Genetic mapping of plant disease resistance gene homologues using a minimal Brassica napus L. population

Genetic mapping of plants traditionally involves the analysis of large segr egating populations. However, not all individuals in a population contribut e equal amounts of genetic information. It is thus possible to achieve roug h mapping using a subset of the most informative individuals in the populat ion. We have designed a minimal Brassica napus mapping population of 23 dou bled-haploid plants and have tested this method using this population in th e mapping of disease resistance gene homologues in B. napus. Several groups have identified such homologues in soybean and potato by amplifying sequen ces corresponding to conserved nucleotide-binding sites from known resistan ce genes. However, the sequence conservation in the leucine-rich repeat dom ain that is present in most of the disease resistance genes isolated has no t been exploited via the polymerase chain reaction (PCR). We present the ge netic mapping of Brassica napus DNA sequences amplified with primers corres ponding to both the nucleotide-binding site and the leucine rich-repeat dom ain of the Arabidopsis thaliana RPS2 gene. We also describe a method for th e quick mapping of resistance gene homologues using the polymerase chain re action.