Oospores in cultures of Phytophthora infestans resulting from selfing induced by the presence of P. drechsleri isolated from blighted potato foliage

A Phytophthora species isolated from blighted potato foliage was identified as P. drechsleri , mating type A2. The isolate was found to be weakly pathogenic on a range of hosts. Pairings in vitro of P. drechsleri with British isolates of P. infestans mating type A1 when separated by a polycarbonate membrane resulted in selfed oospores of both species. The possibility that A1 P. infestans is induced to self in the field and the genetic consequences of such selfing are discussed.