May 05, 2014, BY Andy Hirsch

At one point, between 4 and 5 billion American chestnut (Castanea dentata) trees populated forests stretching across the Appalachian mountains from Alabama to Maine. The massive tree grew into a pillar of America's 19th-century economy. Its lumber was used in myriad ways — from fencing to furniture, flooring to telephone poles. The seeds it produced was not only an important source of food for wildlife and livestock, but trainloads of chestnuts were hauled to towns and cities to be sold on street corners where vendors often roasted them on an open fire.

"The American chestnut played a central role in the forest ecosystem and really was a significant part of the 19th century way of life," said Professor Mark Spiro, biology. "And then, in a relatively short amount of time, the trees all but disappeared."

In the first years of the 20th century, a fungal disease, Cryphonectria parasitica, more commonly known as the chestnut blight, was introduced to North America by way of Chinese chestnuts brought here from Asia. By the mid-1900s the disease had moved swiftly through the American chestnut population, pushing the tree to the brink of extinction.

"The Chinese chestnut evolved in the presence of this fungus and grew resistant to it." Spiro explained. "Separated by an ocean and thousands of miles, the American chestnut had no immunity to the fungus. Once it arrived, the fungus moved quickly and all but wiped out more than 4 billion trees."

Even today, the fungus remains problematic. In fact, root systems belonging to American chestnuts survived the blight, and you can still find young sprouts throughout the East. But with the fungus lingering, there's been little hope of those shoots maturing.

Now, after decades of work, the American Chestnut Foundation believes it has produced a blight-resistant seed that could help bring the American chestnut back to prominence.

"The American Chestnut Foundation has spent years developing these seeds through what's called backcross breeding," Spiro said. "After decades of breeding for this blight-resistant seed, they think they have a tree with the characteristics of the American chestnut but the disease resistance of the Chinese chestnut. We're one of the arboreta they've asked to grow and assess these trees."

The backcross breeding program began 30 years ago by crossing an American chestnut with a Chinese chestnut tree. The next three generations of trees were bred with American chestnuts in order to restore the tree's original characteristics. Each generation of tree was exposed to the blight along the way, and only those that showed strong resistance were selected for additional breeding. The end result is what's referred to as Restoration Chestnut 1.0 — a tree that is almost entirely American chestnut, but with the fungal resistance of the Chinese chestnut.

Click the image for more information on the
backcross breeding program.

"The idea here would be that we can use this as a starting point for reintroducing this tree into the wild," Spiro said. "It's still a work in progress, but it's 94 percent American chestnut, so this restoration chestnut looks very close to an American chestnut in terms of its growth habit, its leaves, its fruit. Within the 6 percent that's Chinese chestnut, there should be all the genes needed to protect it from the blight."

Bucknell recently received four of the Restoration 1.0 seedlings, along with pure American and Chinese chestnuts. With the help of Bucknell's Grounds and Labor Supervisor John Testa and Arborist & Ornamental Plant Specialist William Kuntz, Sprio planted the saplings in the Bucknell University Arboretum. It will be some time before the project can be deemed a success (it takes decades for the trees to reach maturity), but Spiro is optimistic.

"There are really several exciting parts to being a partner in this project. First, we're helping bring back this really important part of our history," Spiro said. "We're also working to increase biodiversity, and restoring the American chestnut would have a ripple effect throughout the ecosystem. This project is also a step toward restoring a healthy native plant community, one of the goals of the Arboretum."

And Bucknell students will benefit from an educational experience few universities can offer.

"We'll be able to bring students to where we've planted these trees and actually show them the differences between the American and the Chinese chestnut. We'll be able to show them the results of generations of backcross breeding. This isn't just reading out of a book; it's history, right here in their own backyard."


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