Genetic architecture and evolution of stripe rust resistance uncovered using diverse panels of wheat lines and North American Puccinia striiformis f. sp. tritici isolates

Newly emerging highly virulent races of Puccinia striiformis f. sp. tritici (Pst) often defeat deployed resistance genes (Yr), highlighting the need for novel sources of durable resistance. A global diversity panel of 377 spring wheat (Triticum aestivum L.) lines was screened for all-stage resistance (ASR) against 20 diverse Pst isolates at the seedling stage and adult plant resistance (APR) against natural mix of field races. Genome-wide association mapping identified 77 unique Yr loci. Of these, 33 overlapped with the previously reported ~1,100 loci, while 44 were likely novel. Nine mapped Yr loci were effective at the adult plant stage and showed no overlap with the known APR genes. Two wheat lines, though lacked the widely effective Yr5 and Yr15 genes, exhibited resistance to all 20 Pst races at the seedling stage and natural field races at the adult stage, suggesting that they may carry novel, broad-spectrum resistance alleles. APR genes Yr18, Yr29, and Yr36 were detected at low frequencies, indicating that much of the observed resistance may arise from less characterized or novel sources. Wheat improvement had no effect on the frequency of ASR alleles but resulted in a three-fold increase in the frequency of APR alleles, suggesting that the latter were subjected to more consistent breeding selection over time. Our findings underscore the value of combined screening of diverse germplasm with the diverse panels of pathogen races to identify novel sources of broad-spectrum resistance for breeding stripe rust resistant cultivars.