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WASHINGTON — Billions of American chestnut trees once covered the eastern United States. They soared in height, producing so many nuts that sellers moved them by train car. Every Christmas, they’re called to mind by the holiday lyric “chestnuts roasting on an open fire.”
But by the 1950s, this venerable tree went functionally extinct, culled by a deadly airborne fungal blight and lethal root rot. A new study out Thursday in the journal Science provides hope for its revitalization, finding that the genetic testing of individual trees can reveal which are most likely to resist disease and grow tall, thus shortening how long it takes to plant the next, more robust generation.
A smaller gap between generations means a faster path to lots of disease-resistant trees that will once again be able to compete for space in Eastern forests. The authors hope that can occur in the coming decades.
“What’s new here is the engine that we’re creating for restoration,” said Jared Westbrook, lead author and director of science at The American Chestnut Foundation, which wants to return the tree to its native range that once stretched from Maine to Mississippi.
The American chestnut, sometimes called the “redwood of the East,” can grow quickly and reach more than 100 feet, produce prodigious amounts of nutritious chestnuts and supply lumber favored for its straight grain and durability.
But it had little defense against foreign-introduced blight and root rot. Another type of chestnut, however, had evolved alongside those diseases. The Chinese chestnut had been introduced for its valuable nuts, and it could resist diseases. But it isn’t as tall or competitive in U.S. forests, nor has it served the same critical role supporting other species.
So, the authors want a tree with the characteristics of the American chestnut and the disease resistance of the Chinese chestnut.
That goal is not new — scientists have been reaching for it for decades and have made some progress.
But it has been difficult, because the American chestnut’s desirable traits are scattered across multiple spots along its genome, the DNA string that tells the tree how to develop and function.
“It’s a very complex trait, and in that case, you can’t just select on one thing, because you’ll select on linked things that are negative,” said John Lovell, senior author and researcher at the HudsonAlpha Genome Sequencing Center.
Breed for disease resistance alone, and the trees get shorter and less competitive.
To deal with this, the authors sequenced the genome of multiple types of chestnuts and found the many places that correlated with the desired traits. They can then use that information to breed trees that are more likely to have desirable traits while maintaining high amounts of American chestnut DNA — roughly 70 percent to 85 percent.
And genetic testing allows the process to move faster, revealing the best offspring years before their traits would be demonstrated by natural growth and encountering disease.
