Nearly a century after fungal pathogens from Asia nearly wiped out the American chestnut, scientists are using modern genomic techniques to bring the species back from functional extinction. Once dominant in Appalachian forests, the tree was devastated by chestnut blight and root rot diseases, killing an estimated 3 billion trees. While new saplings continue to sprout from stumps, the fungus persists, killing them before they can reproduce.

Multiple restoration approaches are underway. Some researchers are crossbreeding surviving American chestnuts with Chinese chestnuts, which evolved resistance to the fungi. Others are identifying naturally resistant trees in the wild, called LSACs (large surviving American chestnuts), which suggest some native resistance existed before the blight. A third approach involves genetic modification, inserting a gene from wheat that produces an enzyme degrading oxalic acid, a key factor in the blight's virulence.

A massive collaboration led by the American Chestnut Foundation is now testing all these methods to determine the most effective path for reintroducing blight-resistant chestnuts to their native range. The research, published in Science, represents one of the most ambitious efforts to restore a functionally extinct species using modern biotechnology and traditional breeding methods.