Disease Note

First Report of Charcoal Rot Caused by Maerophomina phaseolina on Soybean in Wisconsin. G. L. Birrenkott, Department of Plant Pathology, University of Wisconsin, Madison 53706. A. Mengistu, and C. R. Grau, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 68:628. Accepted for publication 2 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-628c.

Charcoal rot was discovered in 1982 on soybeans (Glycine max (L.) Merr.) in Rock County, Wisconsin, in a nonirrigated sandy loam field where 80% of the plants showed symptoms. It was observed again at similar sites during 1983. Foliar chlorosis, necrosis, basal rot, and imbedded sclerotia were noted. Macrophomina phaseolina (Tassi) Goid. was isolated from the plants, and an isolate was used for pathogenicity studies. Corsoy 79 plants grown in steamed soil infested with sclerotia (field isolate propagated in oat straw) and incubated at soil temperatures of 31-33 C showed symptoms and signs of charcoal rot. Only M. phaseolina was recovered from stems of these plants. M. phaseolina appears to be a potential threat to soybeans grown in Wisconsin.