Mapping of crown gall resistance locus Rcg1 in grapevine.

Agrobacteria are efficient plant pathogens. They are able to transform plant cells genetically resulting in abnormal cell proliferation. Cultivars of Vitis vinifera are highly susceptible to many virulent Agrobacterium strains but certain wild Vitis species, including Vitis amurensis have resistant genotypes. Studies of the molecular background of such natural resistance are of special importance, not only for practical benefits in agricultural practice but also for understanding the role of plant genes in the transformation process. Earlier, crown gall resistance from V. amurensis was introgressed into V. vinifera through interspecific breeding and it was shown to be inherited as a single and dominant Mendelian trait. To develop this research further, towards understanding underlying molecular mechanisms, a mapping population was established, and resistance-coupled molecular DNA markers were identified by three different approaches. First, RAPD makers linked to the resistance locus (Rcg1) were identified, and on the basis of their DNA sequences, we developed resistance-coupled SCAR markers. However, localization of these markers in the grapevine genome sequence failed due to their similarity to many repetitive regions. Next, using SSR markers of the grapevine reference linkage map, location of the resistance locus was established on linkage group 15 (LG15). Finally, this position was supported further by developing new chromosome-specific markers and by the construction of the genetic map of the region including nine loci in 29.1 cM. Our results show that the closest marker is located 3.3 cM from the Rcg1 locus that may correspond to 576 kb.