Physiologic Races of Phytophthora megasperma f. sp. glycinea in Indiana, 1973-1979. F. A. Laviolette, Department of Botany and Plant Pathology, Purdue University Agricultural Experiment Station, West Lafayette, IN 47907. K. L. Athow, Department of Botany and Plant Pathology, Purdue University Agricultural Experiment Station, West Lafayette, IN 47907. Plant Dis. 65:884-885. Accepted for publication 17 February 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-884.

More than 1,000 isolates of Phytophthora megasperma f. sp. glycinea were collected during yearly surveys of soybean fields in Indiana from 1973 through 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 eight described races were not found. The effect of resistant cultivars on the occurrence of new races of the pathogen is discussed.