Watermelon

Citrullus
lanatus

 Diploid + Tetraploid = 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. A
paper by Carrier (1924) reports evidence indicating possible American origin.
Early French explorers found Native Americans growing watermelons in the
Mississippi Valley. As early as 1629 the watermelon was grown in Massachusetts,
and by Native Americans 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, belong 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 seeds 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 that small amount
of pollen 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.

 Inbred Tetraploid

image

From

Colchicine
   Treatment

Cutline for chart: 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).

 

Footnote:

Este informe fue preparado por Jefferson Lowe, ingeniero de sistemas
agrícolas. Estos consejos se basan en su propia
experiencia y en la experiencia de otros productores entendidos. Para más información:
plantersguild.com