Plant Loss Response of Soybean Cultivars toPhytophthora megaspermaf. sp.glycineaUnder Field Conditions

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Abstract
Soybean cultivars and lines were evaluated on Brookston clay during 1977-1980 for plant loss caused by P. megasperma f. sp. glycinea. Races 3, 7, and 9 of the pathogen were predominant in the soil. Hypocotyl inoculations with races 1, 3, 4, 7, and 9 indicated that some cultivars and lines carried race-specific resistance that resulted in low plant loss. Other variability in plant loss among entries was ascribed to tolerance. There was no significant cultivar .times. year interaction in 2-yr and 4-yr analyses; broad-sense heritabilities from these analyses were 93 and 96%. Selection for tolerance based on low plant loss, followed by backcrossing to include race-specific resistance, should provide effective, long-term disease control.