Plant Breeding for Pest and Disease Resistance. Studies in the Agricultural and Food Sciences

473 Pages·1978·9.22 MB·English

by  G.E. Russell (Auth.)

STUDIES IN THE AGRICULTURAL
AND FOOD SCIENCES
Consultant Editors:
D J A Cole University of Nottingham
W Haresign University of Nottingham
J Ρ Hudson formerly Director, Long Ashton Research Station,
University of Bristol
G Ε Russell Professor of Agricultural Biology, University of
Newcastle-upon-Tyne
D Ε Tribe Professor of Animal Nutrition, University of Melbourne
STUDIES IN THE AGRICULTURAL
AND FOOD SCIENCES
Plant Breeding for Pest and
Disease Resistance
G.E. RUSSELL, MA, PhD, ScD, Dip Agric Sei, FIBiol
Department of Agricultural Biology,
University of Newcastle upon Tyne
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First published 1978
© Butterworth & Co (Publishers) Ltd 1978
ISBN 0 408 10613 1
British Library Cataloguing in Publication Data
Russell, G Ε
Plant breeding for pest and disease resistance.
1. Field crops - Disease and pest resistance
2. Plant-breeding
I. Title
631.53 SB750 78-40425
ISBN 0-408-10613-1
Typeset and produced by Scribe Design, Chatham, Kent
Printed in England by Billing & Sons Ltd, Guildford & London
PREFACE
It has been estimated that more than 50 per cent of the world's total crop
production is lost each year through the activities of pests and diseases of plants,
in spite of the many control measures that are employed. The importance of
reducing this loss, particularly in the developing countries, hardly needs empha-
sizing and additional control measures are urgently needed. The main purpose
of this book is to review the part played by resistant varieties in reducing damage
by pests and diseases in the past, and to assess the potential value of breeding for
resistance.
The book is arranged in six sections, each ofwhichcanbe read independently;
this arrangement has, inevitably, led to some duplication between sections but
repetition has been kept to a minimum. The first section is concerned with
general principles of pest and disease control by resistant varieties. The following
four sections deal with fungal diseases, diseases caused by viruses, bacteria and
other micro-organisms, animal pests and parastitic weeds, respectively. Within
each section there are chapters relating to the special features which affect
breeding for resistance to the different kinds of parasites. These features are
illustrated by reference to specific examples from some of the world's most
important agricultural and horticultural crop plants. The examples have been
chosen to demonstrate successes and failures in breeding for resistance, with
suggested explanations for the varying degrees of success that have been
achieved. An attempt has been made to pinpoint areas where our knowledge is
inadequate, and where a greater effort and more research facilities seem to be
justified.
The final section comprises some general conclusions and summarizes the
author's view on the future prospects of breeding for resistance.
Each of the main sections contains several hundred references to the original
work that is mentioned in the text and the book should, therefore, be an impor-
tant source of references for many years to come.
It is hoped that the book will be useful both to the plant breeder and to
agricultural specialists in many other disciplines, who may not always appreciate
the full potential of breeding for resistance. In addition, it should be a useful
reference book for postgraduate and undergraduate students working in many
areas of applied biological science.
GORDON E. RUSSELL
ACKNOWLEDGEMENTS
I would first like to express my thanks to Professor Ralph Riley, FRS, Director
of the Plant Breeding Institute, Cambridge, who first suggested several years
ago that I should write a book on this subject. I have been aided so much over
the years by helpful and stimulating discussions with colleagues, former
colleagues and other friends that it seems invidious to single out individuals by
name. However, I would particularly like to mention the help of Dr Martin
Wolfe, Dr Roy Johnson, Dr Peter Scott and Dr Henry Lowe of the Plant
Breeding Institute, Cambridge, Dr Frank Alston and Dr Elizabeth Keep of East
Mailing Research Station, Dr Arnold Dunn and Dr Lindsey Innes of the National
Vegetable Research Station and Mr Chris Parker of the Weed Research Organisa-
tion, Oxford.
I would also like to thank the research workers who, with the approval of
their respective institutions, have given me permission to publish photographs
illustrating their work. The source of each photograph is indicated in the legend
to the figure concerned.
I wish also to record my deep appreciation to Dr Harold Howard, OBE, who
examined the manuscript so scrupulously and made many very helpful comments
and suggestions.
Finally, I would like to thank my wife, Heather, who is a scientific writer and
editor, for all the technical advice and constructive criticism which I received
during the preparation of this book. Without her help and encouragement I
doubt whether the book would ever have been completed.
GORDON E. RUSSELL
I
THE CONTROL OF PESTS AND DISEASES
Economic Importance of Pests and Diseases
Pests and diseases of agricultural crops are as old as agriculture itself. The effects
of mildew diseases and of insect pests, including locusts, are recorded in the Old
Testament. Cereal rusts are known to have been important during the Roman
period and exhaustion of the soil at this time was probably caused by parasitic
nematode pests. The Romans invoked the aid of gods to keep their crops free
from disease and epidemics were attributed to the wrath of the gods. It was not
until many centuries later, after the general acceptance of Pasteur's germ theory,
that diseases of crop plants were recognized as being caused by parasitic
organisms. The specific causal agents of diseases such as potato blight or cereal
rusts were identified as fungal pathogens only in the latter half of the nineteenth
century. Such discoveries helped to end the fatalistic attitude towards the
ravages of pests and diseases and stimulated attempts to discover methods of
controlling them.
One of the best-known examples of a catastrophic epidemic of a plant disease
is the outbreak of potato blight (late blight) which occurred in 1845 and 1846
in western Europe. This disease, caused by a fungus (Phytophthora infestans)
which has airborne spores, was probably introduced into Europe from Mexico
in the early 1840s. Small outbreaks of blight occurred in parts of France,
Belgium and England in 1844, but the dry summer of that year did not favour
the spread of infection. In July 1845, however, the disease became widespread
in northern Europe where it caused severe damage to the potato crop, particularly
in Belgium and Ireland where at least 40 per cent of tubers rotted as a result of
infection. In 1846 the disease attacked the potato crop in Ireland at an earlier
stage of growth, and spread so rapidly that all plants in many crops had been
killed by the beginning of August. The potato was the staple food of the mainly
peasant population of Ireland and widespread famine followed the blight epi-
demics; as a direct result the population of Ireland declined from 8.2 million
in 1841 to 6.2 million in 1851, either from death resulting from starvation or
from emigration to Britain or North America. The impact of potato blight in
other parts of northern Europe was also considerable, although generally less
severe than in Ireland.
Although it is unusual for a single disease to affect the course of history in
this catastrophic manner, many diseases other than potato blight have had
3
4 The control of pests and diseases
serious economic consequences (Klinkowski, 1970). Some such disease epi-
demics have been caused by fungi, including blue mould of tobacco (Peronospora
tabacina) in Europe in 1960, downy mildew ofhops (Pseudoperonosporahumuli)
in Central Europe in the 1920s, Dutch elm disease (Ceratocystis ulmi) in Europe
and North America in recent years, rusts of cereal crops (Puccinia spp.) in many
parts of the world, coffee rust (Hemileia vastatrix) in Sri Lanka (Ceylon) and
brown spot of rice (Helminthosporium oryzae) in Bengal. Other disease epi-
demics have been caused by viruses including swollen shoot disease of cocoa,
sugar cane mosaic and curly top of sugar beet, or by bacteria such as the
bacterial blights of cotton and rice. The resultant losses in economic terms are
impossible to estimate accurately because the severity of a disease varies greatly
from place to place and from year to year. However, it has been shown
experimentally that these losses can be very considerable. For example, virus
yellows can reduce the yield of sugar beet by more than 3 per cent for every
week that a plant shows symptoms (Hull, 1961) and losses of more than 25 per
cent attributable to virus yellows have often been recorded in farm crops. In the
USA in 1935, the loss of yield in wheat due to the stem rust fungus in three
States alone was estimated to be between three and four million tons of grain.
Later outbreaks of this disease in 1954 and 1957 caused estimated losses of 45
million bushels and 150 million bushels of grain respectively in western Canada.
Wheat, barley, maize, potatoes and tomatoes were calculated to have lost,
respectively 6.3, 5.5, 8.6, 18.2, and 12.6 per cent of their potential yields in
the USA from diseases in 1939 (Ordish, 1952). In 1937, insect pests in the USA
were estimated to have caused losses running into millions of dollars in many
crops, particularly cotton (boll weevil and earworm), maize (earworm), wheat
(chinch bug and Hessian fly), potatoes (Colorado beetle and leaf hoppers) and
tobacco (budworm and hornworm). More recent estimates suggest that losses
from pests and diseases are even greater than were suggested by Ordish. Cramer
(1967), for example, calculated that world-wide losses from diseases and insect
pests in wheat were 9.1 and 5.0 per cent of the potential yield respectively.
Corresponding figures for diseases and pests were 7.8 and 3.8 per cent for
barley, 9.4 and 12.4 per cent for maize, 21.8 and 6.5 per cent for potatoes,
and 8.9 and 26.7 per cent for rice. Cramer estimated that average world-wide
losses for the main agricultural crops were 11.8 per cent for diseases and 12.2
per cent for insect pests. The average combined losses caused by diseases, pests
and weeds were put at 33.7 per cent. This figure is considerably less than recent
estimates that more than half of the world's potential crop production is lost
by the action of diseases and weed and insect pests.
Although it is impossible to quantify these losses accurately, the above
estimates emphasize the enormous damage that is caused by pests and diseases.
The development of more effective methods of controlling pests and diseases in
the major crop species is probably the most urgent and daunting task facing
the agricultural scientist today.
Methods of Controlling Pests and Diseases
It is convenient to group control methods into three main categories :
(1) avoidance of pests and diseases, (2) direct control measures, and (3)
biological control.
The control of pests and diseases 5
AVOIDANCE OF PESTS AND DISEASES
Measures to avoid pests and diseases can be considered briefly under the
following nine headings.
Quarantine
Legislation can prevent the introduction of infected plant material, including
seeds and other material for propagation, into areas where a pest or disease is
absent. Most countries have laws controlling the importation of plant material
or its movement from one part of the country to another. These regulations,
which have been discussed by Wheeler (1969), have been successful in preven-
ting or delaying the spread of many important pathogens and pests. For example,
the Colorado beetle (Leptinotarsa decemlineata), which is an important pest
of potatoes in many countries, has so far been denied a foothold in the UK,
mainly because of stringent quarantine and legislative measures. Such quarantine
measures are likely to become less effective in the future, however, because
fresh plant material, either for food or for experimental purposes, can now be
transported much more rapidly and in better condition than in the past. In
addition, plant breeders seeking to exploit germplasm from exotic species in
their breeding programmes, have sometimes unwittingly introduced exotic
pests and diseases with experimental plant material. Quarantine must therefore
be generally considered as a first line of defence which will almost certainly
be breached sooner or later.
Legislation has been used successfully to control the spread of certain pests
and diseases within a particular country or region. For example in England
a *Wart Disease Order', which prohibited the planting of potato varieties that
were very susceptible to the causal fungus Synchytrium endobioticum, was
introduced in 1923. The Order, which was amended in 1941 and 1973, also
controls the movement of potato tubers from infected areas and requires the
destruction of infected tubers. These measures have been strictly enforced and
the disease has become less widespread and damaging as a result.
Apple and pear trees can be attacked by fireblight, a disease caused by a
bacterium, Erwinia amylovora. A 'Fireblight Disease Order', first introduced in
England in 1958 and amended in 1960 and 1966, requires that any known or
suspected cases of fireblight must be reported to the authorities. The Order,
which also prohibits the propagation of very susceptible varieties, has undoubtedly
helped to control the spread of fireblight disease in the UK.
Cropping on land which is known to be heavily infested with the beet cyst
nematode Heterodera schachtii is controlled in England by the terms of the
'Beet Eelworm Order'. This nematode pest can attack other species of crop
plants besides beet, and the Order prohibits the growing of any susceptible
crop until the pest population has been shown by soil sampling to have declined
to a very low level. This Order has helped to confine the pest to certain areas
and has greatly reduced the economic importance of the beet cyst nematode in
England.
These examples and many others which could be cited from numerous
regions show that carefully conceived and strictly enforced legislation can play
a significant part in the control of plant pests and diseases.
6 The control of pests and diseases
Good husbandry
Appropriate cultural practices can often help to avoid or reduce damage from
some pests and diseases. For example, sugar beet crops that are gappy are more
prone to attack by aphids and virus yellows than are those with optimum
populations. Choice of the most suitable time for sowing a crop can also influence
the subsequent development of disease. In the UK early sown crops of sugar
beet have been shown to be less susceptible to virus yellows than crops sown
later. Conversely, early sown crops of winter wheat are often more susceptible
to eyespot, a soil-borne disease caused by Cercosporella herpotrichoides, than
those which are sown later.
Crop rotation
Although this may be considered as an essential part of good husbandry, it is
sufficiently important to be treated separately. Many pests and diseases,
particularly those which are soil-borne, can be adequately controlled by a
suitable rotation of immune and susceptible crops; indeed, in many cases this
is the only practicable and economically feasible control method. Crop rotation
has played an important part in the control of many soil-borne bacterial and
fungus diseases, including brown leaf spot of rice (Helminthosporium oryzae),
club root of crucifers (Plasmodiophora brassicae), take-all of cereals (Gaeu-
mannomyces (Ophiobolus) graminis) and bacterial wilt of many crops
(Pseudomonas solanacearum). In addition, crop rotation can give a good control
of many soil-borne pests, particularly nematodes, including the cyst nematodes
of sugar beet (Heterodera schachtii) and potato (Globodera rostochiensis),
and species of Meloidogyne, some of which have a very wide host range. A
rotation consisting of one susceptible crop followed by two or three resistant
crops is often sufficient to prevent serious damage from these diseases. Other
diseases, however, can be controlled only by unrealistically long crop rotations;
the resting sporangia of the potato wart disease fungus Synchytrium endobioticum
can remain viable for at least 10—12 years in the soil. In addition, crop rotation
cannot control diseases that are spread by air-borne spores or vectors.
Qean seed or propagating material
Seeds, fruits, tubers, bulbs, corms and cuttings, if derived from infected plants,
can harbour certain diseases. As far as possible, therefore, propagating material
of all kinds should be taken only from disease-free plants. Where this is not
possible, control measures, including the application of chemicals or heat to
propagating material, can sometimes be taken to reduce the likelihood of trans-
mission of disease. Certain seed-borne fungal diseases, e.g. bunt of wheat and
covered smut of barley, in which the pathogens are carried on the seed, can be
easily and inexpensively controlled by dressing the seed with an appropriate
fungicide. In others, e.g. loose smut of barley, in which the pathogen is present
as mycelium inside the embryo, most seed dressings are ineffective. In such
diseases, heat treatment of the seed can give a good control and certain systemic
fungicides have also been effective.
The control of pests and diseases 1
All organs of systemically virus-diseased plants are usually infected and, if
used for vegetative propagation, will invariably give rise to diseased progeny.
Although such material can often be freed from viruses by culture of meris-
tematic tissue, sometimes in conjunction with heat treatment, such processes
are laborious and expensive; they are, therefore, usually reserved for material
of special value or importance from which further propagating material will be
produced. Kassanis (1957) obtained plants of the potato variety King Edward
freed from paracrinkle virus by meristem culture, and the new stocks derived
from these virus-free plants had a greater yield than the original virus-infected
stocks.
Tubers, bulbs and runners of plants can also carry fungal pathogens. For
example, potato tubers may be infected with several diseases including gangrene
(Phoma exigua var. foveata), dry rot {Fusarium caeruleum) and stem canker
(Corticum (Rhizoctonia) solani), and such tubers may produce infected plants.
Careful examination of tubers for disease symptoms and the planting of only
healthy tubers will help to control these diseases.
Hygiene or sanitation
The removal of as many potential sources of infection as possible can contribute
greatly to the control of plant diseases. The removal (roguing) of infected
plants within a crop or the excision of diseased parts of trees are examples of
good hygiene which may stop or delay the spread of infection to adjacent
healthy plants. Successful roguing depends largely on the ability of the operator
to recognize diseased plants, preferably at an early stage of infection. This
requires training and skill and is laborious and time-consuming. Roguing is there-
fore generally restricted to perennial crops of high value ; it is normally not
economic to rogue annual crops.
Roguing has made a worth-while contribution to the control of many diseases.
These include leaf roll and virus Y in potatoes in the UK, canker (caused by
Xanthomonas citri) in citrus in the USA, phony disease of peach in the USA
and banana mosaic in Honduras. These and other examples of successful disease
control by roguing have been discussed in greater detail by Wheeler (1969).
There are some diseases in which roguing has been a much less successful
control measure. A large-scale campaign in West Africa to cut down and burn
cocoa trees which showed symptoms of swollen shoot has given only a partial
control of the disease. Similarly, the spread of the Dutch elm disease has been
controlled only to a small extent by destroying diseased trees, and many large-
scale eradication programmes both in the USA and western Europe have been
abandoned because they were ineffective. If a disease spreads rapidly, parti-
cularly if the main source of infection is outside the crop, roguing is unlikely
to be worth-while.
Good hygiene also involves the control of volunteer (self-sown) crop plants,
weed hosts and other potential sources of infection from the vicinity of sus-
ceptible crops. Sugar beet plants remaining in the ground after harvest can be
important sources of virus yellows and downy mildew infections for nearby
crops in the following year. Many common weeds, including shepherd's purse
(Capsella bursa-pastoris), chickweed (Stellaria media) and groundsel (Senecio
vulgaris), are hosts of sugar beet viruses, and infected plants can overwinter in