Plant & Animal Genome VI Conference

P33

MINING FOR GENES CONFERRING RESISTANCE TO SOIL-BORNE VIRUSES IN BARLEY

1. Institute of Plant Genetics and Crop Plant Research, 06466 Gatersleben, Germany
2. Institute of Crop Science and Plant Breeding, 35390 Giessen, Germany
3. Institute for Resistance Genetics, 85461 Gruenbach, Germany
4. Scottish Crop Research Institute, Dundee DD2 5DA, Scotland, UK

Resistance to the barley yellow mosaic virus complex is conditioned by two recessive genes, ym4 and ym5. The first confers immunity to barley mild mosaic virus (BaMMV) and barley yellow mosaic virus type 1 (BaYMV-1). In addition to BaMMV and BaYMV-1, presence of the ym5 gene leads to immunity to another strain termed BaYMV-2, which is virulent on host plants carrying ym4. Both genes form a complex locus mapping to the distal portion of the long arm of barley chromosome 3. Until now, resistance tests have not lead to the identification of recombinant progeny plants in terms of resistance to the individual virus isolates. Hence, the question arises whether this locus consists of several closely linked genes or, if the different resistance specificities are the result of multiple allelism. In addition, only limited knowledge is available on the molecular mechanism(s) leading to resistance. Therefore, a map based cloning approach has been chosen to facilitate isolation and functional analysis of the two genes. To confirm their exact map position, two high resolution maps, based on about 1000 F₂ plants each, have been constructed. Marker saturation of the chromosomal region comprising the resistance genes is being performed by bulked segregant analysis using RAPD and AFLP markers. To investigate the physical structure of the resistance region, several barley YACs showing homology to two markers that flank the ym4 gene, have been isolated and characterized. Insert sizes of individual clones varied between 40 and 300 kb. As expected, end-fragments were mainly composed of repetitive DNA elements.