Association Mapping for Leaf and Stem Rust Resistance Using Worldwide Spring Wheat Collection

Wheat leaf rust (caused by Puccinia triticina Eriks.) and stem rust (caused by P. graminis f. sp. tritici) are among the most common, widespread and devastating diseases in Egypt and worldwide. A total of 2111 spring wheat accessions (882 landraces; 493 breeding lines; 419 cultivars and 317 with uncertain classification) were obtained from a single plant selection from wheat (Triticum aestivum L.) core collection. The wheat accessions were genotyped through the Triticae Coordinated Agriculture Project using the Illumina iSelect 9K wheat array at the USDA-ARS genotyping laboratory in Fargo, ND, USA. The primary objectives of this study were to: 1. Evaluate the spring wheat collection for stem and leaf rust resistance at adult plant stage under field conditions and detect new sources of resistance, and 2. Identify potential QTLs linked with stem or leaf rust resistance genes. Our results indicated that 6.96% (147 accessions) and 5.87% (124 accessions) of the tested accessions were found to be resistant to leaf and stem rust, respectively. Genome-wide association mapping (GWAS) was used to identify QTLs associated with leaf and stem rust resistance genes. Overall GWAS results demonstrated that 46 SNP markers significantly linked with stem rust resistance, while 36 SNP markers were found to be significantly linked with leaf rust resistance. Most of the significant SNP markers were co-located with previously identified stem rust resistance genes (Sr1RSAmigo, Sr21, SrND643, Sr35, Sr52, and Sr22) and leaf rust resistance genes (trp-1,Lr 11, Lr 52 and Lr 47). Future work will focus on crossing several leaf and stem rust resistant accessions to pyramid genes and to develop nested association mapping populations to incorporate multiple resistance genes into elite breeding wheat lines.