How do farmers know if a watermelon is seedless?

Farmers can't tell if watermelons are seedless just by looking at them, but they do know how to produce seedless watermelons using specific methods. Seedless watermelons are typically grown from tetraploid plants, which have twice the normal number of chromosomes. These plants are created by crossing a diploid watermelon plant with a tetraploid plant, resulting in triploid offspring that have three sets of chromosomes. Triploid plants produce fruit without viable seeds.