Fundamentals of

PlantPathology

N.G. Ravichandra

Fundamentals of Plant Pathology

Fundamentals ofPlant Pathology

N.G. RavichaNdRaAssociate ProfessorAICRP (Nematodes)

Department of Plant PathologyUniversity of Agricultural Sciences

GKVK, Bangalore

Delhi-1100922013

Fundamentals oF plant pathologyN.G. Ravichandra

© 2013 by PHI Learning Private Limited, Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher.

IsBn-978-81-203-4703-8

The export rights of this book are vested solely with the publisher.

Published by Asoke K. Ghosh, PHI Learning Private Limited, Rimjhim House, 111, Patparganj Industrial Estate, Delhi-110092 and Printed by Mohan Makhijani at Rekha Printers Private Limited, New Delhi-110020.

To

the fond memories of my beloved fatherShri N. Gurushankaraiah

vii

Foreword xixPreface xxiAcknowledgements xxiii

1. Introduction 1–32. Scope and Objectives of Plant Pathology 4–12

2.1 Introduction 42.2 Definition of Plant Pathology 52.3 Molecular Plant Pathology 52.4 Role of a Plant Pathologist 62.5 Relationship of Plant Pathology with Other Sciences 72.6 Objectives of Plant Pathology 72.7 Definitions of Important Terms Used in Plant Pathology 8Questions 12

3. Importance of Plant Diseases 13–243.1 Introduction 133.2 Significance of Major Plant Diseases 15

3.2.1 Potato Late Blight 153.2.2 Black Rust of Wheat 163.2.3 Leaf Spot of Rice 163.2.4 Bacterial Blight of Rice 163.2.5 Coffee Leaf Rust 173.2.6 Sigatoka Disease of Banana 173.2.7 Downy Mildew 173.2.8 Corn Leaf Blight 183.2.9 Chestnut Blight 19

Contents

viii Contents

3.2.10 Red Rot of Sugarcane 193.2.11 Storage Molds 193.2.12 Diseases on Forest Trees 203.2.13 Lethal Yellowing of Coconut 203.2.14 Bunchy Top of Banana 21

3.3 Diseases Affect Human Beings, Animals and Industries 213.3.1 Ergot of Cereals 223.3.2 Intoxicating Bread 223.3.3 Scabby Grain 22

3.4 Major Worldwide Plant Diseases 23Questions 23

4. History and Development of Plant Pathology 25–384.1 Introduction 254.2 Diseases in Ancient Literature 254.3 Important Milestones 26Questions 38

5. Definition and Concept of Plant Diseases 39–555.1 Introduction 39

5.1.1 Other Important Definitions 395.2 Evolution of Diseases 41

5.2.1 Phases of a Disease Caused by Mould 415.2.2 Phases of Disease Caused by Other Agents 415.2.3 Vectors of Phytopathogenic Agents 41

5.3 Factors Involved in Phytopathology—Relationship 435.3.1 The Disease Triangle 435.3.2 The Disease Pyramid (Tetrahedron) 445.3.3 The Disease Cone 445.3.4 The Disease Prism 45

5.4 Koch’s Postulates 465.4.1 The Pathogenicity Test 465.4.2 Molecular Koch’s Postulates 465.4.3 Koch’s Postulates in 21st Century 475.4.4 Limitations/Exceptions to Koch’s Postulates 48

5.5 Classification of Plant Diseases 485.5.1 Based on the Type of Pathogen Causing the Disease 485.5.2 Based on the Mode of Spread, Severity of Infection and

Geographic Distribution of the Disease 495.5.3 Based on the Extent to Which Diseases are Associated with Host Plants 505.5.4 Based on the Mode of Primary Infection and Kind of Perpetuation 505.5.5 Based on the Host Plant Part Affected 515.5.6 Based on the Symptoms Expressed 515.5.7 Based on the Host Plants Affected 515.5.8 Based on the Number of Generation of Infection 51

Contents ix

5.6 Difference between Disease Cycle and Life Cycle 525.6.1 Disease Cycle 525.6.2 Life Cycle 53

5.7 Logical Approach to Study Individual Plant Disease 53Questions 54

6. Causes of Plant Disease 56–846.1 Introduction 566.2 Abiotic Causes 57

6.2.1 Soil Factors 576.2.2 Meteorological Factors 676.2.3 Cultivation/Agricultural Practices 716.2.4 Chemicals 716.2.5 Industrial By-products/Contaminants (Air and Water Pollution) 736.2.6 Physiological Disorders 776.2.7 Mechanical Injury 78

6.3 Mesobiotic 786.3.1 Viruses 786.3.2 Viroids 796.3.3 Virusoids 79

6.4 Biotic Causes 796.4.1 Eukaryotes 806.4.2 Prokaryotes 82

Questions 83

7. Symptoms of Plant Diseases 85–1437.1 Introduction 85

7.1.1 Definition of Symptoms 857.1.2 Symptom and Sign 857.1.3 Types of Symptoms 86

7.2 General Outline of Symptoms Caused by Plant Pathogens 877.2.1 Discolouration or Change of Colour from Normal 877.2.2 Coloured Spots/Areas/Zones 887.2.3 Shot Hole/Foliage Perforations 887.2.4 Wilting 887.2.5 Necrosis 897.2.6 Stunting/Dwarfing/Atrophy 897.2.7 Hypertrophy and Hyperplasia 897.2.8 Transformation/Replacement of Plant Organs by New Structures 907.2.9 Mummification 917.2.10 Alteration in the Habit and Symmetry 917.2.11 Destruction of Plant Part/Organ 917.2.12 Defoliation, Dropping of Blossoms/Fruits/Twigs 917.2.13 Production of Excrescences and Malformations 927.2.14 Exudations: Guttation and Bleeding Contrasted with Formation

of Exudates 937.2.15 Rotting 93

Fundamentals Of Plant Pathology

Publisher : PHI Learning ISBN : 9788120347038 Author : N G Ravichandra

Type the URL : http://www.kopykitab.com/product/6195

Get this eBook