The structure of mating type, virulence, metalaxyl resistance of Phytophthora infestans in a long-term phenotypic study in distinct location in Eastern Estonia

The potato late blight pathogen Phytophthora infestans was collected from a region of Eastern Estonia during a period of seven years (2001–07). In total, 180 isolates were assessed for virulence, 133 for mating type and 171 for metalaxyl resistance. The average frequencies of mating types A1 and A2 were 59% and 38%, respectively. Considerable differences in the proportion of A1 and A2 between years were found. The data indicate that, in the Estonian population of P. infestans, both mating types occurred simultaneously within fields, with the potential for sexual recombination. The relatively rare virulence factors 5 and 9 and the less frequent virulence factors 2, 6, 8 were found in all studied years. Racial diversity, calculated with normalised Shannon diversity index, was high (0.71) but did not show significant differences between different collection years. The data showed that the response of isolates to metalaxyl did not depend on the year of collection. Still, the interaction was considerable between response to metalaxyl and the year, which means that the proportion of sensitive isolates increased and the proportion of intermediate isolates decreased notably compared to other concentration variants. By contrast, metalaxyl resistant isolates remained at a similar level during the seven year period.