The Origin and Diversity of Brassica napus from Brassica rapa and Brassica oleracea

Brassica napus is a worldwide crop that has been domesticated primarily for oilseed (canola) but also as a leafy green and as a root vegetable (rutabaga or swede). It is an allopolyploid species that evolved from the hybridization of two other species about 7,500 years ago. The ancestors of the two parental species have also been domesticated for multiple uses: Brassica rapa (Chinese cabbage, Pak Choi, turnip, sarson and others) and Brassica oleracea (Brussels sprouts, broccoli, cauliflower, cabbage, kale and others). Characterization of their origin and population structure is not only of fundamental biological interest, but also essential for Brassica napus germplasm conservation and crop improvement. We generated about 10M SNPs from transcriptomic data of Brassica rapa, Brassica oleracea, Brassica napus and outgroup species. We performed population structure and phylogenetic analyses to identify the parental contributions of Brassica rapa and Brassica oleracea to Brassica napus along with the relationships of cultivated varieties within Brassica napus.