Disease resistance. Septoria Tritici Blotch Resistance.
Stb4
Background information
Septoria tritici blotch (STB) is one of the most destructive foliar diseases of wheat worldwide. In many places STB is a major limiting factor for wheat production affecting both quality and yield. The causal agent is the fungus Mycosphaerella graminicola (asexual stage: Septoria tritici). Infection preferentially occurs during wet and and cool weather. First symptoms appear as tan to brownish oval or irregularly shaped lesions on leaves. Later, small brown to black spore-producing specks appear in these lesions (1,2).
Eight major genes for resistance to STB have been identified in wheat so far. Stb1, Stb2 and Stb3 were discovered in varieties Bulgaria 88, Veranopolis and Israel 493, respectively. They were identified using natural infection, probably by a mixture of pathogen genotypes. The other Stb genes, Stb4-8 were found in varieties Tadinia, Synthetic 6x, Flame, Estanzuela Federal and synthetic wheat W7984 respectively (see table below), using defined isolates of the pathogen (2).
Stb4 has been useful for controlling M. graminicola in California for around 30 years, yet its map location and relantioship with other STB resistance genes were just recently discovered. Adhikari et al (1) located the Stb4 gene of Tadinia on chromosome 7D, probably on the short arm, close to the centromere; and also close to Stb5. Based on the available marker data, the authors could not confirm whether Stb4 and Stb5 were allelic, the same gene or closely linked loci.
The resistance conferred by Stb4 gene was effective in the field in California from 1975 through the late 1990s (1). However, the effectiveness of this gene decreased recently in some locations. But even taking into account this loss of effectiveness, Stb4 is still a valuable tool for breeding in other regions, especially if used as part of a pyramiding strategy.
Methods
Adhikari et al (1) reported that several AFLP markers and microsatellite Xgwm111 were linked to Stb4. Since AFLP bands are difficult to use in different genetic backgrounds, Xgwm111 is the best option for marker assisted breeding. This microsatellite locus is located at 0.7 cM proximal to Stb4. The methods section contains a photo of a gel with typical results and more detailed information.
Additional information.
Other sources of STB resistance genes in wheat
| Gene | Location | Markers | Donor parent | Reference |
| Stb1 | 5BL | Bulgaria 88 | 5 | |
| Stb2 | 3BS | Xgwm389, Xgwm533.1 (both distal) and Xgwm493 (proximal) | Veranopolis | 6 |
| Stb3 | 6DS | Xgdm132 (3-cM) (*) | Israel 493 | 6 |
| Stb5 | 7DS | Xgwm44 (proximal 7.2-cM) and Rc3 (Red Coleoptile, distal 6.6-cM) | CS(Synthetic 7D) | 9 |
| Stb6 | 3AS | Senat | 7 | |
| Stb7 | 4AL | Xwmc313 (0.5-cM) | Estanzuela Federal | 8 |
| Stb8 | 7BL | Xgwm146 and Xgwm577, flanking | Synthetic W7984 | 4 |
Chartrain et al. (2) identified several sources of partial resistance to groups of isolates or islate-specific in different lines and cultivars, although they were not mapped.
* S. Goodwin (personal communication) reported that Xgdm132 is not linked toStb3. Other markers known to be close to Xgdm132 are not linked to Stb3 either.
References
1. Molecular Mapping of the Stb4 Gene for Resistance to Septoria Tritici Blotch in Wheat . Adhikari TB, Cavaletto JR, Dubcovsky J, Gieco JO, Schlatter AR, Goodwin SB. In: Phytopathology, 2004, 94:1198-1206 [abstract]
2. Sources of resistance to septoria tritici blotch and implications for wheat breeding. Chartrain L, Brading PA, Makepeace JC, Brown JKM. In: Plant Pathology, 2004, 53:454–-460 [abstract]
3. Single-gene resistance to Septoria tritici blotch in the spring wheat cultivar "Tadinia". Somasco OA, Qualset CO, Gilchrist DG. In: Plant Breeding, 1996, 115:261-267 [abstract]
4. Identification and molecular mapping of a gene in wheat conferring resistance to Mycosphaerella graminicola. Adhikari TB, Anderson JM, Goodwin SB. In: Phytopathology, 2003, 93(9):1158-1164. [abstract]
5. Molecular mapping of Stb1, a potentially durable gene for resistance to septoria tritici blotch in wheat. Adhikari TB, Yang X, Cavaletto JR, Hu X, Buechley G, Ohm HW, Shaner G, Goodwin SB. In: Theoretical and Applied Genetics, 2004, 109(5):944-953.
6. Microsatellite markers linked to the Stb2 and Stb3 genes for resistance to septoria tritici blotch in wheat. Adhikari TB, Wallwork H, Goodwin SB. In: Crop Science, 2004, 44(4):1403-1411. [abstract]
7. A gene-for-gene relationship between wheat and Mycosphaerella graminicola, the Septoria tritici blotch pathogen. Brading PA, Verstappen ECP, Kema GHJ, Brown JKM. In: Phytopathology, 2002, 92(4):439-445. [abstract]
8. Chromosomal location of a race-specific resistance gene to Mycosphaerella graminicola in the spring wheat ST6. McCartney CA, Brule-Babel AL, Lamari L, Somers DJ. In: Theoretical and Appled Genetics, 2003, 107(7):1181-1186. [abstract]
9. Chromosomal location of a gene for resistance to septoria tritici blotch (Mycosphaerella graminicola) in the hexaploid wheat "Synthetic 6x". Arraiano LS, Worland AJ, Ellerbrook C, Brown JKM. In: Theoretical and Applied Genetics, 2001, 103:758-764. [abstract]