Identification of LOCI for Resistance to STEM Rust in a Tetraploid Wheat Collection

Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is one of the most destructive diseases of wheat. Races of the pathogen in the “Ug99 lineage” are of international concern due to their virulence for widely used stem rust resistance genes and spread throughout Africa and into the Middle East. Disease resistant cultivars provide one of the best means for controlling stem rust. To identify quantitative trait loci (QTL) conferring resistance to 5 different stem rust races at the seedling stage, we evaluated an association mapping (AM) panel consisting of 230 tetraploid wheat (T.turgidum L., 2n=4x=28; AABB genome) accessions under greenhouse conditions.The tetraploid wheat collection includes 128 durum wheat varieties plus 102 wild and domesticated accessions. Each accession was genotyped with the wheat 90k iSelect Infinium SNP assay, and more than 20,000 SNPs were identified across the tetraploid genotypes. A high level of phenotypic variation was observed in response to all of the Pgt races in the AM panel, allowing for genome-wide association mapping of resistance QTL in wild, landrace, and cultivated tetraploid wheats. GLM and MLM models were considered for AM, and QTL on many chromosomes were identified. Most of the identified resistance loci were coincident with previously identified rust resistance genes; however, some may be novel. Moreover, loci for resistance to multiple races were observed, together with race-specific QTL.

This study was supported by the Italian Ministry of Foreign Affairs and International Cooperation, with the specialgrant RES-WHEAT.