A century ago, towering forests of chestnut trees blanketed the East Coast of the United States. Then a fungus that hitched a ride on imported Asian chestnut trees began to infect entire woodlands.
The result: Where 4 billion chestnut trees once stretched from Georgia to Maine, only about 400 million remain today. Now scientists aim to bring back the American chestnut by bioengineering a tree to contain a gene that can withstand the Cryphonectria parasitica fungus. If they succeed, new forests of chestnuts could rise across the U.S. in the decades to come, absorbing carbon dioxide from the atmosphere and providing food and shelter for wildlife.
“The fungus took out a quarter of all our eastern forests,” said William Powell, codirector of the American Chestnut Research and Restoration Project, who envisions restoring vast Eastern chestnut forests by reclaiming mining lands and other barren areas.
He began working to bring back the chestnut 26 years ago. He and project codirector Charles Maynard combed through more than 30 plant genes to find one that would help stop the blight. They settled on a gene from a cultivated wheat species that produces an enzyme called oxalate oxidase. (Powell points out that the gene has nothing to do with gluten, and the chestnuts will stay gluten-free.) The gene is also found in strawberries and bananas.
The enzyme detoxifies the oxalate that the fungus uses to form deadly cankers on chestnut stems. “The best thing about this gene is that it does not harm the fungus at all,” said Powell. “The fungus can still survive, but oxalate oxidase takes the weapon away from the fungus.”
Having the fungus survive is important for the safety of both species. Powell explained that the scientists don’t want to put selective pressure on the pathogen to overcome the resistance. “Since the fungus can still grow on the bark of the tree, we’re changing the lifestyle of the fungus,” he said.
Powell, Maynard, and a group of researchers from the State University of New York have published papers on the blight-resistant nature of the transgenic tree and are awaiting approval from the federal government to plant the trees.
The restoration project hopes to grow 10,000 seedlings when it receives government approval. In three to five years, those trees will be available to the public to buy at cost and plant.
Powell cautioned that reviving chestnut forests will take time. “This is a tree that can live a hundred years, not a weed that spreads quickly,” he said. “It’s going to take some time to get them established.”