Diploid + Tatraploid = Triploid
History and Taxonomy
Known culture of the watermelon dates back to pictures made in ancient Egypt. Names for the watermelon have appeared in the old literature of the Arabic, Berber, Sanskrit, Sardinian, and Visigoth languages. Early cultivation of the crop occurred in the Mediterranean area and as far east as India. The diploid watermelon as we know it today was unknown in Europe until the sixteenth century. Africa is considered to be its native home. Point of fact, watermelon was classified as Citrullus vulgaris until 1963 when Thieret called attention to the correct name Citrullus lanatus. Watermelon in both bitter and sweet forms was found growing wild in Africa by Livingston (1857) in regions not previously visited by outsiders. In a paper by Carrier (1924) it reports evidence indicating possible American origin. Early French explorers found Native American’s growing watermelons in the Mississippi Valley. As early as 1629 the watermelon was grown in Massachusetts, and by Native American’s in Florida prior to 1664.The watermelon belongs to the genus Citrullus, of which there are four species, all in tropical Africa. The watermelon C. lanatus and the Citron, or preserving melon, belongs to the same species. According to Shimotsuma in Cytogenetical studies in the genus Citrullus, it was concluded that a bitter-fruited form of C. vulgaris is the ancestor of the cultivated watermelon. The four species, lanatus, colocynthus, naudinianus, and ecirrhosus all have 22 chromosomes according to Shimotsuma’s cytological studies. Although the watermelon is used as a fresh fruit, it is also known to be used in the making of wine and beer, boiled down to make heavy syrup, and in the mid-east and other eastern nations watermelon seeds are enjoyed roasted and eaten.
The Making Of Seedless Triploids
Seedless watermelons (Triploid) were first produced in Japan in 1939 and first described in U.S. literature in 1951. Triploid watermelons (3n) have three sets of chromosomes. Seed for planting is produced by cross-pollinating a diploid (2n) male parent with a tetraploid (4n) female parent. When the number of chromosomes in a diploid plant is doubled by the use of the chemical Colchicine the resulting watermelon plant is a tetraploid having four sets of chromosomes. When the tetraploid plant is bred back, or pollinated by a diploid plant, the resulting seed produces a triploid plant. Triploid watermelons are not a natural occurrence in nature and are sterile, they produce fruit that normally have no seed or have small white soft edible seeds (ovules). Triploid watermelons are self-infertile and cross-pollination is necessary. Triploid watermelons just as diploid watermelons produce both male and female flowers on the same plant. The difference between the flowers of the triploid and diploid is the male flowers of the triploid watermelon produces very little pollen, and what little pollen there is, is incompatible with the female flower of the same plant. Pollen from a diploid watermelon or ‘’Pollinator’’ is necessary to pollinate the female flowers of the triploid to set fruit and stimulate fruit enlargement.
Procedure for producing seed of seedless triploid watermelon.
The tetraploid line must be used as the female parent, because the reciprocal cross using the diploid as female results in empty seed. Seedless melons are the result of stimulative parthenocarpy (pollination with normal diploid pollen).