Effect of Cercospora sojina and Phomopsis sojae Alone or in Combination on Seed Quality and Yield of Soybeans. V. S. Bisht, Former Graduate Research Assistant, Department of Plant Pathology, University of Illinois at Urbana-Champaign, Urbana 61801. J. B. Sinclair, Professor, Department of Plant Pathology, University of Illinois at Urbana-Champaign, Urbana 61801. Plant Dis. 69:436-439. Accepted for publication 27 November 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-436.

Two soybean (Glycine max) cultivars, Corsoy-79, susceptible, and Wells, moderately resistant to a Cercospora sojina isolate and equally susceptible to Phomopsis sojae, were inoculated with either fungus alone or in combination in field plots in 1981 and 1982. Frogeye leafspot, caused by C. sojina, which can cause latent infection in stems, was higher in C. sojina-inoculated plots in both years and showed a negative correlation (r = –0.56 and –0.50, respectively) with yield and 1,000-seed weight and occurred at a significantly higher severity in Corsoy-79 than in Wells. Recovery of C. sojina from pods was predictive of recovery of C. sojina from seeds. Recovery of either pathogen in pods, stems, and seeds was not affected by the presence of the other. Seed germination was lowest in plots inoculated with both fungi (83%), intermediate in plots inoculated with C. sojina or P. sojae alone (86.1 and 84.7%, respectively), and highest in the control (89.6%). C. sojina and P. sojae acted independently and had an additive effect.