Brassica napus (B. napus, AACC, 2n=38) is an economically important oilseed crop which provides approximately 13-16% of the vegetable oil globally. B. napus is originated in the Mediterranean region about 7500 years ago by natural hybridization between two diploid progenitors, B. rapa (AA, 2n=20) and B. oleracea (CC, 2n=18). The genetic pool of B. napus has been broadened by introgression of genes from B. rapa and synthetic materials produced by artificial crossing between the two diploid progenitors. Driven by response to seasonal changes such as vernalization requirement, winter hardiness, and photoperiod-responsive flowering, B. napus has been domesticated with various characteristics. Nowadays, three ecotypes of B. napus are widely distributed in Europe, Asia, Australia and North America. Winter type oilseed rapes (WORs) was firstly cultivated in Europe and it was suggested to be the original form of B. napus. After being introduced into China, Australia and North America in the 20th century, cultivated B. napus has undergone adaptive changes under the combination of natural and artificial selection in order to adapt to different geographical environments and climates.
The concept of pan-genome was proposed to represent a repertoire of genes including core genes and dispensable genes of a species. Pan-genomes have been constructed based on NGS technologies for major crops including soybean, maize, rapeseed and rice using different number of individuals, which played important roles in the identification of SVs including copy number variants (CNVs) and presence/absence variants (PAVs) that are associated with crop agronomic traits.
