Seedless Seeds

During a produce delivery I ran into a coworker from the service shop who had an interesting question. He asked how seedless watermelon become seedless. Obviously if they don’t produce seeds they can’t reproduce and thus exist right?

Well that’s completely right! Seedless watermelon (or any seedless fruit for that matter) can’t reproduce naturally. Seedless fruits are technically a defect. Just like in humans and animals, there are genetic defects that pop up occasionally. That’s why some people have grown to be 8ft tall or have some extra toes.

Fruit is reproduced just like any other living thing. During pollination, bees transport pollen from plant to plant. I won’t give you the “squash and the cucumbers” talk right now, but that’s how the blossoms are fertilized to begin reproduction; making the fruit. Once fertilization happens and DNA is transferred between plants, the fruit can begin to grow and continue the reproduction process!

Well in the case of seedless fruit, they actually contain an extra set of chromosomes. They are called triploid plants (diploid is a normal, seeded plant with two pairs of chromosomes). When the plant is first developing fruit, the three sets of chromosomes don’t have time to pair up before the fruit is set which creates an infertile watermelon; aka seedless! The only problem is that since they are infertile they cannot pollinate themselves. If you plant a field of only seedless watermelon, nothing will grow because they’re all infertile. You actually have to plant some seeded (diploid) watermelon near your seedless so the fertile watermelons can lend their pollen to make the seedless plants produce. Science!

But don’t seedless watermelon grow from seeds!? Where do those seeds come from?

They sure do! Seedless seeds (that sounds funny I know) come from cross pollinating diploid watermelon plants and tetraploid plants. Tetraploid plants have 4 pairs of chromosomes but since it is an even number of chromosomes, they can all match up and still create fruit. Try to keep up! The two different kinds of plants are planted together and allowed to crossbreed through pollination. When those plants fruit, their seeds contain three sets of chromosomes each. Thus, triploid seeds are created! I really wonder who figured all this stuff out…

Some seedless plants that don’t grow from seeds, like grapes and bananas, and are actually perpetuated by cloning. A piece of the seedless plant is cut off and connected to a new root which then grows into a brand new seedless plant with the exact same genetic makeup as the original plant! This process is called grafting. It is also how we maintain different varieties in tree fruit. If you take the seeds from a Red Delicious apple and plant them in the ground, a tree might grow, but it would most likely not produce a Red Delicious apple. It would be the byproduct of whatever the Red Delicious tree cross pollinated with. It might be a Red Delicious/Gala hybrid which is how new varieties are created! Any Red Delicious apple you eat (or any seedless tree or vine fruit for that matter) is an exact clone of the original Red Delicious tree that was naturally created hundreds of years ago. Isn’t that cool!?

Get to know your farm!