Science Video

Cloned Apples
Plant Scientists Graft Apple Trees to Select Disease-Resistant Traits

August 1, 2005 — Grafting -- an ancient way of cloning plants -- enables plant scientists to create new varieties of apples. The selected genetic traits allow trees to resist pests with less pesticides, and to make better-tasting fruits.

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STATE COLLEGE, Penn.--Apple season is right around the corner, but do you know where your apples are coming from? Researchers are using science to make apples better than ever -- and easier on your pocketbooks!

Apples. They're big! And mmm ... Are they good! But do you know where they come from? Trees? Seeds? Close, but actually, all of the apples we eat, whether we buy them at the store or pick them off a tree, are clones! For 2,000 years, growers have attached the root of one tree to the shoot of the desired fruit to clone it through a process called grafting. Making a genetic copy of the preferred fruit is the only way to get reliable apple quality.

"People's children don't look identical to the parents. Same thing with trees, so you might lose those good-tasting characteristics of the fruit in the next generation," says Tim McNellis, a plant pathologist at Penn State University in State College, Pennsylvania.

Now, plant scientists are trying to selectively pick traits to copy by using the root to turn on and off desirable genes in the shoot. For example, taking the root of a small Crab Apple tree and grafting it to the shoot from a tasty Gala apple can produce a small tree with great fruit.

McNellis says the goal is to provide a higher quality product hopefully at a lower cost. Creating trees that are more disease-resistant cuts down on pesticide expenses -- which could mean your $11 bag of apples would cost $7. But the experiments are just beginning.

Professional horticulturist Rob Crassweller says, "We want to see not only how much fruit they produce but how good the fruit is." And if the research pans out, they will only get better.

This research is a slow process. It takes about seven years from grafting a tree to seeing fruit on it. But you could see these smaller trees become reality in the next five years.

BACKGROUND: When we buy apples at the store, they don't come from seeds, but a 2,000-year-old technique. This involves grafting the shoots and branches of an existing apple tree, called a scion, onto a new trunk and root system -- called a rootstock -- and planting the hybrid in the ground. Scientists are now trying to determine the links between specific genes and the most desirable apple traits, especially disease resistance.

WHY WE NEED CLONES: If you plant a Golden Delicious apple seed, you won't get a tree that produces Golden Delicious apples. Each seed has too much genetic variability. Usually this produces a crab apple, the "mutt" of the apple world. Apple breeders must make clones of Gala or Macintosh or other specific varieties, every generation. It has less to do with genetics and more to do with influence. Rootstocks seem to switch on dormant genes already present in the scion.

FUN APPLE FACTS:

The science of growing apples is called pomology
The Greeks, Etruscans, and Romans all practiced grafting their favorite apple varieties to other apple rootstocks
7,500 varieties of apples are grown throughout the world
In 2001, Americans ate an average of 45.2 pounds of fresh apples and processed apple products
The pilgrims planted the first U.S. apple trees in the Massachusetts Bay Colony
The largest apple ever picked weighed three pounds
Actress Gwyneth Paltrow named her baby daughter Apple

Note: This story and accompanying video were originally produced for the American Institute of Physics series Discoveries and Breakthroughs in Science by Ivanhoe Broadcast News and are protected by copyright law. All rights reserved.