QTL analysis of shoot elongation before winter in relation to vernalization requirement in the doubled haploid population L16 × Express617 (Brassica napus L.)

In winter oilseed rape shoot elongation before winter is considered as a critical component of the complex trait winter hardiness. Genotypes with an enhanced shoot length before winter are very much prone to frost damage. However, it is not known to which extent shoot elongation before winter is related to vernalization requirement. Shoot length measured 3 months after sowing of winter oilseed rape in spring has been shown to be a good quantitative estimator for vernalization requirement. The main objective of this study was to analyze inheritance of shoot elongation before winter and in spring-sown field experiments using a doubled haploid population derived from the cross between two inbred lines. A SNP based molecular marker map was used to map QTL for shoot length and flowering time. Significant genotypic effects were detected for shoot length before winter and in the spring-sown environment, but there was no correlation between both traits. Six QTL for shoot length before winter contributed 49.2% to the phenotypic variance. For shoot length in the spring-sown environment three QTL were detected that explained 68% of the phenotypic variance. Flowering time genes CONSTANS (BnaC09g41980D), FLC (BnaC09g42060D) and FT (BnaA02g12130D) were identified within C09 and A02 QTL confidence intervals. No collocation of QTL for shoot length before winter and for shoot length in the spring-sown environment was found. Results show that selection for reduced shoot length before winter would be effective and that this trait is inherited largely independent of vernalization requirement.