Genetic analysis of resistance to stripe rust in durum wheat (Triticum turgidum L. var. durum)

Abstract

Stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst), is an important disease of durum wheat (Triticum turgidum L. var. durum) worldwide. Epidemics of stripe rust can reduce wheat yield more than 70% if infection occurs at early growth stages. Although fungicides can effectively prevent disease development and yield loss, use of resistant cultivars is the best approach for managing stripe rust. Currently, there is a lack of information on the genetic basis of resistance to stripe rust in durum wheat. The objective of this research was to characterize adapted durum wheat germplasm for resistance to prevalent races of stripe rust in Western Canada, to evaluate the inheritance of resistance, and to identify DNA markers associated with stripe rust resistance to assist in breeding for disease resistance. Field and phytotron experiments were assessed on a core collection of 92 diverse cultivars and breeding lines collected from major durum wheat breeding programs globally. The 92 lines were genotyped using a 90,000 single-nucleotide polymorphism (SNP) iSelect assay, which generated 13,539 polymorphic markers to perform association mapping. After adjustment for population structure, a major QTL for stripe rust resistance was identified on the long arm of chromosome 7BL. In the second study, a mapping population consisting of 155 double haploid durum wheat lines from the cross Kofa (susceptible) x W9262-260D3 (moderately resistant) were evaluated for stripe rust resistance in field and greenhouse experiments. Mendelian analysis revealed the presence of at least two resistance genes. Subsequent quantitative trait locus (QTL) analysis was performed using a genetic map consisting of 4,251 polymorphic markers spanning all 14 durum wheat chromosomes. Two significant QTLs were identified on chromosome 5BL (QYr.usw-5B) and 7BL (QYr.usw-7B), and explained 10.7 and 30.4% of the phenotypic variance, respectively. Both QYr.usw-5B and QYr.usw-7B are complementary genes and act together to express resistance. The QTL located on chromosome 7BL, identified in the DH mapping population, was in the same genetic interval as that identified using association mapping. These insights into the genetic basis of stripe rust resistance can be applied to enhance all-stage and durable resistance to stripe rust in durum wheat.