Virulence Structure and Genetic Diversity of Puccinia striiformis f. sp. tritici in Northwest and Southwest China

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), threatens global wheat production. In China, wheat stripe rust generally occurs in northwest and southwest epidemic regions; still, the genetic relationship of Pst populations between these regions is largely unclear. We characterized the virulence structure, genetic diversity, and migration routes by analyzing 202 Pst isolates from the southwestern provinces of Guizhou (GZ) and Sichuan (SC) and northwestern provinces of Shaanxi (SX), Gansu (GS), and Xinjiang (XJ) in 2023. Isolates were phenotyped on 21 Chinese differential hosts and 20 monogenic lines and genotyped using 22 KASP-SNP markers. Phenotype tests showed that CYR34 (7.92%) and G22-316 (6.44%) were the predominant races, with different occurrence frequencies in different regions. Virulence analysis showed that all isolates remained avirulent to Yr5 and Yr15, and virulence to Yr10, Yr1, and Yr9 was generally below 40%. In contrast, high virulence frequencies (>80%) were observed against Yr6, Yr7, Yr17, Yr18, Yr32, Yr43, Yr44, YrTr1, and YrExp2 in multiple regional populations. Genotypic analysis revealed that a total of 156 multilocus genotypes were identified, and genotypic diversity in the XJ population was the highest but exhibited limited gene flow (Nm < 1) with other populations. SC may serve as a bridge connecting Pst populations of southwestern (SC and GZ) and northwestern (SX, GS, and XJ) provinces, showing frequent gene exchange (Nm > 4) with other populations. These findings enhance the understanding of regional differentiation and diversification of Pst in southwest and northwest China.