Lawn & Garden
AUBURN UNIVERSITY, Ala. – For many, watermelons are an all-time favorite summer treat. More recently, consumers are seeing more availability of seedless varieties of watermelons. The genetics of these varieties are quite complex. This complexity may explain why costs are greater with seedless watermelon varieties.
Dr. Joe Kemble, an Alabama Extension vegetable specialist, said the science behind seedless watermelons dates back over five decades.
“Triploid, better known as seedless, watermelons were first developed in Japan over 50 years ago,” Kemble said. “Although, seedless watermelons were not heavily commercialized until the past 15 to 20 years.”
Seedless watermelons are always hybrids. This fact makes seed costlier. One difficulty associated with seedless varieties are the seeds themselves. The embryos of these seeds often develop poorly, usually filling only about 80 percent of the seed cavity.
“These poorly developed embryos have thick seed coats,” he said. “This situation makes it more difficult for them to germinate and can decrease a seedling’s strength.”
Growers must take special steps in germinating these seeds. This includes using controlled temperatures and more precise moisture control during the germination process. According to Kemble, direct seeding into a field generally results in poor, weak stands.
Planting and Growing
Growers should plant triploid seedlings during mild weather, where the seedlings will be protected from harsh environmental conditions. In order for a seedless watermelon to produce fruit, Kemble said that a seeded (diploid) variety of watermelon, or a specifically developed pollinizer, must be planted nearby in order to ensure an adequate supply of viable pollen.
“The flowers of the seedless varieties produce little, to no viable pollen,” Kemble said. “The stigmas, however, are receptive to pollen and require viable pollen in order to initiate the process of fruit development.”
Seed companies have recommended pollinizers or seeded watermelon varieties for each of their seedless watermelon varieties. Pollinators, such as honeybees, also play a critical part in the process. They must be present to transfer the pollen from the seeded variety plants to the seedless plants.
Kemble said that in order to produce correctly, these plants must avoid stressful conditions such as lack of water, too much water or temperature extremes.
Alabama Extension’s article Seedless Watermelons: Why Are Seeds Costly and Why Do They Produce Seeds Sometimes provides further details about seedless watermelons. For more information, visit Alabama Extension online at www.aces.edu or contact your local Extension horticulture agent.