Snap Bean Breeding for Rust Resistance: Validation of Molecular Markers for The Ur-11 Gene Introgression

Bean rust caused by Uromyces appendiculatus fungus is one of the most destructive diseases reported in temperate, tropical, and sub-tropical regions, affecting the quality and quantity of common bean (Phaseolus vulgaris L) yield. The present study aimed to improve the breeding process of snap beans for rust resistance by identification of inheritance patterns of resistant genes using phenotypic and molecular markers. Among the different genes identified, Ur-11 has wide-spectrum resistance to 89 out of 90 reported races of the rust pathogen. Therefore, the common bean cultivar PI 181996, having the Ur-11 gene was used as the rust resistance donor parent while the local popular snap bean variety Kappetipola nil, susceptible to all locally reported races of the rust pathogen in Sri Lanka, was selected as the susceptible (Recurrent) parent. The introgression of the Ur-11 gene from the cultivar PI 181996 in F1, F2, and BC1F1 populations were phenotypically evaluated using standard screening method while validating random amplified polymorphic DNA (RAPD) marker, OPAC 20 and sequence characterized amplified region (SCAR) marker, SAE 19 and GT 2. Coupling markers (OPAC 20 and GT-2) and repulsion marker (SAE 19) showed 95% and 100% of expected results for phenotypically resistant and susceptible lines respectively. The results showed that the Ur-11 gene in PI 181996 can be tagged with SCAR marker GT-2 and SAE 19 and can be used for markerassisted selection to identify the presence of the Ur-11 gene in the snap bean rust-resistance breeding program. Introgression of the Ur-11 gene helped to develop genetic resistance to local races of the rust pathogen, and the selected progenies could be developed as new resistant snap bean breeding lines.