Pathogenic and genetic diversity of Puccinia triticina from triticale in Poland between 2012 and 2015

Variation among Puccinia triticina isolates collected from triticale in Poland between 2012 and 2015 was studied based on virulence and simple sequence repeat (SSR) markers. Two hundred and forty-two single-uredinial isolates from four geographically separated locations were tested for virulence against 33 near-isogenic Thatcher lines containing known Lr resistance genes, and their molecular genotypes were characterized with 34 SSR markers. Structure and relationships of the regional and annual populations of P. triticina were analysed using an assignment-based approach for both the virulence and SSR data. The molecular marker analysis was based on two different models of SSR evolution: the stepwise mutation model with a variable mutation rate (SMMv) and the infinite alleles model (IAM). A highly significant deviation from Hardy–Weinberg equilibrium among SSR genotypes, a high proportion of heterozygotes, and a moderate association of relationships between virulence phenotypes and SSR genotypes were consistent with the occurrence of clonal lineages of related races within the population. While the results suggest that genetic drift and mutation affect variation within the pathogen population, it seems that migration has the most significant role in shaping the population structure of P. triticina occurring on triticale in Poland.