New CAPS Marker for Selection of a Barley Powdery Mildew Resistance Gene in the Mla Locus

In PI466495, a powdery mildew resistance source of wild barley ( Hordeum vulgare ssp. spontaneum), one gene conferring powdery mildew resistance was identified in the Mla locus. In this paper, the RGH1a gene sequence was used as source for the development of a cleaved amplified polymorphic sequence ( CAPS) marker. Co-segregation between this marker and powdery mildew resistance was analysed by specific DNA fragments associated with each allele of the gene using 286 F-2 plants derived from a cross between winter barley (H. vulgare L.) variety 'Tiffany' and PI466495. For the co-dominant marker RGH1aI1a, three fragments, 370 bp, 82 bp and 59 bp in size, were amplified from F2 plants exhibiting resistance reaction types 0 and 0-1 to powdery mildew; whereas two fragments, 429 bp and 82 bp in size, were amplified in susceptible plants. Simple procedures based on polymerase chain reaction and restriction enzyme digestion allowed for identifying the plants susceptible to powdery mildew (Blumeria graminis f. sp. hordei) and plants homozygous or heterozygous for the resistance allele. The RGH1aI1a marker was positioned 0.85 cM to the resistance gene and the efficiency of marker-assisted selection (MAS), evaluated as the probability of crossing-over between the marker and the targeted gene, was 99%. The CAPS marker RGH1aI1a is a valuable candidate for MAS and gene transfer into barley varieties susceptible to powdery mildew.