Every other Friday on Morning Edition NHPR’s Sam Evans-Brown tracks down answers to questions about the environment and outdoors for our listeners in a segment we call “Ask Sam.” This time, producer Taylor Quimby stepped in to answer one.
Donna from Campton asks: “Why can’t I get the same type of apple if I plant an apple seed? Are apples the only kinds of fruits like this or are their others?”
When John Chapman (AKA Johnny Appleseed) was planting loads of apple trees in the 19th century, he wasn’t creating the nice, neat, orderly orchards you’re used to seeing today. Johnny Appleseed’s orchards were a fruitful mix of genetic variation - even though most of the apples that came from them were probably small and bitter: perfect for cider and little else.
When you plant an apple seed, the tree that grows from it produces a completely different tasting (and looking) apple than the parent. That’s because apples are especially ‘heterozygous,’ which is a fancy way of saying that their seeds contain all sorts of different chromosomal traits that, during reproduction, are battling it out for genetic dominance.
If you remember doing Punnett squares in school, that’s the stuff we’re talking about: calculating how two brown-eyed people could have a blue-eyed kid, or what happens if you crossbreed red and white flowers.
But why do apples reproduce this way?
The evolutionary answer is that heterozygous organisms have a natural advantage – basically, all that genetic variation offers them more chances to create successful offspring. After all, a single apple tree is going to produce tons of apples, each apple produces tons of seeds, and each tree that results will be different. One might have a bigger trunk, or smaller apples, or survive well in colder climates, and so on.
Erika Janik is executive producer of Outside/In, and (it just so happens) author of Apple: A Global History.
“One of those seeds is bound to grow into a tree that can survive in whatever climate they happen to be in, and this is how you can find apples all over the world, because they are really adaptable.”
Donna also wanted to know if other fruits do this, and the answer is yes. However, some fruits (like apples and pears) have an especially profound amount of genetic variation, whereas some other fruits are a little less heterozygous.
But to get back to Johnny Appleseed… if every apple seed planted creates a different kind of apple, how did we wind up with such nice neat rows of categorized orchard apples today?
Well, for at least 3,000 years, humans have been propagating their favorite fruit varieties through a process called grafting.
By cutting a thin branch (called a scion) from one apple tree and inserting it into a cut in another tree’s trunk (this is called the rootstock) you can essentially make a new copy of the old tree. Erika puts it this way:
“Basically, what you’re doing when you’re grafting something is you’re cloning something. So say you have a red delicious apple that you’re eating – every red delicious apple that you’ve ever eaten, that ever exists in the world, is some kind of clone from one tree.”
And get this: by grafting different apple branches on the same tree, you can even create a sort of Frankentree that produces several different varieties of apples.
Or, even weirder, you can create a ‘fruit salad tree’by grafting branches that grow oranges, and grapefruits - all on the same plant. Talk about saving yourself a trip to the store.
The downside of grafting is that you miss out on the heterozygous advantage: all that genetic diversity can be a literal lifesaver when it comes to blight, or other adverse conditions that can impact orchards.
