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Responses of Differential Soybean Cultivars to Hypocotyl Inoculation with Phytophthora megasperma f. sp. glycinea at Different Temperatures. B. L. Keeling, Research Plant Pathologist, USDA-ARS, Soybean Production Research, P.O. Box 196, Stoneville, MS 38776. Plant Dis. 69:524-525. Accepted for publication 14 December 1984. 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-69-524.

The responses of differential soybean (Glycine max) cultivars (Harosoy, Sanga, Harosoy-63, Mack, Altona, PI 103091, PI 171442, and Tracy seedlings) were determined when hypocotyl-inoculated with mycelium of races 1, 2, 7, or 10 of Phytophthora megasperma f. sp. glycinea and maintained at 21, 24, 27, 32, or 38 C. Temperature affected host response in most cultivar-race combinations. The magnitude of the temperature effect varied with the cultivar-race combinations. Disease development was usually suppressed in cultivars susceptible to the pathogen at 21 C, and a significant number of plants of some cultivars resistant to the pathogen were susceptible at 27 or 32 C. Disease symptoms in inoculated seedlings did not develop at 38 C. The optimum temperature for classifying races of P. megasperma f. sp. glycinea on these differential cultivars was 24 C.

Keyword(s): Phytophthora megasperma var. sojae, Phytophthora rot, race identification.