Virulence and Molecular characterization reveal sign of sexual genetic recombination of Puccinia striiformis f. sp. tritici and Puccinia striiformis f. sp. hordei in Tibet.

Stripe rust of wheat and stripe rust of barley are caused by different formae speciales, Puccinia striiformis f. sp. tritici ( Pst ) and P. striiformis f. sp. hordei ( Psh ), respectively. To understand the relationship between the populations of the two formae speciales, a total of 260 P. striiformis isolates, including 140 from barley and 120 from wheat collected from Linzhi, Tibet, China from 2018 to 2020, were tested on 18 barley and 13 wheat genotypes, and genotyped with 26 single-nucleotide polymorphism (SNP)-based Kompetitive Allele Specific PCR (KASP) markers. As a result, 260 isolates were identified as 83 virulence phenotypes (VPs), 115 of which as 9 VPs and can only infect wheat (wheat population), 111 as 54 VPs and can only infect barley (barley population), and 34 belonged to 20 VPs that can attack both wheat and barley (mixed population). Of 149 multi-locus genotypes (MLGs) that were identified, 92 were from wheat, 56 from barley, and 1 from both wheat and barley. Phenotypic and genotypic diversity was high in the populations from wheat and barley. Low linkage disequilibrium was found in most of sampling sites of both crops, indicating strong signs of sexual reproduction (| ¬r(_)d | = 0.022-0.393, P = 0.004-0.847). Whereas, it was not observed in the overall population (wheat and barley sources), and the wheat, barley, and mixed populations, which may be due to complex composition of isolates. Population structure analyses based on phenotyping and SNP-KASP genotypes supported the separations of the two formae speciales. However, MLGs and clusters containing isolates from both wheat and barley indicated obvious indication of sexual genetic recombination between the two formae speciales. The results of the study provided an insight into evolution of Pst and Psh , and showed the importance of management strategy for stripe rust of wheat and barley in regions where both crops are grown.