Table Of ContentPrinciples
of
Seed Pathology
Volume II
Authors
Vijendra K. Agarwal, Ph.D.
Associate Professor
Department of Plant Pathology
G. B. Pant University of Agriculture and Technology
Pantnagar (Nainital), India
James B. Sinclair, Ph.D.
Professor
Department of Plant Pathology
College of Agriculture
University of Illinois at Urbana-Champaign
Urbana, Illinois
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PREFACE
The science of seed pathology is relatively young, having its beginnings in seed health
testing and control of seedborne pathogens. Since the late 1970s there has been a world
wide increase in research, outreach, and training activities relating to seed pathology.
Seedborne pathogens have had special consideration in seed production areas and in
plant quarantine activities. Recognition of the increased interest and importance of
this branch of plant pathology was given by the creation of the Danish Government
Institute of Seed Pathology for Developing Countries, Copenhagen, in 1967, the Seed
Pathology Committee by the American Phytopathological Society in 1976, and the
International Society of Plant Pathology in 1977.
This book was written to serve those interested in seed pathology. It is designed to
serve as a textbook as well as a reference book for students, teachers, and researchers,
and for seed health testing, seed production, and plant quarantine personnel. It is to
be used as a guide to the literature. Much of the illustrative material has come from
the authors’ files used for teaching or from their own research. Teachers will want to
supplement this book with examples from their own experience and research or with
information and data from other seed pathology programs.
The authors hope that this book, in addition to being of value to seed and plant
pathologists, will be useful to agriculturalists interested in crop production. It was
written in part to stimulate research in seed pathology and its importance to the role
of seedborne inoculum in the epidemiology and control of plant diseases.
The authors wish to thank G. B. Pant University of Agriculture and Technology
(GBPUAT) and the University of Illinois at Urbana-Champaign (UIUC) for the use of
library facilities in preparation of the manuscript. Thanks are given to M. L. Verma
(GBPUAT) and Janice A. Draper (UIUC) for typing the initial and subsequent drafts,
respectively, of the manuscript. The authors are indebted to Aliza Halfon-Meiri, De
partment of Seed Research, The Volcani Center, Bet-Dagan, Israel; and Indra K. Kun-
war, Visiting Research Associate (UIUC), for helpful suggestions, advice, and proof
reading of the manuscript. Drawings are by Lenore Gray.
V. K. Agarwal wishes to thank GBPUAT for permission to take up the task of
preparing the material for this book and is especially grateful to Y. L. Nene, formerly
from GBPUAT and now at the International Crops Research Institute for the Semi-
Arid Tropics, Andhra Pradesh, India, for his guidance, inspiration, and encourage
ment throughout the author’s career. He owes special regard and gratitude to his
grandfather, Babu Ram Prasad (deceased) and to his parents for their guidance and
inspiration, and to his wife, Kiran, and his daughters, Priyanka and Sheelu, for their
patience and cooperation during the preparation of the manuscript.
THE AUTHORS
Vijendra K. Agarwal, Ph.D., is Associate Professor of Plant Pathology in the De
partment of Plant Pathology, College of Agriculture, Govind Ballabh Pant University
of Agriculture and Technology (GBPUAT), Pantnagar, U.P., India.
Dr. Agarwal obtained his B.Sc.(Honours) Agriculture and Animal Husbandry in
1965, the M.Sc.(Agriculture) in Plant Pathology in 1967, and his Ph.D. in Plant Pa
thology in 1975 under the guidance of Dr. Y. L. Nene from GBPUAT. He joined the
Department of Plant Pathology in July 1967 and served as Senior Research Assistant,
Assistant Professor, and Associate Professor. He worked as Research Scholar at the
Danish Government Institute of Seed Pathology for developing countries, Copen
hagen, from January 1969 to February 1970.
Dr. Agarwal has taught basic courses in plant pathology and seed pathology at the
graduate and postgraduate levels. He has developed research and teaching programs in
seed pathology at GBPUAT. His research has concentrated on standardization of tech
niques for the detection, seed transmission, seed certification, and control of seedborne
pathogens. He has published over 55 research papers, 2 books, and 60 other research
abstracts and technical articles all in the area of seed pathology. Dr. Agarwal has
attended and presented invitational lectures at several national and international con
ferences, seminars, workshops, and the like.
James B. Sinclair, Ph.D., is Professor of Plant Pathology in the Department of
Plant Pathology, College of Agriculture, University of Illinois at Urbana-Champaign,
Urbana (UIUC). Professor Sinclair received his B.Sc. degree from Lawrence Univer
sity, Appleton, Wisconsin in 1951 and his Ph.D. in plant pathology from the Univer
sity of Wisconsin, Madison in 1955 under J. C. Walker with whom he continued to
work with a postdoctoral appointment until 1956, when he accepted a position in the
Department of Plant Pathology, Louisiana State University, Baton Rouge (LSU). At
LSU he served as an Assistant Professor, Associate Professor, and then Professor until
1968. Also, he was an Administrative Assistant to the Chancellor from 1966 to 1968.
He joined the Department of Plant Pathology, UIUC in 1968 as a professor of inter
national plant pathology. He was campus, then all-university coordinator for the Illi-
nois-Tehran Research Unit, 1974—1978.
Professor Sinclair has taught five graduate courses in plant pathology; has planned,
participated in and given invitational lectures at numerous national and international
conferences and workshops; has worked in over 40 countries professionally; and has
directed the research of 56 graduate students, of whom 15 have completed a portion
of their thesis research at an overseas institution. He is a member of many national
and international professional organizations. Professor Sinclair formed and was chair
man of the Inter-American Seed Pathology Group and initiated the formation of seed
pathology committees in the American Phytopathological Society and International
Society of Plant Pathology. He served from 1979 to 1983 as the Chairman, Seed Pa
thology Committee, International Society of Plant Pathology.
Professor Sinclair’s research has been primarily on seed- and soilborne pathogens of
soybeans and other crops and their control, and on the uptake and translocation of
systemic fungicides in various crop plants. He has done pioneer research in the pathol
ogy of soybean seeds.
He has published over 188 refereed research papers; 196 research abstracts; and
authored, edited or co-edited 17 books and 198 other articles. The most recent recog
nition for his accomplishments was the presentation of the ICI/American Soybean
Association Research Recognition Award in 1983 and the Paul A. Funk Award in
1984.
TABLE OF CONTENTS
Volume I
Chapter 1
Introduction......................................................................................................................1
I. Terminology.......................................................................................................1
II. Historical Development.......................................................................................2
III. Development of Seed Health Testing..................................................................3
IV. Significance..........................................................................................................4
A. Reduction in Crop Yields.........................................................................4
B. Loss in Germination.................................................................................9
C. Development of Plant Diseases................................................................9
D. Discoloration and Shrivelling.................................................................11
E. Biochemical Changes in Seed.................................................................11
F. Toxin Production....................................................................................11
References.......................................................................................................................12
Chapter 2
Seedborne Pathogens.....................................................................................................17
I. Fungi....................................................................................................................17
II. Bacteria...............................................................................................................18
III. Mycoplasmalike Organisms.................................................................................18
IV. Ricketsialike Organisms.....................................................................................39
V. Spiroplasmas.......................................................................................................39
VI. Viruses.................................................................................................................39
VII. Viroids.................................................................................................................40
VIII. Nematodes...........................................................................................................40
References.......................................................................................................................57
Chapter 3
Seed Structure and Development in Relation to Infection..........................................77
I. Reproductive Processes in Higher Plants.........................................................77
II. Pollination and Fertilization in Higher Plants..................................................79
III. Development of Fruits and Seeds in Higher Plants............................................81
References.......................................................................................................................83
Chapter 4
Location of Seedborne Inoculum..................................................................................85
I. Seed Infection.....................................................................................................85
A. Embryo.....................................................................................................85
B. Endosperm and Perisperm......................................................................87
C. Seed Coat and Pericarp..........................................................................89
D. Glume Infection......................................................................................92
II. Seed Infestation or Contamination...................................................................93
References.......................................................................................................................95
Chapter 5
Mechanism of Seed Infection........................................................................................99
I. Seed Infection......................................................................................................99
A. Systemic Infection through Flower, Fruit, or Seed Stalk.......................99
B. Penetration through the Stigma............................................................100
C. Penetration through the Ovary Wall and Seed Coat.........................101
D. Penetration through the Natural Openings and Injuries......................104
II. Seed Infestation or Contamination.................................................................105
A. Pathogens Adhering to the Seed Surface..............................................105
B. Seed Concomitant Contamination........................................................106
1. Pathogenic Structures.................................................................106
2. Mixed Infected Plant Parts........................................................106
3. Soil..............................................................................................107
References.....................................................................................................................107
Chapter 6
Factors Affecting Seed Infection.................................................................................113
I. Host Genotype..................................................................................................113
II. Environment......................................................................................................114
A. Moisture.................................................................................................114
B. T emper ature...........................................................................................115
C. Wind Velocity........................................................................................115
D. Rainfall...................................................................................................115
E. Irrigation.................................................................................................115
III. Crop Management.............................................................................................115
A. Plant Population....................................................................................115
B. Fertilizers................................................................................................116
C. Weeds......................................................................................................116
D. Harvesting Time....................................................................................116
IV. Stages of Plant Infection...................................................................................116
V. Severity of Mother Plant Infection..................................................................118
VI. Insect Infestation..............................................................................................118
VII. Antagonism and Synergism..............................................................................118
References.....................................................................................................................120
Chapter 7
Longevity of Seedborne Pathogens..............................................................................125
I. Longevity...........................................................................................................125
II. Factors Influencing the Longevity...................................................................125
A. Host Genotype.......................................................................................125
B. Inoculum.................................................................................................130
C. Seed Storage Containers.......................................................................131
D. Storage Environment............................................................................131
E. Storage Period........................................................................................132
F. Presence of Antagonistic Microflora....................................................132
References.....................................................................................................................133
Chapter 8
Seed Transmission and Inoculation............................................................................139
I. Seed Transmission..............................................................................................139
A. Systemic Seed Transmission..................................................................139
1. Embryo Infection.......................................................................139
2. Nonembryonic Infection............................................................141
3. Seed Coat Contamination.........................................................142
B. Nonsystemic Seed Transmission............................................................145
1. Embryo Infection.......................................................................145
2. Seed Coat Infection....................................................................145
3. Seed Coat Contamination.........................................................146
4. Concomitant Contamination.....................................................146
II. Seed Inoculation.................................................................................................148
References.....................................................................................................................152
Index..............................................................................................................................157
Volume II
Chapter 9
Factors Affecting Seed Transmission..............................................................................1
I. Crop Species..........................................................................................................1
II. Environment...........................................................................................................2
A. Moisture....................................................................................................2
B. Temperature..............................................................................................3
C. Wind-Blown Rain......................................................................................4
D. Light...........................................................................................................4
III. Inoculum................................................................................................................4
A. Minimum Effective Level of Inoculum for Seed Transmission
and Establishment in Seedlings or Plants..................................................5
B. Inoculum Location....................................................................................5
C. Type of Inoculum......................................................................................5
IV. Survival of Inoculum...........................................................................................7
V. Cultural Practices...................................................................................................7
A. Soil Type....................................................................................................7
B. Soil Reaction..............................................................................................7
C. Seeding Rate..............................................................................................7
D. Depth of Sowing........................................................................................7
E. Sowing Time..............................................................................................8
F. Fertilizers...................................................................................................8
VI. Seed Abnormalities...............................................................................................8
VII. Seed Germination..................................................................................................9
A. Epigeal (or Epigeous)................................................................................9
B. Hypogeal (or Hypogeous).......................................................................10
VIII. Seed Leachates....................................................................................................11
IX. Presence of Other Microflora.............................................................................11
References.......................................................................................................................12
Chapter 10
Epiphytology of Seedborne Diseases.............................................................................17
I. Introduction.........................................................................................................17
II. Classification of Seedborne Diseases Based on Epiphytology...........................18
A. Monocyclic or Simple-Interest Diseases................................................18
B. Compound-Interest or Polycyclic Diseases............................................18
References.......................................................................................................................21
Chapter 11
Nonparasitic Seed Disorders..........................................................................................23
I. Genetic Effects......................................................................................................23
II. Mechanical Injuries............................................................................................23
III. Environmental Effects........................................................................................23
A. Temperature............................................................................................23
B. Humidity..................................................................................................24
IV. Mineral Deficiencies............................................................................................24
V. Insect Damage.....................................................................................................25
References......................................................................................................................27
Chapter 12
Detection of Seedborne Pathogens...............................................................................29
I. Major Objectives of Seed Health Testing..........................................................29
II. Choosing Seed Health Testing Methods............................................................30
III. Testing Methods for Seedborne Fungi...............................................................30
A. Examination of Dry Seeds......................................................................30
1. Seed Discoloration........................................................................30
2. Morphological Abnormalities......................................................33
3. Mixed Fungal Fruiting Structures...............................................33
4. Observations Using a Bright-FieldM icroscope...........................34
5. Observing Seeds under Near-Ultraviolet Light (NUV)................34
B. Examination After Softening or Soaking Seeds....................................34
C. Seed-Washing Test..................................................................................34
D. Incubation Methods..................................................................................35
1. Blotter Method..............................................................................35
2. Agar-Plate Method......................................................................37
a. Fusarium culmorum..........................................................37
b. F. moniliforme.................................................................37
c. Phoma betae.....................................................................39
d. A. triticina.........................................................................39
e. D. oryzae and Pyricularia oryzae....................................39
3. Blotter vs. Agar-Plate Method....................................................40
4. Factors Affecting Results of Various Incubation
Methods........................................................................................40
a. Sampling...........................................................................40
b. Physical Condition of the Seed........................................40
c. Storage of Seed.................................................................40
d. Incubation Containers......................................................41
e. Incubation Media.............................................................41
f. Light..................................................................................41
(1) Stimulated Sporulation.........................................41
(2) Inhibited Sporulation............................................43
(3) Insensitive Fungi...................................................43
g. Temperature.....................................................................43
h. Humidity...........................................................................43
i. Pretreatment.....................................................................43
j. Length of Incubation Period............................................44
k. Amount and Type of Inoculum......................................44
l. Interfungal and Fungal-Bacterial Interactions................44
E. Seedling-Symptom Test..........................................................................45
1. Rolled Paper Towel Test..............................................................45
2. Blotter Test...................................................................................45
3. Agar Test in Test Tubes...............................................................46
4. Soil Tests.......................................................................................47
F. Fluorescence Method..............................................................................47
G. Histopathological Tests..........................................................................48
H. Embryo-Count Method..........................................................................49
I. NaOH Seed-Soak Method......................................................................50
IV. Testing Methods for Seedborne Bacteria..........................................................50
A. Visual Observations of Dry Seeds...........................................................51
B. Isolation on Agar Media.........................................................................52
C. Seedling Symptomatology Test...............................................................53
D. Infectivity Test........................................................................................54
E. Serology....................................................................................................55
F. Phage-Plague Method.............................................................................55
V. Testing Methods for Seedborne Viruses............................................................56
A. Examination of Dry Seeds......................................................................56
1. Discoloration...............................................................................56
2. Reduced Seed Size........................................................................59
3. Shriveled and Wrinkled Seeds.....................................................59
B. Biological Tests........................................................................................60
1. Growing-On Test.........................................................................60
2. Infectivity or Indicator-Inoculation Test....................................61
C. Biochemical Tests.....................................................................................61
1. Serology........................................................................................61
a. Microprecipitin Test..........................................................62
b. Gel-Diffusion Test............................................................62
(1) Single or Radial Diffusion....................................62
(2) Double Diffusion..................................................62
c. Agglutination Tests...........................................................63
d. Labeled Antibodies............................................................64
e. Immunofluorescence Microscopy Test............................64
f. Radioisotope-Labeled Antibody......................................64
g. ELISA...............................................................................64
h. Serologically Specific Electron Microscopy
(SSEM)..............................................................................65
i. Solid-Phase Radioimmunoassay.....................................65
2. Staining Techniques.......................................................................65
D. Biophysical Tests......................................................................................66
E. Contact Radiography with X-Rays........................................................66
VI. Testing Methods for SeedborneN ematodes.......................................................66
A. Examination of Dry Seeds......................................................................66
B. Examination of Water on Soaking Seeds..............................................66
C. Fenwick’s Small Culture Cells................................................................67
D. Extraction of Nematodes from Plant Pieces and Soil Clods.................67
References......................................................................................................................67
Chapter 13
Deterioration of Grains by Storage Fungi..................................................................77
I. Field and Storage Fungi......................................................................................77
II. Invasion by Storage Fungi..................................................................................77
III. Losses...................................................................................................................78
A. Decrease in Germinability........................................................................79
