Mapping of rhizoctonia root rot resistance genes in sugar beet using pathogen response-related sequences as molecular markers

Rhizoctonia root and crown rot caused by the fungus Rhizoctonia solani is a serious disease of sugar beet. An F-2:3 population from a cross between a resistant and a susceptible parent has been tested for R. solani resistance and a genetic map has been constructed from the corresponding F-2 parents. The map encompasses 38 expressed sequence tags (ESTs) with high similarity to genes which are involved in resistance reactions of plants (R-ESTs) and 25 bacterial artificial chromosomes (BACs) containing nucleotide binding site (NBS)-motifs typical for disease resistance genes. Three quantitative trait loci (QTL) for R. solani resistance were found on chromosomes 4, 5 and 7 collectively explaining 71% of the total phenotypic variation. A number of R-ESTs were mapped in close distance to the R. solani resistance QTL. In contrast, the NBS-BACs mapped to chromosomes 1, 3, 7 and 9 with two major clusters of NBS-BACs on chromosome 3. No linkage between NBS-BACs and R. solani resistance QTL was found. The data are discussed with regard to using R-ESTs and NBS markers for mapping quantitative disease resistances.