Genome Wide Association Study of Seedling and Adult Plant Leaf Rust Resistance in a Resistance Enriched Association Mapping Panel Consisting of Predominantly Wheat Cultivars or Lines from the Americas.

Leaf rust is an important disease, threatening wheat production annually. Identification of resistance genes or QTLs for effective field resistance, could greatly enhance our ability to breed resistant varieties. In this study, we utilized a genome wide association study (GWAS) approach and the wheat iSelect 90K SNP array to explore resistance QTLs in 338 wheat cultivars and breeding lines from public and industrial sectors that are predominately based in the Americas. A total of 46 QTLs were identified (for field and seedling traits); approximately 30 of them confer field resistance in varying degrees. The most significant 10 QTLs for field resistance explained 29% of the total variation, while the 10 best QTLs for seedling resistance to different races explained 28-32% of the variation after correcting for population structure. Two potentially novel QTLs (QLr.umn-1AL, QLr.umn-4AS) were designated. Both of them contributed to field resistance. QLr.umn-1AL also contributed to seedling resistance against a mixture of races. Identification of novel QTLs and validation of previously identified genes/QTLs for seedling and especially adult plant resistance will enhance our understanding of leaf rust resistance and assist breeding for resistant wheat varieties. We also developed small utility computer programs to automate field and seedling rust phenotype data conversions.