*Corresponding authors: katharina.jung@ieu.uzh.ch; nasuda.shuhei.5z@kyoto-u.ac.jp; kentaro.shimizu@uzh.ch

The global spread of aggressive races of yellow rust (Puccinia striiformis f.sp. tritici) poses a significant threat to wheat production worldwide. To address this challenge, genetic loci associated with yellow rust resistance were identified, and the role of the near-Himalayan region in the conservation and evolution of resistance loci was explored in this study.

A nested association mapping (NAM) population (1060 recombinant inbred lines (RILs)) was utilized. These RILs were derived from the common paternal parent Norin 61, crossed with a diverse set of maternal lines, which comprises 13 traditional and modern Asian bread wheat varieties originating from around the Himalayan Mountains, China, and Japan. The overlap between the origins of these varieties and the proposed origin of the yellow rust pathogen adds interest to this study. Moreover, most of the Asian germplasm exhibits significant yet underrepresented genetic diversity.

Extensive field trials spanning two years and two locations were conducted for both parental lines and Recombinant Inbred Lines (RILs) under intense artificial disease pressure created through the establishment of artificial epidemics.

A combined mapping approach for the whole NAM population was employed to identify Quantitative Trait Loci (QTL) in each environment, implementing IBD-based mixed models specific for multi-parent populations (statgenMPP). The analysis is based on a consensus map that spans 3,699 cM, including 3757 SNP markers with unique map positions. Our findings underscore the prevalence of yellow rust resistance within traditional wheat varieties situated in high-disease pressure areas south of the Himalayan mountains and in the lowlands of China.

The detection of two well-known rust resistance genes (Lr34/Yr18 and Lr67/Yr46) validates our results and their respective origins in China and Pakistan. Additionally, the identification of two potentially novel resistance genes on chromosome 3D and 5B presents promising candidates for integration into breeding programs.

By utilizing diverse wheat varieties in the NAM population originating from key geographic regions, we have gained valuable insights into the geographic distribution and evolution of yellow rust resistance.