A candidate gene association analysis for tocopherol content and composition in rapeseed (Brassica napus)

Tocopherol, also called vitamin E, is an essential nutrient for humans and animals due to its antioxidant and radical scavenging abilities. Increasing the tocopherol content is a target of rapeseed breeding. Measuring tocopherol by HPLC, however, is laborious and expensive. Therefore, we aim to identify polymorphisms within candidate genes and to analyze their association with variation in tocopherol content and composition in rapeseed. Two diverse panels of 96 and 133 rapeseed accessions were phenotyped and high heritabilities were observed. Polymorphisms were identified by re-sequencing fragments of 13 candidate genes in the 96-accession panel. Two models were used for association analysis: A general linear model, which includes population structure information, and the PK mixed model, which accounts for population structure and familial relatedness between accessions. Applying both models, the number of SNPs with significant (P<0.05) associations to the investigated traits ranged between 26 and 13. Two of these explained 6.37 - 11.21 % of the genetic variance for tocopherol composition and 4.96 - 8.8 % for total tocopherol content. Several significant SNPs were converted to markers and used for genotyping the 133-accession panel. The results clearly indicate that the allelic variation in the analyzed tocopherol genes affects the tocopherol content and composition. Thus, promising molecular markers were detected which can be used as selection markers for breeding rapeseed with enhanced tocopherol content or altered composition.