Structure of Russian Yellow Rust Populations in 2023 As Revealed with Virulence Tests and SSR Markers.

The severity of wheat yellow rust, which is caused by Puccinia striiformis f. sp. tritici (Pst), has increased worldwide in the past decades. The aim of this work was to characterize the virulence and molecular polymorphism of Russian Pst populations in 2023. Leaves with Pst urediniopustules were collected in the Northwestern (Leningrad oblast), North Caucasian (Dagestan and Krasnodar Krai) and Lower Volga (Saratov oblast) regions. Fourteen isogenic lines (AvocetNIL) and 15 differentiator varieties served as virulence testers. Twenty markers recommended by the Global Rust Reference Center were used in microsatellite analysis. SCAR markers (SCP19M: 24a1, 24a2, 26a1, and 26a2) were involved to a search for the invasive races PstS1 and PstS2. Virulence analysis included 70 isolates: 34 from Dagestan, 12 from Krasnodar Krai, 6 from Saratov oblast, and 18 from Leningrad oblast. The genes Yr5, Yr10, Yr15, Yr24, and Yr26 showed a high efficiency. An increase in virulence was noted for the Yr17 gene, which was previously efficient in Russia. No significant changes in virulence frequencies were detected for the other Yr genes. High phenotypic diversity was characteristic of the regional Pst populations in 2023, like in 2019-2022. In total, 45 phenotypes (races) were detected (23 in the Dagestan, 3 in the Krasnodar, 2 in the Saratov, and 17 in the Leningrad collection). Two common virulence phenotypes were observed in the Krasnodar and Leningrad Pst collections. According to the Fst index, the Dagestan, Krasnodar, and Leningrad populations were highly similar, while the Saratov population was moderately differentiated from them. Microsatellite analysis included 55 (28 Dagestan, 18 Leningrad, 6 Krasnodar, and 3 Saratov) isolates. Ten out of 20 loci were found to be polymorphic, each having two alleles. Significant deviations from the Hardy-Weinberg equilibrium were observed for 11 loci. Genotypic diversity of the geographic populations by microsatellite loci was lower than by virulence tests. Twenty multilocus genotypes (MGs) were detected in total (14 in the Dagestan, 7 in the Leningrad, 2 in the Krasnodar, and 1 in the Saratov collection). Common MGs were found in the Dagestan, Krasnodar, and Leningrad Pst collections (MG_1); the Dagestan and Leningrad collections (MG_2); and the Dagestan and Saratov collections (MG_3). Three MGs (MG_4-MG_6) were each observed in at least two isolates; the others, in a single isolate. As in the virulence analysis, the Dagestan, Krasnodar, and Leningrad populations were highly similar in SSR markers (Fst index), and the Saratov population differed moderately. Mantel's test showed a high correlation between the virulence and microsatellite results (r = 0.93). Using the SCAR markers, single PstS2 isolates of were identified in the Leningrad and Dagestan populations, like in previous years. A high variability of the Russian yellow rust populations was thus established in the combined analysis, warranting annual studies of their polymorphism for virulence and the SSR loci. Donors of highly efficient Yr genes were recommended to use in breeding for yellow rust resistance. Lack of differentiation between the North Caucasian and Northwestern Pst samples indicates that a single population occurs in the regions.