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

Abstract

Abstract 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.