Identification and mapping of resistance gene analogs and a white rust resistance locus in<Emphasis Type="Italic"> Brassica rapa</Emphasis> ssp.<Emphasis Type="Italic"> oleifera</Emphasis>

The objective of this investigation was to tag a locus for white rust resistance in a Brassica rapa ssp. oleifera F₂ population segregating for this trait, using bulked segregant analysis with random amplified polymorphic DNA (RAPD) markers, linkage mapping and a candidate gene approach based on resistance gene analogs (RGAs). The resistance source was the Finnish line Bor4109. The reaction against white rust races 7a and 7v was scored in 20 seedlings from each self-pollinated F₂ individual. The proportion of resistant plants among these F₃ families varied from 0 to 67%. Bulked segregant analysis did not reveal any markers linked with resistance and, therefore, a linkage map with 81 markers was created. A locus that accounted for 18.4% of the variation in resistance to white rust was mapped to linkage group (LG) 2 near the RAPD marker Z19a. During the study, a bacterial resistance gene homologous to Arabidopsis RPS2 and six different RGAs were sequenced. RPS2 and five of the RGAs were mapped to linkage groups LG1, LG4 and LG9. Unfortunately, none of the RGAs could be shown to be associated with white rust resistance.Communicated by H.C. BeckerThe nucleotide sequence data reported has been deposited in the Genbank under the accession numbers AF315081–AF315087.