Genotype X environment interactions and heritability of tocopherol contents in canola

Tocopherols are natural antioxidants found in all vegetable oils. They are important dietary nutrients and thus breeding for increased tocopherol content is a new and important objective in canola (Brassica napus L.). Tocopherols exist in four forms (alpha-, beta-, gamma-, and delta-tocopherol) differing in molecular structure and biological effectiveness. In the seed oil of canola, mainly a- and gamma-tocopberol are found with an alpha/-gamma-tocopherol ratio of about 0.5. Three canola populations of doubled haploid lines were grown in three to four field environments to analyze genetic variance and genotype X environment interactions as well as heritability of tocopherols and correlations with other seed components. Significant genotypic differences occur, but large genotype X environment interactions are the major source of variation. Heritability of tocopherol was low in all three populations; the estimates ranged from 0.23 to 0.44 for alpha-tocopherol and from 0.33 to 0.50 for gamma-tocopherol. Heritability for tocopheroll content is considerably lower than heritability of oil content (0.56-0.90), protein content (0.43-0.76), or glucosinolate content (0.91-0.95). No correlation between alpha- and gamma-tocopherol or between tocopherol and oil, protein, and glucosinolate content was detected. Individual tocopherols can be increased independently of each other and without affecting other major quality traits.