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 isolat ion, a population consisting of 950 F-2 individuals derived from a cross be tween the near-isogenic lines 'P01' (Mla1) and 'P10' (Mla12) was used to co nstruct a high-resolution map of the Mla region. A fluorescence-based AFLP technique and bulked segregant analysis were applied to screen for polymorp hic, tightly linked AFLP markers, Three AFLP markers were selected as suita ble for a chromosome-landing strategy. One of these AFLP markers and a clos ely linked RFLP marker were converted into sequence-specific PCR markers. P CR-based screening of approximately 70 000 yeast artificial chromosome (YAC ) clones revealed three identical YACs harbouring the Mla locus. Terminal i nsert sequences were obtained using inverse PCR. The derived STS marker fro m the right YAC end-clone was mapped distal to the Mla locus.