QTL-seq identifies BnaFT.A02 and BnaFLC.A02 as candidates for variation in vernalisation requirement and response in winter oilseed rape (Brassica napus).

Winter, spring and biennial varieties of Brassica napus that vary in vernalisation requirement are grown for vegetable and oil production. Here, we show that the obligate or facultative nature of the vernalisation requirement in European winter oilseed rape is determined by allelic variation at a 10Mbp region on chromosome A02. This region includes orthologues of the key floral regulators FLOWERING LOCUS C (BnaFLC.A02) and FLOWERING LOCUS T (BnaFT.A02). Polymorphism at BnaFLC.A02 and BnaFT.A02, mostly in cis-regulatory regions, results in distinct gene expression dynamics in response to vernalisation treatment. Our data suggest allelic variation at BnaFT.A02 is associated with flowering time in the absence of vernalisation, while variation at BnaFLC.A02 is associated with flowering time under vernalising conditions. We hypothesise selection for BnaFLC.A02 and BnaFT.A02 gene expression variation has facilitated the generation of European winter oilseed rape varieties that are adapted to different winter climates. This knowledge will allow for the selection of alleles of flowering time regulators that alter the vernalisation requirement of oilseed rape, informing the generation of new varieties with adapted flowering times and improved yields.