NUCLEAR-DNA CONTENT, ALLOZYME PHENOTYPES AND METALAXYL SENSITIVITY OF PHYTOPHTHORA-INFESTANS FROM JAPAN

Thirty isolates of Phytophthora infestans from all districts of Japan (15 of A1 mating type and 15 of A2 mating type) were analyzed for nuclear DNA content (ploidy), allozymes and response to metalaxyl. Twenty-one isolates produced sufficient zoospores for analysis of nuclear DNA content; all A1 mating type isolates were putative tetraploids, while A2 isolates were all putative triploids. Each mating type was strongly associated with specific phenotypes at the polymorphic allozyme loci Gpi (glucosephosphate isomerase) and Pep (peptidase). All A2 isolates had the phenotype Gpi 100/100 Pep 100/100, whereas the A1 isolates were either Gpi 86/100 Pep 92/100 or Gpi 86/100 Pep 100/100. Metalaxyl resistance was only noted among isolates of A2 mating type. Our data suggest that the 1988 Japanese P. infestans population was likely comprised of two separate non-interbreeding subpopulations of opposite mating type.