Fundamentals of Plant Pathology Department of Plant Pathology, JNKVV, Jabalpur Importance of Plant Disease, Scope and Objective of Plant Pathology Shraddha Karcho [email protected] JNKVV College of Agriculture ,Tikamgarh ------------------------------------------------------------------------------------------------------ Plant Pathology is a branch of agricultural science that deals with the study of fungi, bacteria, viruses, nematodes, and other microbes that cause diseases of plants. Plants diseases and disorders make plant to suffer, either kill or reduce their ability to survive/ reproduce. Any abnormal condition that alters the appearance or function of a plant is called plant disease. The term ‘Pathology’ is derived from two Greek words ‘pathos’ and ‘logos’, ‘Pathos’ means suffering and ‘logos’ Means to study/ knowledge. Therefore Pathology means “study of suffering”. Thus the Plant Pathology or Phytopathology (Gr. Phyton=plant) is the branch of biology that deals with the study of suffering plants. It is both science of learning and understanding the nature of disease and art of diagnosing and controlling the disease. Importance of Plant Diseases The study of plant diseases is important as they cause loss to the plant as well as plant produce. The various types of losses occur in the field, in storage or any time between sowing and consumption of produce. The diseases are responsible for direct monitory loss and material loss. Plant diseases still inflect suffering on untold millions of people worldwide causing an estimated annual yield loss of 14% globally with an estimated economic loss of 220 billion U. S. dollars. Fossil evidence indicates that plants were affected by different diseases 250 million year ago. The Plant disease has been associated with many important events in the history of mankind of the earth. The crop loss due to diseases is estimated to be approximately 30-50%. 1 Fundamentals of Plant Pathology Department of Plant Pathology, JNKVV, Jabalpur Cultivated plants are often more susceptible to diseases than are their wild relatives. Important environmental factors that may affect development of plant diseases are temperature, relative humidity, soil moisture, soil pH, soil type, and soil fertility. Each pathogen has an optimum temperature for growth. High soil-moisture levels favors development of destructive water mold fungi, such as species of Aphanomyces, Pythium, and Phytophthora. High humidity favors development of the great majority of leaf and fruit diseases caused by fungi and bacteria. Soil pH, a measure of acidity or alkalinity, markedly influences a few diseases, such as common scab of potato and club root (Plasmodiophora brassicae) of crucifers. Raising or lowering the levels of certain nutrients also influences the development of some infectious diseases. Most control measures are directed against inoculums of the pathogen and involve the principles of exclusion and avoidance, eradication, protection, host resistance and selection, and therapy. Important Famine in World Late blight of potato-1841-51 (Irish famine): The late blight of potato, a diseased caused by the fungus, Phytophthorainfestans, is a famous example of what a plant disease can do to change the course of history. In 1845, this diseasedestroyed the potato crop of Ireland where potato constituted the staple diet of the majority in rural areas. The disease had started in Ireland, England and part of the continental Europe as early as 1830 and was causing some damage every year, resulting in food shortage. It was reported that in 1840 the population of Ireland was 8 million which was reduced to 4 million after the famine. Coffee rust 1867-1870 (Sri Lanka):The coffee and tea were equally consumed in England because these were available in plenty from such occupied countries as India, Sri Lanka and Malaysia. Sri Lanka used to produce maximum 2 Fundamentals of Plant Pathology Department of Plant Pathology, JNKVV, Jabalpur coffee in the world. In 1867, coffee rust attacked the plantations in Sri Lanka and by 1893, export of coffee from Sri Lanka had declined by 93%. The economic crisis forced the planters to cut down coffee plants and take to tea planting. When coffee rust was spreading in Sri Lanka the science of plant pathology was just developing and control measure of the disease were not known. The system of monoculture in coffee plantations of Sri Lanka was considered a contributoryfactor in devastations caused by the coffee rust which was not prevalent in coffee growing countries of South America. Bengal Famine 1942 (India): In the last year of Second World War (1943) Bengal had to face a serious famine. One of the reasons to which this famine has been attributed was the loss in yield of the rice crop due to attack of Helminthosporium leaf spot which had been affecting the crop for the last several years. Situation was similar to the Irish potato famine but not so catastrophic. In India wheat rust had been considered to cause a loss of over Rs. 40 million annually. In the year of epidemics there have been a losses amounting to Rs. 500 million or more. Although introduction of dwarf high yielding varieties has reduced the losses to a great extent even now thefarmers lose 8-10%of the expected yield due to rusts. The loose smut of wheat is estimated to cause an average loss of 3% every year. The ‘Molya’ disease, caused by a nematode is another example. The disease of wheat and barley prevalent in most parts of Rajasthan causes a loss of Rs. 30 million in barley and 40 million in wheat every year. Different smuts of sorghum are responsible for an annual loss of Rs. 100 million. 5% to 75% loss in chickpea due to Ascochyta blight was reported from Rajasthan during 1982. Wilt of pigeon pea causes 5-10% loss every year in U.P. and Bihar. Scope and Objectives of Plant Pathology Scope and responsibilities of plant pathology is unlimited. Its ultimate goal is to prevent and control plant diseases of economic importance. Responsibilities of the science of plantpathology may be summarized as under. 3 Fundamentals of Plant Pathology Department of Plant Pathology, JNKVV, Jabalpur Study of etiology, symptoms, predisposing factors and recurrence of such diseases. Plant pathology deals with different aspects of plant diseases and has wide scope than human pathology which only deals with only one aspecti.e. plant health. The branch focuses on understanding how hosts, pathogens, and environments interact to cause plant diseases and on understanding how to control plant diseases. In recent years plant pathologists have begun to specialize in particular aspect. The fields in which notable advances have been made are: Interaction between host and pathogen at chemical, molecular and genetic level. Plant virology, Mycology, chemistry of fungi toxicity. Disease forecasting and Plant Quarantine. On practical aspects much advances have been made in plant protection chemicals; breeding for disease resistance. Increased population emphasizes the application of all possible means to meet the food requirements Expansion of crop area Improved methods of cultivation Increased use of fertilizers Improved varieties Increased irrigation Crop protection The science of plant pathology has four main objectives: 1. To study the living, non-living and environmental causes of plant diseases.(Etiology) 2. To study the mechanisms of disease development by pathogens.(Pathogenesis) 3. To study the interactions between the plants and the pathogen.(Epidemology) 4. To develop the methods of controlling the diseases and reducing the losses caused by them.(Control/ Management) 4 Fundamentals of Plant Pathology Department of Plant Pathology, JNKVV, Jabalpur L. 02 History of Plant Pathology with special reference to Indian work Pawan Amrite [email protected] JNKVV, Jabalpur ------------------------------------------------------------------------------------------------------------------- The development of science of Plant Pathology in the modern era in India as in other countries followed the development of mycology. The study of fungi in India was initiated by Europeans in the 19th century. They used to collect fungi and send the specimens for identification to the laboratories in Europe. During 1850-1875, D.D. Cunningham and A. Barclay started identification of fungi in India itself. Cunningham made a special study of rusts and smuts. DD Cunningham identified the causal organism of red rust of tea in Assam caused by Cephaleurous virescens. K.R. Kirtikar Pusa (1885) was the first Indian scientist who collected and identified the fungi in the country. TS Ramakrishan Studies and contributed to genera Pythium, Phytophthora, Colletotrichum, and the rusts. Wrote monograph on 'Diseases of Millets' published by ICAR E.J. Bulter who is also known as the ‘Father of Plant Pathology’ in India, initiated an exhaustive study of fungi and diseases caused by them in 1901 at Imperial Agricultural Research Institute at Pusa (Bihar). During his stay of 20 years in this country, he made a scientific study of mostly fungal plant diseases known in India at that time. The diseases studied by him for the first time included wilt of cotton and pigeon pea, different diseases of rice, toddy palm, sugarcane, potato and rusts of cereals. He wrote a monograph on 5 Fundamentals of Plant Pathology Department of Plant Pathology, JNKVV, Jabalpur ‘Pythiaceous and Allied Fungi’; and a classic text book, ‘Fungi and Diseases in Plants’ in 1918. J.F. Dastur (1886-1971), a colleague of Butler, was the first Indian Plant Pathologist who is credited with detailed studies of fungi and diseases in plants. He studied the genus Phytophthora and diseases caused by it in castor and potato. He is internationally known for the establishment of Phytophthora parasitica from castor. T.S. Sadasivan developed the concept of vivotoxins and worked out the mechanism of wilting in cotton due to Fusarium oxysporum f.sp. vasinfectum. Mitra in 1937 AD recorded Tilletia indica, a new bunt (Karnal bunt) on wheat. The disease was thought, erroneously, to be soil borne. Later studies showed that it was air borne, and the infection was not systemic (Mundkar, 1943 AD) G.S.