Physiologic Races ofPhytophthora megaspermaf. sp.glycineain Indiana, 1973-1979

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Abstract
More than 1000 isolates of P. megasperma f. sp. glycinea were collected during yearly surveys of soybean [Glycine max] fields in Indiana [USA], in 1973-1979, and the physiologic race of each isolate was determined. Before 1973, only race 1 was found in Indiana, and it was found in most parts of the state. New races were found in 22 counties in the central and northern parts of the state. Race 3 comprised 48% of all isolates, followed by race 7 (18%), race 1 (17%), race 9 (12%), race 4 (3%), race 8 (2%), race 5 (0.2%) and race 13 (0.1%). The other 8 described races were not found. The effect of resistant cultivars on the occurrence of new races of the pathogen is discussed.