The first of multiple unsuccessful efforts to restore the American chestnut tree began in the 1920s, barely two decades after an invasive fungus decimated the tree.
Another wave of restoration efforts began in the late 1980s after decades of inactivity, and a recently published paper offers positive signs on the progress.
“It’s a cautious optimism,” said co-author Sara Fitzsimmons, the director of restoration at The American Chestnut Foundation and a researcher at Penn State.
The paper, published in New Forests, analyzed restoration efforts and found researchers are on the right track to successfully breeding a blight-resistant American chestnut tree. And while it concludes that day is still decades away, the findings mark a significant milestone in the quest to revive the functionally extinct tree.
“This is a conservation rescue mission that is much more complicated than anything else I’m aware of,” said lead author Kim Steiner, who is also a professor of forest biology at Penn State.
The American Chestnut tree was always rare in Arkansas, but the Ozark Chinquapin, a member of the chestnut family, was common throughout Arkansas and Missouri, according to Tamara Walkingstick, associate director of the Arkansas Forest Resource Center and associate professor of forestry for the University of Arkansas System. The wave of blight that swept across the country made both exceedingly rare in the Ozarks and Southern Plains.
The Ozark Chinquapin may be saved by the same restoration techniques being developed for the chestnut tree, according to a University of Arkansas System article published in May 2016.
The degree of difficulty in restoration efforts is in part due to the pervasive nature of the pathogen. It lives on other hosts, including some oaks, and the vulnerability of American chestnuts to the blight is “nearly universal,” the paper states. To overcome those challenges, rescue efforts can only be successful by developing a blight-resistant American chestnut.
Two main processes are being researched. Both involve moving a small number of blight-resistant genes into the genome of the American chestnut while still preserving its other qualities and characteristics.
In one process, the partially dominant resistance gene comes from the Chinese chestnut. Researchers cross the two species to create a progeny — the term used for offspring — that is half American, half Chinese.
Researchers then “backcross” the progenies carrying the resistance gene with an American chestnut, which helps preserve all characteristics of the American chestnut other than blight susceptibility.
The second process involves genetic transformation. Researchers in the early 1990s identified a blight-resistance gene in wheat, which they have been able to transfer to embryonic material of the American chestnut through lab procedures. From there, scientists needed to create roots and shoots.