Disease Note.

Corynespora cassiicola Isolated from Soybean Roots in the Red River Valley of Minnesota and North Dakota. J. Hansen, Department of Plant Pathology, North Dakota State University, Fargo 58105. B. Nelson, Department of Plant Pathology, North Dakota State University, Fargo 58105, and C. E. Windels, Northwest Experiment Station, University of Minnesota, Crookston 56716. Plant Dis. 78:1122. Accepted for publication 13 July 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1122E.

Soybeans (Glycine max (L.) Merr.) in the Red River Valley of Minnesota and North Dakota were surveyed for fungal root rot pathogens in 1991-1992. Root segments (1 cm) with lesions were surface-treated in 0.5% NaOCI for 30 sec and placed on 2% water agar with streptomycin sulfate (150 ppm). Of 1,863 fungal isolates, 4% were Corynespora cassiicola (Berk. & MA. Curtis) C.T. Wei. This pathogen was detected in 57 of 705 fields surveyed. Four cultures from single conidia were tested for pathogenicity on McCall soybean. Inoculum of C. cassiicola was grown on sterilized barley grains for 14 days. Four colonized grains were appressed (at a depth of 2 cm) against wounded and nonwounded taproots of 2- to 5-wk-old plants in a greenhouse at 20-28 C. Plants were evaluated for disease after 21 days. All four cultures produced dark reddish brown to black lesions, which often girdled the taproot. Decay of cortical tissues was generally not extensive and did not extend into the stele. C. cassiicola was reisolated from inoculated plants. Although C. cassiicola is found in most soybean-growing areas of the United States and Canada (1), this is the first report of the pathogen in the Red River Valley