Field Evaluation of Pathogenic Variability in Isolates of Septoria glycines. T. A. Kamicker, Graduate Research Assistant, Department of Plant Pathology, University of Illinois and USDA Agricultural Research, Urbana 61801. S. M. Lim, Professor and Research Plant Pathologist, Department of Plant Pathology, University of Illinois and USDA Agricultural Research, Urbana 61801. Plant Dis. 69:744-746. Accepted for publication 6 March 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/PD-69-744.

Isolates of Septoria glycines were evaluated for their pathogenic variability on the susceptible soybean cultivar Williams 79 in the field. Twelve isolates from different states in the United States were evaluated in 1981 and 15 isolates were evaluated in 1982. Treatments included inoculation, fungicide application, and check (natural infection) in both years. All isolates evaluated produced typical brown spot lesions (angular brown spots surrounded by a yellow area) on leaves of infected plants. In 1981, there were significant differences in brown spot severity among some isolates at the R6 growth stage. In 1982, however, there were no significant differences in brown spot severity. In both years, there were significant differences in brown spot vertical progress among isolates but no differences in defoliation. Area under the disease progress curve was similar among isolates. No significant differences in either soybean yield or 300-seed weight were found among inoculated and check plots for either year. Although there were significant differences in the severity and vertical progress of brown spot among some isolates, results were not consistent and indicate that pathogenic variability among isolates of S. glycines was not detectable by quantifying the development of brown spot in the field.

Keyword(s): Glycine max.