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Factors Affecting Charcoal Rot of Soybean Seedlings. W. A. Meyer, Graduate Research Assistant, Department of Plant Pathology, University of Illinois, Urbana 61801, Senior author’s present address: Warren’s Turf Nursery, Palos Park, Illinois 60464; J. B. Sinclair(2), and M. N. Khare(3). (2)Professor, Department of Plant Pathology, University of Illinois, Urbana 61801; (3)Associate Professor, Department of Plant Pathology, J. Nehru Krishi Vishwa Vidyalaya, Jabalpur, M. P., India. Phytopathology 64:845-849. Accepted for publication 14 January 1974. DOI: 10.1094/Phyto-64-845.

During the rainy season in India, soil in field plots was infested with either mycelium or sclerotia of Macrophomina phaseolina, or mixed with soybean stubble containing M. phaseolina. The emergence of soybean seedlings was significantly reduced and the percentage of emerged infected seedlings was increased. Yields were not reduced. Symptoms on seedlings in field plots appeared first as reddish-brown lesions on the hypocotyls close to the cotyledons, then turned ashy-gray to black. Sclerotial and mycelial inoculum were almost equally effective in causing seedling disease under controlled and field conditions. Seedling disease was greatest at 30 and 35 C although some infections occurred on soybean seedlings at 20 and 25 C. Infected seedlings may serve as a latent source of inoculum for the mature-plant phase of the disease over a wide temp range. The percentage of diseased seedlings increased slightly with an increase in number of viable M. phaseolina propagules in soil.