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Population structure and location of genes for resistance to Mycosphaerella graminicola: Recent advances in Argentina

Leaf blotch of wheat [Septoria tritici Rob. ex Desm., teleomorph Mycosphaerella graminicola (Fückel) Schröt. in Cohn] causes significant losses in wheat. Results about genetic variability of the pathogen and location of the resistance to the disease, carried out in Argentina are presented. A study with 126 isolates from several locations revealed the existence of 81 different haplotypes, indicating a high degree of genotypic
diversity. Furthermore, a high gene flow was found between subregions without significant genetic differences between populations. Virulence tests were conducted on nine selected Argentinean wheat cultivars and 14 foreign cultivars with some level of resistance to the pathogen inoculated with 16 different isolates molecularly characterized in the previous work in two environments. Cultivars with good levels of partial and complete resistance to some isolates were detected in seedlings and the adult
stage. During the last decade, 18 Stb major genes conferring resistance to the pathogen and several QTL have been identified around the world. Our group determined that chromosome 7D of “Synthetic 6x” had a major resistance QTL against the two isolates tested in seedlings and the adult stage which mapped to the centromeric region (marker Xgwm44) of the 7D chromosome and it is likely that the gene involved was Stb5, which
proved to be effective against isolates originating from both Europe and South America. Major gene effects were also found on chromosomes 5A and 5D of “Synthetic 6x. In addition, a source of resistance has been mapped on chromosome 7D of spelt wheat. Two regions of the chromosome were associated with isolate-specific QTL, one expressed at the seedling in the centromeric region of chromosome 7D (QStb.ipk-7D1) which corresponded to the location of the major resistance gene Stb4 originated from bread wheat cultivar “Tadinia” and Stb5 originated from Triticum tauschii. and another at the adult plant stage on the short arm of chromosome 7D (QStb.ipk-7D2) in a similar position to the locus Lr34/Yr18, known to be effective against multiple pathogens. Furthermore, using an ITMI mapping population (W7984 × Opata 85), three loci were
discovered on the short arms of chromosomes 1D, 2D and 6B at the seedling stage effective to two isolates. At the adult plant stage, two isolate-specific QTL were found at the long arms of chromosomes 3D and 7B.
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