Inheritance, differential expression, and candidate gene analyses for Avr2 in Phytophthora sojae

Phytophthora sojae is an oomycete responsible for seed, root and stem rot of soybean plants. Managing this disease relies on growing soybean cultivars with race-specific resistance (Rps) genes that deliver complete host immunity in the presence of corresponding pathogen avirulence (Avr) effector proteins. The aims of this study were to characterize virulence towards Rps2 among different P. sojae strains, track the inheritance of this trait, and attempt to identify an Avr2 gene. Fifteen P. sojae strains were tested for virulence towards Rps2 and crosses were performed between selected virulent and avirulent strains to follow the inheritance of virulence. Although parental strains were consistent in their virulence phenotype, many progeny were unstable. Of two candidate genes for Avr2 tested, neither showed co-segregation with the Rps2virulence trait. Overall, results indicate that virulence towards Rps2 is inherited in a nonMendelian fashion; the factors responsible could include epistasis, gene conversion, or other epigenetic phenomena.