Highly Diverse Phytophthora infestans Populations Infecting Potato Crops in Pskov Region, North-West Russia

There is limited understanding of the genetic variability in Phytophthora infestans in the major potato cultivation region of north-western Russia, where potato is grown primarily by small households with limited chemical treatment of late blight. In this study, the mating type, sensitivity to metalaxyl, and genotype and population genetic diversity (based on 12 simple sequence repeat (SSR) markers) of 238 isolates of P. infestans from the Pskov region during the years 2010–2013 were characterized. The aim was to examine the population structure, phenotypic and genotypic diversity, and the prevalent reproductive mode of P. infestans, as well as the influence of the location, time, and agricultural management practices on the pathogen population. The frequency of the A2 mating was stable over the four seasons and ranged from 33 to 48% of the sampled population. Both mating types occurred simultaneously in 90% of studied fields, suggesting the presence of sexual reproduction and oospore production in P. infestans in the Pskov region. Metalaxyl-sensitive isolates prevailed in all four years (72%), however, significantly fewer sensitive isolates were found in samples from large-scale conventional fields. A total of 50 alleles were detected in the 141 P. infestans isolates analyzed for genetic diversity. Amongst the 83 SSR multilocus genotypes (MLGs) detected, 65% were unique and the number of MLGs varied between locations from 3 to 20. These results, together with the high genotypic diversity observed in all the locations and the lack of significance of linkage disequilibrium, suggest that sexual recombination is likely responsible for the unique MLGs and the high genetic diversity found in the Pskov region population, resembling those of north-eastern European populations

Population changes and phenotypic diversity of phytophtora infestans isolates from Estonia and Finland

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The variability of Phytophthora infestans isolates collected from Estonian islands in the Baltic Sea

Knowledge of a pathogen's genetic variability and population structure is of benefit to effective disease management. In this study, 193 isolates of Phytophthora infestans collected from three Estonian islands, were characterized over three years using SSRs marker data complemented by information on their mating type and resistance to metalaxyl. In combination with SSR marker data from samples in the neighbouring Pskov region of north west Russia, the impact of regional and landscape structure on the level of genetic exchange was also examined. Among the Estonian islands 111 P. infestans isolates, forty-nine alleles were detected among twelve SSR loci, and 59 SSR multilocus genotypes (MLGs) were found, of which 64% were unique. The genetic variation was higher among years than that among islands, as revealed by AMOVA. The frequency of metalaxyl-resistant isolates increased from 9% in 2012 to 30% in 2014, and metalaxyl resistant was most frequent among A1 isolates. The test for isolation by distance among the studied regions was not significant, and coupled with the absence of genetic differentiation revealed gene flow, and the absence of local adaptation. The data are consistent with a sexual population in which diversity is driven by an annual germination of soil-borne oospores. The absence of shared genotypes over the years has important implications when it comes to the management of disease. Such population diversity can make it difficult to predict the nature of the outbreak in the coming year as the genetic makeup are different for each year.</p