Leaf stripe resistance gene in Barley: marker assisted selection and fine mapping of the resistance gene Rdg2a

A barley gene conferring resistance to the leaf stripe agent has been mapped on the chromosome arm 7HS. This resistance gene, named as Rdg2a, confers resistance towards several isolates having therefore a useful range of activity. To verify the reliability of a PCRbased marker (MWG2018) associated to the resistance gene to assess the leaf stripe resistant phenotype in barley breeding programs, several resistant lines obtained from several crosses were tested for the allelic composition at the MWG2018 locus. The results showed that the resistant phenotype of the lines was always associated with the resistant allele of the molecular marker, evidentiating the reliability of this marker to select for leaf stripe resistance; this marker is routinely used in practical breeding. To saturate the Rdg2a chromosomal region with molecular markers, two approaches have substantially been used: 1) several RGAs have been tested for co-segregation with Rdg2a; 2) by exploiting the syntenic relationships between the telomeric regions of barley chromosome 7H and rice chromosome 6, rice ESTs informations have been used to generate PCR-based markers then mapped in the Rdg2a mapping population. By using these approaches, we have observed tight association of RGAs with Rdg2a and conservation of syntenic relationships between the telomeric regions of barley chromosome 7H and rice chromosome 6 for the Rdg2a chromosomal region.