QTL analysis of wheat leaf rust resistance in the ‘Lakin’ x ‘Roelfs F2007’ backcross population

Abstract

Leaf rust, caused by the fungus Puccinia triticina, is a major disease of wheat in North America. Breeding efforts to achieve resistance have historically been plagued by a cycle in which an all-stage resistance gene is discovered, deployed, and rapidly defeated, thus wasting valuable sources of resistance. Adult-plant resistance genes, however, can potentially contribute to race-nonspecific resistance to the pathogen which is durable for many years. In this study, the moderately susceptible Kansas winter wheat cultivar, ‘Lakin’, was backcrossed to the CIMMYT-developed spring wheat cultivar, ‘Roelfs F2007’, which is known to possess very good adult-plant resistance (APR) to leaf rust. The 297 BC₁F₆-derived progeny of this cross were screened for resistance in five location-years at field nurseries in Kansas and Texas, as well as in two greenhouse studies. Genotyping-by-Sequencing (GBS) generated 2,541 high-quality genome-wide markers used for the construction of a linkage map covering all 21 chromosomes. Quantitative trait locus (QTL) analysis identified reproducible APR QTLs on chromosome arms 3BS, 5DS, 7BS, and 7BL. Three QTLs contributed by Roelfs F2007 appeared to correspond to locations of known APR genes Lr74 (3BS), Lr78 (5DS), and Lr68 (7BL). The APR QTL on 7BS contributed by Lakin appeared to be novel. Together, the four QTLs accounted for 45% and 46% of the variation in least-squares means for disease severity and infection type, respectively. These results confirm that both Roelfs F2007 and Lakin contain APR loci which may be used in breeding for resistance to infections by P. triticina.