001) Peach handling and marketing in Italy. In: Proceedings of 60th National Peach Council Convention, Hershey, Pennsylvania, 30 January–1 February, pp. 39–45. Crisosto, C.H. (1994) Stone fruit maturity indices: a descriptive review. Postharvest News and Information 5, 65–68. Crisosto, C.H. (2002) How do we increase peach consumption? Acta Horticulturae 592, 601–605. Crisosto, C.H. and Labavitch, J.M. (2002) Developing a quantitative method to evaluate peach (Prunus persica) flesh mealiness. Postharvest Biology and Technology 25, 151–158. Crisosto, C.H. and Mitchell, F.G. (2002) Peach, nectarine and plum. In: Kader A.A. (ed.) Postharvest Technology of Horticultural Crops. Special Publication No. 3311. University of California, Division of Agriculture and Natural Resources, Oakland, California, pp. 345–351. Crisosto, C.H. and Parker, D. (1997) Stone fruit ripening protocol for receivers. Slide set v98-c with cassette. University of California, Division of Agriculture and Natural Resources, Oakland, California. Crisosto, C.H., Johnson, R.S., Luza, J.G. and Crisosto, G.M. (1994) Irrigation regimes affect fruit soluble solids concentration and rate of water loss of ‘O’Henry’ peaches. HortScience 29, 1169–1171. Crisosto, C.H., Mitchell, F.G. and Johnson, S. (1995) Factors in fresh market stone fruit quality. Postharvest News and Information 6, 17–21. Crisosto, C.H., Johnson, R.S., DeJong, T. and Day, K.R. (1997) Orchard factors affecting postharvest stone fruit quality. HortScience 32, 820–823. Crisosto, C.H., Garner, D., Cid, L. and Day, K.R. (1999a) Peach size affects storage, market life. California Agriculture 53, 33–36. Crisosto, C.H., Johnson, R.S., Day, K.R., Beede, B. and Andris, H. (1999b) Contaminants and injury induce inking on peaches and nectarines. California Agriculture 53, 19–23. Crisosto, C.H., Mitchell, F.G. and Ju, Z. (1999c) Susceptibility to chilling injury of peach, nectarine, and plum cultivars grown in California. HortScience 34, 1116–1118. Crisosto, C.H., Day, K.R., Crisosto, G.M. and Garner, D. (2001a) Quality attributes of white flesh peaches and nectarines grown under California conditions. Journal of the American Pomological Society 55, 45–51.

Harvesting and Postharvest Handling

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Crisosto, C.H., Slaughter, D., Garner, D. and Boyd, J. (2001b) Stone fruit critical bruising thresholds. Journal of the American Pomological Society 55, 76–81. Crisosto, C.H., Garner, D.T., Andris, H.L. and Day, K.R. (2004) Controlled delayed cooling extends peach market life. HortTechnology 14, 99–104. Fernández-Trujillo, J.P. and Artés, F. (1998) Chilling injuries in peaches during conventional and intermittent warming storage. International Journal of Refrigeration 21, 265–272. Fernández-Trujillo, J.P., Martínez, J.A. and Artés, F. (1998) Modified atmosphere packaging affects the incidence of cold storage disorders and keeps ‘flat’ peach quality. Food Research International 31, 571–579. Ferrer, A., Remón, S., Negueruela, A.I. and Oria, R. (2005) Changes during the ripening of the very late season Spanish peach cultivar Calanda. Feasibility of using CIELAB coordinates as maturity indices. Scientia Horticulturae 105, 435–446. Garner, D., Crisosto, C.H. and Otieza, E. (2001) Controlled atmosphere storage and aminoethoxyvinylglycine postharvest dip delay post cold storage softening of ‘Snow King’ peach. HortTechnology 11, 598–602. Gil, M.I., Tomás-Barberán, F.A., Hess-Pierce, B. and Kader, A.A. (2002) Antioxidant capacities, phenolics compounds, carotenoids, and vitamin C content of nectarine, peach, and plum cultivars from California. Journal of Agricultural and Food Chemistry 50, 4976–4982. Goristein, S., Martín-Belooso, O., Lojek, A., Ciz, M., Soliva-Fortuny, R., Park, Y.S., Caspi, A., Libman, I. and Trakhtenberg, S. (2002) Comparative content of some phytochemicals in Spanish apples, peaches and pears. Journal of the Science of Food and Agriculture 82, 1166–1170. Gorny, J.R., Hess-Pierce, B. and Kader, A.A. (1999) Quality changes in fresh-cut peach and nectarine slices as affected by cultivar, storage atmosphere and chemical treatments. Journal of Food Science 64, 429– 432. Harding, P.L. and Haller, M.H. (1934) Peach storage with special reference to breakdown. Proceedings of the American Society for Horticultural Science 32, 160–163. Kader, A.A. and Mitchell, F.G. (1989a) Maturity and quality. In: LaRue, J.H. and Johnson, R.S. (eds) Peaches, Plums, and Nectarines: Growing and Handling for Fresh Market. Publication No. 3331. University of California, Division of Agriculture and Natural Resources, Oakland, California, pp. 191–196. Kader, A.A. and Mitchell, F.G. (1989b) Postharvest physiology. In: LaRue, J.H. and Johnson, R.S. (eds) Peaches, Plums, and Nectarines: Growing and Handling for Fresh Market. Publication No. 3331. University of California, Division of Agriculture and Natural Resources, Oakland, California, pp. 158–164. LaRue, J. (1989) Introduction. In: LaRue, J.H. and Johnson, R.S. (eds) Peaches, Plums, and Nectarines: Growing and Handling for Fresh Market. Publication No. 3331. University of California, Division of Agriculture and Natural Resources, Oakland, California, pp. 1–2. Lavilla, T., Recasens, I., López, M.L. and Puy, J. (2002) Multivariate analysis of maturity stages, including quality and aroma, in ‘Royal Glory’ peaches and ‘Big Top’ nectarines. Journal of the Science of Food and Agriculture 82, 1842–1849. Lill, R.E., O’Donoghue, E.M. and King, G.A. (1989) Postharvest physiology of peaches and nectarines. Horticultural Reviews 11, 413–452. Martínez-Romero, D., Valero, D., Serrano, M., Burló, F., Carbonell, A., Burgos, L. and Riquelme, F. (2000) Exogenous polyamines and gibberellic acid effects on peach (Prunus persica L) storability improvement. Journal of Food Science 65, 288–294. Mitchell, F.G. (1987) Influence of cooling and temperature maintenance on the quality of California grown stone fruit. International Journal of Refrigeration 10, 77–81. Mitchell, F.G. and Kader, A.A. (1989a) Factors affecting deterioration rate. In: LaRue, J.H. and Johnson, R.S. (eds) Peaches, Plums, and Nectarines: Growing and Handling for Fresh Market. Publication No. 3331. University of California, Division of Agriculture and Natural Resources, Oakland, California, pp. 165– 178. Mitchell, F.G. and Kader, A.A. (1989b) Field handling and packing. In: LaRue, J.H. and Johnson, R.S. (eds) Peaches, Plums, and Nectarines: Growing and Handling for Fresh Market. Publication No. 3331. University of California, Division of Agriculture and Natural Resources, Oakland, California, pp. 197– 208. Moltó, E., Selfa, E., Ferriz, J., Conesa, E. and Gutierrez, A. (1999) An aroma sensor for assessing peach quality. Journal of Agricultural Engineering Research 72, 311–316. Nanos, G.D. and Mitchell, F.G. (1991) High-temperature conditioning to delay internal breakdown development in peaches and nectarines. HortScience 26, 882–885.

596

C.H. Crisosto and D. Valero

Okie, W.R. (1998) Handbook of Peach and Nectarine Varieties: Performance in the Southeastern United States and Index of Names. USDA Agriculture Handbook No. 714. US Department of Agriculture, Washington, DC. Proteggente, A.R., Pannala, A.S., Paganga, G., Van Buren, L., Wagner, E., Wiseman, S., Van de Put, F. and Dacombe, C. (2002) The antioxidant activity of regularly consumed fruit and vegetables reflects their phenolic and vitamin C composition. Free Radical Research 36, 217–233. Romani, R.J. and Jennings, W.G. (1971) Stone fruits. In: Hulme, A.C. (ed.) The Biochemistry of Fruits and Their Products, Vol. 2. Academic Press, New York, pp. 411–436. Ruiz-Altisent, M., Lleó, L. and Riquelme, F. (2006) Instrumental quality assessment of peaches: fusion of optical and mechanical parameters. Journal of Food Engineering 74, 490–499. Sansavini, S., Corelli Grappadelli, L., Costa, G., Lugli, S., Marangoni, B., Tagliavini, M., Ventura, M., Abeti, D., Feralli, S., Marani, G., Mascanzoni, G., Molducci, S., Proni, R., Sama, A., Spada, G., Vitali, S., Turroni, P., Minguzzi, A. and Randi, M. (2000) Ricostituzione degli impianti e nuovi indirizzi produttivi della peschicoltura romagnola. In: Atti XXIII Convegno Peschicolo, Ravenna, 12–13 September 1997, pp. 62–74. Serrano, M., Martínez-Romero, D., Castillo, S., Guillén, F. and Valero, D. (2004) Effects of pre-harvest sprays containing calcium, magnesium and titanium on the quality of peaches and nectarines at harvest and during post-harvest storage. Journal of the Science of Food and Agriculture 84, 1270–1276. Shewfelt, R.L., Meyers, S.C., Prussia, S.E. and Jordan, J.L. (1987) Quality of fresh-market peaches within the postharvest handling system. Journal of Food Science 52, 361–364. Smith, W.H. (1934) Cold storage of Elberta peaches. Ice and Cold Storage 37, 54–57. Steiner, A., Abreu, M., Correia, L., Beirão-da-Costa, S., Leitão, E., Beirão-da-Costa, M.L., Empis, J. and MoldaoMartins, M. (2006) Metabolic response to combined mild heat pre-treatments and modified atmosphere packaging on fresh-cut peach. European Food Research Technology 222, 217–222. Thompson, J.F. (2002) Cull utilization. In: Kader, A.A. (ed.) Postharvest Technology of Horticultural Crops. Special Publication No. 3311. University of California, Division of Agriculture and Natural Resources, Oakland, California, pp. 41–43. Thompson, J.F., Mitchell, F.G., Rumsey, T.R., Kasmire, R.F. and Crisosto, C.H. (eds) (1998) Commercial Cooling of Fruits, Vegetables, and Flowers. Publication No. 21567. University of California, Division of Agriculture and Natural Resources, Oakland, California. Tomás-Barberán, F.A., Gil, M.I., Cremin, P., Waterhouse, A.L., Hess-Pierce, B. and Kader, A.A. (2001) HPLCDAD-ESIMS analysis of phenolic compounds in nectarines, peaches, and plums. Journal of Agricultural and Food Chemistry 49, 4748–4760. USDA (2003) Composition of Foods: Fruits and Fruit Juices – Raw, Processed, Prepared. USDA Agriculture Handbook No. 8–9. US Department of Agriculture, Washington, DC (www.nal.usda.gov/fnic/foodcomp). Valero, D., Serrano, M., Martínez-Madrid, M.C. and Riquelme, F. (1997) Polyamines, ethylene, and physiochemical changes in low-temperature-stored peach (Prunus persica L. cv. Maycrest). Journal of Agricultural and Food Chemistry 45, 3406–3410. Von Mollendorff, L.J. (1987) Woolliness in peaches and nectarines: a review. 1. Maturity and external factors. Horticultural Science/Tuinbouwetenskap 5, 1–3. Von Mollendorff, L.J., Jacobs, G. and De Villiers, O.T. (1992) Postharvest factors involved in the development of chilling injuries in peaches and nectarines. Journal South African Horticultural Science 2, 58–68.

Index

10-Point Management Programme 395, 518 see also Peach tree short life (PTSL)

Acari see Mites Adaptation 69 AFLP see Ampliﬁed fragment length polymorphism Aggregation pheromone 478, 484 Agrobacterium spp. Agrobacterium radiobacter 420, 423 Agrobacterium tumefaciens 99–100, 194, 203–204, 206, 208, 409, 418, 510–511 see also Crown gall Allergenicity 563–564 see also Nutritional value Alternate host 357 Ampliﬁed fragment length polymorphism (AFLP) 86, 93, 97 Anarsia lineatella see Peach twig borer Aneuploid 68 Anthocyanin 10, 18–19, 30, 63, 176, 183, 186, 188, 341, 561, 565, 577 anthocyaninless 10, 18, 22, 63, 67, 71, 165 deﬁciency 10, 63, 67 Anthracnose Colletotrichum acutatum and Colletotrichum gloeosporiodes 401–403 Gloeosporium laeticolor Berk 55 Antioxidants 537, 539, 562–563 ascorbic acid 576–577, 592 capacity 577 carotenoids 576–577 phenolics 576–577 catechin 577

chlorogenic acid 577 cyanidin-3-glucoside 577 epicatechin 577 ﬂavonols 577 Aphids 55, 88, 334, 341, 436, 468, 487, 494–496 green peach aphid, Myzus persicae 55, 495–496 Peach latent mosaic viroid (PLMVd) vector 454 Plum pox virus (PPV) vector 441–442, 494 resistance 11, 63, 70, 74–75, 162, 164, 204 Apical meristem culture 447 see also Propagation Apoplastic phloem loading 248–249 Appearance see Fruit Apple chlorotic leaf spot virus (ACLSV) 456–457, 459 Apricot latent virus 456 Arabidopsis 85, 92, 96 A. thaliana 554, 567 Arabis mosaic virus (ArMV) 457, 524 Armillaria root rot (syn. oak root rot, shoe string root rot) 355, 386, 388–392, 394 A. mellea 355, 389, 390, 403 A. mellea (oak root rot) 198, 205, 207, 210, 212, 214 A. ostoyae 355, 389 A. tabescens 198, 355, 389 A. tabescens (oak root rot) 198, 205 rhizomorph 355, 389–392, 403 Armoured scale (Hemiptera: Diaspididae) San Jose scale (SJS), Quadraspidiotus perniciosus 492–494 white peach scale (WPS), Pseudaulacaspis pentagona 491–492, 494 597

598

Index

ArMV see Arabis mosaic virus Aroma (fragrance) 17, 19–21, 537–539, 550, 561, 576, 584 benzaldehyde 550, 562 δ-decalactone 550, 562 γ-decalactone 550, 562 linalool 550, 562 Aromia bungii (Trunk borer) 55 Ascorbic acid 576–577, 592 see also Antioxidants ATS 294 ‘Axis central’ see Training system

Bacillus thuringiensis 474 Bacteria and bacterial diseases 407–409, 411–423 characteristics of bacteria 407–408 bacterial streaming 419 environment 416 epiphytes 416 Bacterial artiﬁcial chromosome (BAC) 92–96 BAC insert (contig) 93–96, 97 Bacterial canker complex (BCC) 409, 411–416, 515–516, 518 bacterial canker (Pseudomonas syringae pv. syringae) 197, 205, 209–211, 214, 515–516, 518, 520 Bacterial decline syndrome 411 symptoms 412–415 canker 413 cold injury 411, 414, 415 dead bud 412 discoloured streaks in wood 413, 414 sucker growth 412 Bacterial leaf spot (Xanthomonas pruni) 55, 409, 416 infection conditions 417 management 417–418 chemical 418 copper 418 host resistance 417 oxytetracycline 418 pathogen overwintering 417 resistance 143, 145–146, 153 symptoms 416–422 leaf chlorosis and lesions 416–417 lesions on mature fruit 416, 420 lesions on young fruit 416, 419 newly formed leaf lesions 416, 418 spring cankers 416–417, 421–422 summer cankers 417, 421 Xanthomonas arboricola pv. pruni 409 BCC see Bacterial canker complex Beer 51 BG33R 520–521 Bioﬁx 472, 475, 494 Biofumigation 519, 527 Biolistics (particle bombardment) 99–100

Biological control 480, 492, 494 Black knot (Apiosorina morbosa) 401–402 Blush (overcolour) see Colour Boron 314–316 deﬁciency 314–316 toxicity 315 Botryosphaeria dothidea see Fungal gummosis Botryosphaeria fruit rot (B. dothidea, B. obtusa and B. rhodinia) 401–402 Botrytis cinerea (grey mould) 356, 396, 398, 401, 577 Brachytic dwarf 165–166, 199 Breeding (classical) 68–81 Breeding goals cold-hardiness 142–144, 151–152, 154, 165–167 low-chill breeding Australia 113 Brazil 117–118 current 110–121 heritability 122–123, 125, 132 history 108–110 inbreeding 110 Mexico 118–119 nectarine 145, 147–151, 153–163, 165, 167–169 South Africa 119 Taiwan 119 Thailand 119 tree architecture 146, 151, 153–154, 165–166 USA 119–121 low-chill breeding management 129–133 hybrid seed production 129–131 seedling populations 132–133 testing advanced selections 133 low-chill breeding objectives 121–129 blind nodes 123, 124 bud drop 123 disease resistance 127–129 ﬂower bud density 123 fruit development period 123–125 fruit ﬁrmness 126–127 fruit shape 125–126 low chilling requirement 121–122 time of ﬂowering 122–123 Breeding programmes 139–174 Anderson 147–149 Arkansas 153 Bradford 159 Bulgaria 161 Burchell 159–160 California 146–150, 154–160 China 166, 168 conventional 44, 45 early history 140–141 England 141, 173 ﬂat shape 151, 154, 158, 162, 167–168

Index

France 161–163, 166 Georgia 141, 144–145, 150, 154 Greece 163 Hungary 163 Ilinois 142–143 Iowa 142–143 Italy 146, 161, 163–166 Japan 168–169 Korea 169 Louisiana 146, 153–154 Maryland 141, 144 Massachusetts 143 Merrill 147 Michigan 144, 151–153 New Hampshire 143–144 New Jersey 143, 151 New York 142 New Zealand 169 North Carolina 145–146, 154 Ontario 143, 153 Poland 165 Romania 166–167 Serbia 167 South Africa 169 Spain 167 Sun World 160–161 Texas 141, 144, 160 Ukraine 167 USDA 144–145, 150–151, 154–158 Virginia 143 West Virginia 144, 151 Zaiger 158–159 Brown rot (Monilinia fructicola, M. fructigena, M. laxa) 55, 118, 127–128, 338, 353–354, 356–360, 396, 401 blossom blight 357–359, 361, 396 green fruit rot 354, 357–358, 361, 396 fruit rot 356–359, 396–397 mummiﬁed fruit (mummy) 357–358, 400 resistance 143, 163–164, 166–167 twig blight 357–358 Budding 237, 239 see also Propagation Bulked segregant analysis 88, 97

Calcareous soil 195, 206–207, 209–212, 214 Calcium 310–311 deﬁciency 310–311 fruit quality 311 Candida inconspicua (sour pit) 401–402 Canker (Valsa leucostoma (Pers.) Fr.) 55, 70, 151, 205, 295, 354, 375–378, 394 see also Leucostoma canker Canopy assimilation 247, 255 Canopy shading 246 Carbamate insecticides 472, 476, 477, 498

599

Carbaryl 296 Carbon assimilation 245 partitioning 284–285 Carboxylation efﬁciency 245 Carotenes 52, 561 Carotenoids 17–18, 182–183, 562, 576–577 β-carotene 562 β-cryptoxanthin 562 Vitamin A 562 Cat-facing injury 334–335, 341, 481–483 Catechin 577 Catharathus roseus 411 Cells 290, 292 Cellulose 562 Central leader 55, 70, 255, 274–276 density 274 photographs 275–276 pruning 70, 274 training 274 see also Training system Certiﬁcation programmes 403, 442–443, 447, 449–450, 458 see also Viruses, indexing Character inheritance 61–66 Chemicals 293–294, 296 fertilizers 51 plant growth regulation 48 Cherry rasp leaf virus (CRLV) 524 Chilling injury see Deterioration problems; Internal breakdown (IB) Chilling requirement 17, 26–27, 30, 48, 55, 107, 117, 119, 121–122, 131–132, 144, 159–160, 164–165, 212, 223, 231, 252, 279 China Fruit Plant Monograph – Peach Flora 45 Chinese Spring Festival holiday 57 Chip budding 449 see also Propagation, clonal Chipmunk, northwestern (Eutamias amoenus) 340 Chlorogenic acid 562, 577 Chlorophyll 561 Chromosomal walk 97 Chromosome 85 Citrate 557 Codling moth Cydia pomonella 472–473 distinction from oriental fruit moth 470 Coefﬁcient of regression 66 Cold hardiness 69, 92, 141–143, 151, 164–166, 168, 196, 201–202, 204–205, 214, 270, 319, 378, 394 Coleoptera 477–480 Colour, ﬂesh 17–19, 21, 27, 30 see also Fruit, ﬂesh Colour, skin 12, 17–19, 537–538, 540–546, 551, 557, 561–562 anthocyanins 561

600

Colour, skin continued blush (overcolour) 29, 110, 118–119, 140, 168–169, 183, 186, 551, 582 carotenes 561 chlorophyll 561 CIE electronic colorimeter 551 ground (undercolour) 551 xanthophylls 561 Comparative test for cultivar release 80 Conotrachelus nenuphar see Plum curculio Constriction canker (Phomopsis amygdali) 355, 380–383 confused with brown rot twig blight 380 fusicoccin 381 Consumer acceptance 537–539, 543 Controlled atmosphere storage 551, 565 high carbon dioxide (CO2) 566 acetaldehyde, ethanol 566 low oxygen 565 Cooling 551, 564–565 see also Temperature Copper 318 Cotyledon 98–99 Covering materials and reﬂective ﬁlms 48, 341, 545 Crop load 246 interactions with stress 297–298 modifying 291–297 quantifying 290–291 Cross-breeding 68 Crown gall Agrobacterium radiobacter 420, 423 Agrobacterium tumefaciens 99–100, 194, 203–204, 206, 208, 409, 418, 510–511, 515 galls on peach seedlings 422 infection 420, 423 T-DNA 420 management 423 Crown rot see Phytophthora root and crown rots Cull utilization 590–592 other uses 592 potential uses 590–591 cattle feed 590–591 drying 591 fuel alcohol 591 situation in California 591–592 Cultivar replacement time 53 Cultivars Chinese traditional cultivars and landraces 52 development 52 early 45, 52 ﬂat peach and ornamental peach 45 high-performance 45 hypoallergenic 564 mid-season 45, 52

Index

named cultivars (partial list) ‘Ailihong’ 54 ‘Armking’ 45, 278–280, 555 ‘Babygold’ 44–45, 542 ‘Bai Tao’ 42 ‘Baifeng-2’ 45 ‘Baihua’ 44, 46 ‘Baimangpantao’ 45 ‘Baixianglu’ 45 ‘Baiyu Tao’ 42 ‘Beinong Zaoyan’ 45 ‘Beinong-2’ 45 ‘Bositao’ 46 ‘Chan Tao’ 42 ‘Chengxiang’ 45 ‘Chenpupantao’ 45 ‘Chinese Cling’ 2, 69, 141–142, 168 ‘chrysanthemum’ peach 55 ‘Chunhua’ 45 ‘Chunle’ 45 ‘Cullinan’ 45 ‘Datuanmilu’ 45 ‘Dayu Tao’ 42 ‘Dong Tao’ 42 ‘Dunhuadongtao’ 46 ‘Early red-2’ 46 ‘Elberta’ 2, 46, 69, 108–109, 124, 141–144, 146, 154, 161, 166, 200, 223, 290, 304, 451, 512 ‘Erse Tao’ 42 ‘Fang Tao’ 42 ‘Feicheng Tao’ 44 ‘Feichengtao’ 46 ‘Fenghuapantao’ 45 ‘Fenzhou Tao’ 42 ‘Fertilia Morettini’ 45 ‘Fillips’ 46 ‘Flavorlate’ 45 ‘Guang Tao’ 42 ‘Guoyan red’ 42 ‘Hakuho’ 44 ‘Hangshengpantao’ 45 ‘Hanli Tao’ 42 ‘Hanlum’ 44 ‘Hehuan Erse Tao’ 42 ‘Hongliguang’ 46 ‘Hongrang Tao’ 42 ‘Huaguang’ 45 ‘Huangroupantao’ 46 ‘Huayumi’ 44 ‘Huiyulu’ 45 ‘Japan-89’ 45 ‘J.H. Hale’ 14, 64, 69, 109, 141–142, 144, 146, 161, 164, 166, 179, 566 ‘Jiaqingpantao’ 46 ‘Jin Cheng Tao’ 40 ‘Jin Tao’ 42

Index

‘Jincheng’ 46 ‘Jingmi’ 46 ‘Jingyu’ 46 ‘Jinxiu’ 46 ‘Kunlun Tao’ 42 ‘Kurakato’ 45 ‘Li Tao’ 42 ‘Lianhuang’ 45 ‘Lihepantao’ 46 ‘Long 1-2-4’ 46 ‘longevity’ peach 55, 56 ‘Longhuashuimi’ 46 ‘Luosi white’ 42 ‘Mi Tao’ 42 ‘Myoujou’ 45 ‘Nai Tao’ 40 ‘NJC88’ 45 ‘Okubo’ 44 ‘Pan Tao’ 42 ‘Pang Tao’ 42 ‘Putian Tao’ 42 ‘Qi Di Tao’ 40 ‘Qiangyefei’ 42 ‘Qianye Tao’ 42 ‘Qin Tao’ 40 ‘Qingzhoubaipimitao’ 46 ‘Redhaven’ 5, 45, 75, 81, 100, 142, 144–145, 151–152, 163, 166, 198, 278, 510, 552 ‘Renmian Tao’ 42 ‘Ruiguang-2’ 45 ‘Ruiguang-3’ 45 ‘Sahuahongpantao’ 45 ‘Shanghaishuimi’ 44 ‘Shenzhou’ 46 ‘Shenzhouhongmi’ 46 ‘Shenzhoushuim’ 44 ‘Shiyue Tao’ 42 ‘Shouxing Tao-1’ 45 ‘Shuang Tao’ 40 ‘Shuguang’ 45 ‘Sunagawase’ 45 ‘Wanshuomi’ 46 ‘Wuyuexuanbiangang’ 45 ‘Xianghui-1’ 45 ‘Xiao Tao’ 42 ‘Xinbaihua’ 46 ‘Xizhuang-1’ 46 ‘Yanguang’ 45 ‘Yanzhi Tao’ 42 ‘Yexiandongtao’ 46 ‘Yin Tao’ 42 ‘Yinhualu’ 45 ‘You Tao’ 42 ‘Yuhualu’ 44, 45 ‘Yulupantao’ 45 ‘Zao Tao’ 42

601

‘Zaohongzhu’ 45 ‘Zaohuangpantao’ 45 ‘Zaokuimitao’ 45 ‘Zaolupantao’ 45 ‘Zaoshoumi’ 45 ‘Zaoxialu’ 45 ‘Zaoxiangyu’ 45 ‘Zhaohui’ 44, 45 ‘Zhaoxiang’ 45 ‘Zhonghuashoutao’ 46 ‘Zhongyoupantao’ 45 ‘Zi Wen Tao’ 40 ‘Ziye DaTao’ 42 ornamental peach 41, 45, 55 Cyanidin 562, 577

Dagger nematodes (Xiphinema spp.) 196–198, 334, 449–451 biology 525 control 526 diagnosis 526 economic importance 525–526 geographical distribution 524–525 host range 525 identiﬁcation 526 species 524–525 survival 525 see also Nematodes; Xiphinema Dandelion (Taraxicum officinale) 334, 341 alternate host for Tomato ringspot virus 198, 334, 449 alternate host for ring nematode 341 Decay see Deterioration problems Deer mouse (Peromyscus maniculatus) 340 Degree day (°D) development models 472–473, 474, 475, 477 Deterioration problems 577–580 Botrytis cinerea (grey mould) 356, 396, 398, 401, 577 chilling injury (CI) see internal breakdown (below) decay 538–542, 545, 577, 579, 584, 592 defects 537, 542, 543 inking 580, 586 foliar nutrients 580 fungicides 580, 584, 588 heavy metal contaminants 580 internal breakdown (IB) 537–538, 543–544, 565, 577–579, 582, 584, 590 bleeding 578 controlled atmosphere (CA) 578–579 ﬂesh translucency 577 modiﬁed atmosphere packaging (MAP) 579, 592 severity 578–579, 584 susceptibility 578

602

Index

Deterioration problems continued internal breakdown (IB) continued taste 578 texture 577 mechanical injury 41, 579–580 bruising, abrasion 579 bruising, compression 579 bruising, impact 579 bruising, vibration 579 critical impact bruising thresholds 579 plant growth regulators 579 Monilinia fructicola see Brown rot peach skin discoloration see inking (above) staining see inking (above) Dichocrocis punctiferalis (Pyralid moth) 55 Diplodina fruit rot (D. persicae) 401–402 Diptera 486–487 Disease resistance 127–129, 442 bacterial spot 143, 145–146, 153 brown rot 143, 163–164, 166–167 leaf curl 161–162, 164, 166–167 powdery mildew 161–162, 164, 166–167 DNOC 294 Dodder (Cuscuta spp.) 409, 427 Domestication 38, 40, 43, 57 Dormancy 27, 30, 43, 49, 75, 78, 92, 97, 107, 121–122, 128, 223–224, 249, 251, 411, 416 Dormant oil 474, 493–494, 499 Double petals 52 Drought 2, 48, 97–98, 167, 194, 199, 206–209, 212–214, 245, 248, 295, 297, 298, 340, 508, 510, 514 tolerance 43 see also Water stress Dwarﬁsm 4–5, 45, 48, 52–55, 62, 66, 70, 90, 100, 108, 140, 146, 151, 153, 161, 165–167, 199

Emasculation 74, 76–77 Embryo 98–100 Embryo culture 25, 78–79, 98, 131, 155 deﬁnition 236 methodology 236, 238 Endocarp 2, 15, 16, 19, 22, 24, 25, 30 Entomopathogenic nematode 521 see also Heterorhabditis; Steinernema Epicatechin 577 Eradication 442–443, 458 Ermine (Mustela erminea) 340 ESTs see Expressed sequence tags Ethephon 293, 296 Ethylene 22–24, 27, 30, 65, 127, 185, 293, 296, 537–539, 551–558, 560–562, 565–567, 592 1-methylcyclopropene (1-MCP) 555, 561–562 action inhibitor (2, 5-norbornadiene) 556 aminoethoxyvinylglycine (AVG) 552, 554, 560

analogue (propylene) 552, 556 autocatalytic action 552 biosynthesis 551–552, 554 1-aminocyclopropane-1-carboxylate (ACC) 552, 565 1-aminocyclopropane-1-carboxylate oxidase (ACO) 552–553 1-aminocyclopropane-1-carboxylate synthase (ACS) 552, 554 ACO isogenes (Pp-ACO1, Pp-ACO2) 554 ACS isogenes (Pp-ACS1, Pp-ACS2, PpACS3) 552, 554 perception 551–552, 554 European red mite see Mites European stone fruit yellows (ESFY) 409–410, 428–431 apple proliferation (AP) group 430 apricot chlorotic leaf roll (ACLR) 429 group 16Sr X 430 management 430 plant hosts 430 plum leptonecrosis (PLN) 429 psylla 430 symptoms 429, 430 vector hosts 430 Evapotranspiration (ET) 228, 319–321, 542 Evergreen 97 Evergrowing 97 Expansins (Pp-Exp1, Pp-Exp2, Pp-Exp3) 557 Expressed sequence tag (EST) 93–96, 567

Feeding site 509, 517 Fibre 562 Field harvesting, hauling and packaging 585–590 fruit hauling 579, 580, 585–586 fruit packaging 580, 587–588, 590 harvesting 579–582, 585–586, 592 shipping and transportation 590 sorting and sizing operation 588–590 ranch or ﬁeld packed 588 tray-packed 588–589, 593 volume-ﬁll 588 Flavonols 577 Flower bud 3, 291–293 density 123, 270, 292 differentiation 270 Flower colours 10, 42, 52, 89 diversity 14 double colours 42 double ﬂower 64 purple 42 red 42 type 13, 64 white 42 Flowering, time of 122–123, 207, 408–409, 426

Index

Food cell 517 Fresh market, harvest and postharvest handling 576–594 Frosty mildew (Leucotelium pruni-persicae) 401–402 Fructose 247–251, 559–560 Fruit 11 colour 42 see also Colour composition 576 aroma 576, 584 immature 576 mature 576 minerals 576 organic acids 576, 592 titratable acidity (TA) 537–539, 543–545, 576 development 123–125, 551 fruit development period 564, 566 stage I (cell division) 551, 561, 564 stage II (pit hardening) 551, 557, 561, 564 stage III (cell elongation/ﬁnal swell) 551, 557–558, 560–561, 564 stage IV (ripening) 551–552, 561 ﬂesh acids 17, 19, 21 colour 17–19, 21, 27, 30 ﬁrmness (puncture pressure) 537–538, 543, 551–553, 556, 581, 592 ﬁrmness, at retail stores 590, 592–594 ﬂavour 19 melting type 18, 21–24, 30, 42–46, 51, 53, 65, 67, 108, 110, 119–121, 127, 140, 151, 153–154, 176, 185–186, 538, 551–552, 555–556, 561, 563, 581 non-melting type 2, 12, 18, 21–22, 24, 27, 30, 41, 53, 65, 67, 71, 108, 110, 118–121, 126–127, 140, 153, 155, 163–167, 169, 176–177, 185–186, 189, 539, 551–552, 555–556, 561, 563 phenolics 19, 21 ready to buy 592 ready to eat 593 slow-ripening mutant 552 softening and melting 555 stony-hard (hd) 552, 554 see also Stony-hard sugars 19–21, 27, 30 texture 16, 21–25, 27, 30 growth 254–255 handling fruit buyer handling 592–593 fruit preparation for consumers 592 at retail distribution 592–594 hauling 579–580, 585–586 injury 468–486

603

cat-facing 481, 483 gumming 482 russetting 484 silvering 484, 485 water soaking 482 internal breakdown see Deterioration problems maturity see Ripening photosynthesis 246 preharvest factors affecting peach quality 536–547 quality, deﬁnition 537 quality, factors affecting canopy manipulation 544–547 canopy position 544, 545 cracking 544, 542 crop load 544 fruitlet thinning 544 see also Thinning girdling 545–546 leaf removal 544–546 reﬂective materials 48, 341, 545 summer pruning 544 quality, genotype 539–540 quality, irrigation 542–544 calcium 541–542 iron 542 mineral nutrition 540–542 nitrogen 540–541 partial root zone drying (PRD) 543 potassium 542 regulated irrigation deﬁcit (RID) 542–543 sensory properties of quality appearance 537, 540 aroma 537–539 ﬂavour 537–540, 545 taste 537 texture 537, 542 respiration 246, 252, 255–256 ripening delaying 48 maturity deﬁnition 581 stage 578, 585, 592 stimulation 48 ripening, maturity indices 581 background colour 581 ﬁeld application 581–582 ﬂesh colour 581 see also Fruit, ﬂesh ﬂesh ﬁrmness 581, 592 harvest date 581 maximum maturity 581 skin colour 581–582, 589 ripening, maturity and quality 537–539, 580–581 ethylene 537–539

604

Index

Fruit continued ripening, maturity and quality continued ﬂavour 576, 578–581, 590 harvest 537–545 immature fruit 581 market life 537–538, 544–545, 580 mature 581, 592 non-destructive techniques 539 over-mature 581 quality potential 580 ripening 537–540, 544 storage potential 539, 543, 545 shape 15–16, 18, 25, 30, 42 size 15–16, 25, 29, 537, 540, 542–546 skin 2, 10, 12, 16, 17, 18, 19, 21, 25, 27, 30 storage cold storage 51 controlled-atmosphere storage 51 low-pressure storage 51 low temperature storage 564–565 see also Postharvest; Temperature Fungal gummosis (Botryosphaeria dothidea) 55, 355, 378–381 Fungicide resistance 360 Fusetto see Central-leader Fusicladosporium carpophilum see Scab

Genetic diversity, assessment 52 Genetic map 95 Genetic resistance see Resistance Genetic transformation see Transformation Genome 85, 88, 91–92, 94, 96–97, 100, 215, 419, 446, 449–451, 453, 459, 556, 567 Genome Database for Rosaceae (GDR) 93, 97, 100, 256 Genotyping, high-throughput 55 Geotrichum candidum (sour rot) 356, 398, 400–401 Germplasm 44–45, 52, 68, 91, 99, 108, 110, 117–118, 120, 122–123, 131, 133–134, 143, 153, 163–168, 170, 181, 189, 213, 443, 459, 511, 515, 523 Giant cell 508, 509 Gibberellins 292–293 Gilbertella decay (G. persicaria) 356, 396, 398–399 Girdling 41, 48, 545–546 Glucose 247–251, 559–560 Graft compatibility 194–199, 202–205, 207–213 incompatibility 194, 199, 206–207, 211 Grafting techniques 43 see also Propagation, clonal Grapholita molesta 468–472, 475 see also Oriental fruit moth Green June beetle (GJB), Cotinis nitida 480–481 Green peach aphid, Myzus persicae 204, 454 Greenhouse cultivation 48, 55

management 49 microclimate 48 semi-ground 49 spacing 49 see also Protected cultivation Grey mould (Botrytis cinerea) 356, 396, 398, 401, 577 Ground cover 339, 519 beneﬁcial effects 334 fertilization 341–342 organic mulch 342 insect habitat 339–340 predacious mite, Neoseiulus fallacies 339 twospotted spider mite, Tetranychus urticae 339 irrigation 341 killed sod 333 small mammals 340 types 340–341 chewing fescue (Festuca rubra) 340 common bermudagrass (Cynodon dactylon) 333 fodder radish (Raphanus sativus v. olieferus) 344 hard fescue (Festuca longifolia) 340 Kentucky bluegrass (Poa pratensis) 340, 346 perennial ryegrass (Lolium perenne) 340 Phacelia (Phacelia tenacetifolia) 344 subterranean clover (Trifolium subterraneum) 340 tall fescue (Festuca arundinacea) 333 turnip (Brassica rapa v. rapa) 344 vetch (Vicia spp.) 340 white clover (Trifolium repens) 335, 342, 345 winter rye (Secale cereale) 344 Growth habit see Tree Gummosis see Fungal gummosis

Haploid 66, 68–69, 74, 93, 96 Hardiness see Cold hardiness Hardwood cuttings 203–204, 206–211, 213 see also Propagation, clonal Harvesting 576–594 Heat requirements 26 Helicobasidium mompa (violet root rot) 401–402 Hemicellulose 562 Hemiptera 480–484, 491–496 Herbicides 296, 335–337, 346 for organic production 337, 346 pre-emergent types 335–336 post-emergent types 335–336 residue carryover 337 resistance development 335 Heritability 3–4, 21, 27, 66, 68, 72, 122–123, 125, 132, 162, 179, 181, 187

Index

Heterorhabditis bacteriophora 521 Higher-density orchard 53 High-throughput genotyping 55 History, in China 38–40 Eastern and Western Han Dynasty ErYa 40 HanShu 40 from Wei–Jin Dynasty to Sui–Tang Dynasty and Five Dynasties period Eastern Jin period 40 GuangZhi 40 KuaiYuanTianBaoYiShi 41 Northern Wei period 40 QiMinYaoShu 40, 41 Tang Dynasty 41 TangShu 41 TaoFu 41 Wei–Jin to Sui–Tang 41 Pre-Qin Dynasty 38, 40 GuanZi 40 HanFeiZhi 40 LüShiChunQiu 39 ShiJing 38, 39 YeZhongJi 40 Hormones 252 HuangHe, Yellow River 40 Hydrolases β-galactosidase (β-GAL) 555 β-(1, 4)-glucanase (syn. cellulase) (EG) 555–556, 566 pectinmethylesterase (PME) 555–556, 565 polygalacturonase (PG) 555–556, 565 Hypoallergenic cultivars 564

Ilarviruses 443–447 In vitro culture 98–99 see also Propagation, clonal Inbreeding 16, 73, 110 Inking see Deterioration problems Insecticides, organophosphate 472–474, 476, 479, 490–491, 494 Insects 55 growth regulator (IGR) 468, 473, 477, 494 scale see Armoured scale see also named insect species and groups Integrated pest management (IPM) 472–473, 484, 496 see also Ground cover Intercropping systems 49 International Rosaceae Genome Consortium (IRGC) 93 Intraspeciﬁc cross 72, 86 Iron 316–317 chlorosis 204, 207, 212–213 deﬁciency symptoms and correction 316–317

605

Irrigation 318–321 Isozyme 86

Jacket rot (Botrytis cinerea, Sclerotinia sclerotiorum) 354, 360–362, 396 Japanese beetle (JB), Popillia japonica 479–480 Juice 44, 51, 175–176, 187–188, 557, 559, 565, 591–592

KAC-V see Training system; Y-shaped tree Kaempferol 562 Kaolin particle ﬁlms 479

LAI 268 Late season cultivars 46, 52 Layering 41, 206, 208, 210, 237 Leaf 6 age 245 area index 247 mass area 267 nitrogen content 267 speciﬁc weight 247 water potential 245 Leaf curl (Taphrina deformans (Berk) Tul.) 2, 9, 55, 70, 88–90, 161–162, 164, 166–167, 358, 368–370 resistance 161–162, 164, 166–167 Leaf:fruit ratio 254, 290–291 Leaf-footed bugs (Hemiptera: Coreidae) 481–483 Leaf moth (Thosea sinensis) 55 Leaf rust (Tranzchelia discolour) 127–128 Lepidoptera 468–477, 487–491 Leptoglosus phyllopus 481–483 Leucostoma (Cytospora or Valsa) canker (Leucostoma cincta) 205, 214, 354, 375–378 trunk painting 378 see also Peach tree short life Light distribution 268 interception 247, 269–270 penetration 268 Linkage 61, 67–68 Linkage groups 62–65, 86–87, 89–92 Linkage map 86 Lipid-transfer proteins (LTPs) 563–564 Low acid 21, 23 see also Fruit, ﬂesh; Organic acids Low-chill 48, 196 genetic resources 52 Low-chill cultivars 107, 108, 109, 110, 112, 113, 114–117, 118, 119, 120, 121, 122, 123, 124, 125, 127, 128, 130, 131, 133 deﬁnition 107, 121 Low-density orchards see Orchard

606

Index

Lygus spp., plant bugs 334 Lygus elisus 334, 481 Lygus hesperus 334, 481 Lygus lineolarius (tarnished plant bug) 341, 481–482, 484 Lygus rugulipennis 481

Magnesium 311 Manganese 229, 317–318 Marker-assisted selection 22, 55, 88, 162, 179, 212, 514 Mating distruption (pheromone) 129, 468–469, 472–473, 475, 488, 491 Maturity see Fruit ripening Meadow-orchard 278–279 density 279 spacing 278 see also Orchard Mealiness (chilling injury) see Deterioration problems; Internal breakdown (IB) Mechanical injury see Deterioration problems Mediterranean fruit ﬂy, Ceratitis capitata 486–487 sterile male release 486 Meloidogyne spp. 506–515 biological cycle 508–509 biology 508–509 control 510–515 dissemination 509 economic importance 510 environmental factors 510 host range 510 identiﬁcation 507 M. arenaria 506, 512–514 M. floridensis 196–197, 203–204, 207–210, 212–215, 507, 511–514 M. hapla 196–197, 203–204, 207–210, 212–215, 506 M. hispanica 506, 513 M. incognita 196–197, 203–204, 207–210, 212–215, 506, 512–514 M. javanica 196–197, 203–204, 207–210, 212–215, 506, 512–514 M. mayaguensis 513 polymorphism 507 survival 509 symptoms 507–508 see also Root-knot nematode Melting 18, 21, 22, 23, 24, 30, 42, 45, 51, 53 see also Fruit, ﬂesh Mendelian inheritance, traits 3–4, 7, 24, 29, 62, 71, 74, 80, 86, 93 Mesocriconema spp. 506, 521 biology 516 control 518–517 disease complexes 515, 517–518 dissemination 517

economic importance 517 host range 518 M. curvatum 515 M. rusticum 515, 521 M. xenoplax (ring nematode) 196–197, 207–208, 210–211, 341, 394, 512–513, 515–521, 523 survival 517 symptoms 515 see also Ring nematode Methyl bromide 222, 338, 392, 395, 510, 517, 519, 526 MIA see Y-shaped tree Microclimate see Greenhouse cultivation Micrografting 236, 446 see also Propagation, clonal Micropropagation see Propagation, clonal Mites European red mite (ERM), Panonychus ulmi 496–499 Paciﬁc spider mite, Tetranychus pacificus 497 Peach bud mite, Eriophyes insidiosus 456 Predacious mite, Neoseiulus fallacies 339 Silver mite 254, 498 Two-spotted spider mite (TSM), Tetranychus urticae 339, 496–499 Model 247, 250–251, 254, 256–257 Modiﬁed atmosphere packaging (MAP) 565, 579, 592 Molecular marker 61, 86, 93, 96, 179 Mollicutes 407 Monilinia spp. see Brown rot Monoploid see Haploid Mouse-ear 43 Mucor decay (Mucor piriformis) 356, 396, 398 Mutagenesis 72 Mycelium 353, 355, 361, 364, 367–368, 371, 387, 391, 393, 396, 398 Mycoplasma-like organisms 239, 407 characteristics 408–409, 410 classiﬁcation 409–410 detection 409 general introduction 407–410 geographical distribution 410 hosts 410 management 409 myricetin 562 phytoplasma environment 407 vectors 407, 410 dodder (Cuscuta spp.) 409, 427 leafhoppers 409 psyllids 409 periwinkle 409, 411, 427 Myrobalan plum (Prunus cerasifera) 194–198, 200, 202, 210, 212–213 resistance gene 513–515 resistance to Meloidogyne spp. 513–515

Index

NAA 296 Nematicide treatment threshold 518, 520, 523 Nematodes 196, 479, 488, 506–527 dagger 524–525 ectoparasitic 515, 524 endoparasitic 506, 521 entomopathogenic 521 identiﬁcation Meloidogyne 507 Xiphinema 526 peach root-knot 196–197, 203–204, 207–210, 212–215, 507, 511–514 plant parasitic 506–527 ring 196–197, 207–208, 210–211, 515–521, 523 root-knot 88, 196–197, 203–204, 207–210, 212–215, 506–515 root-lesion 521–523 resistance 201–202 see also Heterorhabditis; Steinernema Neochlorogenic acid 562 Nepoviruses 198, 448–451, 457, 524–526 Nimblewill 335, 340, 519 Nitrogen 267, 305–308, 540–541 deﬁciency 306, 308 excess 306 fertilization efﬁciency 307–308 foliar applications 306–307 Non-melting see Fruit, ﬂesh Nutrient sampling 304–305 deviation from optimum percentage (DOP) 305 diagnostic and recommendation integrated systems (DRIS) 305 ﬂowers 304 leaves 304 Nutritional value 562–563 allergenicity 563–564, 567 hypoallergenic cultivars 564 lipid-transfer proteins (LTPs) 563–564 peeling 564 antioxidant activity 562 carotenoids 562 β-carotene 562 β-cryptoxanthin 562 vitamin A 562 ﬁbre 562 phenolics 562 cyanidin, chlorogenic acid, neochlorogenic acid 562 quercetin, kaempferol, myricetin 562

Open centre see Training system; Vase Orchard design 265, 267, 270 ﬂoor management 196, 332–351, 484–485

607

ﬂoor vegetation cultural dwarﬁng 343 establishment 342–344 inﬂuences 346–347 soil temperature 346 management systems 342–346 permanent vegetation management by mowing 345 vegetation-free tree rows in summer with control of cover crops 344 vegetation-free tree rows with vegetated drive alleys 342 vegetation-free tree rows year-round 345 year-round vegetation-free 342 Organic acids 550, 557 citrate 557 high-acid fruit types 557, 559 low-acid fruit types (sub-acid) 21, 557, 559 malate 557 phosphoenolcarboxylase (PEPC) 557–558 Oriental fruit moth (Grapholita molesta) 468–472, 475 distinction from codling moth 470 Origin 1–2, 37–38, 576 Gansu 37, 38, 45, 48 Hemudu village 37 Neolithic 37 Taixi village of Gaochen city 37 Tibet 37, 38 Osmotic adjustment 248, 322–323

Packaging, modiﬁed atmosphere (MAP) 565, 579, 592 Palmette 272–274 density 273 hedgerow 273 photograph 274 pruning 273 training 273 yield 273 see also Training system Particle bombardment (biolistics) 99–100 Peach asteroid spot virus 456, 458 Peach bud mite (Eriophyes insidiosus) 456 Peach dapple (PD) 454–455 Hop stunt viroid (HSVd) 454–455 Peach latent mosaic disease (PLM) 451–454 Peach latent mosaic viroid (PLMVd) 451, 453–454 Peach leaf curl (Taphrina deformans) 2, 9, 55, 70, 88–90, 161–162, 164, 166–167, 354, 358, 368–370 resistance 161–162, 164, 166–167 Peach mosaic virus (PcMV) 455–456 Cherry mottle leaf virus (CMLV) 455

608

Index

Peach rosette (PR) 410, 427–428 group 16Sr III 428 management 428 peach yellows strain 428 X-disease group 428 Peach rosette mosaic virus (PRMV) 451, 524–526 Peach sooty ringspot virus 456–457 Peachtree borers (Synanthedon spp.) Lesser peachtree borer (LPTB), Synanthedon pictipes 487–491 Peachtree borer (PTB), Synanthedon exitiosa 487–491 Wasp mimic 488 Peach tree short life (PTSL) 197, 203–206, 210–211, 355, 393–395, 515, 517–520, 523 ‘Guardian’ rootstock 395 Pseudomonas syringae 394 ring nematode 394–395 Peach tree short life complex 411 bacterial ﬂuorescence 415 bacterial toxins 415 management 416 persicomycin 415 syringomycin 415 Pseudomonas syringae pv. persicae 409, 414 Pseudomonas syringae pv. syringae 204, 394, 409, 413–414, 515 Peach twig borer (Anarsia lineatella) 473–475 Peach X-disease 410, 424–426 group 16Sr III 426 leafhoppers 426 little peach 426 management 426 plant hosts 424 plant reservoirs 426 red suture 426 rosette 426 symptoms 424, 425 Peach yellow leaf roll (PYLR) 410, 428 apple proliferation (AP) group 428–429 group 16Sr X 428 pear decline (PD) 428, 429 psylla 429 Peach yellows 410, 426–427 group 16Sr III 427 little peach 426 management 427 plant hosts 426 plum leafhopper 427 red suture 426, 427 Pectin 21–22, 24, 186, 555, 562–563, 565 Pest management see Integrated pest management Phenolics 19, 21, 127, 186–187, 225, 233, 237, 545, 550, 561–562, 576–577 Phenology 29 phenological classiﬁcation 30 phenological phases 27

Pheromones 129, 468, 469, 472–473, 474, 475, 488, 491 monitoring 473, 475, 478–480, 494 see also Mating disruption Phony (phoney) peach disease 408–409, 423 dwarﬁng symptoms 423 hosts, reservoir and secondary spread 424 vectors 424 Phosphoenolpyruvate carboxylase 247 Phosphorus 308 deﬁciency 308 excess 308 Photoperiod 233, 247–248 Photosynthesis 17, 244–248, 254–255, 267, 281, 290, 296–297, 316–318, 321 C3 267 CER 267 whole-canopy 281 Photosynthetic assimilate 290, 295–298 photosynthetically active radiation (PAR) 245 Phymatotrichum root rot (Phymatotrichopsis omnivora) 401–402 Physical map 91, 93–94, 97, 100 Phytophthora root and crown rots 198, 203, 205, 207–210, 212, 319, 353, 355, 383–387, 403 chlamydospores 353, 355–356, 383, 385, 387 oospores 353, 383, 385, 387 P. cactorum 355, 383 P. cambivora 355, 383 P. cinnamomi 355, 383 P. citricola 355, 383 P. citrophthora 355, 383 P. cryptogea 355, 383 P. drechsleri 355, 383 P. megasperma 355, 383 P. parasitica 356, 383 P. syringae 356, 383 zoospore 353, 355–356, 383, 385, 387 Phytoplasmas and phytoplasma diseases 80, 407, 424–429 Pip fruit 44 Pit see Endocarp Plant bugs (Hemiptera: Miridae) 480 tarnished plant bug (TPB), Lygus lineolarius 481–482, 483 other species, L. hesperus, L. elisus, L. rugulipennis 481 Plantation distance 78 see also Orchard Planting density and yield 281–282 see also Orchard Platforms 272–274, 284 Platynota idaeusalis (Tufted apple bud moth) 475–477 Plum, rootstock 512–514 see also Rootstocks

Index

Plum curculio (PC) (Conotrachelus nenuphar) 477–479 Plum pox virus (PPV/Sharka) 2, 80, 88, 96, 162, 437–443, 447, 487, 494–495 Potyvirus 440, 442 PPV-D 441 PPV-M 441 PPV-EA 441 PPV-C 441 PPV-W 441 PPV-Rec 441 Plum rust (Tranzschelia pruni-spinosae) 209 see also Rust Podosphaera spp., powdery mildew P. clandestina 354, 369 P. leucotricha 354, 369 P. pannosa 209, 254, 354, 368–369, 371–374 Pollen and pollination 13–14, 44, 64, 66, 68, 74, 77, 122, 129, 131, 141, 310, 314, 409, 436, 447, 454, 458 Polymerase chain reaction (PCR) 24, 100, 389, 409, 419, 424, 428, 441, 447, 449–450, 453, 507, 526, 554, 556, 560 cooperational-PCR (Co-PCR) 441 heminested-PCR 441 nested-PCR 441 PCR-ELISA 447 real-time-PCR (RT-PCR) 441, 447, 455, 554, 556, 560 reverse transcription and PCR 453 squash capture-PCR 441 Polyphenolics 21, 550 Polyploidization 72, 507 Pomology 68–69, 163, 165 Postharvest handling 49–52, 98, 181–182, 398–401, 540, 551, 576–594 Potassium 229, 308–310, 542 deﬁciency 309, 310 Powdery mildew 209, 254, 354, 368–369, 371–374 resistance 161–162, 164, 166–167 see also Podosphaera spp. PPV see Plum pox virus (PPV/Sharka) Pratylenchus spp. (root-lesion nematodes) 196–197, 202–205, 207–208, 212–214, 506, 512 biology 521–522 control 523 disease complexes 523 dissemination 522 economic importance 522 host range 523 P. brachyurus 521 P. convallariae 521 P. neglectus 521 P. penetrans 513, 521–523, 525 P. pratensis 521 P. sefaensis 521

609

P. vulnus 513, 521–523 P. zeae 521 survival 522 symptoms 521 see also Nematodes PRMV see Peach rosette mosaic virus Processing peach 117, 119, 175–192, 200, 205, 223, 255–256, 469 blanching 186–187 breeding 178, 180, 185 canning 184–185, 187 endopolygalacturonase 186 ﬂavour 176 ﬂesh texture 177 freezing 187 fruit quality 182 colour 182–183 ﬁrmness 183, 185–186 ﬂesh browning 187 pit quality 184 soluble solids 187 germplasm 178–179, 189 grading 182 harvest 176–177 marker-assisted selection 179 marketing 188 maturity index 184 nectarine 188 orchard life 178 pasteurization 188 peeling 186 phytonutrients 183, 188, 189 postharvest 182 processed products beer 51 drinks 51 fruit jelly 51 peach candies 51 uniform ripening 178 varieties 178–179 ripening times 179 yield 178 case yield 188 heritability 179 Production in China 46–47 systems 53 see also Orchard top ﬁve producing countries 46 Progeny 3–5, 17, 66, 72–73, 80, 86, 91, 97, 122, 145, 162, 166, 180–182, 185, 189, 212, 508 Prokaryotes 407–434 see also Bacteria; Phytoplasmas Propagation, clonal apical meristem culture 447 budding 237, 239 chip budding 238, 239, 449

610

Index

Propagation, clonal continued hardwood cutting 203–204, 206–211, 213, 224 auxin treatment 225 bottom heat 226 collecting time 225 collapse 226 deﬁnition 224 indole-3-butyric acid 225 mother plants 224 rootstocks 226 transplanting 226 washing 226 graft take 238 herbaceous grafting 240 in vitro propagation (micropropagation) 55, 98–99, 206, 208–210, 215, 230–236, 458 application of mycorrhizal fungi 236 explants sterilization 231 material preparation 230 plantlets acclimatization 233 problems during in vitro culture 235 problems during plantlet acclimatization 235–236 shoot proliferation 232 shoot proliferation, culture medium 232, 234 shoot proliferation, cytokinins 232 shoot rooting 233 shoot rooting, auxins 233 June budding 239 micrografting 239, 446 see also Micrografting semi-hardwood cutting 227 acclimatization 229 auxin leaf spraying 228 auxin treatment 228 basal cutting 229 grafting techniques 43 mist propagation 227 perlite 228 soluble auxins treatment 228 time for budding 229 softwood cuttings 195, 208 vegetative bud 239 Propagation, seed nursery site 221 peach seedling propagation 223 Prunus sylvestris 223 seed dormancy 223 seed supply 223 soil type 221 Protected cultivation 48, 52, 58, 59, 279–280 see also Greenhouse cultivation Pruning 41, 55, 70, 151, 177, 199, 251–253, 265–269, 271–274, 276, 278–283, 285, 293–294, 296–297, 306, 321–322, 343, 346, 354–355,

365, 374–375, 378–379, 382, 395, 400, 416, 424, 454–455, 458, 474, 544 heading cuts 273 roots 48 summer 48, 49, 55, 266, 272–274, 279–280, 283, 424, 544 thinning cuts 273 ‘tutta cima’ 265 Pruning systems 55 see also Training system Prunus spp. 2, 194, 442, 456, 459 P. americana 195–196 P. amygdalus 100 P. angustifolia (Chickasaw plum) 195, 428, 478 P. armeniaca 86, 442 P. avium 100, 442 P. belsiana 512 P. besseyi 195, 208, 442 P. cerasifera (Myrobalan plum) 86, 194–198, 200, 202, 210, 212–213, 430, 442, 512–514 P. cerasus 86, 442 P. cistena 442 P. davidiana 2, 40, 85, 87, 143, 162, 194–195, 200, 202, 204, 207, 209–210, 212–213, 443, 511 P. domestica 86, 194–196, 200, 202, 206, 210–211, 430, 442, 513 P. dulcis 2, 85, 185, 194–195, 200, 202, 442, 512 P. emarginata 426 P. ferganensis 3, 85, 87, 89, 161, 194 P. fremonti 523 P. hortulana 195, 428 P. humilis Bunge 53 Chinese dwarf cherry 54 P. incana 196, 202 P. insititia 194–195, 200, 202, 206, 211, 213, 442, 513 P. japonica 195, 199, 215 P. kansuensis 3, 38, 45, 85, 194 ‘GansuTao-1’ 45 P. mariana 442 P. mira 3, 38, 85, 194 P. munsoniana 428, 513 P. persica 1, 40, 97, 193–198, 200, 202, 204, 207–210, 212–213, 215, 256, 442, 451, 506, 512, 514, 576 P. polytricha Koehne 53 dense-pubescent cherry 53 P. pseudocerasus 100 P. pumila 195, 199, 202, 207 P. salicina 86, 194–195, 197, 200, 202, 208, 210–211, 410, 416, 442–443, 513 P. serrulata 410, 443 P. spinosa 194–195, 200, 206, 210–211, 430, 442, 513 P. subcordata 195

Index

P. subhirtella autumno rosa 100 P. sylvestris 223 P. tomentosa 195–196, 199, 202, 215, 256, 442, 523 P. triloba 442 P. virginiana 410, 424, 426 P. vulgaris 200 Pseudomonas syringae pv. syringae 515–516 see also Bacterial canker; Peach tree short life Pseudosclerotia 353, 396 PTSL see Peach tree short life Pure line 73–74 Pyralid moth (Dichocrocis punctiferalis) 55 Pyrethroid insecticides 472, 476, 477, 479, 496

QTL see Quantitative trait locus Quantitative character 66 Quantitative trait locus (QTL) 86, 88–90, 92–93 Quarantine 198, 230, 403, 408–409, 431, 442–443, 449, 451, 456, 458, 527, 567 Quarantine pests 472, 480, 486–487 Quercetin 233, 562

Rafﬁnose 250 Raised bed 333–334, 338, 355, 385, 392 Randomly ampliﬁed polymorphic DNA (RAPD) 86 RAPD see Randomly ampliﬁed polymorphic DNA Reﬂective ﬁlms 48, 341, 545 Regeneration 98–100, 278, 333, 443 Replant 518, 522–523 see also Orchard Resistance to nematodes Meloidogyne spp. 63, 511–515 Mesocriconema spp. 519 Pratylenchus spp. 523 Xiphinema spp. 526 Resistance gene 96, 162, 212, 460, 508, 513–515 gene analogue (RGA) 96 management 472–473, 477, 496–497 Respiration, climacteric 550–554, 557–558, 560, 567 Restriction fragment length polymorphism (RFLP) 86, 88, 91–94, 524 RFLP see Restriction fragment length polymorphism Rhizopus rot (Rhizopus stolonifer) 396, 398–399, 401 Ribulose bisphosphate carboxylase (RUBISCO) 245 Ring nematode 196–197, 202, 204–205, 207–208, 210–211, 341, 378, 394–395, 512–513, 515–521, 523 see also Mesocriconema spp. RNAse protection assay (RPA) 556 Root pruning 48 Root rots see Phytophthora root and crown rots

611

Root-knot nematodes (Meloidogyne spp.) 55, 63, 88, 196–197, 202–205, 207–210, 212–215, 334, 506–512, 514–515, 517–519, 521 resistance 45, 88–89 see also Meloidogyne spp. Root-lesion nematodes (Pratylenchus vulnus, Pratylenchus penetrans) 196–197, 202–205, 207–208, 212–214, 512, 521, 523 see also Nematode Rootstock 2–3, 10–11, 48, 53–55, 88, 93, 99, 117, 120, 128–131, 140, 145, 150, 158, 163, 166–167, 193–215, 222–226, 229–230, 232–235, 237–240, 246, 254, 256, 265, 267, 270, 272–273, 278, 283–284, 317, 355–356, 385, 392–397, 412, 416, 423–424, 430, 442, 444, 495, 506–507, 509–512, 514–515, 518–520, 522–524, 526–527, 536, 539, 564 ‘Adafuel’ 195, 201, 209, 226, 512 ‘Adarcias’ 195, 199, 201, 209 ‘Adesoto’ 101 195–197, 199, 202, 206, 226 ‘Alcaniz’ 512 ‘B-S6’ 512 ‘Bailey’ 89, 99, 143, 197, 199–201, 203, 205, 214, 223, 523, 552 ‘Barrier 1’ 195–197, 199, 202, 210 ‘Bergasa’ 512 ‘Bokhara’ 512 ‘Brompton’ 225, 513 ‘Cachirulo’ 512 ‘Cadaman’ 195, 202, 209–210, 512, 522–523 ‘Castore’ 201, 208–209 ‘Citation’ 214, 226, 512 ‘Controller 5’ 199, 202, 208 ‘Damas’ 63, 194, 206, 210, 237, 513 dwarﬁng 48, 194–195, 199–200, 208–209, 211–212, 214–215, 256, 267 see also Dwarﬁsm ‘Elberta’ 200, 512 ‘Felinem’ 195, 197, 201, 214, 512 ‘Fermoselle’ 512 ‘Flordaguard’ 10, 99, 116, 128, 196–197, 214, 511–513, 523 ‘Garnem’ 195, 197, 201, 214, 512, 522 ‘GF 31’ 513 ‘GF 43’ 206–207, 225, 234, 513 ‘GF 305’ 197–198, 201, 203, 210, 438, 442, 448–450, 452–453, 512 ‘GF 557’ 208, 512, 514 ‘GF 655/2’ 206, 211, 225, 237 ‘GF 677’ 195, 198, 201–204, 207–210, 214, 225–226, 233–234, 267, 278, 317, 430, 512 ‘GF 1869’ 194, 206, 210, 225, 513 ‘GF 8-1’ 513 ‘Guardian’ 197–198, 200–201, 203, 205, 214, 223, 395, 509, 511–512, 518–523 ‘Halford’ 178–179, 200–201, 203, 205, 223

612

Index

Rootstock continued ‘Hansen 2168’ 201, 209, 214, 226, 232, 511–512 ‘Hansen 536’ 201, 209, 214, 226, 232, 511–512 ‘Harrow Blood’ 196, 214, 223, 512 ‘Ishtara’ 197–199, 202, 210–211 ‘Julior’ 195–196, 199, 202, 211 ‘Krymsk 1’ 196–199, 202, 214 ‘Krymsk 2’ 196–197, 199, 202, 214 ‘Krymsk 86’ 196–197, 201, 214 ‘Lovell’ 87, 93, 96, 142, 146, 197–198, 200–203, 205, 207, 223, 510, 512, 518–520, 522–523 ‘Marianna 2624’ 194, 513 ‘Missour’ 200, 512 ‘Montclar’ 198, 201, 203–204, 223, 430, 512, 523 ‘Montizo’ 195–196, 202, 513 ‘Mr.S. 2/5’ 195–196, 198–199, 201, 210, 233–234, 239 ‘Mr.S. 2/8’ 195, 198, 210 ‘Myrabi’ 512 ‘Myran’ 197–199, 202, 210, 226 ‘Myrobalan P-2175’ 512 ‘Myrobalan P-2980’ 513 ‘Myrobalan 29C’ 513 ‘Myrobalan 605’ 513 ‘Myrobalan B’ 513 ‘Myrobalan franc’ 513 ‘Nemaguard’ 99, 145, 150, 197, 200–205, 207, 210–211, 214, 223, 234, 254, 507, 511–512, 514–515, 519–520, 522–523 ‘Nemared’ 87–94, 96–97, 99, 150, 197, 200, 203, 205, 214, 223, 509, 511–512, 514, 522 ‘Nickels’ 201, 214 ‘Okinawa’ 110, 122–123, 128, 131, 196–197, 214, 228–229, 507, 509, 511–512 ‘P-2032’ 514 ‘P-2175’ 512–514 ‘P-2980’ 513–514 ‘P.S.B2’ 197, 199, 201, 203–204, 223, 225–226, 232 ‘PSM 101’ 513 ‘Penta’ 196–197, 201, 207, 226 plum 512–514 ‘Polluce’ 201, 208–209 ‘Pumiselect’ 195, 199, 202, 207 ‘Rancho Resistant’ 512 ‘Redglow’ 513, 523 resistance to nematodes see Resistance ‘Rubira’ 11, 162, 197, 199, 201, 203–204, 223, 430, 512, 514 ‘Rutgers Red Leaf’ 430, 512, 523 ‘Saint Julien 655-2’ 206, 513 ‘S-37’ 214, 510–512 ‘Shalil’ 197, 214, 512, 514

‘Siberian C’ 166, 196, 200–201, 205, 214, 223, 512 ‘Sirio’ 195, 199, 201, 208 ‘Tetra’ 196–197, 199, 201, 207, 226 ‘Torinel’ 513 ‘Titan’ 512 ‘Viking’ 202, 208, 214 ‘Yunnan’ 197, 210, 214, 512 Rose chafers, Mycrodactylus subspinosus 479 Rosellinia root rot (Rosellinia necatrix) 401–402 Rust (Tranzschelia discolor, Tranzschelia prunispinosae) 209, 354, 365–368

Sanitary state 80, 221, 240, 431, 451, 591 Sanitation 129, 354–357, 365, 368, 374, 379, 382, 400, 402, 409, 443, 452, 506, 577 Scab (Fusicladosporium carpophilum) 354, 363–365, 383, 416 confusion of symptoms with bacterial leaf spot (Xanthomonas arboricola) 364–365 Scarab beetles (Coleoptera: Scarabaeidae) 479–481, 498 green June beetle (GJB), Cotinis nitida 480–481 Japanese beetle (JB), Popillia japonica 479–480 rose chafers, Mycrodactylus subspinosus 479 Sclerotium stem rot (S. rolfsii) 401–402 Seed 2, 3, 15, 16, 25, 41, 66, 68–69, 75, 78, 94, 97, 99–100, 108, 122, 129–131, 133, 140–142, 144, 146, 150, 155, 163, 167, 195, 200, 204–205, 212, 222–224, 236, 254, 333, 335–338, 342, 344, 409, 423, 447, 450, 454, 561 Selection 14, 19, 22, 27, 40–41, 44–45, 54–55, 57, 66, 72, 74, 78, 80, 88, 92, 99, 113, 119–123, 126, 129, 131–134, 145, 141, 153, 162–164, 167, 175–176, 178–179, 181–182, 184, 194–195, 199, 205–207, 212–214, 254 Selection index 80 Self-compatible 86 Self-pollination 4–5, 16, 21, 25, 68, 72–75, 78, 163, 165, 182 Semi-ground greenhouses 49 Sequence tagged site (STS) 97 Sharka see Plum pox virus Shot hole Corineum beijerinckii 209–210 Wilsonomyces carpophilus 354, 361–364, 403 Silver leaf disease (Chondrostereum purpureum) 206, 354, 373–376 Silver mite 254, 498 Simple sequence repeat marker (SSR) 86, 88, 91 Single trait 61 Mendelian trait 62–65 see also Qualitative character Sink demand 246

Index

Sink strength 246 Site selection 355–356, 395, 408–409, 506 Slender spindle see Central leader; Training system Softwood cuttings 195, 208–209 see also Propagation, clonal Soil solarization 222, 333, 393, 521, 527 Soluble solids concentration (SSC) 19–21, 198–199, 209–210, 249, 538–545, 551, 559–560, 564, 566, 576, 581–582 Somatic embryogenesis 98, 240 Sorbitol 20, 187, 247–251, 255–256, 314–315, 322, 559–560 Sour pit (Candida inconspicua/Torulopsis inconsipicua) 401–402 Sour rot (Geotrichum candidum) 356, 398, 400–401 Sphaerotheca pannosa see Podosphera pannosa Stachyose 250 Starch 15, 237, 247–251, 290–291, 555, 576 Steinernema glaseri 521 Steinernema riobrave 521 Sterile male 486–487 see also Mediterranean fruit ﬂy Stink bugs (Hemiptera: Pentatomidae) 334–335, 339, 341, 469, 480–484 brown, Euschistus servus 481–482 Euschistus tristigmus 481 green, Acrosternum hilare 481 southern green, Nezara viridula 481 Stomatal conductance 245–246, 321–322 Stone see Endocarp Stony-hard 18, 22, 23, 24, 30, 31, 32, 65, 127, 140, 146, 151, 165, 185, 552, 554 see also Fruit, ﬂesh Stoolbed and layering 208, 237 see also Propagation, clonal Stooling 207–208 see also Propagation, clonal Strawberry latent ringspot virus (SLRV) 449–451, 524–526 Suckering 202, 204–207, 210–211, 213, 394, 412, 414, 444, 516 Sucrose 20, 90, 187, 234–237, 247–251, 255–256, 322, 416, 559–561, 576 SUGAR model 250, 559–560 Sulfur 311–312, 561 Summer pruning 48–49, 55, 266, 272–274, 279, 280, 283, 424, 544, 582 Summer tipping 49 Surfactant 294 Sweet kernels 52, 65, 67, 88, 90 Sweetness (sugars) 88, 187, 255, 537, 559–560 Synteny 88, 92, 96

Taraxicum officinale see Dandelion Target leaf spot (Phyllosticta persicae) 401–402

613

Tarnished plant bug (TPB), Lygus lineolarius 339, 341, 481–482, 483 Taphrina deformans see Leaf curl Temperature, affecting fruit 245, 252, 255, 357, 361, 363–364, 368, 371, 374, 381, 392, 396, 398, 400, 564–565 chilling injury see Deterioration problems; Internal breakdown (IB) ideal storage conditions 582, 584 low temperature storage 564–565 new temperature management approach 584–585 fresh-cut 592 forced-air cooling 582–583 hydro-cooling 400, 582–583 preconditioning 579, 584–585, 594 ready to buy 584, 585, 592, 594 ready to eat 585, 592–594 water loss control 576, 579, 581, 584, 590 fruit waxes or coatings 584, 587–588, 590 Thermotherapy 447, 452, 454 Thinning 15, 25, 123, 142, 177, 179, 182, 199, 252–253, 255, 273, 282, 285, 289–299, 357, 368, 544 by hand 289, 293–296 Thosea sinensis (Leaf moth) 55 Thrips (Thysanoptera) 17, 341, 447, 468, 484–485 other species, T. meridionalis, T. major 484 Western ﬂower thrips, Frankliniella occidentalis 484–486 Tobacco ringspot virus (TRSV) 524–525 Tomato ringspot virus (ToRSV) 198, 334, 447–449, 524–526 Prunus stem pitting disease 198, 448–449, 525 ToRSV see Tomato ringspot virus Torulopsis inconspicua (sour pit) 401–402 Training system 264–284 ‘axis central’ see Central leader central leader 55, 274–276 delayed vase 203, 269, 271, 273 free shape 273 ‘forma libera’ 272 Fs-Tatura 278 ‘fusetto’ see Central leader hedgerow see Palmette KAC-V see Y-shaped tree meadow-orchard 278–279 MIA see Y-shaped tree open centre see Vase palmette 269, 272–274 PCR pruning 49 slender spindle see Central leader V-form 271, 468, 474 vase 55, 271–272, 468, 474 ‘vaso californiano’ 271 ‘vaso de plataformas’ 271

614

Index

Training system continued ‘vaso italiano’ 271 Y-shaped tree 55, 269, 276–278, 474 Y-trellis see Y-shaped tree Transformation 55, 97–101, 240, 443, 459 transgenic 99 Tranzchelia discolor (leaf rust) 127–128 Tranzschelia pruni-spinosae (plum rust) 209, 354, 365–368 Tree wall systems, pillar 70 Triploid 68 TRSV see Tobacco ringspot virus Trunk borer (Aromia bungii) 55 Tufted apple bud moth (TABM/Platynota idaeusalis) 475–477 Two-spotted spider mite see Mites

herbicides 335–337, 346 mechanical cultivation 334, 337 johnsongrass, Sorghum halepense 333 mulching 337–339 Nicotiana spp. 451 pest habitat 334 poison ivy, Toxicodenron radicans 333 preplant control 333 sheep sorrel, Rumex acetosella 449 Virginia creeper, Parthenocissus quinquefolia 333 yellow nutsedge, Cyperus esculentus 333 Winter chilling see Chilling requirement Wilthin 294 Woolliness (chilling injury) see Deterioration problems; Internal breakdown (IB)

Unique expressed gene (unigene) 94, 96, 567

Xiphinema spp. 196–198, 506, 524–527 biology 525 control 526 diagnosis 526 economic importance 525–526 geographical distribution 524–525 host range 525 identiﬁcation 526 species 524–525 survival 525 X. americanum group 196–198, 449, 524–526 sensu lato 524–525 sensu stricto 524–525 X. brevicolle 524 X. bricolensis 524–525 X. californicum 449, 524–525 X. coxi 450 X. diversicaudatum 450, 524–526 X. pachtaicum 524 X. pacificum 524 X. rivesi 449, 524–525 X. vuittenezi 524, 526 see also Nematodes

Vase see Training system Verticillium wilt (Verticillium dahliae) 203–204, 208–209, 356, 392–394, 403 microsclerotia 356, 392 Violet root rot (Helicobasidium mompa) 401–402 Viruses 80 indexing 200, 436, 442, 449–451, 455–456, 459 see also Nepoviruses Vole, montane (Microtus montanus) 340

Water stress 228, 236, 245, 253, 297–298, 319, 321–323, 542–543 beneﬁcial effects 321–322 managing 322–323 negative effects 321 regulated deﬁcit irrigation (RDI) 322–323 see also Drought Waterlogging 43, 194–196, 202–212, 319, 333, 513–514 Weeds alternate host for virus 334 Chenopodium spp. 449, 451 chickweed, Stellaria spp. 334 host for stink bugs, plant bugs, catfacing injury to fruit 334, 339, 341 dandelion, Taraxicum officinale 334, 341, 451 alternate host for Tomato ringspot virus 334 alternate host for ring nematode 341 economic thresholds 335 ﬂame weeding 337

Yield 3, 25, 43, 46–47, 51, 53, 55, 74, 80, 118, 128, 164, 176–179, 181–182, 188–189, 193, 196, 198–200, 203–204, 208–211, 214, 254–256, 269–274, 276, 278–285, 291–292, 295–297, 304–306, 308, 311, 313, 317, 321–322, 333–335, 339, 341, 343–344, 346–347, 379, 384, 424, 444, 468–469, 494, 496, 506, 508, 510, 517, 522, 537, 540, 542–544, 550–551, 567, 590 average peach and nectarine 47 planting density 281–282 training systems 280–283

Index

Y-shaped tree 276–278 density 277, 278 light interception 277 photograph 277 protected cultivation 278 spacings 278 see also Training system

Y-trellis see Training system

Zinc 312–314

615