Seedling Infection of Soybean by Isolates of Rhizoctonia solani AG-1, Causal Agent of Aerial Blight and Web Blight of Soybean. X. B. Yang, Former Graduate Research Assistant, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. G. T. Berggren, and J. P. Snow. Professor, and Professor, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. Plant Dis. 74:485-488. Accepted for publication 29 November 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0485.

Infection of soybean (Glycine max) cotyledons, hypocotyls, and shoot apices by Rhizoctonia solani, anastomosis group 1, sasakii- and microsclerotia-type, was observed. The same isolates infected soybean seedlings and caused aerial blight or web blight on soybean in both greenhouse and field experiments. The relationship between initial inoculum level and diseased seedlings (%) was best described with quadratic equations with coefficients of determination (R²) from 0.70 to 0.90 (P <0.001) for two sampling times. The isolate of R. solani had little effect on the number of seedlings emerging and surviving. Diseased seedlings became sources of inoculum by producing mycelium that grew to and infected neighboring plants. Seedling infection at an early stage thus can have a significant effect on subsequent disease development.