Biocontrol Of Plant Diseases

K. G. Mukerji, K.L. Garg

• Publisher: CRC Press
• Year: 2020
• eBook ISBN: 9781000697728
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

First Published in 1988, this set offers a comprehensive insight into controlling diseases in plants. Carefully compiled and filled with a vast repertoire of notes, diagrams, and references this book serves as a useful reference for biologists, horticulturalists, other practitioners in their respective fields.

Chapter 1

BIOCONTROL OF RUST AND LEAF SPOT DISEASES*

J. K. Sharma and K. V. Sankaran

TABLE OF CONTENTS

I.	Introduction
II.	Biological Control in Nature A. Hyperparasitism 1. Rust 2. Leaf Spots B. Antagonism 1. Naturally Occurring Antagonists 2. Foreign Antagonists C. Immunization D. Hypovirulence
III.	Future Prospects

Acknowledgment

References

I. INTRODUCTION

Among the greatest hazards in crop production, unfavorable weather conditions, insect pests, and diseases are the main factors. Any one of them can upset the crop yields with catastrophic suddenness. Of all the plant diseases, foliar diseases, especially rusts and leaf spots, are the important group of diseases causing large-scale destruction of agricultural and horticultural crops. There are about 4000 species of rust fungi belonging to 100 genera, many of which are capable of causing widespread epidemics. A few notable examples are those of cereal rusts (Puccinia graminis f. sp. tritici, P. graminis f. sp. secalis), cedar rust of apple (Gymnosporangium juniperi-virginianae), and white pine blister rust (Cronartium ribicola), which are well known for causing economic losses. Cereal rusts are known to have changed the cropping pattern of different regions and food habits of the population. Wheat leaf rust created an economic disaster in 1916 in the U.S. and Canada. An even worse disaster struck in 1935 when about 100 million bushels of wheat were lost. In India, according to an estimate during 1971 to 1972, a brown rust (Puccinia recondita) epidemic in northwestern India resulted in a loss of 1.5 million tonnes of wheat.⁷⁹ Epidemics of the coffee rust compelled Sri Lanka to bring more land into tea plantations and to abandon coffee cultivation for years. This way coffee rust changed the entire economy of Sri Lanka in 1875 due to the widespread rust epidemic. Leaf spot diseases are equally significant in causing economic disasters. To name a few, late blight of potato (Phytophthora infestans), blast of rice (Pyricularia oryzae), Helminthosporium leaf spot of maize (H. turcicum, H. maydis, H. carbonum), and bean anthracnose (Colletotrichum lindemuthianum) are known to have affected crop yields drastically. The potato famine of Ireland in 1845, due to late blight, which gradually spread to the whole of the European continent, is the most cited example to indicate destruction and aftereffects of diseases on a large population. Rice blast disease, reported from 70 countries has affected up to 90% of the yield depending upon the part of the plant infected. In the 1950s in Florida, losses of winter-grown sweet corn due to leaf spot caused by H. turcicum amounted to 20 to 90%/field. These examples provide documented proof of the extent of damage caused by rusts and leaf spots. For combating these diseases successful measures of chemical control have been developed over the years. Though chemicals have played a significant role in maximizing the crop productivity, extensive, often excessive use of broad spectrum compounds, some of which are nondegradable, has resulted in a variety of harmful and undesirable effects not only on man and wildlife, but on the ecosystem as a whole. This way, relative short-term effective control of a disease makes this method less attractive. Control of plant diseases through genetic resistance of the host is often successful. But pathogens can and do mutate and, therefore, many of the promising resistant varieties succumb to disease in the field sooner or later. Besides, in tree diseases, both of these methods of disease control may not find a direct or immediate application due to the long period of the host’s life. In this situation, with the increasing awareness of the problems and expense of conventional methods of disease control, including fungicides and costly and time-consuming breeding programs, biological control of plant pathogens has many attractions.

In many plant diseases the interaction of host, pathogen, and physical environment is readily apparent. The recognition of a fourth component, namely other organism(s) which affect the course of disease either by their direct influence on the pathogen or indirectly through their effect on the host or environment, provides the basis for our concept of biological control. The term “biological control” was first used by Smith¹⁴⁴ to signify the use of natural enemies to control insect pests. Stanford and Broadfoot¹⁵² were the first to use the term “biological control” in plant pathology while working on the control of wheat take-all fungus. The scope and relevance of biological control has expanded over the decades. Debach⁴² discussed the semantics of the term “biological control” and concluded that it is a natural phenomenon relating to those biotic agents that prevent the normal tendency of populations of organisms to grow in an exponential fashion and to the mechanisms by which such growth is prevented or regulated. Later definitions provided by Garrett⁶² and Baker¹² agreed with Debach, but excluded man as a biotic agent. Snyder¹⁴⁶ takes a much broader view in his definition that “biological control relies largely upon an interruption of host-parasitic relationships through biological means … and may be accomplished by imparting resistance to the host … or by modifying the cultural practices of the crop so as to reduce the infection.” Swell,¹⁵⁶ Baker and Cook,^11,37 and Cook³⁶ subscribe to this broader definition. Whatever the scope of definition one accepts, the original concept intended that in biological control the fourth component, namely “other living organisms,” is brought in to play an important role regardless of its initiation. It is in this context that biological control is used here. Biological control by conventional methods such as cultural practices,^76,113 selection, and breeding for resistance⁹⁷ has been excluded and emphasis has been placed on microbiological biocontrol of plant pathogens.

Certain microorganisms have long been known to be associated with other pathogenic microorganisms in a variety of ways. The surface of aerial plant parts provides a habitat for epiphytic microorganisms.^23,46,140 They are also found in soil, on the roots of plants, and even within the plant tissues. To what extent the microorganisms are capable of direct or indirect biological control of rust and leaf spot diseases and how this capability can be exploited is the purpose of this review. An attempt has been made to bring together the scattered information on these two groups of diseases. The examples cited here may have some applications in the biocontrol, if not in practice then in principle, of rust and leaf spot diseases.

II. BIOLOGICAL CONTROL IN NATURE

In nature, microbial pathogens frequently cause epiphytotics, which help to maintain the balance of fungal populations.⁷² Baker and Cook¹¹ point out that antagonists are likely to be acting continuously against potential pathogens, thus contributing to the absence of disease in a majority of the situations; biological control is thus already working in the field. How can the effectiveness of natural mechanisms of biological control be maximized with reference to the foliar environment? Two means of achieving this are apparent: (1) to allow natural control mechanisms to proceed as far as possible unhindered, or (2) to manipulate the system so as to give increased control. The former means could be aided by avoiding, as far as possible, the indiscriminate use of fungicides which destroy the epiphytic flora.^45,71 The latter approach ...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• Editor
• Contributors
• Table of Contents
• Chapter 1 Biocontrol of Rust and Leaf Spot Diseases
• Chapter 2 Biological Control, Genetic Engineering, and Crop Disease Management
• Chapter 3 Plant Breeding Strategies for Biological Control of Plant Diseases
• Chapter 4 Application of Biological Control Agents
• Chapter 5 Potential for Biological Control of Aspergillus flavus and Aflatoxin Contamination
• Chapter 6 Control of Toxigenic Molds in Cereal Seeds
• Chapter 7 Aflatoxin Contamination in Maize and its Biocontrol
• Chapter 8 Dutch Elm Disease, A Model Tree Disease for Biological Control
• Chapter 9 Hypovirulence: A Natural Control of Chestnut Blight
• Chapter 10 Biological Control of Agrobacterium Species
• Chapter 11 Biological Control of Diseases of Fruits
• Chapter 12 Antagonism and Biological Control
• Chapter 13 Biocontrol of Storage Mold Diseases of Seed
• Index