Molecular Study On The Classification And Phylogeny Of Brassica Rapa L.

Brassica rapa L. has a long history of cultivation with vast genetic diversity. it is not only important vegetables, but also important oil crops. The classification and evolution of Brassica rapa are not very clear although some research have been done. In this research 63 accessions of Brassica rapa from different regions were used to study their phylogeny and classification by nuclear and chloroplast DNA analysis. The results are shown as follows:1. The characteristics of 63 accessions were use for clustering: all accessions are classified into 3 groups. The group I included two sub-groups, the first sub-group includes zicaitai, 5 taicai; the second sub-group included 7 Turnip rape, one Broccoletto, Pak choi(Zhengzhou black cabbage). Groupâ…¡included 13 Pak choi, 3 caixin, 2 Chinese cabbage, two Yellow heart cabbage ,7 Wuta-tsai, 5 turnip. Groupâ…¢included 14 Chinese cabbage and one Pak choi.2. The ITS of 18 different types of Brassica rapa L. were amplified by PCR and sequenced, and used to construct the NJ tree. The results showed that the sequences of the ITS of Brassica rapa L. had no variations among different types. That indicates that he sequences of ITS of Brassica rapa L. were very conservative. Among Brassicas, Brassica rapa L. is closer to B. napus, B.olereacea than to B. juncea, B. nigra. The relationship of the brassica species by the ITS sequences is as the same as shown by U-triangle.3. SSR and SRAP were used to the genetic diversity of 63 accessions of Brassica rapa L. Seventy two pairs of primers were selected. One hundred and fifty six polymorpsim bands were obtained. The results showed that cultivars of non-heading Chinese cabbage were clustered into Group I. turnip rapa and caitai were included in Group II. Heading Chinese cabbage was Group III. Turnips existed at Group II and Group III respectively. Three distinct gene pools exist among the accessions of Brassica rapa.4. Thirty three chloroplast genome cpSSR markers were amplified for the study of genetic diversity. The results showed that there was no polymorphic bands between 63 Brassica rapa accessions, namely the chloroplast genome was very conservative and had no genetic diversity by the SSR markers.5. The atpB-rbcL and the trnL-trnF gene spacers were amplified in 6 Brassica rapa accessions. Both of amplified bands were 700 bp approximately. TrnL-trnF sequence was not found differences among Brassica rapa accessions. AtpB-rbcL sequence had obvious variations among tested accessions. atpB-rbcL sequences were used to construct the phylogeny evolution tree. Brassica rapa, Brassica oleracea and Brassica napus were didvided into different branches. Brassica rapa accessions also were divided into two branches.