Seedless watermelons were invented over 50 years ago, and they have few or no seeds. When we say seeds, we are talking about mature seeds, the black ones. Oftentimes, the white seed coats where a seed did not mature are assumed to be seeds. But this isn’t the case! They are perfectly safe to swallow while eating, and don’t worry - no seeds will grow in your stomach.
So, how are seedless watermelons grown? Chromosomes are the building blocks that give characteristics, or traits, to living things including plants and watermelons. Watermelon breeders discovered that crossing a diploid plant (bearing the standard two sets of chromosomes) with a tetraploid plant* (having four sets of chromosomes) results in a fruit that produces a triploid seed. (Yes, it has three sets of chromosomes). This triploid seed is the seed that produces seedless watermelons!
In other words, a seedless watermelon is a sterile hybrid which is created by crossing male pollen for a watermelon, containing 22 chromosomes per cell, with a female watermelon flower with 44 chromosomes per cell. When this seeded fruit matures, the small, white seed coats inside contain 33 chromosomes, rendering it sterile and incapable of producing seeds. This is similar to the mule, produced by crossing a horse with a donkey. This process does not involve genetic modification.
Source: National Watermelon Promotion Board
*A tetraploid watermelon plant results when the chemical colchicine is applied. Learn more at https://youtu.be/ohN0y03yMco