2010 Volume 55 Pages 19-25
This study investigated disease occurrence of Phytophthora stem rot of soybean (caused by Phytophthora sojae) in Glycine max (L.) Merr. cv. Tanbakuro producing areas in Hyogo from 2005-2007, pathogenic races of P. sojae, and effectiveness of five Rps genes and eight soybean cultivars to several races. Disease incidence at 93 different fields in seven regions of Hyogo ranged from 3.3 to 23.5% in 2005 to 2007. Ninety-three isolates of P. sojae were recovered from the 93 fields. Six Japanese differential soybean cultivars were used for race determination of the 93 isolates with the agar medium inoculation method. The results showed that race E was a major component of all the P. sojae population, followed by races A, L, K, M, G, N and new race O. This result was subsequently integrated with the previous data with 51 isolates derived from 2002-2004. Race E tended to be dominant from 2002-2007 throughout seven regions of Hyogo. Cvs. Enrei, Sachiyutaka, Rps6 in cv. Altona, Rps1a+Rps7 in cv. Harosoy 63, and Rps1k in cv. L77-1794, considered to be strongly resistant in the USA, were susceptible to most of 144 isolates, suggesting that they were ineffective. Rps1d in cv. PI103091 was not defeated by the 144 isolates, nor was cv. Gedenshirazu-1. Cv. Ohojyu was resistant to 140 of the 144 isolates. These results indicate that three soybean cultivars were still potential sources of resistance to breed new resistant cultivars with the desirable characteristics of cv. Tanbakuro.
