Physiologic Specialization of Diaporthe phaseolorum var. caulivora in Soybean. P. M. Higley, Graduate Research Assistant, Department of Plant Pathology, Iowa State University, USDA-ARS, Ames 50011. H. Tachibana, Professor, Department of Plant Pathology, Iowa State University, USDA-ARS, Ames 50011. Plant Dis. 71:815-817. Accepted for publication 23 April 1987. 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, 1987. DOI: 10.1094/PD-71-0815.

Two isolates of Diaporthe phaseolorum var. caulivora (D. p. var. caulivora) from Mississippi and one from Iowa were used to inoculate seedlings of four soybean cultivars adapted to Mississippi and six to Iowa. The percentages of resistant, moderately susceptible, and highly susceptible plants were recorded for each cultivar. The three D. p. var. caulivora isolates showed physiologic specialization. Some variability in plant response occurred. Because soybean cultivars have not been selected for resistance to stem canker, they may be genotypically heterozygous for response to D. p. var. caulivora. Soybean cultivars Blackhawk, Harosoy, L4404, Nathan, Tracy M, and Williams were susceptible to the Iowa isolate and resistant to the Mississippi isolates; Clark, J77-339, and Pike were susceptible to all three isolates. It is proposed that the Iowa isolate be designated race 1 and the Mississippi isolates be designated race 2.