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

Abstract

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 28.3 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.