MOLECULAR MARKER ANALYSIS OF GENES-CONTROLLING MORPHOLOGICAL VARIATION IN BRASSICA-RAPA (SYN CAMPESTRIS)

Construction of a detailed RFLP linkage map of B. rapa (syn. campestri s) made it possible, for the first time, to study individual genes con trolling quantitative traits in this species. Ninety-five F-2 individu als from a cross of Chinese cabbage cv 'Michihili' by Spring broccoli were analyzed for segregation at 220 RFLP loci and for variation in le af, stem, and flowering characteristics. The number, location, and mag nitude of genes underlying 28 traits were determined by using an inter val mapping method. Zero to five putative quantitative trait loci (QTL ) were detected for each of the traits examined. There were unequal ge ne effects on the expression of many traits, and the inheritance patte rns of traits ranged from those controlled by a single major gene plus minor genes to those controlled by polygenes with small and similar e ffects. The effect of marker locus density on detection of QTL was ana lyzed, and the results showed that the number of QTL detected did not change when the number of marker loci used for QTL mapping was decreas ed from 220 to 126; however, a further reduction from 126 to 56 caused more than 15% loss of the total QTL detected. The detection of putati ve minor QTL by removing the masking effects of major QTL was explored .