Mapping of loci affecting the cultural efficiency of microspore culture ofBrassica rapa L-syn. campestris L-using DNA polymorphism

A linkage map of Brassica rapa was constructed based on random amplified po lymorphic DNAs (RAPDs), isozymes and restriction fragment length polymorphi sm (RFLP), using an F-2 population derived from the crossing of a Chinese c abbage line,'Homei 09' and a club-root-resistant turnip line, 'Siloga S2'. The map covered 851 cM, about half of the genome, and consisted of 16 linka ge groups. 'Homei 09' is highly responsive to microspore culture unlike 'Si loga S2'. To identify the loci affecting embryogenesis in microspore cultur e, frequencies of RAPD in a microspore-derived population obtained from an F-1 of the same parentage were scored. Several parts of the linkage map sho wed a conspicuous distortion toward 'Homei 09' alleles. The microspores of another F-2 population from the same parentage were cultured. Embryogenic a bility and RAPD genotype of the each F-2 plant were scored. Embryogenic abi lity of the plants for two marker types (presence and absence) was determin ed at each RAPD locus. In some parts of the linkage map, the plants carryin g 'Homei 09' alleles showed a higher ability of embryogenesis than those of 'Siloga S2' homozygotes, Comparison of the distortion data with those in t he embryogenesis of the F-2 suggested that at least one part of the linkage map affected the embryogenic process in microspore culture. Genes in these areas of 'Homei 09' may play a key role in triggering the embryogenesis or in embryo development at the early stage of microspore culture.