Quantitative Trait Loci Analysis of a Novel Source of Barley Seedling Resistance Effective Against the Virulent North...

Wheat stem rust, caused by the obligate biotrophic fungal pathogen Puccinia graminis f. sp. tritici (Pgt), is an important disease of barley and wheat worldwide. Alarmingly, the Pacific Northwest contains a highly virulent Pgt population on barley. This population includes the Pgt isolate Lsp21, which is virulent on the barley stem rust resistance genes Rpg1, Rpg2, Rpg3, rpg4, Rpg5, and rpg8. The virulence on barley lines containing Rpg1 and the rpg4/Rpg5-mediated resistance locus, when stacked together, is a Pgt virulence profile on barley not previously reported. Thus, this population contains the most virulent Pgt isolates on barley resistance genes characterized worldwide. The Elliot line (PI 592261) was identified from the world barley core collection as containing effective seedling resistance to Pgt isolate Lsp21. To genetically characterize the resistance present in Elliot, 129 recombinant inbred lines were developed by advancing a population from the cross Elliot (resistant) × Palmer (susceptible) to the F₆ generation. The population was phenotyped with Pgt isolate Lsp21 at the seedling stage and genotyped with the Illumina 50K bead express single-nucleotide polymorphism chip, resulting in 7,284 high-quality single-nucleotide polymorphism markers. Two significant resistance quantitative trait loci (QTLs) (EPRpg_4H-1 and EPRpg_5H-1) contributed by Elliot were identified on chromosomes 4H and 5H, respectively. The major QTL, EPRpg_4H-1, is novel, whereas EPRpg_5H-1 localized to a region approximately 9 Mbp distal of the rpg4/Rpg5-mediated resistance locus within a region of the barley genome that contains previously identified stem rust resistance loci. These QTLs should be useful in developing barley cultivars with resistance to the virulent Pacific Northwest Pgt population.