If you’ve enjoyed a delicious seedless watermelon, you might wonder how they are grown.
It starts by treating watermelon seedlings with a chemical that makes the plant have 4 times (4X) their normal number of chromosomes. After planting, when this watermelon flowers, it receives pollen from a nearby normal (2X) watermelon.
The result is a fruit that has seeds that are 3X . Part of the result of crossing of a 4X plant with a 2X plant is that the fruit has less than the normal number of seeds, which makes them very expensive for farmers to buy. Nonetheless, when these 3X seeds are planted the resulting watermelon fruit has few seeds ….and even if it has seeds, they are crunchy and eminently edible.
By the way, here’s how the seedlings are treated to get the 4x chromosome plants:
The 2X chromosome line of interest is planted in a greenhouse When the first leaves (cotyledons) emerge from the soil, the growing point is treated with colchicine to stop chromosome division and result in a shoot with four sets of chromosomes rather than two. (Colchicine is extracted from autumn crocus, Colchicum autumnale. As such, it’s considered to be a natural product.)
For homeowners, getting 3X seeds to grow successfully is tough. Better to buy seedless watermelons from a grocery and enjoy!