Rpg7: A New Gene for Stem Rust Resistance from Hordeum vulgare ssp. spontaneum.

Wheat stem rust (causal organism: Puccinia graminis f. sp. tritici; Pgt) is an important fungal disease that causes significant yield losses in barley. The deployment of resistant cultivars is the most effective means for controlling this disease. Stem rust evaluations of a diverse collection of wild barley (Hordeum vulgare ssp. spontaneum) identified two Jordanian accessions (WBDC094 and WBDC238) with resistance to a virulent pathotype (Pgt-HKHJC) from the USA. To elucidate the genetics of stem rust resistance, both accessions were crossed to the susceptible landrace Hiproly. Segregation ratios of F2 and F3 progeny indicated that a single dominant gene confers resistance to Pgt-HKHJC. Molecular mapping of the resistance locus was performed in the Hiproly x WBDC238 F2 population based on 3,329 SNP markers generated by genotyping by sequencing. Quantitative trait locus (QTL) analysis positioned the resistance gene to the long arm of chromosome 3H between the physical/genetic positions of 683.8 Mbp/172.9 cM and 693.7 Mbp/176.0 cM. Since this resistance gene is novel, it was assigned the new gene locus symbol of Rpg7 with a corresponding allele symbol of Rpg7.i. At the seedling stage, Rpg7 confers resistance against a number of other important Pgt pathotypes from the USA (MCCFC, QCCJB, and TTTTF) and Africa (TTKSK) as well as an isolate (92-MN-90) of the rye stem rust pathogen (P. graminis f. sp. secalis) from Minnesota. The resistance conferred by Rpg7 can be readily transferred into breeding programs due to its simple inheritance and clear phenotypic expression.