Molecular Mapping of the Leaf Rust Resistance Gene Rph6 in Barley and Its Linkage Relationships with Rph5 and Rph7

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Abstract
The barley cv. Bolivia carries two leaf rust (Puccinia hordei) resistance genes, Rph2 and Rph6, and is the only known source of the latter gene. A resistant line (Bolivia-Rph6) carrying Rph6 only was obtained in the F4 generation of a cross between cv. Bolivia and the susceptible cv. Bowman via progeny testing with differential isolates of the leaf rust pathogen. Genetic analyses and bulk segregant analysis using amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) markers localized Rph6 on the short arm of barley chromosome 3H at a distance of 4.4 centimorgans (cM) distal from RFLP marker MWG2021 and 1.2 cM proximal from RFLP marker BCD907. The allelic relationship of Rph6 to other leaf rust resistance genes mapping to this region of chromosome 3H (namely Rph5 and Rph7) were tested using crosses among cvs. Magnif 102 (carrying Rph5), Bolivia-Rph6 (Rph6), and Cebada Capa (Rph7). Segregation analyses indicated that Rph6 is allelic to Rph5 and closely linked to Rph7. The data generated from this study will facilitate breeding for leaf rust resistance via marker-assisted selection and provide a starting point for positional gene cloning.