RESUMO
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 F3 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.