|Wallwork, Hugh - SARDI-ADELAIDE,AUSTRALIA|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2003
Publication Date: November 1, 2003
Citation: Adhikari, T., Wallwork, H., Goodwin, S.B. 2003. Microsatellite markers linked to the STB2 and STB3 genes for resistance to septoria blotch in wheat. Crop Science. 44:1403-1411. Interpretive Summary: Breeding wheat for resistance is the most effective means to control Septoria tritici blotch (STB), caused by the fungus Mycosphaerella graminicola (Septoria tritici is the name for its asexual stage). At least eight genes conferring resistance in wheat to STB have been identified. Among these, the Stb2 and Stb3 genes were identified in the cultivars Veranopolis and Israel 493, respectively. However, no molecular markers linked to either of these genes are available and their map locations are not known, so neither gene has been used extensively in plant-improvement programs. To rectify this situation, two mapping populations derived from crosses between the resistant cultivars Veranopolis and Israel 493 with the susceptible Australian breeding line RAC875-2, were evaluated for disease resistance and molecular mapping. The analyses confirmed the existence of a single major resistance gene in each of the resistant parents. Five molecular markers linked to the Stb2 resistance gene were identified near the tip of wheat chromosome 3B, which also contains previously mapped resistances against a wide array of fungal pathogens. One molecular marker was linked to the Stb3 gene on the short arm of chromosome 6D. Mapping these two resistances will be of great interest to plant pathologists and wheat breeders. Locating Stb2 within a cluster of resistance genes can guide wheat breeders for making plants with multiple resistances. The molecular markers will allow both genes to be utilized immediately for maximum effect. Plant breeders worldwide can use the molecular markers to select for resistant individuals instead of performing inoculations, which will facilitate combining Stb2 and Stb3 with other STB resistance genes into a single wheat cultivar for durable resistance to M. graminicola.
Technical Abstract: Septoria tritici blotch (STB) of wheat caused by the fungal pathogen Mycosphaerella graminicola (anamorph: Septoria tritici) occurs naturally in all wheat production areas around the world. Two genes for resistance to this disease, Stb2 and Stb3, have been identified in wheat germplasm and together confer resistance to the most prevalent strains of M. graminicola in Australia and the USA. However, so far neither gene has been mapped in the wheat genome and their linkage relationships to other markers are not known. The objectives of this study were to identify molecular markers linked to the STB resistance genes Stb2 and Stb3 and to map these genes in the wheat genome. Genetic families of doubled-haploid populations segregating for Stb2 and Stb3 were evaluated in the greenhouse for STB reaction during the spring and fall seasons of 2002 and 2003. Genomic DNA isolated from each segregating population was analyzed with microsatellite or simple-sequence repeat (SSR) markers in bulked-segregant analysis to identify those that co-segregated with the STB phenotypes. Linkage analysis indicated that two flanking SSR markers, Xbarc133 and Xgwm389, were linked to the Stb2 gene on the distal region of the short arm of chromosome 3B at distances of 3.7 and 1.9 cM, respectively. In addition to Stb2, this genomic region contains multiple genes conferring resistance to taxonomically diverse fungal pathogens of wheat. The SSR marker Xgdm132 was linked to the Stb3 gene at a distance of approximately 3.0 cM on the short arm of chromosome 6D. The microsatellite markers identified in this study should facilitate marker-assisted selection and pyramiding of Stb2 and Stb3 with other STB resistance genes for more durably resistant wheat.