ASSOCIATION OF RFLP MARKERS WITH TRAIT LOCI AFFECTING CLUBROOT RESISTANCE AND MORPHOLOGICAL CHARACTERS IN BRASSICA-OLERACEA L

Resistance to Plasmodiophora brassicae Wor. race 7, the causal agent o f the disease clubroot, was examined in an F-2 population of a cross b etween a clubroot resistant broccoli (Brassica oleracea var. italica) and a susceptible cauliflower (B. oleracea var. botrytis). A genetic l inkage map was constructed in the same population based on the segrega tion of 58 dispersed restriction fragment length polymorphism (RFLP) m arkers. Associations between the inheritance of RFLP marker genotypes and segregation for disease resistance, morphological and maturity cha racteristics were examined. For each trait examined, several chromosom al regions marked by RFLP probes appeared to contain trait loci, sugge sting that each trait was under polygenic control. RFLP marker linkage to a major factor imparting dominance for clubroot resistance from th e broccoli parent was observed in this population. Additionally, RFLP marker linkage to an independently segregating factor contributing clu broot resistance from the cauliflower parent was observed, indicating that it should be possible to use RFLP markers to facilitate selection of transgressive segregants having the combined resistance from both parental sources. In some instances, RFLP markers from the same or clo sely linked chromosomal regions were associated with both clubroot res istance and morphological traits. Analysis of RFLP marker genotypes at linked loci should facilitate the selection of desired disease resist ant morphotypes.