The effect of nitrogen fertilization on tocopherols in rapeseed genotypes

Tocopherols (alpha-, beta-, gamma- and delta-tocopherol) are naturally occuring antioxidants in vegetable oils. In rapeseed oil, alpha- and gamma-tocopherols are the predominant isomers, while delta-tocopherol contributes much lower amounts to the total tocopherol content. Enhanced tocopherol content in seeds appears favourable, and breeding for tocopherol content has become an increasingly important objective in winter oilseed rape. The main objectives of this research were to quantify the amount of tocopherols in a number of rapeseed varieties and to investigate the effect of nitrogen fertilization on tocopherol concentration in the seed. The field trials were carried out in 2004-2005 and 2005-2006 at Dardanos, Canakkale on the Turkish West Coast (10 km south of the city centre) with 13 varieties, three replications and three nitrogen levels (N(0): 0 kg/ha, N(1): 130 kg/ha and N(2): 260 kg/ha). The trial used a randomized complete block design with 6 m(2) plots. Tocopherol analysis was done using an HPLC system. Significant differences were found among the varieties and between the nitrogen levels. The average total tocopherol concentration was 118.7 mg kg(-1) for N(1), 134.1 mg kg(-1) for N(2) and 133.6 mg kg(-1) for N(3) fertilization level. MDS analysis indicated a rough grouping of line versus hybrid varieties and suggested that hybrids require more breeding effort to reach the level of tocopherols existed in line varieties.