SSR Variability of Stem Rust Pathogen on Spring Bread Wheat in Russia.

Wheat stem rust, caused by Puccinia graminis f. sp. tritici, which used to be a harmful disease of winter wheat in the southern part of Russia, has been largely affecting the yield of spring bread wheat in the territories of the temperate climate zone since 2009. In total, 222 P. graminis f. sp. tritici 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 simple-sequence repeat (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 P. graminis f. sp. tritici population is subdivided into two large clusters in the territory of the Russian temperate climate zone: the "European" population (the Central region) and the "Asian" one (the Volga region and two main wheat provinces of Western Siberia). Both of the P. graminis f. sp. tritici 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 P. graminis f. sp. tritici 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 P. graminis f. sp. tritici isolates should attract special attention in the monitoring of stem rust in order to disclose unexpected rapid changes of the pathogen in the corresponding regions and to prevent disease outbreak.

Primary hexaploid synthetics: Novel sources of wheat disease resistance.

Climate change is leading to increased occurrence of and yield losses to wheat diseases. Managing these diseases by introducing new, effective and diverse resistance genes into cultivars represents an important component of sustainable wheat production. In 2016 and 2017 a set of primary hexaploid synthetic wheat was studied under high disease pressure: powdery mildew, leaf and stem rust in Omsk; Septoria tritici and S. nodorum in Moscow. A total of 28 synthetics (19 CIMMYT synthetics and 9 Japanese synthetics) were selected as having combined resistance to at least two diseases in both years of testing. Two synthetics (entries 13 and 18) originating from crosses between winter durum wheat Ukrainka odesskaya-1530.94 and various Aegilopes taushii accessions, and four synthetics (entries 20, 21, 23 and 24) from cross between Canadian durum wheat Langdon and Ae. taushii were resistant to all four pathogens. Pathological and molecular markers evaluation of resistance suggests presence of new genes and diverse types of resistance. The novel genetic sources of disease resistance identified in this study can be successfully utilized in wheat breeding.