High density genetic mapping of stripe rust resistance in a ‘Strongfield’ / ‘Blackbird’ durum wheat population

Resistance breeding is an effective strategy against wheat stripe (yellow) rust caused by Puccinia striiformis f. sp. tritici (Pst). To identify and map quantitative trait loci (QTL) associated with stripe rust resistance, a durum wheat doubled haploid population (n = 87) derived from ‘Strongfield/Blackbird’ was evaluated for disease severity near Toluca, Mexico (2017–2019) and Lethbridge, Canada (2016–2019). The population was genotyped with the wheat 90 K Illumina iSelect single nucleotide polymorphism (SNP) array and simple sequence repeat (SSR) markers, and QTL analysis was performed with MapQTL 6. We identified stripe rust-resistance QTL contributed by ‘Blackbird’ on chromosomes 3A (2 loci, designated QYr.spa-3A.1, QYr.spa-3A.2) and 5B (QYr.spa-5B), and ‘Strongfield’ on 2B (QYr.spa-2B). All seem to represent QTL not reported previously. The QYr.spa-3A.2 was most consistently effective against Pst races across the Lethbridge and Toluca nurseries. With a LOD value of 4.9, QYr.spa-3A.2 explained a maximum phenotypic variation of 22.7% observed at the Toluca 2019 nursery. The QYr.spa-2B from ‘Strongfield’ and QYr.spa-3A.1 from ‘Blackbird’ expressed in multiple years at Toluca but were not detected at Lethbridge. QYr.spa-5B was identified in the Lethbridge 2016 environment. The identified QTL should be valuable in diversifying resistance genes used in breeding durum wheat cultivars with stripe rust resistance. ‘Blackbird’ was particularly useful for introducing the new QTL QYr.spa-3A.2 resistance that is effective in Canada and Mexico into traditional durum wheat germplasm. SNP markers associated with QTL will have application in marker-assisted breeding of resistance to Pst in durum wheat.