Where Do Seedless Watermelons Come From?

This past week we had a Vegetable Production Tour around Taylor and Thrall. On this tour we talked about a lot of things including melons and melon production. I have been asked on occasion “Where Do Seedless Watermelons Come From?” and since we are very close to enjoying the first seedless melons of the season I thought we might learn about this great tasting treat.
How do you get seed from a seedless watermelon? Well the process is simple but lengthy taking two generations. First, you need to understand a little about chromosomes, the threadlike bodies that contain genes for development. A regular watermelon has two sets of chromosomes and is called a diploid (di for two). A plant breeder will take a diploid watermelon seed and treat it with a chemical called colchicine. Colchicine will cause the seed to develop a melon with four sets of chromosomes called a tetraploid (tetra for four). This melon is grown out and the seed harvested for the next growing season. This tetraploid seed is planted and begins to grow but the plant is covered with a spun row cover to prevent any pollination so that the plant breeder can pollinate at the right time with a diploid melon variety. These melons will grow and the seed from them will be harvested. The cross of tetraploid plant with a diploid plant results in triploid seed. This plant has three sets of chromosomes and is the “mule” of the watermelon family. This seed when planted will produce a seedless melon meaning it is sterile.
Seedless melons are really a favorite of the urban clientele. They don’t buy grapes with seeds and they don’t like melons with seeds (what do you do with the seeds in a nice restaurant). They are excellent for salad bars and are sold in grocery stores sliced and ready to eat. Seedless watermelon are typically smaller and so fit easily in the refrigerator, another plus for the urban American.
Growing seedless melons are a little different than the typical watermelon. First this seed is very fragile and must be germinated under higher than normal germination temperatures. We will germinate seeds in chambers with 90+ degree temperatures. This forces the seed to quickly germinate and begin to grow versus a cold soil in the field which will slow seed germination enough that most seedless plants won’t make it. Because of its temperamental nature a seedless watermelon is grown as a transplant first and then moved into the field later after getting a good root system established. These seeds cost from 17¢ to 25¢ a piece and growing the actual plant in a pot to be transplanted costs another 10¢ for a total of approximately 32¢ per plant. The germination percentage is low for seedless, around 80%, so that cost can go up even more. It takes about 1500 to 1700 plants per acre or about $450.00 per acre of planted seedless melons, a lot money and still 80 days till harvest.
Seedless have other good traits besides being seedless. They are very productive generally producing more melons than any hybrids if grown properly. They are also disease tolerant plants resisting many of the diseases that other melons quickly die from and seedless are good shippers, holding flavor for a long time.
I mentioned that the seedless is the “mule” of melons, well a watermelon produces both male and female flowers so that we can plant one variety in a field and bees can pollinate with no trouble. A seedless melon produces a male flower that cannot pollinate another melon so to get by this we have to plant seeded melon rows next to the seedless rows to insure good pollination. I have seen mix ups in the field where seedless plants covered 10 solid rows so that the outside two rows were they only ones with melons. Having a pollinator row for seedless is mandatory if you want seedless melons, a fact you should know if you want to try seedless in your garden.