Disease resistance. Septoria Tritici Blotch Resistance.
Stb4
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.
Breeding wheat for resistance is the most effective means to control Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici). At least eight genes that confer resistance to STB in wheat 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 77 F10 recombinant-inbred lines (RILs) derived from a threeway cross between the resistant cultivar Tadinia and the susceptible parent (Yecora Rojo × UC554) was evaluated for disease resistance and molecular mapping. The RILs were tested with Argentina isolate I 89 of M. graminicola for one greenhouse season in Brazil during 1999, with an isolate from Brazil (IPBr1) for one field season in Piracicaba (Brazil) during 2000, and with Indiana tester isolate IN95-Lafayette-1196-WW-1-4 in the greenhouse during 2000 and 2001. The ratio of resistant:susceptible RILs was 1:1 in all three tests, confirming the single-gene model for control of resistance to STB in Tadinia. However, the patterns of resistance and susceptibility were different between the Indiana isolate and those from South America. For example, the ratio of RILs resistant to both the Indiana and Argentina isolates, resistant to one but susceptible to the other, and susceptible to both isolates was approximately 1:1:1:1, indicating that Tadinia may contain at least two genes for resistance to STB. A similar pattern was observed between the Indiana and Brazil isolates. The gene identified with the Indiana tester isolate was assumed to be the same as Stb4, while that revealed by the South American isolates may be new. Bulked segregant analysis was used to identify amplified fragment length polymorphism (AFLP) and microsatellite markers linked to the presumed Stb4 gene. The AFLP marker EcoRI-ACTG/MseICAAA5 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 4 cM from Stb4. The Stb4 gene was in a potential supercluster of resistance genes near the centromere on the short arm of wheat chromosome 7D that also contained Stb5 plus five previously identified genes for resistance to Russian wheat aphid. The microsatellite marker Xgwm111 identified in this study may be useful for facilitating the transfer of Stb4 into improved cultivars of wheat.
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.
Twenty-four wheat cultivars and breeding lines were screened for isolate-specific resistance to septoria tritici blotch (STB) caused by 12 isolates of Mycosphaerella graminicola. New isolate-specific resistances that could be used in wheat breeding were identified. Major sources of resistance to STB used in world breeding programmes for decades, such as Kavkaz-K4500, Veranopolis, Catbird and TE9111, have several isolate-specific resistances. This suggests that ‘pyramiding’ several resistance genes in one cultivar may be an effective and durable strategy for breeding for resistance to STB in wheat. Several cultivars, including Arina, Milan and Senat, had high levels of partial resistance to most isolates tested as well as isolatespecific resistances. Resistance to isolate IPO323 was common, present in all but one of the major sources of resistance tested. This suggests that resistance to IPO323 may be an indicator of varietal resistance to STB in the field.
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.
Resistance to Mycosphaerella graminicola causal agent of Septoria tritici blotch, was identified in progenies of crosses with European winter wheat cultivars, Tadorna and Cleo. This resistance was used to develop the resistant spring wheat cultivar Tadinia, selected from 'Tadorna'/'Inia 66', released in 1985. Evaluation of the progeny of intercrosses between 'Tadorna', 'Cleo', 'Tadinia', and two short-statured resistant lines derived from hybrids with 'Tadinia' as one parent indicate the resistance was inherited as a single gene showing partial to strong dominance. The gene in 'Tadinia' was designated Stb4. Crosses between another resistant cultivar, 'Bulgaria 88', and 'Tadinia' suggest that 'Bulgaria 88' does not have Stb4. Successful introgression of Stb4 into RhtI + Rht2 short-statured lines revealed that plant stature and resistance to M. graminicola segregated independently. The Stb4 gene has been effective since 1975 against M. graminicola extant in California. A high positive correlation between seedling and adult plant disease scores, based on scoring of lesions producing pycnidia, indicated that the Stb4 gene is expressed throughout the life cycle under both field and greenhouse conditions, confirming that disease screening can be carried out on seedling plants. Separate assessment of necrotic lesions with and without pycnidia indicated that leaf necrosis without pycnidia, observed, especially under greenhouse conditions, can confound disease evaluations and lead to inaccurate genotype classification.
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.
Septoria tritici leaf blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici), is an economically important disease of wheat. Breeding for resistance to STB is the most effective means to control this disease and can be facilitated through the use of molecular markers. However, molecular markers linked to most genes for resistance to STB are not yet available. This study was conducted to test for resistance in the parents of a standard wheat mapping population and to map any resistance genes identified. The population consisted of 130 F10 recombinant-inbred lines (RILs) from a cross between the synthetic hexaploid wheat W7984 and cv. Opata 85. Genetic analysis indicated that a single major gene controls resistance to M. graminicola in this population. This putative resistance gene is now designated Stb8 and was mapped with respect to amplified fragment length polymorphism (AFLP) and microsatellite markers. An AFLP marker, EcoRI-ACG/MseI-CAG5, was linked in repulsion with the resistance gene at a distance of approximately 5.3 centimorgans (cM). Two flanking microsatellite markers, Xgwm146 and Xgwm577, were linked to the Stb8 gene on the long arm of wheat chromosome 7B at distances of 3.5 and 5.3 cM, respectively. The microsatellite markers identified in this study have potential for use in marker-assisted selection in breeding programs and for pyramiding of Stb8 with other genes for resistance to M. graminicola in wheat.
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.
Septoria tritici blotch (STB) of wheat (Triticum aestivum L.), caused by the fungal pathogen Mycosphaerella graminicola (Fuckel) J. Schrdt. in Cohn (anamorph: Septoria tritici Roberge in Desmaz.), 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 cosegregated with the STB phenotypes. Linkage analysis identified five SSR markers near the Stb2 gene on the distal region of the short arm of chromosome 3B. Loci Xgwm389 and Xgwm533.1 were approximately 1 cM distal to Stb2, which itself was 3.7 cM distal to Xgwm493. In addition to Stb2, this genomic region contains multiple genes conferring resistance to taxonomically diverse fungal pathogens of wheat, including a major quantitative trait locus for resistance to Fusarium head blight (caused by Fusarium graminearum Schwabe). The SSR marker Xgdm132 was linked to the Stb3 gene at a distance of approximately 3 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.
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.
Specific resistances to isolates of the ascomycete fungus Mycosphaerella graminicola, which causes Septoria tritici blotch of wheat, have been detected in many cultivars. Cvs, Flame and Hereward, which have specific resistance to the isolate IPO323, were crossed with the susceptible cv. Longbow. The results of tests on F1 and F2 progeny indicated that a single semidominant gene controls resistance to IPO323 in each of the resistant cultivars. This was confirmed in F3 families of Flame x Longbow, which were either homozygous resistant, homozygous susceptible, or segregating in tests with IPO323 but were uniformly susceptible to another isolate, IPO94269. None of 100 F2 progeny of Flame x Hereward were susceptible to IPO323, indicating that the resistance genes in these two cultivars are the same, closely linked, or allelic. The resistance gene in cv. Flame was mapped to the short arm of chromosome 3A using microsatellite markers and was named Stb6. Fifty-nine progeny of a cross between IPO323 and IPO94269 were used in complementary genetic analysis of the pathogen to test a gene-for-gene relationship between Stb6 and the avirulence gene in IPO323. Avirulence to cvs. Flame, Hereward, Shafir, Bezostaya 1, and Vivant and the breeding line NSL92-5719 cosegregated, and the ratio of virulent to avirulent was close to 1: 1, suggesting that these wheat lines may all recognize the same avirulence gene and may all have Stb6. Together, these data provide the first demonstration that isolate-specific resistance of wheat to Septoria tritici blotch follows a gene-for-gene relationship.
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 Applied Genetics, 2003, 107(7):1181-1186.
Septoria tritici blotch, caused by Mycosphaerella graminicola, is a serious foliar disease of wheat worldwide. Qualitative, race-specific resistance sources have been identified and utilized for resistant cultivar development. However, septoria tritici blotch resistant varieties have succumbed to changes in virulence of M. graminicola on at least three continents. The use of resistance gene pyramids may slow or prevent the breakdown of resistance. A clear understanding of the genetics of resistance and the identification of linked PCR-based markers will facilitate the recovery of wheat lines carrying multiple septoria tritici blotch resistance genes. The resistance gene in ST6 to isolate MG2 of M. graminicola was mapped with microsatellite markers in two populations, ST6/Erik and ST6/Katepwa. Bulk segregant analysis identified a marker on chromosome 4AL putatively linked to the resistance gene. A large linkage group was identified in each population using additional microsatellite markers mapping to chromosome 4AL. The resistance gene in ST6 mapped to the distal end of chromosome 4AL in each mapping population and was designated Stb7. Three of the microsatellite loci, Xwmc313, Xwmc219 and Xgwm160, mapped within 3.5 cM of Stb7; however, none flanked Stb7. Xwmc313 was the closest and mapped 0.3 and 0.5 cM from Stb7 in the crosses ST6/Katepwa and ST6/Erik, respectively. WMC313 will be very useful for marker-assisted selection of Stb7 in Canadian breeding programs because the ST6 allele of Xwmc313 was not identified in any of the Canadian common wheat cultivars tested.
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.
Septoria tritici blotch, caused by the fungus Mycosphaerella graminicola, is currently the major foliar disease of wheat world-wide, and new sources of resistance and knowledge about the genetics of resistance are needed to improve breeding for resistance to this disease. Sears's 'Synthetic 6x' hexaploid wheat, derived from a hybrid of Triticum dicoccoides and Triticum tauschii, was resistant to 12 of 13 isolates of M. graminicola tested. Chromosome 7D of 'Synthetic 6x' was identified as carrying resistance to all 12 isolates in tests of seedlings of inter-varietal chromosome substitution lines of 'Synthetic 6x' into 'Chinese Spring' and to two isolates in tests of adult plants. A septoria tritici blotch resistance gene, named Stb5, was identified using the M. graminicola isolate IPO94269 and mapped on the short arm of chromosome 7D, near the centromere, in a population of single homozygous chromosome-recombinant lines for the 7D chromosome.