SELF-FERTILE ISOLATES OF PHYTOPHTHORA-INF ESTANS

Self-fertile isolates (SFI) of P. infestans (Mont) de Bary populations from Russia have normal vegetative growth, sporangia, and zoospores. They formed abundant oospores and were stable after cloning. Their sel f-fertility was relative: sometimes they convert to A1 or A2 self-ster ile strains depending on the vegetative compatible group (vcg) of SFI (SFI with vcg1 properties convert to A1, those with vcg2 to A2. At the boundary of colonies of vegetative incompatible isolates, SFI produce more oospores than at the boundary of compatible isolates. Some self- sterile strains are able to convert to SFI under the influence of fung icide metalaxyl. Synthesis of SFI after inoculation of solid or liquid nutrient media with a mixture of A1 and A2 isolates was not successfu l, possibly due to their vegetative incompatibility. Therefore, SFI ar e not heterokaryons of A1 and A2 strains.