Detection And Identification Of Phytophthora Sojae And Transmission Of Phytophthora Root Rot Of Soybean

The pathogen causing Phytophthora disease of soybean in Heilongjiang Province and Mongolia Region in China was studied on morphology, physiology. pathogenicity, serology, isozymes, RAPD, virulence and transmission. This pathogen was the same as causing Phytophthora root rot of soybean in United States, that is Phytophthora sojae Kaufmann & Gerdemann; The soluble mycelia antigen of Ps was used to immunize male rabbit to make polyclonal antibodies, which may detect Ps in culture and in inoculated plants specifically; Isozyme analysis was used to study 23 isolates of the species Phytophthora. Interspecific diversity for EST and SOD isozyme banding was identified among the eight species assayed,? sojae, P capsici, P parasitica, P infestans, P cactorum, P citrophthore, P palmivora and? cinnamomi. Intraspecific isozyme diversity was not present among IS isolates of P sojae that were recovered from many geographical origins. Of the 151 RAPD bands, which amplified using 12 random primers, 84% were polymorphism. RAPD analysis indicated that genetic diversity existed within isolates of Phytophthora sojae collected from the same location as well as different locations, and there was no interrelation between DNA polymorphism of isolates of Ps and its geographical origin. The relationship between virulence patterns and RAPD markers was presented in some isolates. RAPD analysis also indicated that there was genetic diversity between Phytophthora species. Genetic distances between isolates of Phytophthora sojae and seven other Phytophthora species were calculated and cluster analysis was made to study generate dendrogram. It showed that Phytophthora sojae was far away from seven other Phytophthora species in genetic distances. Among 15 P sojae isolates, which collected from Heilongjiang Province and Mongolia Region of China, three were identified as race 38, consisting of 20% of the isolates. Undescribed virulence phenotypes constituted 80% of the isolates. A number of these new races were virulent on Harlon, the source of Rps Ia, Williams79, the source of Rpslc, and Williams82, the source ofRpslk. It showed that Phytophthora root rot of soybean is mainly transmitted by soil and debris that naturally infected with pathogen. The seeds can be infected when the young capsule is inoculated with pathogen. When planted, these seeds can result in nearby plants to be infected although they cannot germinate themselves. So far we have no sufficient evidence to testify the seeds naturally infected with the pathogen can transmit this disease.