Pathotype characterization, frequency shift, and geographical distribution of <i>Puccinia striiformis</i> f. sp. <i>tritici</i> in north India from 2019 to 2024 and identification of genetic resistance in cultivated wheat varieties

Yellow (stripe) rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a serious threat to wheat crops grown in northern India. This study involved surveying wheat fields in North Indian states over five consecutive cropping seasons (2019-2024) to collect yellow rust samples, deciphering genetic diversity among the pathotypes, and identifying the sources of rust resistance. A total of 866 yellow rust samples were collected and analyzed using 30 Indian differentials to identify Pst pathotypes and understand their virulence spectrum. Phenotypically, eleven distinct Pst pathotypes 46S119, 110S119, 238S119, 78S84, 110S84, 46S103, 47S103, 7S0, 6S0, 79S68, and 14S64 were identified . Overall, pathotype 238S119 was the most frequent (44.9%), followed by pathotype 110S119 (26.0%) and 46S119 (23.6%). Resistance genes Yr5, Yr10, Yr15, Yr16, Yr24, Yr32, and YrSP were effective against the Pst population. Genetic diversity among the pathotypes was determined using 25 polymorphic SSR markers. A total of 68 alleles were amplified, with an average of 2.72 alleles per locus. Polymorphic information content (PIC) and expected heterozygosity (Hexp) values ranged from 0.24 to 0.37 and from 0.28 to 0.50, respectively. Principal component analysis (PCA) explained 37.35% and 15.39% variance in horizontal (PC1) and vertical (PC2) axes, respectively. Of the 43 screened wheat varieties, only PBW725, PBW757, PBW761, and PBW869 were resistant (infection types: 0; or ;) to all Pst pathotypes. The field resistance of these varieties is attributed to Yr15 and uncharacterized seedling or adult plant rust resistance. These findings are crucial for rust resistance breeding and the deployment of resistant varieties in the field to manage yellow rust effectively.