Identification, Validation, and Evidence of Frequent Exchange of HD Alleles in Puccinia striiformis Reveal High Genetic Diversity of Chinese Stripe Rust Population

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive wheat disease with global prevalence, in which novel races of Pst may arise through sexual recombination. Direct evidence of the role of mating-type (MAT) genes in sexual recombination and genetic diversity in Pst populations has been scarce. Herein, we identified 11 pairs of homeodomain (HD) alleles in Pst and two pairs of HD alleles in P. striiformis f. sp. hordei (Psh). Through selfing and crossing experiments on barberry as alternate hosts, we infer the mating system of Pst to be tetrapolar and responsible for sexual genetic recombination mediated by the HD genes. The identification and genetic analysis of HD genes in Chinese Pst populations revealed greater genetic diversity in the northwest oversummering hotspot. Overall, these results demonstrate that sexual recombination via MAT alleles drives genetic diversity, providing crucial insights for disease control in regions where sexual reproduction occurs.