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Purple Seed Stain of Soybeans. K. W. Roy, Graduate Research Assistant, Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907; T. S. Abney, Research Plant Pathologist, Agricultural Research Service, USDA, U.S. Department of Agriculture, West Lafayette, Indiana 47907. Phytopathology 66:1045-1049. Accepted for publication 12 March 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1045.

Field plantings of four genetically different soybean lines were inoculated with Cercospora kikuchii. Inoculations at different stages of host development in the same environment and inoculations at similar host stages in varying environments were compared. Incidence of purple-stained and total infected seed was not correlated with the length of the flowering period, but it was affected by weather conditions at the time of inoculation. Young pods were more susceptible to infection than old pods. Inoculated plants matured earlier, had smaller seed, and yielded less than noninoculated plants. Seed infection resulting from C. kikuchii inoculations in different environments at the full-bloom stage of host development ranged from 3% to 30% for P.I. 80837, the most resistant entry, and from 30% to 85% for Amsoy, the least resistant soybean entry. Soybean entries differed in the expression of purple stain in infected seed.

Additional keywords: seed infection, Glycine max, seed-borne disease.