Carotenoids are responsible for the different flesh colors in watermelon fruit, such as white, salmon yellow, orange, pale yellow, canary yellow, crimson red, and scarlet red. In red-fleshed watermelons lycopene constitutes the major pigment and b-carotene the secondary. The predominant carotenoid in yellow-fleshed watermelon is neoxanthin. Lycopene content in watermelon is related to genotype and ploidy level, harvest maturity, and growth and development conditions. Watermelon flesh colors are controlled by several gene loci. There are two or three alleles identified at each gene locus. Up to now several full-length cDNAs or gene fragments encoding enzymes in the carotenoid metabolic pathway have been isolated and characterized from mature watermelon fruits. Differential expression of carotenogenic genes was examined in flesh, ovary, leaf, and root tissues across different colored fleshes (white, canary yellow, salmon yellow, orange, and red). Carotenogenic gene expression was also analyzed at three fruit developmental stages (10, 20, and 30 days postanthesis) in five flesh colors of watermelon cultivars (red, pink, orange, yellow, and white).