Wednesday, July 7, 2004

In 1783, President Washington commissioned his staff at Mount Vernon to plant sycamore trees on the verdant grounds. More than 220 years later, Mount Vernon horticulturalists have planted a clone of a sycamore tree from that era on the grounds and are cloning other trees already on the property dating to Washington’s salad days.

Tree cloning isn’t as scientifically intricate as human cloning, nor is it anything new. Plato, for example, referred to cloning fruit trees in his writings.

Today, fruit growers, vineyard operators and even historical gardeners clone plants and trees for a wealth of reasons. Each plant is an exact duplicate, down to the DNA, of the source material.

At Mount Vernon, horticulturalists have taken tissue samples from 13 trees still standing from George Washington’s days in hope of creating replacements when the trees fall from natural disaster or old age.

“We’ll be able to plant an exact duplicate,” says Dean Norton, Mount Vernon’s director of agriculture.

The 13 trees at Mount Vernon — which include white mulberries, white ashes, poplars and American hollies — “are the only living witnesses we have to George and Martha’s time,” he says.

Mount Vernon officials began cloning the trees in August 2001 with help from an Oregon nursery that specializes in the procedure. Additional clones are sent to Harvard University’s Arnold Arboretum for safekeeping.

Plus, the genetic information gleaned from the plants will be stored so scientists worldwide can study it.

Mr. Norton says cloning must be completed using existing plants, not their seeds. The latter source, he says, would give the horticulturalist only 50 percent of the genes from a particular parent, not an identical copy.

Although the practice of tree cloning is common, Mr. Norton hadn’t heard of any institution trying to clone historic trees for conservation purposes until recently. Now, he says, Mount Vernon has heard from the caretakers of Sherwood Forest in England looking for advice on cloning its aged trees.

The cloning process can be time-consuming, in part because of the age of the trees in question.

“When you’re working with old tissue, it doesn’t go well,” he says.

David Milarch, co-founder of Champion Tree Project International, says trees lose a certain amount of hormones and enzymes as they age, which makes reproduction harder.

Mr. Milarch says we are dependent on plant clones, even if we’re not aware of it.

“When you eat an apple or a grape, you’re eating a clone. Most of the vegetables in our salad are clones,” says Mr. Milarch, whose project promotes the reproduction of the country’s oldest and hardiest trees in the hopes that their clones will prove similarly hale. Cloning comes into play when the fruit in question produces no viable seeds, such as a seedless orange or grape.

Mr. Milarch founded the project eight years ago with his son to archive the genetics of the last of the “great” trees to make living libraries for future historians and researchers.

He says horticulturalists have several ways to clone plants and trees, from common techniques such as grafting to more involved processes, including tissue culturing.

Grafting requires the horticulturist to cut the bark or branch covering of a young, healthy tree in the shape of a cross or “T.” Then a bud or small growth on the tree to be copied is placed within the cut area and tied tightly in place, where it should begin to grow.

Cutting, the most rudimentary technique, involves placing branches in a rooting solution.

Tissue culturing involves extracting a single cell from a part of the plant or tree tissue and letting it grow into an exact genetic fingerprint of the host. It takes up to two years for a plant to grow from such a modest start, Mr. Milarch says.

Horticulture professor emeritus Frank Gouin of the University of Maryland says it can take seven or eight years of growing a modern-day plant to see how its offspring will turn out. That means gardeners often must wait several years before deciding whether to clone a certain plant or tree.

Growers worldwide turn to cloning to reproduce sturdy trees or to propagate, say, a particularly sweet grape. A forest full of clones isn’t such a swell idea, however, Mr. Gouin says.

“They want the genetic diversity,” he says. “When you work with the clone, every plant is susceptible to the same thing.”

A worst-case cloning scenario occurred with grapes years earlier, he says. One variety of grapes did well in California, so it was cloned and brought to the East Coast, where it was wiped out by powdery mildew.

Margaret Pooler, a research geneticist with the National Arboretum, says cloning practices are helping replace the cherry trees around the District’s tidal basin and in other areas of the city.

The original cherry trees, a gift from Japan in 1912, have been in decline for years, Ms. Pooler says.

Gardeners initially brought cherry trees from other parts of the country to replace those that had withered away. Then the National Park Service, which kept strict records of where the original trees still bloomed, asked the arboretum to clone the originals so future replacements would be identical to the Japanese originals.

Cloning the cherry trees serves two purposes.

“It’s very hard to bring prunus species (such as cherries, plums and peaches) to the U.S., for quarantine issues,” she says. Laws exist to prevent diseases from entering the country.

More important, the cloning helps reinforce the historical nature of the cherry blossoms, she says.

Ms. Pooler says people get confused when the topic of plant cloning arises.

“Oh, they’re cloning, but it’s not at all like Dolly the sheep,” she says. “Everyone’s mom probably did it with African violets. But it is cloning.”

Mr. Milarch says the number of requests for historic tree clonings has jumped over the past four years.

His project recently completed cloning five trees at Monticello and in December cloned trees on Sagamore Hill on Long Island, the home of Theodore Roosevelt.

“We’re being flooded with requests from all over the world,” he says.

For more information on tree cloning, visit www.championtree. org.

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