Creating the Sterile Melon
In the middle of the 20th century, plant breeders found a way to rid a watermelon of the black seeds that make eating one messy and a nuisance. The seedless watermelon arises from a hybrid cross between plants that are incompatible based on their chromosomal numbers. The male pollen from a normally numbered watermelon plant's flower is brushed upon the female flower parts on a blossom on a tetraploid watermelon vine.
The tetraploid plant has four sets of chromosomes in its cells, making its fruits and other plant parts physically larger. The resulting fruits and seeds that form are only triploid (three sets of chromosomes) and will germinate, but those plants will not form fruits with seeds.
In essence, the fruits that arise on the hybrid's vine are sterile; in fact, they fail to fully form and remain white seedcoats. Although these seedcoats remain in the juicy, tasty watermelon's flesh, they are soft and almost unnoticeable, much like the seeds of a salad cucumber. Only rarely will a lone, black viable seed ever be encountered in an entire seedless watermelon fruit.
The hybrid seedless watermelon varieties require more resources than the usual, traditionally seeded watermelons. While a regular watermelon seed germinates when soil temperatures are as low as 55 degrees Fahrenheit, seeds of seedless watermelon plant need temperatures of at least 80 degrees to sprout. The seedlings are also much slower to sprout, increasing the chances that a soil-borne fungus will harm it.
Another dilemma facing seedless watermelon plants in youth is that the seedcoat often sticks to the emerging seedlings, potentially blocking the development of the first leaves.
One advantage seedless watermelon plants have over seed-making watermelons is that seedless types tend to continue flowering and producing more fruits during the growing season. As long as growing conditions are optimal and diseases are avoided, seedless types do not expend energy in the creation of seeds and will continue to flower and form more fruits for harvest. In seeded watermelons, flowering and fruit production diminishes once the plant has formed fruits.
Producers of seedless watermelons are continually producing new varieties for possible introduction into the market. Some popular varieties include the following.
"Crimson Trio" is an oval, wide fruit with dark green stripes on a light green background.
"Genesis" is a rounded to oval fruit with medium green stripes on a light green background.
"King of Hearts" is a mid-season hybrid with box-like, oblong fruit, a thick rind and a stripe pattern.
"Scarlet Trio" bears oval fruit with thin dark green stripes on a light green background.
"Tiffany" is an early-season type with a round-oval fruits and wide dark green stripes on a medium green background.
Additional varieties of seedless types exist, many protected, guarded and used by the watermelon growers who developed them.