Development of Local Breeding Lines for Rust Resistance in the Common Bean (<em>Phaseolus vulgaris</em>) through the Incorporation of Rust-Resistant Genes

Bean rust is one of the major diseases of the common bean (Phaseolus vulgaris) reported in Sri Lanka and at the global level. This study aimed to develop rust-resistant snap bean breeding lines via gene pyramiding assisted by molecular markers. Resistant sources; PI 181996, BelMiNeb-RMR-8, and BelDakMi-RMR-19, enriched with the rust-resistant genes Ur-3 and Ur-11, were selected as donor parents to obtain a wide range of resistance to the rust pathogen. Resistant genotypes were crossed with popular local varieties Kappetipola nil and Galpalama Kalu (Capri) to introgress Ur-3 and Ur-11 resistant genes. Successive F1, F2, and BC (backcross) generations were obtained with the self-pollination and backcrossing processes. Standard phenotypic disease screening methods were applied to identify resistant lines. Phenotypically resistant plants obtained from these crosses were tested with sequence-characterized amplified region (SCAR) markers linked to two rust-resistant genes: SK 14 (linked to Ur-3) and SI 19 (linked to Ur-11). Molecular marker SI-19 showed higher reproducibility (50% to 80%) with the availability of relevant banding patterns for phenotypically resistant F1, F2, and BC1 progenies. However, SK 14 showed lower reproducibility (30–60%) for the same progenies. Approximately 450 genotypes introgressed with rust-resistant genes (Ur-3 and Ur-11)were produced. Among them, four advanced resistant lines obtained from the different cross combinations (Kappetipola nil x BelDakMi-RMR-19, Galpalama Kalu x BelMiNeb RMR-8, Kappetipola nil x PI 181996, and Kappetipola nil x BelMiNeb RMR-8) with preferred agronomic characters were selected for further variety development. All new genotypes will be important for future bean-resistant breeding programs in Sri Lanka.