Major QTL for carrot color are positionally associated with carotenoid biosynthetic genes and interact epistatically in a domesticated × wild carrot cross
Investigations on the inheritance of root color in carrot (Daucus carota L.) were carried out by crossing uniformly colored roots to various tinge type roots, i.e. roots of which the xylem differs in color from the phloem. A single major gene (Y) was found to be responsible for the observed differences in progenies of orange x tinge orange-white (orange referring to phloem color, white to xylem color) crosses. Plants carrying the dominant Y-allele had either white or tinge orange-white roots, whereas plants with orange roots were of the genotype yy. Similarly one major gene (Y 2) determined the segregation found in progenies of orange x yellow crosses. In the latter crosses, plants having the dominant Y 2-allele had either yellow or tinge orange-yellow roots while the recessive would be orange. Variation in phloem color, i.e. differences between white and tinge orange-white or between yellow and tinge orange-yellow, was apparently caused by minor genes, modifiers, gene interactions, or by genes that are not involved in carotenogenesis in a direct way. When both the Y- and Y 2-genes were present, the roots were always white. Usually white roots gave a digenic segregation pattern in the F2 when crossed to orange, but there was some evidence that a third gene (Y 1) was segregating in some crosses. Tinge orange-white x yellow crosses gave approximately the same results as orange x white crosses, confirming that the same Y- and Y 2-genes were segregating. In crosses between orange lines and a light yellow line (RY) certain F1 's appeared to have a light orange xylem and a fairly dark orange phloem, which seems to be some evidence for the existence of recessive yellow. Although almost nothing is known yet about the genetics of RY it is assumed that it still carries a dominant inhibitor gene which may be leaky in heterozygous condition. The value of such a line as an aid in the selection of superior orange lines is discussed. Alpha- and beta-carotene were found to be the major pigments in orange carrot tissue; phytofluene, zetacarotene, gamma-carotene and xanthophylls were shown to be present in smaller amounts. Besides xanthophylls and a small amount of beta-carotene dark yellow carrot tissue appeared to contain an appreciable amount of an unidentified pigment (pigment I). Light yellow and white phloem or xylem tissue were low in total carotenoids.