A genetic map based on RAPD, RFLP, isozyme, morphological markers and QTL analysis for clubroot resistance in Brassica oleracea

We analyzed 124 markers for linkage in 138 F2 plants derived from a cross between 2 inbred lines, cabbage and kale (both Brassica oleracea). Ninety-nine RAPDs, 21 RFLPs, 2 isozyme genes, and 2 morphological characters were used to construct a genetic map spanning 9 linkage groups covering 823.6 cM of the B. oleracea genome. The number of mapped loci for each linkage group ranged from 9 to 23. The average interval between 2 loci was 7.16 cM. The maximum distance between two loci in the linkage groups was 283 cM. Most of the markers segregated in a normal Mendelian ratio. However, biased segregation was observed at 10 loci. Most of the loci were clustered in a particular area of the genome, and showed an over-abundance of the male parent, indicating the presence of a lethal allele in the neighborhood of these markers or a quantitative selection advantage for one or more alleles. One QTL for resistance to clubroot disease was identified. QTL mapping confirmed the identification of the probable location and effect of a QTL on linkage group 3. The QTL was separated from the nearest marker by a distance of 1.0 cM, and its R2 value was 0.300 indicating phenotypic variation