Molecular Mapping of Rsp1, Rsp2, and Rsp3 Genes Conferring Resistance to Septoria Speckled Leaf Blotch in Barley

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Abstract
Septoria speckled leaf blotch (SSLB) caused by Septoria passerinii is a common disease in barley. SSLB resistance genes Rsp1, Rsp2, and Rsp3 have previously been identified in the United States Department of Agriculture National Small Grains collection accessions CIho 14300, CIho 4780, and CIho 10644, respectively. Populations of 100 to 120 F2 individuals were evaluated for SSLB resistance in the greenhouse. Inheritance was evaluated in F2:3-derived families in the field. Partial molecular maps for three Rsp genes were constructed on F2 and F2:3 families derived from crosses between Robust and the resistant accessions CIho 14300, CIho 4780, and CIho 10644. The resistant locus Rsp1 was mapped to the short arm of chromosome 3H with two flanking diversity arrays technology (DArT) markers, bPb-6978 (8.9 cM) and bPb-9945 (16.3 cM), and two random amplified polymorphic DNA (RAPD) markers, OPC2441R (3.0 cM) and UBC285158R (4.3 cM). The genes Rsp2 and Rsp3 were positioned on the short arm of barley chromosome 1H with two restriction fragment length polymorphism (RFLP), six DArT, and three RAPD markers. An RFLP marker, MWG938, and an RAPD marker, OPAH5545C, were tightly associated with Rsp2 at a distance of 0 cM. Five DArT markers spanning the short arm of 1H surrounded Rsp3 at a distance of 2.3 and 5.8 cM, while two RAPD markers—OPBA12314C (2.4 cM) in coupling and OPB17451R (3.5 cM) in repulsion—flanked Rsp3. Molecular marker data associated with Rsp2 and Rsp3 indicated that the two genes are closely linked on chromosome 1HS. A total of 17 of 154 simple sequence repeats (SSRs) tested were associated with Rsp genes on chromosome 1H and 3H, and they were also integrated into genetic linkage maps of the three F2 Robust populations. Knowledge about the map position of Rsp genes on barley chromosomes will be useful for breeding for SSLB resistance in barley and eventual gene cloning.