A seedless grapevine is grown from a bit of stem cut from a mature seedless vine. But where do we get seedless grapevines?
They originated thousands of years ago in the Middle East, in the area of present day Iran or Afghanistan, no one knows exactly when or where. Raisins from seedless grapes are mentioned in the Bible.
Early Near Eastern tribes cultivated ordinary seeded grapes to make wine and raisins. A genetic mutation must have occurred in some tribesman’s grape seedlings, which gave the plant an oddity in its yearly reproductive cycle: every time its flowers were pollinated and fertilized, ready to produce seeds for a new generation of plants, the seeds in the making aborted without developing the hard seed casings we have to spit out.
This kind of spontaneous abortion is called stenospermoscarpy. The fruit of such a vine is seedless, and the plant cannot reproduce in the conventional way, that is, by dropping seeds. It can only produce more plants vegetatively, by growing another individual from a broken off piece of itself.
Our tribesman must have been very pleased that such a convenient plant had arisen in his arbor, and he must have grown others by cutting off pieces of it and letting them root in the ground. Our modern green seedless grape, called a Thompson seedless, has come down to us from that first plant, passed along over the centuries by cuttings transplanted from one arbor to another. If you slice open a seedless green grape from the supermarket, you can still see the beginnings of a pit that never formed.
It would probably surprise most people to learn that if you plant the seed of any ordinary fruit grown for commerce, a seeded grape, peach, apple, blueberry, cherry, or strawberry, you will not get a plant that gives fruit similar to the piece you ate.
A McIntosh apple seed probably won’t grow a tree that makes McIntosh apples. The fruit it puts out will most likely have a noticeably different taste, shape, consistency, and size from the apple that yielded the seed.
This occurs because natural sexual reproduction, which produces seeds in plants and fertile eggs in animals, makes for wide variation among the offspring: each offspring receives a different assortment of genes from each parent, and so develops its own unique set of traits. Variation is a boon to a species’s survival in the wild, since it increases the chance that some members will flourish in an environment subject to violent change.
In commerce, however, genetic variation is just confusing, a grower wants to be able to depend on a characteristic taste and appearance in his fruit, so that he won’t disappoint his customers. He can’t very well take a bite out of each cherry to make sure it tastes all right.
So all commercially sold fruit (except for citrus) is grown on trees and vines that start as cuttings taken from a plant with the qualities the grower wants to duplicate. This bypasses the sexual phase of the plants altogether and makes offspring that are genetically identical to the parent. All of a given variety of Bing cherry, McIntosh apple, Anjou pear, and Thompson grape have exactly the same collection of genes and produce nearly identical fruit.
Currently, about 90 percent of all the grapes used in United States commerce for eating fresh and for making wine and raisins are Thompson seedless grapes, which are grown in California and New Mexico.
Viticulturists at the Cornell University School of Agriculture have nearly perfected a seedless variety like the Thompson which can grow in the harsher climate of the Northeast. As in the animal world, thoroughbred plants are more vulnerable to disease than “mongrel” fruit and need to be sprayed and fertilized frequently; the Cornell scientists are making their northeastern seedless as resistant as possible to insect and fungal predators.
The original Concord grapevine in Concord, Massachusetts, only recently died. One wonders if the first Thompson seedless is still putting out grapes somewhere along the Persian Gulf.