Bioengineered Tree Could Restore America’s Once-Vast Chestnut Forests

February 2, 2016 | Joanne Kennell

American chestnut trees
Photo credit: Daderot/Wikipedia (CC0)

Designed to co-exist with the fungus that nearly wiped it out

It was not that long ago that the East Coast of the United States was covered in vast and towering forests of chestnut trees.  However, that came to an unfortunate end when the Cryphonectria parasitica fungus hitched a ride on imported Asian chestnut trees and began infecting entire forests.

Where four billion chestnut trees once spanned from Georgia to Maine, only 400 million remain thanks to the fungus.  Now, scientists hope to bring back the American chestnut tree by bioengineering a tree that contains a gene to withstand C. parasitica.  If successful, new forests of chestnuts could once again rise across the United States.

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“The fungus took out a quarter of all our eastern forests,” William Powell, co-director of the American Chestnut Research and Restoration Project told Katharine Gammon of Take Part.  He has been working to bring back the chestnut tree for more than 26 years.  Powell and project co-director Charles Maynard searched through more than 30 plant genes to find one that would stop the fungus.

They finally settled on a gene from a cultivated wheat species that produces an enzyme called oxalate oxidase — it is a gene also found in strawberries and bananas.  This enzyme detoxifies the oxalate that the fungus uses to form nasty and deadly cankers on chestnut tree 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.”

It may sound counter-intuitive to leave the fungus alive, but it actually makes a lot of sense biologically.  Powell explained that the scientists do not want to put selective pressure on the fungus oxalate so it feels the need 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.  This guarantees the safety of both species.

It will take awhile to revive the chestnut forests.  “This is a tree that can live a hundred years, not a weed that spreads quickly,” Powell said.  “It’s going to take some time to get them established.”

Powell, Maynard, and a group of researchers from the State University of New York are now awaiting approval from the federal government to plant the trees.  Once approved, the restoration project hopes to grow 10,000 seedlings, and in three to five years, the trees will be available for the public to buy at cost and plant.

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