SSR variability of stem rust pathogen on spring bread wheat in Russia.

Abstract

Wheat stem rust caused by Puccinia graminis f. sp. tritici Erikss. & E. Henning (Pgt), which used to be a harmful disease of winter wheats in the southern part of Russia, has been largely affecting the yield of spring bread wheat in the territories of temperate climate zone since 2009. A total of 222 Pgt isolates were obtained from samples of susceptible cultivars of spring bread wheat in Central and Volga regions, and Omsk and Novosibirsk provinces in 2019. Genotyping of the isolates was carried out at 16 SSR loci. Number of alleles, proportion of heterozygotes and deviation from Hardy-Weinberg equilibrium were determined at each SSR locus. Based on genetic variability of SSR genotypes, it was shown that the Pgt population is subdivided into two large clusters in the territory of Russian temperate climate zone: "European" population (the Central region) and "Asian" one (the Volga region and two main wheat provinces of Western Siberia). Both the Pgt populations are characterized by a mixed mode of reproduction (sexual and clonal), but different sources of inoculum seem to shape a genotype structure within them. A group of Pgt genotypes with high variability, the inbreeding coefficient closed to zero and low observed heterozygosity was revealed among samples from Omsk. Moreover, two singular SSR genotypes identified among the Asian samples of Pgt isolates should attract a special attention in monitoring of stem rust in order to disclose unexpected rapid changes of the pathogen in the corresponding regions and to prevent the disease outbreak.