INCREASED GENOTYPIC DIVERSITY VIA MIGRATION AND POSSIBLE OCCURRENCE OF SEXUAL REPRODUCTION OF PHYTOPHTHORA-INFESTANS IN POLAND

Genetic changes in populations of Phytophthora infestans in Poland were determined by analyzing 247 isolates collected from 1985 through 1991. All isolates collected from 1985 through 1987 were Al mating type and consisted of a single clonal lineage based on allozyme and DNA fingerprint analyses. The appearance of new genotypes in Poland, presumably due to migration, was first detected in 1988 with the identification of the A2 mating type, three allozyme, and a number of DNA fingerprint alleles that had not been detected previously. This migration resulted in dramatic changes. Gene and genotype diversity and the frequency of uniquely detected genotypes all increased beginning in 1988, and reached a peak in 1990. A new clonal genotype, first detected in 1988, increased in frequency and made up almost 50% of all isolates collected in 1991. In contrast, the old clonal lineage that dominated populations from 1985 to 1987 was not detected after 1988. The frequency of A2 isolates reached 44% by 1989, then decreased to 12% in 1991. There was almost no genetic differentiation among regions within Poland. In addition to the major impact caused by migration, four lines of evidence indicated that sexual reproduction also might have occurred in Poland: genotypes at most loci were in Hardy-Weinberg equilibrium; there was no genetic differentiation between A1 and A2 isolates; there was a high proportion of genetically unique individuals that would not be expected in populations restricted to asexual reproduction; and a new genotype (90/90) at the allozyme locus glucose-6-phosphate isomerase was detected that could have been produced from sexual recombination.