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Molecular Mapping and Marker-Assisted Selection of Genes for Septoria Speckled Leaf Blotch Resistance in Barley

Septoria speckled leaf blotch (SSLB), caused by Septoria passerinii, has emerged as one of the most important foliar diseases of barley in the Upper Midwest region of the United States. To map and tag genes for SSLB resistance, we developed two populations derived from the resistant accessions CIho 4780 and CIho 10644 and the susceptible malting cv. Foster. Segregation analysis of F₂ plants or F_2:3 families from the Foster/CIho 4780 and Foster/CIho 10644 populations revealed that a single dominant gene conferred resistance at the seedling stage. Bulked segregant analysis identified an amplified fragment length polymorphism marker, E-ACT/M-CAA-170, that co-segregated with the SSLB resistance gene Rsp2 in the Foster/CIho 4780 F₂ population. Southern hybridization analysis with DNA from the wheat/barley addition lines localized E-ACT/M-CAA-170 on the short arm of the barley chromosome 5(1H). Restriction fragment length polymorphism analysis with DNA clones previously mapped to the short arm of chromosome 5(1H) placed Rsp2 at a position flanked by the markers Act8 and ksuD14. A sequence-characterized amplified region (SCAR) marker (E-ACT/M-CAA-170a) was developed that co-segregated with not only Rsp2 in the Foster/CIho 4780 population but also resistance gene Rsp3 in the Foster/CIho 10644 population. This result indicates that Rsp3 is closely linked to Rsp2 on the short arm of chromosome 5(1H). The utility of SCAR marker E-ACT/M-CAA-170a for selecting Rsp2 in two different breeding populations was validated.