Fundamentals of Plant Pathology

MODERN EXPERIMENTAL PLANT PATHOLOGY

• The foundation of modern experimental plant pathology was laid by the German scientist Heinrich Anton de Bary (1831-1888). He made a great contribution to the understanding of science of Plant Pathology and is suitably regarded as Father of Modern Plant Pathology. His major contributions are:
• He confirmed the findings of Prevost in 1853.
• In 1861, he experimentally proved that Phytophthora infestans was the cause of late blight of potato. He is credited with the ultimate proof of the organisms being plant pathogens.
• He studied other diseases like rusts, smuts, downy mildews and rots.
• He reported the heteroecious nature of rust fungus in 1885.
• He also reported the role of enzymes and toxins in tissue degradation caused by Sclerotinia sclerotiorum in 1886.
• de Bary was first to report that lichen consists of a fungus and an alga, and coined the term symbiosis.
• He studied in detail the life cycle of downy mildew fungi and their parasitism.
• His well known text book “Morphologie und Physiologie der Pilze Flechten und Myxomyceten” written in 1866 and 1884 records the broad classification of fungi.
• He trained a large number of students from all over the world who came to his laboratory.
• More than 60 of them became prominent in field and carried his techniques.
• Famous among them were M.S. Woronin of Russia, who studied club root of crucifers caused by Plasmodiophora brassicae; P.A. Millardet of France; HM ward of England, who studied coffee rust in Sri Lanka and gave ‘bridging host theory’, Fallow of U.S.A., who spent his long active career as cryptogamic botanist, and provided leadership in study of parasitic fungi; and A. Fisher of Switzerland worked on bacterial Plant Pathology and is known for the infamous Fisher –Smith controversy regarding the role of bacteria in causing plant diseases.
• J.G. Kuhn, who was a contemporary of de Bary and his countryman, was, initially a farm manager. He contributed significantly to the studies on infection and development of smut in wheat plant and development and application of control measures, particularly seed treatment for cereals.
• He wrote the first book on Plant Pathology “Diseases of Cultivated Crops, Their Causes and Their Control” in 1858 in which he recognized that plant diseases are caused not only by an unfavourable environment, but can also be caused by parasitic organisms such as insects, fungi and parasitic plants.
• The theory of spontaneous generation was a major impediment in the development of science of Plant Pathology, which was finally disproved by Louis Pasteur who established the ‘germ theory of the disease’ in case of anthrax in relation to man and animals. It changed the way of thinking of scientists and led to a tremendous progress.
• Significant impetus to this progress was added by Robert Petri, who developed artificial nutrient media for culturing of microorganisms and Brefeld (1875,1883,1912) who contributed greatly to Plant Pathology by introducing and developing modern techniques for growing microorganisms in pure culture.
• Robert Koch (1876) who was a Germen Physician and co-worker of Pasteur established that for proving that a certain microorganism was the cause of some infectious disease, certain necessary steps (Koch’s postulates) must be carried out and certain conditions must be satisfied. They are:
• A specific organism must always be associated with the disease.
• The organism has to be isolated in pure culture.
• The organism must produce specific disease in a healthy susceptible host when the latter are inoculated with it.
• The organism must be re-isolated from the experimental (diseased) host in pure culture and its identity be established and it must have the characteristics as the organism in step 2.