Principal component analysis (PCA) and unweighted pair group matrix algorithm (UPGMA) tree describing genetic relationships among 212 winter, spring and semi-winter type B. napus accessions. Q1, Q2 and Q3 are the three subgroups identified by STRUCTURE, assigned with the maximum membership probability, while the mixed subpopulation contains accessions that could not be specifically assigned by STRUCTURE to a single subpopulation. a) PCA analysis of 212 semi-winter, winter and spring-type accessions. b) PCA analysis of only the 203 Chinese semi-winter accessions. c) UPGMA analysis of only the 203 Chinese semi-winter accessions.