Plant Genome III Conference Plant Genome III Conference
Barley mild mosaic virus and barley yellow mosaic virus represent a serious threat to the cultivation of winter barley in Central Europe. During the winter season, virus particles are delivered by the soil-borne fungus polymyxa graminis into root cells of young plants from where they spread systemically. Large portions of the acreage in Central Europe are already infested by these viruses and the cultivation of disease resistant plants provides the only opportunity for a sustainable barley production in these areas. A recessive gene (ym4) conferring resistance has been localized on the distal end of chromosome 3 where it is tightly flanked by several RFLP-markers. In order to facilitate marker assisted selection in a practical breeding program, a closely linked RFLP marker was converted into a codominant sequence tagged site marker. Due to its location on the telomeric portion of the chromosome arm, where the ratio between physical and genetic distances is expected to be favourable for a map based cloning approach, a high resolution RFLP map around this locus is being developed. Based on the RFLP marker genotypes of ca. 2000 F2 plants, those plants will be identified which carry a recombination in an interval of about 5 cM around the Ym4 locus. Thus, the effective mapping population is expected to consist only of about 1 00 plants which will be subsequently tested for their resistance to BAMMV. In an attempt to further explore the genetic basis of virus resistance in barley, several genes, non allelic to the ym4 gene, have been identified in germplasm originating from East Europe and the Near East. RFLP-mapping of one of those genes was performed in a segregating population of 69 Fl anther derived doubled haploid barley lines. The recessive gene, designated ym7, has been localized on the short arm of chromosome 1 H, close to the centromere where it is marked by a cosegregating RFLP marker.