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Stunting of Soybeans by Pythium debaryanum. J. F. Strissel, Graduate Assistant, and Research Plant Pathologist, Crops Research Division, ARS, USDA, Department of Botany and Plant Pathology, Iowa State University, Ames 50010; J. M. Dunleavy, Professor, Department of Botany and Plant Pathology, Iowa State University, Ames 50010. Phytopathology 60:961-963. Accepted for publication 14 January 1970. DOI: 10.1094/Phyto-60-961.

Pythium debaryanum caused unusual symptoms on soybeans. The fungus incited dry, necrotic lesions on the cotyledons, death of the apical meristem, development of axillary shoots at the cotyledonary node, and a swelling of the hypocotyl. Infected plants of susceptible cultivars were severely stunted, and death of seedlings often resulted. This resulted in a 40% reduction in stand. The stand was increased when cyano-(methyl-mercuri) guanidine was applied as a seed treatment. Plant height was a reliable measure of disease resistance. Mandarin (Ottawa) was the most resistant, and Ontario and Manchu T3 were the most susceptible of 22 soybean cultivars tested.