Breeding poplars , ' for 56 disease resistance . , ," . { " , .' ,./' -. .~. , FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Breeding poplars for disease resistance The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organilation of the United Nations concerning the legal status of any country. territory. city or area or of its authorities. or concerning the delimitation of its frontiers or boundaries. M-32 ISBN 92-5-102214-3 All rights reserved. No part of this publication may be reproduced. stored in a retrieval system. or transmitted in any form or by any means, electronic. mechanical, photocopying or otherwise, without the prior permission of the copyright ·owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy. - iii - FOREWORD Poplars are amongst the oldest contemporary angiosperm genera with over 125 species recorded as fossils and 30 to 40 species ~xisting today.They are dioecious and are more frequently propagated from cuttings than seed, Lending themseLves to the creation of cLones and the cuLtivation of recognizabLe and cLonally reproducible hybrids. They have Long been cuLtivated in Asia as welL as in Europe but their more recent deveLopment dates from the 18th century when North American poplars were imported to form hybrids with European species, a trend which is now extending to West and East Asia. Their utiLity lies in ~he frequently rapid growth potentiaL of species, their hybrids and certain clones as weLL as the wide use to which popLars can be put to provide industriaL wood, fodder for animaLs, sheLter, energy and timber for domestic and farm use. At the 17th Session of the FAO InternationaL PopLar Commission in October 1984, it was noted that whereas saLes of popLar wood were decLining indeveLoped countries, they were vigorously increasing in deveLoping countries under the stimuLus of LocaL demand. PopLars, generaLLy dependent on good soiLs and adequate soiL moisture for their best development, are frequentLy associated with agricuLturaL crops. The expansion of their range to Less favourabLe sites as welL as the increase in their resistance to disease and insect attack is a chaLLenge to popLar breeders working with basicaLly fast-growing and weLL-formed cuLtivars of the genus. Imparting wide adaptabiLity coupled with durable disease resistance is an extremeLy important aspect of this breeding programme. PrincipLes and strategies which can be applied are elements of the modern armoury of techoLogy which can be transferred to deveLoping countries to improve the culture of popLars, aLLeviate serious deficits in the suppLy of domestic wood, energy and fodder and pressure on degraded naturaL vegetation resources essentiaL for the protection of soiLs and environment. This paper, prepared under a contract with FAO by Professor B.A. ThieLges of the CoLLege of AgricuLture, University of Kentucky, USA, under the auspices of the FAO InternationaL PopLar Commission, was presented as a background paper to the session of the ad ho~ Committee on PopLar Breeding during the 17th Session of the IPC at Ottawa, Canada, in October, 1984. The work was partLy conducted in the CommonweaLth Forestry Institute (U.K.) and incLuded traveL in Europe. The heLp of aLL contributing nationaL institutions: INRA, Institut NationaL de Recherche Agronomique, OLivet (OrLeans), France; SAF, Istituto di Sperimentazione per La Pioppicoltura, CasaLe Monferrato, ItaLy; Station de PopuLiculture, Geraardbergen, BeLgium, is gratefulLy acknowLedged. Director Forest Resources Division Forestry Department - v - TABLE OF CONTENTS Page FOREWORD iii INTRODUCTION 1 Poplars as a World Resource 4 Major species of sections Aigeiros and Tacamahaca in Plantation Culture 5 Section Aigeiros 5 Section Tacamahaca 6 Some major Disease Problems of Populus 6 Melampsora Leaf Rusts (Melampsora spp.) 7 Marssonina Anthracnose or Leaf spot (Marssonina spp.) 8 Bacterial Canker (Xanthomonus populi Ride) 10 Dothiciza Canker (Dothiciza populea Sacco and Briard) 12 Septoria Leaf Spot and Canker (Septoria musiva Peck) 13 Other Potentially Dangerous Diseases 13 Disease Severity in Natural Stands and Plantations 14 Populus breeding programmes and Disease Resistance 17 Genetics, Epidemiology and Durable Disease Resistance in Wild Pathosystems 21 Wild Pathosystems, Agroecosystems and Populus Plantations 27 Breeding Strategies and Adaptability to Change 31 Opportunities, Constraints and Breeding Programme Objectives 35 Biological factors 35 Socio-economical Factors 37 Institutional Factors 37 Alternative Breeding Methods for Populus 38 Identifying, Exploiting and Maintaining Heterogeneity in the Source Population 38 Identifying and Exploiting Outstanding Parental Combinations 41 Flexible and Adaptive Breeding Strategies 44 A Breeding Strategy for Populus deltoides 47 Gains in Productivity from a Strategy Employing Population-based Resistance to Diseases - An Example of a CLonal Mixture 52 Summary and Conclusions 57 Literature Cited 59 FIGURES Figure 1 Hypothesized System for Host-Pathogen Co-Evolution (From Browning, 1979) 24 Figure 2 Schematic of Discontinuous Wild Pathosystem. 25 Figure 3 CLO and SYN as Complementa~y Breeding Methods in Perennial Outbreeders (From Simmonds, 1979) 46 - V1 - Figure 4 Flow Chart Outlining General Disease-Resistant Breeding Strategy Utilizing Sexual and Asexual Propogation in Breeding Phases. Production Populations are Multiclonal Lines (from Thielges and Land, 1976). 49 TABLES Table 1 Comparison of P. deLtoides Growth Data at Selection Age 2 and Age 10, expressed as XIS of Population, Family and Clone 54 Table 2 P. deltoides SeLection Differentials compared at Selection Age 2 and at Age 10 55 Table 3 Comparison of Age 10 P. deLtoides yields through altering Selection Index (at Age 2). 55 ILLUSTRATIONS: 1. Mixed PopLar hybrid plot, Geraardsbergen, BeLgium 2 2. Euramerican hybrid at Geraardsbergen 2 3. Bacterial canker on hybrid poplar near Nantes, France 9 4. High magnification photo of Marssonina Leaf spot 9 5. PopLar Leaves, one infected one not infected with Melampsora 11 6. Leaf sections infected with Melampsora in an in-vitro test. 11 7. Mixed stand of ~. deLtoides, ~. nigra and hybrids near OrLeans, France 22 8. CeLL culture of Prunus and ~opulus in the INRA Laboratory at Orleans, France 53 9. Mixed stand of poplar hybrids in BeLgium 53 - 1 - Introduction The genus Populus represents a significant component of the world's potential renewable resources for the 21st Century. Readily-propagated, fast-growing and amenable to pLantation culture, poplars have been planted for pulp and wood products in temperate and subtropical regions. They contribute significantly to some national and regional wood markets (Viart 1979a), and also serve as a substantial source of farm income in some countries (Prevosto 1979). It seems quite possible that popLar culture may offer some potentiaL to provide a significant amount of biomass for energy production, especially on a regional level in developing nations (Zsuffa and Morgan 1982). Moreover, there is an admirabLe record of major gains in productivity through genetic selection and breeding, and improvement in cultural techniques. ALL of these attributes serve to make popLar an attractive option for pLanting in both deveLoped and deveLoping nations. Because of the history, scaLe, and intensity of research and deveLopment programs in PopuLus there is a relatively large amount of information and experience available that may be applied to new programs in deveLoping nations. Almost six decades have passed since the sustained popLar breeding efforts of Stout, Schreiner and McKee (Stout, et !l. 1927) and, in the interim, the number of scientists engaged in poplar research and development has increased dramatically. For example, the most recent World Directory of Forest Geneticists and Tree Breeders (Nienstaedt 1978) lists almost 200 persons with some interest or involvement in the genetic improvement of Populus species. To assist in the direction and coordination of this work, the International Poplar Commission of the F.A.O., was established in 1947 and now includes 32 member nations. Three of these countries maintain special institutes devoted to popLar research and development programs for poplars and other "fast-growing species". The investment in research and deveLopment has been justified and major strides have been made to improve the productivity and utilization of poplars. There is a less psositive aspect of this 60-year record of accomplishment, however. Species of poplars are now commonLy planted outside of their natural ranges and frequentLy in stressfuL environments in terms of bioLogicaL agents as weLL as physicaL factors. The genetic base of selection and breeding programs in many countries remains essentialLy the same as it was at the inception of the program, and often is precariousLy narrow. At the same time, the genetic variability of populations of indigenous Populus species has been destroyed or significantly eroded, often as a direct consequence of major national genetic improvement programs and agricultural and reforestation practices utilizing introduced species and/or interspecific hybrids. In a criticaL review of the history and current status of genetic