Taxonomic relationship between Chinese kale and other varieties in Brassica oleracea L.

The taxonomic relationship has been studied between Chinese kale and the other varieties of Brassica oleracea L.,two Chinese kale cultivars,two broccoli cultivars,two kohlrab cultivars and two cabbage cultivars.Crosses have been made among Chinese kale and broccoli,kohlrab,cabbage,the three varieties of Brassica oleracea,the cross compatibility indexes were investigated,and the resulting hybrids were self-crossed to assess and self-compatibility index.Botanic characters of eight parents and 24 cross combinations were adopted to perform cluster analysis.Our results showed successful crosses between Chinese kale and the three representative varieties of Brassica oleracea with an average compatibility index of 13.4.All resulting hybrids developed into normal and fertile plants,and they had a compatibility index of 14.1 when self-crossed.The hybrids showed combined morphologies of their parents,with different degrees of biases toward broccoli,kohlrab,cabbage,respectively.It was also found that the F2 seeds germinated normally.Cluster analysis with euclidean distance 2.78 implied that two Chinese kale cultivars could be classified into one group,two cabbage cultivars and eight F1 hybrids crossed with two cabbage cultivars and two Chinese kale cultivars could be classified into one group,two broccoli cultivars and eight F1 hybrids crossed with two broccoli cultivars and two Chinese kale cultivars could be classified into one group,and two kohlrab cultivars and eight F1 hybrids crossed with two kohlrab cultivars and two Chinese kale cultivars could be classified into one group.The relationship between Chinese kale and cabbage was closer than that between Chinese kale and broccoli or kohlrabi.Therefore,we conclude that Chinese kale and Brassica oleracea L.most likely belong to the same species,and hypothesize that Chinese kale as another variety of Brassica oleracea may be evolved from cabbage.