Races of Phytophthora sojae and Their Virulences on Soybean Cultivars in Heilongjiang, China.

Phytophthora root and stem rot, caused by Phytophthora sojae, is an economically important disease of soybean (Glycine max) in Heilongjiang Province, China. The objectives of this research were to determine the race profile of P. sojae in Heilongjiang and evaluate soybean cultivars for reactions to the pathogen races. A total of 96 single-zoospore P. sojae isolates were obtained from soil samples collected from 35 soybean fields in 18 counties in Heilongjiang from 2005 to 2007. Eight races of P. sojae, including races 1, 3, 4, 5, 9, 13, 44, and 54, were identified on a set of eight differentials, each containing a single resistance Rps gene, from 80 of the 96 isolates. Races 1 and 3 were predominant races, comprising 58 and 14 isolates, and representing 60 and 7% of the pathogen population, respectively. Races 4, 5, 44, and 54 were identified for the first time in Heilongjiang, and each was represented by two to three isolates only. Sixty-two soybean cultivars commonly grown in Heilongjiang Province were evaluated for their resistance to the eight P. sojae races identified using the hypocotyl inoculation technique. Based on the percentage of plant mortality rated 5 days after inoculation, 44 cultivars were resistant (<30% mortality) to at least one race. These cultivars may be used as sources of resistance in soybean breeding programs.