Seedless watermelons have grown in popularity since their growth in the early 1950s. According to the University of California Vegetable Research Center, more than half of the watermelons grown in California are seedless. The fact that they’re seedless, raises a question: Should seedless watermelons produce no seeds, how do mothers develop the next generation of melons? The reply to that question can be found in the lab in which the parents of seedless watermelons start their lives.
Watermelons normally have 22 chromosomes per cell. Should you treat a watermelon seedling using colchicine, that seedling will create watermelons with double the number of chromosomes — 44 chromosomes per cell. If you then take a 44-chromosome female watermelon flower and fertilize it with pollen from a 22-chromosome watermelon, you get a triploid, a 33-chromosome watermelon. Triploid watermelon plants create seedless melons.
The issue with triploid watermelons is that they’re sterile. Normal watermelon plants have both male and female blossoms. Pollen from the male blossoms fertilizes the female flowers, and from the fertilized flowers develop melons. Triploid watermelons also have female and male flowers. The female flowers of a triploid watermelon are able to create melons, however, also the pollen from the male areas of the plant is tight and not good quality, therefore the female flowers don’t get fertilized reliably.
The solution to triploid watermelons’ fertility issues is to develop them next to ordinary 22-chromosome watermelons. The normal watermelons create the male genetic material, which fertilizes the female areas of the triploid plants. The majority of the watermelons that develop on the triploid plants possess the seedless trait from the mother, so that they are seedless. In commercial antiviral fields, between 66 and 75 percent of those plants in the area are triploid. The remainder are the pollinating plants.
Triploid watermelons aren’t simply sterile, they also have a tendency to be weaker compared to 22-chromosome watermelons. Triploid melons themselves tend to be smaller compared to their 22-chromosome counterparts. The seeds also have a tendency to germinate badly. For this reason, most growers plant triploid seeds in apartments so that they can be grown to seedlings in the climate-controlled environment of a greenhouse. Seedless melons often cost more in the shop since the plants aren’t as hardy or prolific, part of the area must be planted with seeded pollinators and additional breeding is needed to create the seeds.