| The crops of Brassica oleracea, including kale, cabbage, savoy cabbage, red cabbage, brussels sprouts, kohlrabi, broccoli, cauliflower, and Chinese kale, are cultivated all over the world. They can be used as vegetable, fodder and ornamental plant, and has important economic value. Different varieties of B. oleracea can be hybridized easily each other and the offspring has normal seed vigor. Their origins and phylogenetic relations aroused great interest of researchers. Previous studies of B. oleracea genetic relationships had been carried out and analyzed the origin and phylogenetic relations of the cabbage, savoy cabbage, red cabbage, brussels sprouts, kohlrabi, broccoli and cauliflower. However, the studies remained limitations in quantity and the representation of the materials, and the relative lack of evidence on molecular level, and the controversy in the origin and genetic relationships among varieties in B.oleracea, particularly for Chinese kale. Based on the development of EST-SSR (Expressed sequence tag SSR) markers in B. oleracea, therefore this study used some wild cabbages, and inbred lines, local cultivars, and hybrids of crops of B. oleracea as materials to analyze the genetic diversity among them, and to understand the origin and genetic relationships of B. oleracea on molecular level.First,we investigated the botanical characters of B. oleracea. One detailed phylogenetic tree of 109 B. oleracea was generated by UPGMA clustering based on 14 botanical characters. 109 accessions were divided into three groups, (1) wild cabbge, kale, cabbage, savoy cabbage, red cabbage, kohlrabi, and brussels sprouts, (2) broccoli and cauliflower, (3) Chinese kale.Then EST-SSR was used to study the genetic relationships 183 accessions of B. oleracea. 174 polymorphic fragments were amplified from 61 primers of EST-SSR. The genetic similarity coefficients were calculated by software NTSYSpc2.11 based on EST-SSR results, and one detailed phylogenetic tree was generated by UPGMA clustering. In the study of EST-SSR, all accessions were divided into three groups on coefficient of 0.62, the group of coasts of Northwest Europe included wild cabbge, kale, cabbage, savoy cabbage, red cabbage, kohlrabi, and brussels sprouts, the group of coasts of Mediterranean included broccoli and cauliflower, and the group of South China was all Chinese kale. This result supported the view that Chinese kale originated from China. Most accessions of the wild cabbage, introduced from UK and belonged to B. oleracea, were clustered to the group of coasts of Northwest Europe and showed close genetic relationships with kale, common cabbage, savoy cabbage, red cabbage, brussels sprouts and kohlrabi. Except for wild cabbage the other accessions were divided into five groups on coefficient of 0.65, (1) kale and kohlrabi, (2) heading cabbage (savoy cabbage, common cabbage, and red cabbage), (3) brussels sprouts, (4) cauliflower and broccoli, (5) Chinese kale. The result suggested that above five groups evolved from different evolutionary pathways. Last, To be more comprehensively reveal the origin and genetic relationships among the varieties of B. oleracea, we obtained some gSSR markers to study the genetic relationships 183 accessions of B. oleracea. 129 polymorphic fragments were amplified from 49 primers of gSSR. Combined EST-SSR markes and gSSR markers together and Compared with the EST-SSR results without gSSR markers, kohlrabi, kale, brussels sprouts, and wild cabbage clustered into one group, wild cabbage gathered much close, and savoy cabbage, red cabbage and common cabbage were clustered more close than before.EST-SSR markers were developed from a large number of EST fragments of cDNA. Due to the amplified products of EST-SSR were associated with the phenotypic characteristics, it was suitable to analyze the origination and domestication of B. oleracea. Combined EST-SSR markes and gSSR markers together, this study obtained more accurate results for the origin and genetic relationships of different varieties in B. oleracea. |
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