Extension Educator, Horticulture
We can thank plant geneticists for many modern conveniences – seedless grapes, seedless oranges and seedless watermelon. But sometimes it's nice to relive moments of our youth when all a summer party needed was an ice cold watermelon and a good place to spit. I seldom won watermelon seed spitting contests, but it wasn't for lack of practice. My seeds were more high divers than long jumpers.
Seeded watermelon can have as many as a thousand seeds in one fruit, enough to keep a kid spitting for hours. However the seeds are a bother when making a fruit salad or a smoothie. In addition seedless watermelons are usually considered sweeter.
Seedless watermelons are self-sterile hybrids that develop normal-looking fruits but no fully developed seeds. You may notice a few white soft seedcoats, not worth spitting.
The production of seedless watermelons is all about genetics. The normal chromosome number in most living organisms, including people, is diploid; one set from your mom and one set from your dad. The seeds for growing seedless watermelons are produced by crossing a normal diploid watermelon with one that has been changed genetically, usually through a chemical treatment, into a tetraploid with four sets of chromosomes. The seeds from this cross are triploid with three sets of chromosomes rendering them highly sterile. These seeds are planted. The resulting plants produce seedless melons. However since their flowers are sterile, the seedless watermelon plants must be interplanted with seeded melons for the necessary pollination for fruit to develop. Seedless watermelon production is labor intensive which accounts for their higher price.
Whether they are seeded or seedless, red fleshed or yellow fleshed, watermelons do not continue to ripen after they have been harvested. How do you pick out the best watermelon?
Use a combination of the following indicators:
I often hear the statement that watermelons are not very sweet or flavorful because they crossed with other vine crops in the garden. Canvas the audience because it's not the reason. Although watermelon varieties can cross with one another, cross-pollination is not apparent unless seeds are saved and planted the next year. Watermelons do not cross with muskmelons, squash, pumpkins or cucumbers. The poor quality of melons is likely the result of unfavorable weather conditions such as high rainfall or cool weather. The sweetest watermelons grow during long hot summers. Poor quality may also be due to diseased vines or too short a growing season.
For more information on growing watermelon http://urbanext.illinois.edu/veggies/