Isoenzyme polymorphism and segregation in isolates of Phytophthora infestans from Japan

Isoenzyme variation of 198 isolates of Phytophthora infestans collected from many locations in Japan during 1987–90, and of four pre‐1987 isolates, was examined using starch gel electrophoresis. A previously unreported allele at malic isoenzyme locus/ME (90) was observed. An association between mating types and isoenzyme genotypes at three isoenzyme loci, glucosephosphate isomerase (GPI‐1), peptidase (PEP‐1) and ME, was found. At PEP‐1, the A2 isolates from Japan had a previously unreported genotype (96/96). Normal segregation at the malic isoenzyme locus occurred in a cross of Japanese and Mexican parents. The results provide evidence of a change in the population genetic structure of P. infestans in Japan.