Development of carrot (Daucus carota) germplasm with elevated levels of carotenoids and tocopherols, and effects of the Rp locus on phytochemical composition

Carotenoids and tocopherols are valuable health functional phytochemicals, serving as powerful antioxidants in both plants and animals. The two chemicals classes are synthesized in related pathways, arising from the common precursor geranyl-geranyl pyrophosphate (GGPP). Increasing the content of both in plants would increase their nutritive value. Seed oil contains high levels of tocopherols, but little is known of their levels in the edible portions of most horticultural crops.; To ascertain levels of tocopherols in edible plant organs, a one-pass semi-quantitative extraction and detection method was developed to measure tocopherols and carotenoids. A screening of carrot hybrid lines showed levels of alpha-tocopherol and alpha- and beta-carotene of 0.12 ppm, 589 ppm, and 889 ppm, respectively. This protocol was used to screen a variety of carrot germplasm, including the reduced pigment (rp) mutation. Alpha-tocopherol and beta-carotene showed a significant (p < 0.001) correlation (r = 0.65), suggesting the ability to select for both in carrots. The rp mutation caused a 97% reduction in carotenoid levels.; Populations were developed from diverse germplasm to increase levels of tocopherols and carotenoids. An increase of 0.30 ppm was seen for alpha-tocopherol under direct selection, with heritability estimates of 0.156 to 0.721. Environmental interaction was a major factor in the diverse levels of heritability. A screening of colored carrot germplasm found accessions higher in gamma-tocopherol, ranging from undetectable to 3.0 ppm. Although only 2 cycles of selection have been completed, these results indicate breeding for increased alpha-tocopherol levels is feasible in carrot.