Prof. T.S. Sadasivan became Director of the University of Botany Laboratory, Chennai in 1944. He reoriented the research programmes of the department and established a very strong school of Soil Microbiology with special reference to Economic Botany. He initiated research on the physiology of host pathogen relationship in the country and made path breaking findings related to cotton wilt and rice blast diseases, ion uptake and osmoregulation in pathogenesis, fungal toxins and enzymes, plant virology, symbiotic nitrogen fixation by bacteria and fungal systematics. The research on algology was also given equal emphasis. The research work done in the department under his leadership earned international recognition and the University Grants Commission recognized Botany Department of Chennai as the Center for Advance Study in 1964. His pioneering work in Plant Pathology made him one of the leading Plant Pathologists in the world. He was the Vice- President of the first International Congress of Plant Virology held in London in 1968.
Prof. Sadasivan was the recipient of many honours, which include the Fellowship of the Indian Academy of Sciences, the Indian National Science Academy and the National Academy of Agricultural Sciences. He was a member of the Deutsche Akademie Der Naturforschugn, and Editor of Phytopathologiche Zeitschrift. He was President of the Indian Academy of Science (1971-73), Vice-President of International Botanical Congress (1959, 1964, 1969 & 1975), President of Botany Science Congress (1958), President of Indian Botanical Society (1963-64) and the Indian Phytopathological Society (1963). He was recipient of Dr. Shanti Swarup Bhatnagar Award for Biological Science (1960), the Birbal Sahni Medal of the Indian Botanical Society (1962), the Sunderlal Hora Medal of the Indian National Science Academy (1973), Dr. K.C. Mehta Award of National Academy of Agricultural Sciences (1995) and Prof. Birbal Sahni Birth Centenary of the Indian Science Congress (1999). He was invited to the Birbal Sahni Chair at the Birbal Sahni Institute of Palaeobotany (1977-79). He was honoured with Padma Bhushan by the President of India in 1974.
Prof. Sadasivan superannuated from service in 1973, but he continued his deep interest in science and he was always a source of inspiration and guiding force for the scientists in general and plant pathologists in particular in the country.
Prof. T.S. Sadasivan, expired on August 18, 2001 after a prolonged illness.