eli5: Why do certain fruits keep growing, even though we have genetically modified many fruits not to have seeds?
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all fruits will grow from a seed. we have two main ways of making “seedless” fruit. one by spraying/neutering the fruit before they develop seeds themselves, or by genetically modifying them to not grow seeds after they are planted. however, it’s typically easier to just spray them with chemicals to prevent them from developing seeds. b/c you still need seeds in the future.
Cloning.
You take a cutting from the tree and start a new plant from it. Instead of a seed.
Like bananas.
Most seedless plants are grown from cuttings, which makes the plants all genetic clones of each other.
Potatoes for example have flowers and seeds, but if you plant the seeds the resulting plant won’t make potatoes you recognize. Specific Potato varieties are so heavily modified that they can only be grown from cuttings.
While this is good from a volume and consistency perspective in farming, this can actually pose some serious problems.
Supermarket Bananas for example are all the same cloned plant. The specific variety we know and love is called the Cavendish but because all the trees are clones they are vulnerable to a specific fungus that is killing them all off.
Banana plantations are also full of trees that are all the same age because they were planted at the same time and large plantations are starting to either lose all their trees due to age, or they are being killed off or forcibly burned down due to the fungus.
Within a decade or two the bananas we know will be functionally extinct. The good news is we’ll just start eating a different variety, and this has actually happened before. The Gros Michel banana that was widely eaten in the late 19th and early 20th century went extinct for the exact same reason.
I actually worked on a farm for two summers that grew the seeds for seedless watermelon. It was all done by careful cross breeding. So you would have several strains of watermelon plant that when cross pollinated will produce a plant whose seeds grow infertile plants. This farmer had been working on these plants for about 15 years and he has continued in the 15 years since. He also grew yellow and orange watermelon and even had produced a tie-dye red and orange.
Seedless fruits are produced several ways. One way is to cross two different species to make a hybrid that has no seeds (like crossing a donkey and a horse to get a sterile mule).
Another way is to take branches from a plant that has seedless fruit and graft them onto another plant. You have seedless oranges and want more? Cut a twig from the seedless orange tree and make a cut in a different tree to inset the twig into. Cover the cut and use string to hold the twig in place, and it “scans over” becomes part of the other tree where it grows into a branch that produces the same fruit (you can even graft multiple kinds of fruit the same tree).
Another way is simply planting cuttings from seedless varieties (like grapes).
Genetic engineering is not used, if that’s what you are asking. People learned to propagate seedless varieties of fruits during the Roman empire, and we still look for naturally seedless crosses of varieties and propagate them the same ways.
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