Molecular mapping of septoria tritici blotch resistance in hexaploid wheat (Triticum aestivum L.)
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Septoria tritici blotch (Stb) is a major foliar disease of wheat worldwide caused by the fungal pathogen Mycosphaerella graminicola. This project mapped the chromosomal locations of Stb resistance, which will be useful for wheat cultivar enhancement. In the first study of this project, Stb resistance and grain yield quantitative trait loci (QTL) were identified in a winter wheat doubled-haploid (DH) population produced from the cultivars Pastiche (resistant) and Torfrida (susceptible). A genetic map of the population was constructed using 104 microsatellite and 202 DArT markers. Separate disease and yield field trials were conducted in north-western Europe to measure natural Stb infection and grain yield, respectively. A resistance QTL from Pastiche was identified (QStb.jic-2A) that reduced flag leaf pycnidial density by 31.2% compared to the population mean. A second QTL from Pastiche (QYld.jic-2A) co-localized with QStb.jic-2A, and conferred an increase in grain yield of approximately 2.0% (0.19 t ha-1). The second study determined the map location of the third multiple-isolate resistance gene in the hexaploid landrace Salamouni. A population was developed using the resistant DH line 98S05B*13 (Salamouni/Katepwa) crossed to the susceptible cultivar Katepwa. The parent 98S05B*13 was found to contain the resistance gene Stb14 on chromosome 3BS, therefore, to minimize the effect of this gene, individual plants of the F2 population were selected for self-pollination based on presence or absence of Stb14 using flanking microsatellite markers. The Stb14(+) F2:3 families were screened with M. graminicola isolate MG96-36. Bulked segregant analysis identified a possible linkage to the gene of interest on chromosome 3AS. Polymorphic microsatellite markers on 3AS were used to construct a linkage group. The markers barc321 and barc12 were found to flank the resistance gene at genetic distances of 1.9 and 2.5 cM, respectively. This position on 3AS has not been previously linked to Stb resistance and this gene will be designated StbSm3. The third population was developed to fine map the isolate-specific resistance gene Stb14 located on chromosome 3B of Salamouni. A large population of 84 fixed recombinant F4 families was developed using the co-dominant microsatellite markers flanking Stb14. Attempts to identify clearly polymorphic molecular markers within the interval containing Stb14 were unsuccessful.