Chromosome landing at the Mla locus in barley (Hordeum vulgare L.) by means of high-resolution mapping with AFLP markers

The complex Mla locus of barley determines resistance to the powdery mildew pathogen Erysiphe graminis f. sp. hol dei. With a view towards gene isolation, a population consisting of 950 F-2 individuals derived from a cross between the near-isogenic lines 'P01' (Mla1) and 'P10' (Mla12) was used to construct a high-resolution map of the Mla region. A fluorescence-based AFLP technique and bulked segregant analysis were applied to screen for polymorphic, tightly linked AFLP markers, Three AFLP markers were selected as suitable for a chromosome-landing strategy. One of these AFLP markers and a closely linked RFLP marker were converted into sequence-specific PCR markers. PCR-based screening of approximately 70 000 yeast artificial chromosome (YAC) clones revealed three identical YACs harbouring the Mla locus. Terminal insert sequences were obtained using inverse PCR. The derived STS marker from the right YAC end-clone was mapped distal to the Mla locus.