Genome-Wide Association Study of a Worldwide Collection of Wheat Genotypes Reveals Novel Quantitative Trait Loci for Leaf Rust Resistance

Abstract

The emergence of new virulent Puccinia triticina races requires a continuous search for novel sources of resistance to combat leaf rust (LR) disease Twenty-two wheat genotypes resistant to four P. triticina races were identified in this study A genome-wide association study detected 11 quantitative trait loci for LR resistance; five of them were detected on genomic regions where no LR resistant genes have been detected. Wheat (Triticum aestivum L.) production worldwide is being challenged by several biotic and abiotic factors. Leaf rust (LR), caused by Puccinia triticina, is a major biotic constraint of wheat production worldwide. Genetic resistance is the most efficient and cost-effective way to control LR. Seventy-nine LR resistance genes have been identified to date but the frequent emergence of new virulent P. triticina races every year demands a constant search for new sources of resistance with novel quantitative trait loci (QTL) or genes. The objectives of this study were to identify putative novel sources of effective resistance against the current prevalent races of P. triticina in the southeast United States and to map genomic loci associated with LR resistance via a genome-wide association study (GWAS) approach. Evaluation of 331 diverse wheat genotypes against four prevalent P. triticina races (MFGKG, MBTNB, MCTNB, and TCRKG) revealed that the majority of the genotypes were susceptible and only 22 genotypes (6.6%) were resistant to all four P. triticina races. The GWAS detected 11 QTL on nine chromosomes for LR resistance. Of these, six QTL were identified in the vicinity of known genes or QTL; therefore, more studies are warranted to determine their relationship. Five QTL (QLr.uga-1AL, QLr.uga-4AS, QLu.uga-5AS, QLr.uga-5AL, and QLr.uga-7AS) were identified on genomic regions where no LR resistance genes have been identified in wheat, representing potential novel loci for LR resistance. The highly resistant wheat genotypes and novel QTL reported in this study could be used in breeding programs to improve LR resistance.