Linkage relationships of genes affecting bitterness and flesh color in watermelon

The genetic basis of two traits of watermelon fruit was investigated in a backcross generation resulting from hybridization between an interspecific F₁ hybrid of Citrullus lanatus and C. colocynthis with the cultivated parent C. lanatus. Bitterness of the fruit, a trait that characterizes wild C. colocynthis, was found to be governed by a single dominant gene (Bi) linked to the isozyme marker Pgm-1 at a distance of 11.3 cM. The appearance of red color in the fruit is determined by a single recessive gene (red) that is linked to the isozyme marker Gdh-2 at a distance of 12.8 cM. These two marker loci and the two newly identified genes are on linkage group 3. Using another backcross population between C. lanatus and C. colocynthis and an F2 population between C. colocynthis and C. ecirrho-sus, we identified three new linkage groups: linkage group 5 with 6Pgd-1 and Aps-2, linkage group 6 with Dia-1 and For-1, and linkage group 7 with Est-1 and Adh-1. Three marker loci–Prx-2, Prx-3, and Got-4– were added to linkage groups 1 and 4.