Mapping of Loci Affecting the Cultural Efficiency of Microspore Culture of Brassica rapa L. syn. campestris L. using DNA Polymorphism

A Iinkage map of Brassica rapa was constructed based on random amplified polymorphic DNAs (RAPDs), isozymes and restriction fragment length polymorphism (RFLP), using an F_2 population derived from the crossing of a Chinese cabbage 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 linkage groups. `Homei 09' is highly responsive to microspore culture unlike `Siloga S2'. To identify the loci affecting embryogenesis in microspore culture, 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 showed a conspicuous distortion toward `Homei 09' alleles. The microspores of another F_2 population from the same parentage were cultured. Embryogenic ability and RAPD genotype of the each F_2 plant were scored. Embryogenic ability of the plants for two marker types (presence and absence) was determined at each RAPD Iocus. In some parts of the linkage nrap, the plants carrying `Homei 09' alleles showed a higher ability of embryogenesis than those of `Siloga S2' homozygotes. Comparison of the distortion data with those in the 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.