Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/12/2004
Publication Date: 10/12/2004
Citation: Adhikari, T., Cavaletto, J.R., Dubcovsky, J., Gieco, J., Schlatter, A.R., Goodwin, S.B. 2004. Molecular mapping of the stb4 gene for resistance to septoria tritici blotch in wheat. Phytopathology. 94:1198-1206. Interpretive Summary: Breeding wheat for resistance is the most effective means to control septoria tritici leaf blotch (STB), caused by the fungus Mycosphaerella graminicola (Septoria tritici is the name for its asexual stage). At least eight genes that confer resistance in wheat to STB have been identified. Among them, the Stb4 gene from the wheat cultivar Tadinia showed resistance to M. graminicola at both seedling and adult plant stages. However, no molecular markers linked to this gene are available and its map location remains unknown, which has limited its usefulness in plant-improvement programs. To solve these problems, a mapping population derived from a cross between the resistant wheat cultivar Tadinia and a susceptible parent was evaluated for disease resistance and molecular mapping in the field and greenhouse. Both the field and greenhouse results confirmed a single gene controlling the Stb4 resistance to M. graminicola. Twelve molecular markers linked to the resistance gene were identified, the closest of which was a repetitive marker with a known map location. Stb4 was mapped close to the center of wheat chromosome 7D, near the Stb5 gene for resistance to M. graminicola and very close to a cluster of genes for resistance to Russian wheat aphid. This information will be of great interest to plant pathologists and geneticists, as it identifies a cluster of resistance genes with specificities to fungal and insect pests. The molecular markers will allow the Stb4 gene to be utilized immediately to its maximum potential. Plant breeders worldwide can use the molecular markers to select for resistant individuals instead of performing inoculations, which will facilitate combining Stb4 with other STB resistance genes into a single wheat cultivar for durable resistance to M. graminicola.
Technical Abstract: Breeding wheat for resistance is the most effective means to control septoria tritici leaf blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici). At least eight genes that confer resistance in wheat to STB have been identified. Among them, the Stb4 locus from the wheat cultivar Tadinia showed resistance to M. graminicola at both seedling and adult plant stages. However, no attempt has been made to map the Stb4 locus in the wheat genome. A mapping population of 83 F10 recombinant-inbred lines (RILs) derived from a cross between the resistant cultivar Tadinia and the susceptible parent (Yecora Rojo x UC554) was evaluated for disease resistance and molecular mapping. The RILs were tested under high disease pressure in California and artificially inoculated with an Indiana tester isolate of M. graminicola in the greenhouse during 2000 and 2001. Both field and greenhouse phenotypic data segregated in a 1:1 ratio, confirming the single-gene model for control of Stb4 resistance to M. graminicola. Bulked segregant analysis was used to identify amplified fragment length polymorphism (AFLP) and microsatellite markers linked to the Stb4 gene. The AFLP marker EcoRI-ACTG/MseI-CAAA5 and microsatellite Xgwm111 were closely linked to the Stb4 locus in coupling at distances of 2.1 and 0.7 cM, respectively. A flanking marker, AFLP E-AGG/M-CAT10, was distal to the other tightly linked markers and was 4 cM from Stb4. Stb4 was mapped near the centromere on the short arm of wheat chromosome 7D, near a cluster of genes for resistance to Russian wheat aphid. The microsatellite marker Xgwm111 identified in this study will be useful in marker-assisted breeding for STB-resistant wheat.