In the early 1970s, plant pathologist Gary Griffin of Virginia Polytechnic Institute was hunting in the Blue Ridge Mountains when he stumbled on something far more valuable than the grouse he’d planned to bag. “I walked past an enormous chestnut tree,” he recalls. “It had died, but it still had intact bark.” Another man wouldn’t have given the snag a second glance. But such stately old trees—dead or alive—are essential to Griffin’s plans to rescue the majestic species from a tragic end.

Copyright © Great Smoky Mountain National Park, Courtesy of the American Chestnut Foundation

A family photo circa 1920 captures the majesty of a stout American chestnut in Tremont Falls, Tennessee. A mature American chestnut tree is typically about 100 feet tall with a trunk about 5 feet wide. Chestnut timber is as rot resistant as redwood and lighter than oak. Rural Americans also prized chestnuts, which they harvested to sell as a cash crop or to feed to farm animals.

Unless you’re of a certain age, the only chestnuts you know are probably the modest Asian types imported as ornamentals. American chestnuts, by comparison, were giants as large as California’s redwoods. They made up more than a quarter of eastern woodlands, and their stout, straight trunks supplied unusually strong and rot-resistant timber. Then in the early decades of the 20th century, blight wiped out American chestnuts. The disease was discovered on trees at the Bronx Zoo exactly 100 years ago, and it soon spread throughout the chestnut’s natural range, from Maine to Mississippi. More than 3 billion trees died. Some survived as ravaged stumps, sending up shoots that would inevitably be attacked and die back over and over again.


Chestnut blight is caused by a fungus, Cryphonectria parasitica, that was probably imported on Japanese chestnut trees purchased by a Long Island nursery in the late 1800s. Mail-order sales of chestnut cuttings may have spread the fungus far and wide long before the disease was recognized. The fungus grows in and under the bark, creating large, visible sores called cankers that prevent the flow of sap. If the cankers fully encircle the trunk, they effectively strangle the tree, and it dies from that point upward. “Functionally, it’s not that much different from taking an ax and girdling the tree,” says William MacDonald, a forest pathologist at West Virginia University in Morgantown.

Of the four chestnut species—Chinese, Japanese, European, and American—American chestnuts are by far the most susceptible to the Cryphonectria blight. Because the Asian varieties seemed to have natural resistance to the fungus, silviculturists from the U.S. Department of Agriculture began interbreeding Asian and American chestnuts in the early 1900s with the hope of producing a blight-resistant hybrid. The Asian-American crosses do yield resistant trees, but they are also much shorter than the pure American species. In a forest, the diminutive hybrids can’t compete with maples, beeches, ashes, and oaks. They lack the spirit as well as the stature of the purebreds. “The American chestnut is a remarkable tree,” says MacDonald. “It will outcompete anything until it gets the blight.”

Courtesy of the American Chestnut Foundation

When the Cryphonectria fungus infects an American chestnut tree, it creates nasty-looking cankers in the bark. Over time, the fungus reduces a towering giant to a stump. The tree cannot grow back because the fungus persists in the roots.

In the 1980s, the American Chestnut Foundation launched a program in which Chinese-American hybrids were repeatedly backcrossed with American trees. The breeders hoped that a small proportion of each backcrossed generation would retain the high blight resistance of the Chinese trees while looking and acting more American. “You’re progressively diluting out the Chinese genes, except for the blight resistance, which we’re selecting for,” says Fred Hebard, the plant pathologist at the foundation’s breeding farm in Meadowview, Virginia. “The whole point of backcrossing is to get rid of as many of the Chinese genes as you can.”

So far, Hebard says, the scheme is working. A small percentage of each cross does have strong resistance to the blight, and with successive backcrosses, the trees are showing more American traits. But the process is achingly slow. Hundreds of trees need to be pollinated by hand; thousands of seeds must be harvested and sown. Each generation of saplings can’t be tested for resistance until it’s at least three years old. The tests involve injecting fungus into the bark with a cork borer and waiting for cankers to show. After 15 years at the foundation, Hebard has finally planted the progeny of the third generation of backcrosses. They’re still too young to inoculate, and even if they turn out to be both big and resistant, it will be another 10 to 20 years before they can prove they are competitive in the wild. “How many backcrosses do we need? We don’t know that yet,” Hebard says, “and we won’t know until we see 100-foot trees two or three feet in diameter that are doing really well in the forest.”

To speed things up, biotechnologist William Powell and forest geneticist Charles Maynard, both of the State University of New York at Syracuse, are turning to genetic engineering. Their plan is to make a transgenic chestnut with genes that inhibit the growth of the fungus. Ideally, they could insert the resistance genes from Asian chestnuts into American ones. But those genes haven’t been identified, so Powell and Maynard are looking for alternatives. Their favorite candidate is a wheat gene whose enzyme product destroys the Cryphonectria acid that eats away at chestnut bark. In test-tube studies of transgenic chestnut tissue, the gene has protected the formation of lignin, the chemical scaffold of bark.