Once upon a time, up to four billion American Chestnuts grew on this continent. The tallest of them stood twelve stories high. Then came the fungus.
American Chestnuts were once the grandest of all trees in Eastern North America. They resembled huge buttressed castles with tops that emerged from the canopy and produced a reliable crop of tasty nuts that supported forest creatures. Early farmers even fed the nuts to their pigs and goats. Then, in the first half of the 20th century, a fungus from China raced through the forest, killing virtually all of them. The forest had lost its king.
In 1983, the American Chestnut Foundation (ACF) set up shop with the ambitious and optimistic goal of bringing the chestnut back. Chinese chestnut trees were very resistant to the fungus that they had co-evolved with. Long before CRISPR was developed, the ACF set to work importing this resistance to American chestnuts using the “back-cross method.” They hybridized American and Chinese chestnuts, and then they crossed the offspring with American chestnuts multiple times. In each generation, they kept only the seedlings that retained resistance to the blight. To cover the whole forest, the project continues at the ACF orchard in Virginia, and at 16 volunteer-led orchards that are breeding locally adapted blight-resistant trees from Alabama to Maine.
The ACF is also working with a group at the State University of New York College of Environmental Science and Forestry to explore the possibilities of a chestnut that expresses a resistance gene derived from wheat. Crossing these trees with the few surviving American chestnuts in the wild can “capture” the remaining genetic diversity before those old trees die.
Eventually, blight-resistant trees will be planted in the forest, and the king of the East can retake its throne. This effort is perhaps the oldest and furthest-along of all transgenic conservation projects. “If it can be done with the chestnut tree, then it should be possible to restore ash, hemlock, and other trees that are imperiled,” says Jared Westbrook, Director of Science at the ACF. “This is a proof of concept for something bigger.”
Emma Marris is a freelance environmental writer. She lives in Klamath Falls, Oregon.