Can you recall your middle school biology class? I do! I teach it every day. Seedless watermelons are sterile hybrids, just like a mule. To get more mules, you need more horses and donkeys. To get more seedless watermelons, you need to cross male pollen that contains 22 chromosomes per cell (standard amount) with a female flower that has 44 chromosomes. when you plant those seeds, the fruit will mature, but the inside won’t contain any viable black watermelon seeds, only small white seed coats, which are edible.
To get a female flower to have double the number of chromosomes of a typical watermelon, scientists treat them with colchicine. This chemical is derived from a crocus.
If you think seedless watermelons taste blander than those with seeds, it’s your imagination. They have the same genes as their seeded siblings, and have three sets instead of two.