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

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