Preface Food, clothing and shelter are the basic needs for the survival and existence of all humans, and plants are the chief source for providing all these things. Not only man, all other living beings also require food for their survival, which is derived from plants. Crop husbandry deals with increasing the production of crop produce to meet these requirements. The world population is increasing at an alarming rate, especially in the developing and under-developed countries. Though there is slight reduction in the birth rate due to adoption of various family planning measures, the longevity of human life has gone up due to advancement in various fields of medical sciences, which has also contributed to the increase in population. The population in India as on 2008 has crossed 100 crores. This has resulted in increase in the demand for food and other commodities. Cultivable land is dwindling gradually. Vast areas of arable land, which were under cultivation, have been converted into housing plots and industrial establishments. Further, many sources of irrigation, such as tanks and lakes have been converted into bus stands and play grounds. Even forest areas have been encroached to a considerable extent for purposes other than agriculture. With limitations in the availability of more land for crop husbandry, several methods, such as introduction of high yielding, high fertilizer responsive varieties, use of better and quality seeds, soil testing and application of balanced dose of fertilizers and micro-nutrients, adopting improved cultural operations and better irrigation practices, cultivation of disease and pest resistant varieties etc. are being advocated to boost production to meet the ever increasing demand for food and other materials derived from plants. Sophisticated life style and high living standards have also indirectly increased the demand for various products derived mostly from plants. Diseases take a heavy toll in the production of crop produce. Plant diseases are caused by various pathogenic microorganisms, such as fungi, bacteria, viruses, mycoplasma, protozoa and nematodes; plant parasites, such as algae, lichens and phanerogamic parasites; abiotic agents, such as deficiency due to lack of macro and micronutrients, toxicity due to excess of macro and micronutrients, light and heat stress, as well as presence of some toxic chemicals in the air, soil or water. No plant species on this planet is free from attack by any disease. Some plant species are vulnerable to attack by several diseases. Diseases may attack specific plant parts, such as roots, stems, foliage, fruits, seeds etc. or the entire plant and all these diseases ultimately result in the reduction of yield or quality of the produce or death of some parts or the entire plant. Some pathogens cause extensive damage and death of seedlings, both in the nurseries and main fields. Even stored grains or other produce are subjected to attack by certain microbes leading to spoilage. Some microorganisms produce certain toxins, such as mycotoxins in the grains or food products, which may be lethal to humans and other live stocks. To obtain maximum yield from plants according to their genetic potential, they have to be protected from attack by pathogenic organisms. Similarly stored grains and other food products have to be protected from ravages by microorganisms. Plant protection is a special-branch of agricultural science, which aims at protecting the plants from attack by pathogenic organisms through various methods, such as exclusion, evasion, eradication, protection and immunization. An integrated approach including all the above methods is most effective in controlling the diseases. However, under certain circumstances, especially when the disease intensity crosses the economic threshold level, direct control measures by the use of plant protection chemicals have to be resorted to, so as to control the disease and avoid economic loss. For the survival, perpetuation, spread and initiation of diseases by pathogens, nature has provided a number of means. So, for a concerted effort for the control of diseases, a basic knowledge about the disease symptoms, the causal organisms responsible for causing the diseases, their life cycle, reproductive capacity, mode of survival and spread of the pathogens etc. go a long way in adopting appropriate control measures to combat the diseases. In plant protection, the various measures to be taken to combat the different diseases and the plant protection chemicals to be applied, whenever necessary, differ depending upon the causal organisms and other characteristics of the pathogens. Some of the recently introduced systemic fungicides and antibiotics, as well as some other chemicals are pathogen-specific and are capable of controlling only specific diseases, while some of the broad-spectrum fungicides can control many diseases. So, selection of appropriate plant protection chemicals, the correct dosage of the chemical formulation to be applied, the time and method of application of the chemicals are very important. Several virus and mycoplasma diseases are transmitted by various insect and non-insect vectors in a persistent, semi-persistent or non-persistent manner and for the control of these vectors, specific pesticides having quick knock- down effect have to be applied at the proper time. So, a knowledge about the vectors capable of transmitting such diseases and the pesticides to be used for controlling them are also of vital importance. In the recent past, cultivation of edible mushrooms is gaining momentum. Mushroom cultivation requires less of land and agricultural wastes can be used as substrates for preparing mushroom beds. Further, mushrooms serve as an excellent protein substitute. Mushroom beds and mushrooms are subjected to attack by several fungal, bacterial and virus pathogens, resulting in poor production and spoilage of mushrooms. Cultivation methods of some of the popular mushroom varieties and measures of controlling pathogens attacking mushroom beds and mushrooms have also been included. In this book, which has been compiled as per the syllabus of B.Sc.(Ag.) degree course of Agricultural Universities, the authors have endeavored to give a detailed account of all the major diseases that occur on important field crops and horticultural crops, including control measures to combat the diseases. Besides that, a list of diseases considered to be of minor importance, but which may assume serious proportions, when environmental conditions become favorable for the causative pathogens have also been included. A large number of illustrations, all hand-drawn by the authors have been incorporated to substantiate and highlight the text. The authors hope that this book will be of immense help and guidance, not only to the under graduate students, but also to students in pursuit of higher studies, people working in the Department of Agriculture, people involved in scientific agriculture and the general Public. The authors are extremely thankful to Dr.J. Vasanthakumar, Dean, Faculty of Agriculture, Annamalai University, Chidambaram, Tamil Nadu for being kind enough to give the foreword to the book. Acknowledgements are also due to friends, colleagues and well wishers, who have inspired, helped and encouraged the authors in taking up this venture and complete the work successfully. The authors wish to express their sincere thanks and appreciation to M/s New India Publishing Agency, 101, Vikas Surya Plaza, Pitam Pura, New Delhi-88 for the excellent manner in which the book has been brought out.

CEREALS Rice (Oryza sativa) 1. Rice blast Pyricularia oryzae ‘Rice blast’ occurs in more than 80 countries across the world. The disease is more prevalent in Thailand, Japan, America, Guyana, Philippines and India. It is particularly serious in places, where rice is irrigated or receives heavy rainfall and where high levels of nitrogenous fertilizers are applied. Rice blast was first reported in China in 1637, in Japan in 1704 and in India in 1913. In India, it is found in all rice growing states, particularly in Telungu Desam, Karnataka, Maharashtra, Uttar Pradesh. Assam, Tripura, West Bengal, Bihar, Orissa, Himachal Pradesh, Punjab, Madhya Pradesh, Gujarat, Kerala, Tamil Nadu and Pondicherry and causes considerable damage to rice crop. In Tamil Nadu, the disease occurs in all rice growing districts and attains epidemic proportions in some seasons. Several rice blast epidemics have occurred in different parts of the world, causing yield losses ranging from 50 to 90 %. In Tamil Nadu, a serious epidemic of the disease occurred in 1919 in the Thanjavur Delta. Symptoms. The disease, though chiefly a foliage disease, attacks other parts of rice plants, such as leaf sheath, rachis, joints of the culms and even the glumes. On the leaves, the initial symptoms appear as small bluish or grayish specks, which remain circular in older leaves. On young leaves, they enlarge and become eye-shaped, diamond-shaped or spindle-shaped spots, extending over several centimeters in length and about 1.0 cm. in width. The central portion of the lesion appears pale green or grayish green and water-soaked in the beginning. In older spots, the center becomes white to gray with a dark-brown margin surrounded by a yellow hallow. The lesions may coalesce, cover large area of the leaves and eventually the entire leaves are killed. The shape, size and color of the spots vary depending upon the variety, growth stage of the plants and environmental conditions. Similar spots may be formed on the leaf sheath also. During severe incidence, large areas of the leaves dry and die and the entire crop presents a burnt appearance. Hence the disease is known as ‘blast disease’. Leaf blast is more severe during the seedling and maximum tillering stages. In the nursery, the seedlings show numerous spots on the leaves, which wither and die. In case of severe infection, large number of seedlings may die. Blast also affects the leaf collar, which results in the death of the entire leaf. The disease attacks the stem-nodes at the heading stage leading to production of ‘white panicles’ or the stem may break at the infected node. Rarely the internodes are affected. Further, at heading the fungus also attacks the panicle neck, which is girdled and becomes shining black and shrivelled. This is the most destructive phase of the disease and is known as ‘neck blast’, ‘neck rot’ or ‘panicle blast’. If infection of the panicle neck occurs early, the grains become chaffy and the panicle remains erect. If panicle neck infection occurs late, the grains become partially filled and because of the weight of the grains, the panicle breaks at the neck- node and droops. Sometimes, only parts of the panicle and joints of the culms and some glumes are infected and develop brown to black spots (Fig. 1). Under conditions highly favorable for the pathogen, even the varieties resistant to the fungus under normal conditions are also attacked and small, round or short elliptical spots develop. However, the spots normally do not enlarge as typical blast spots.

FRUIT CROPS Banana (Musa species) 1. Panama disease of banana Fusarium oxysporum f.sp. cubense ‘Panama disease’, ‘Fusarium wilt’ or ’vascular wilt’ of banana is one of the most serious and destructive diseases of the crop. The disease was first reported from Australia in 1874. Now, it is widely distributed all over the world, including America, Africa, Sri Lanka, Burma, Thailand, Malaysia, Indonesia, Hawai, Fiji, the Philippines, India, Australia and New Zealand. In India, it is prevalent in the states of Assam, Bihar, Karnataka, Kerala, Tamil Nadu, Telungu Desam, Maharashtra and West Bengal. Symptoms. Usually the symptoms are manifested, when the banana plants are about 5 months old. However, under highly favorable conditions for the pathogen, even 2 - 3 months old plants show wilt symptoms. Initial visible symptoms appear as pale yellow streaks, lengthwise in the petioles of the oldest, lowermost leaves. Two types of symptoms follow this. In the first type, the old leaves turn yellow progressively and finally they break from the petiole and hang down. In the second type, the leaves break from the petiole and hang down, without becoming chlorotic. Gradually, all the leaves collapse and hang down, except the crown, which alone stands upright. The newly formed leaves show yellow blotches and wrinkling of the lamina. Often, the leaf sheaths covering the pseudostem show longitudinal splitting above the ground level. But, sometimes this symptom may not appear. The affected plants may die completely in about 4-6 weeks after the appearance of yellow streaks on the petioles. The vascular strands show discoloration varying from yellow to dark- brown, which is the characteristic internal symptom of the disease. The discoloration usually appears first in the outer leaf sheaths and extends to the vascular strands of the pseudostem. Vascular discoloration is more pronounced in the corms, but is not common in the roots. When the rhizome of an infected plant is cut transversely, the discoloration of the vascular bundles is distinctly seen as numerous, pin-point like dots all over the cut surface. The roots of affected plants become black and rotten. The suckers growing from the diseased corms are systemically affected and they wilt and die very soon (Fig. 71). The causal organism. The mycelium of the fungus is hyaline, septate, much branched and mostly intracellular. Few hyphae may also be present in the intercellular spaces. The hyphae are largely confined to the vascular bundles, often filling the cavity of the vessels. The fungus produces three types of spores viz., macroconidia, microconidia and chlamydospores. The sporodochia bearing conidiophores and conidia emerge through the stomata on the petioles and leaves. The conidiophores are vertically branched. Macroconidia are borne at the apical ends of the main and lateral branches and are formed in succession one after another. They are thin-walled, hyaline, pedicellate, sickle-shaped, with both ends somewhat pointed, 2 - 5 septate, mostly 3-septate and measure 22.0 - 36.0 x 4.0 - 5.0µ in size. Microconidia are produced from the branches of conidiophores or from the tips of hyphae in very large numbers. They are single-celled or two-celled, thin-walled, hyaline, ovate or elongated and measure 5.0 - 7.0 x 2.5 - 3.0µ in size. Terminal or intercalary chlamydospores are formed from the hyphae, as well as from the conidial cells. They are oval or spherical, thick-walled and usually occur in pairs. They measure 7.0 - 13.0 x 7.0 - 8.0µ in size (Fig. 71). The fungus is a facultative parasite. It can invade the host mainly through wounds in the corms or roots. After entry, the fungus develops extensively in the vascular tissue of the corm and then proceeds systemically to the leaf sheaths and pseudostem through the vascular system. The fungus colonizes the vascular bundles and produces masses of mycelium, which bear conidia and chlamydospores, filling the cavity of the vessels. The plugging of vascular elements by the fungus obstructs the translocation of water and nutrients to the aboveground parts of the plant leading to wilting and death of affected plants. Mode of survival, spread and epidemiology. The fungus is soil-borne in nature. It can survive saprophytically in the diseased corms and other plant parts for prolonged periods and cause fresh infection. The chlamydospores can also remain in a viable state in the soil and diseased plant parts for a long time. The disease can be easily spread through spores present in the infected banana trash and soil, which may be carried in surface flooded water. Suckers used for planting from diseased areas to other places spread the disease easily. Contact of the roots of healthy plants with the roots of diseased plants carrying the spores also leads to fresh infection. The entry of the pathogen is mostly through wounds in the roots or corms, especially deep wounds up to the xylem vessels, caused incidentally during cultural operations or by soil-inhabiting pests, particularly nematodes. Light textured, sandy loam soils, with acid reaction and low soil moisture of 25 % favor the occurrence and development of the disease. Ratooning of infected banana plants increases the disease incidence to a great extent and leads to continuous accumulation of soil inoculum.

‘Fungi’ including ‘mushrooms’ are ‘Thallophytes’, which do not possess chlorophyll and have been classified under the Kingdom - Myceteae. They do not have stems, roots and leaves and they lack a vascular conducting system as in the case of plants. They propagate by means of spores, either asexual or sexual. Though almost all the fungi are microscopic, the mushrooms are among the largest fungi and had attracted the attention Scientists and Naturalists of many countries dating back to centuries. The Greek word ‘mykes’, which means ‘cap’, was given to the mushrooms because of the ‘cap-like’ appearance of the pileus and the Greek word ‘Mycology’ (mykes = mushroom + logos = discourse) denotes the study of mushrooms. What we call mushrooms, are actually the sporocarps produced by several species of fungi, while the mycelium that produces them live in various types of substrata and obtain nourishment from them. Usually, the fleshy, macroscopic fruiting bodies or sporocarps produced by fungi belonging to Basidiomycetes and Ascomycetes are called ‘mushrooms’ The Romans attributed the appearance of mushrooms and truffles to lightning hurled by Jupiter to the earth. Even now in India and several other countries, people believe that mushrooms appear only after lightning and thunder. The Greeks believed mushrooms as ‘Food for the Gods’. The Romans supplemented mushrooms in the food of soldiers for strength and vitality. The much-priced mushrooms were supposed to be the food delicacy of the elite society of the Romans and Greeks in olden days. The Chinese consider mushrooms as a cure for many diseases and they believe that mushrooms increase the longevity. A number of medicines in all forms are prepared from mushrooms by the Chinese.

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