A century after the introduction of the fungus that decimated the American chestnut tree population in the Northeast, Penn State researchers are working to produce a tree that resists the blight.

In partnership with The American Chestnut Foundation (TACF), the College of Agricultural Sciences planted new American chestnut trees at the Penn State arboretum, at the agricultural research center in Rock Springs and at the experimental forest in Stone Valley.

"One out of 64 of the trees will be fully blight-resistant," said Sara Fitzsimmons, the tree-breeding program coordinator for Penn State and data manager for the Pennsylvania chapter of TACF.

Brought over from Asia, the blight killed 3 billion to 4 billion mature American chestnut trees between 1904 and the 1940s.

"The American chestnut just [had] no resistance to it whatsoever," Fitzsimmons said.

The American chestnut tree never evolved the genes for resistance because it was never exposed to the fungus, unlike the Chinese and Japanese chestnut trees, said John Carlson, associate professor of molecular genetics and director of the Schatz Center for Tree Molecular Genetics.

"It just jumped from tree to tree, basically unhindered," Fitzsimmons said.

The fungus, which spreads by wind, animals and rain, only kills the chestnut tree from the ground up, so some trees survived by resprouting, but no American chestnut trees avoided the blight, said Kim Steiner, professor of forest biology and director of the Penn State arboretum.

The researchers' goal is to develop a plant that resembles the original American chestnut tree but has the blight-resistant genes of the Chinese chestnut.

"My long-term goal is to make this a renewable, reusable timber resource," Fitzsimmons said. "It's such a fast-growing tree and it sprouts vigorously."

Before the blight, the chestnuts themselves were a source of food for Appalachian wildlife and people, who also sold the nuts as a source of income 100 years ago, Steiner said.

The American chestnut "used to be the most common tree species in Pennsylvania," he said.

By breeding an American chestnut with a Chinese chestnut, researchers hope to create a blight-resistant tree. That hybrid is then bred with American chestnuts a minimum of four times to develop a tree that looks American but can survive the fungus.

The "breeding program has generated tens of thousands of individual plants," Carlson said.

Geneticists use the dot-blot technique to evaluate the DNA of the new chestnut trees in addition to assessing the trees visually, he said.

This technique allows scientists to identify genetic similarity between plants.

"It has to also perform and grow like an American chestnut," Steiner said.

Though the disease-resistant trees may resemble the pre-blight American chestnut trees, a plant that is not exactly original is technically not the same tree, he said.

The blight-resistant forms of the gene from the Chinese chestnut tree make it a hybrid.

"We'd like to plant in the forest but the only way to do that is to cut trees down," Steiner said.

The American chestnut tree, sometimes called the "Redwood of the east," can grow up to 110 to 120 feet tall and spread eight feet in diameter, Fitzsimmons said.

The narrow, supple leaves grow to five or six inches long in a "canoe" shape, tapering at the end, she said.

The Chinese chestnut tree grows only to about 83 feet tall -- a height insufficient for competing in the eastern hardwood forests, Fitzsimmons said.

Steiner said the long-term goal of replenishing the forest with American chestnut trees will take decades.

However, "it's something that we should be doing," he said.