Virulence and Diversity of Puccinia striiformis f. sp. tritici Populations in Northwestern and Southwestern Oversummering Regions of China

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is the most devastating fungal disease affecting wheat in China, particularly in the northwestern (Qinghai, Gansu, and Ningxia) and southwestern (Sichuan, Yunnan, and Guizhou) oversummering regions. In this study, 302 isolates collected from these six provinces were analyzed using virulence testing and single-nucleotide polymorphism (SNP) markers. Virulence testing on 19 Chinese differentials identified 38 previously reported and 49 novel races. CYR34 was the most prevalent race in both the northwestern and southwestern oversummering regions, with frequencies of 24.00% and 21.05%, respectively. In the northwestern oversummering region, the prevalence of CYR32 (10.70%) and G22-14 (10.67%) was nearly identical, whereas in the southwestern oversummering region, CYR32 (13.20%) and G22-14 (9.87%) exhibited significant differences. Additionally, 112 races were identified using 18 Yr single-gene differentials, although none of the isolates showed virulence to either Yr5 or Yr15. The virulence diversity of Pst populations was greater in the southwestern than in the northwestern oversummering region, as indicated by the differential sets. Further molecular analysis with 20 pairs of polymorphic KASP-SNP markers confirmed that the southwestern Pst population exhibited higher genetic diversity than the northwestern population. Both virulence phenotypes and genotype data demonstrated that the Pst population was more diverse in the southwestern oversummering region, despite presence of the exchange of Pst sources between regions. In addition, mutant isolates indicating resistance to tiadimefon fungicide were detected in both regions. This study provides a systematic comparison of Pst populations in the northwestern and southwestern oversummering regions based on virulence phenotyping and SNP marker genotyping, and the findings are crucial for the integrated management of wheat stripe rust in these regions and across the country.