A high-resolution genetic map and a diagnostic RFLP marker for the Mlg resistance locus to powdery mildew in barley

The semi-dominantly acting Mig resistance locus in barley confers race-specific resistance to the obligate biotrophic fungus Erytsiphe graminis f.sp, hordei. A high-resolution genetic map was constructed at Mig based on a cross between the near-isogenic barley lines Pallas BC5 Mig and Pallas mlg. A total of 2000 F-2 progeny were inspected by cleaved amplified polymorphic sequence (CAPS) analysis, defining a 4.47 cM interval encompassing the resistance locus. Pathogen challenge of the segregants with multiple powdery mildew isolates uncovered a novel resistance specificity in Pallas BCS Mig. Probes from within 4.0 cM of Mig were mapped in rice, revealing orthologues on five different rice chromosomes and suggesting multiple breaks of chromosomal collinearity in this region between the two grass species. The most tightly Mig-linked RFLP marker, MWG032, was shown to reliably detect the presence of the resistance allele in a collection of 30 European barley cultivars.