Deciphering the Genetic Control of Yield and Yield Components of Winter Oilseed Rape (Brassica napus L.) Grown Under Nitrogen Constraints with Combined Linkage and Association Analyses

Nitrogen Use Efficiency (NUE) is a breeding trait of major importance for many crop species, as it may be a lever for a more environmentally and economically sustainable agriculture. This quantitative complex trait is suspected to be sensitive to ‘genotype x environment’ interactions. Therefore, combining multiple trials and populations may be a powerful approach to study it. Rapeseed is a major oil crop with a relatively low NUE making its production highly dependent on N inputs. The objectives of this work were to determine the genomic regions associated with yield in winter oilseed rape (WOSR) and to assess their stability under contrasted N conditions, in order to improve the NUE. To achieve this, a combined linkage disequilibrium-linkage analysis (LD-LA) was conducted on a diversity set of 93 accessions and two doubled-haploid populations respectively. Those populations were densely genotyped with a 60K SNP Illumina Brassica array and tested in a multi-trial design including three French locations, five growing seasons (2009 to 2013) and two N nutrition levels (N+ optimal and N- low). Yield and yield-related traits were scored and N-responsive traits were calculated as N-/N+ and DN/N+. Very few ‘genotype x N’ interactions were detected and a great stability of the QTLs was assessed between the N conditions. On the contrary, strong ‘genotype x site’ interactions were found with most of the QTLs specific to one site only. This work came up with the detection of several QTL regions of interest. A particular dense region was identified on the A5 linkage group with QTL stable across sites and N conditions. In addition, a workflow specific to B. napus was developed for in silico analysis of the genes underlying these regions and preliminary promising results will be presented.