A new race of Phytophthora megasperma f.sp. glycinea on soybean in Australia

An isolate of Phytophthora megasperma f.sp. glycinea from soybean cv. Ridley growing near Forbes in the Lachlan Valley, New South Wales, was classified as race 4 after hypocotyl inoculation on a United States differential set consisting of Harosoy, Harosoy 63, Sanga, Wells II, PI 103091, PI 86972-1 and Altona. This is the first record of race 4 in Australia. The cultivars Nessen, Ridley and Lachlan, all immune to the other races of P. megasperma f.sp. glycinea in Australia (viz. races 1 and 15), were susceptible to the new race. The appearance of race 4 is undoubtedly due to the growing of cultivars with race-specific resistance.