Using Molecular Markers to Detect Favorable Linkages Between Sr2 and Fhb1 In SRWW Germplasm.

Since the 1930s, the gene Sr2 has served as a source of durable adult plant resistance to stem rust of wheat, caused by Puccinia gramini f. sp. tritici Pers.. The T. turgidum L. ssp. dicoccum- derived introgression carrying Sr2 is located on the short arm of chromosome 3B in the same region as the Fhb1 locus conferring resistance to Fusarium head blight, caused by Fusarium graminearum Schwabe. Isolation of Sr2 and Fhb1 in the same cultivar requires selection for recombination between the resistance genes. This favorable recombination event has been difficult to select for using traditional disease screening given the large population sizes needed and the quantitative nature of resistance conferred by Fhb1 and Sr2. We used simple sequence repeat and single nucleotide polymorphism markers to detect recombination on 3BS in a population of 384 F2 plants generated from crosses between soft red winter wheat germplasm carrying the introgressed genes. The observed linkage distance between the marker UMN10 (closely linked to Fhb1) and csSr2 (closely linked to Sr2), was approximately 10 cM. Fourteen recombinant plants having marker alleles associated with resistance in coupling were identified. Test-crosses with susceptible lines were made that will be used to confirm the presence of Sr2 and Fhb1 in coupling by disease screening. In addition, crosses have been made to pyramid these linked genes with other rust resistance genes in SRWW backgrounds. Pyramiding of FHB and stem rust resistance genes should generate useful germplasm for wheat breeding programs.