Inheritance and Characterization of Rph27: A Third Race-Specific Resistance Gene in the Barley Cultivar Quinn

The barley cultivar Quinn was previously reported to carry two genes for resistance to Puccinia hordei, viz. Rph2 and Rph5. In this study, we characterized and mapped a third resistance gene (RphCRQ3) in cultivar Quinn. Multipathotype testing in the greenhouse on a panel of barley genotypes previously postulated to carry Rph2 revealed rare race specificity in four genotypes in response to P. hordei pathotype (pt.) 222 P+ (virulent on Rph2 and Rph5). This suggested either the presence of a race-specific allele variant of Rph2 or the presence of an independent uncharacterized leaf rust resistance locus. A test of allelism on 1,271 F2 Peruvian (Rph2)/Quinn (Rph2 + Rph5) derived seedlings with P. hordei pt. 220 P+ (avirulent on Rph2 and virulent on Rph5) revealed no susceptible segregants. To determine whether the race-specific resistance in Quinn was due to an allele of Rph2 on chromosome 5H or a third uncharacterized resistance gene, we tested the Peruvian/Quinn F-3 population with 222 P+ and observed monogenic inheritance. Subsequent bulked segregant analysis indicated the presence of complete in-phase marker fixation near the telomere on the short arm of chromosome 4H, confirming the presence of a third resistance locus in Quinn in addition to Rph2 and Rph5. In accordance with the rules and numbering system of barley gene nomenclature, RphCRQ3 has been designated Rph27.