Effect of Metalaxyl on Mating Type of Phytophthora infestans and P. parasitica

Abstract

Two single-oospore isolates (1 A¹ and 1 A²) of P. infestans formed oospores in sectors when grown on medium containing metalaxyl. Single-zoospore cultures obtained from the oospore sector of either isolate consisted of both A¹ and A² mating type. All the single-zoospore cultures from the non-treated isolates had the same mating type as the parent isolate. Metalaxyl also caused mating type change in 3 A¹ isolates of P. parasitica. The conversion of A¹ to A² mating type by metalaxyl in infected host tissues is postulated as a possible origin of A² isolates of P. infestans in Europe.