Families would gather fallen chestnuts by the bushels and sell them in neighboring towns for a profit. Wood from the trees made for sturdy log cabins and furniture. The nuts, at least the ones not chomped away by wild critters, were cooked and eaten. Hence the famous “chestnuts roasting on an open fire” line from “The Christmas Song.”
But in the early 1900s, an exotic fungus, Cryphonectria parasitica , was accidentally introduced into the United States from Japanese nursery stock, causing chestnut blight. Within 40 years, an estimated four billion American chestnut trees died. The ones that are left are deformed and only just surviving.
One forest pathologist at West Virginia University is working toward restoring the American chestnut to its glory days. He and his students are helping do that by applying an applesauce-like substance around the cankers of chestnut trees. They’re combating the disease with another disease, a virus-treated fungus.
“We’re using a hypovirus that debilitates the chestnut blight fungus,” said Matt Kasson, assistant professor of forest pathology in the Division of Plant and Soil Sciences. “It makes the fungus sick and weakens it so it can’t grow as aggressively as it would under normal conditions.”
Kasson, a Pennsylvania native, is a younger faculty member who speaks enthusiastically and at length about forest health and revitalization. He didn’t come to WVU to work on the chestnut’s resurrection. But he soon realized the importance of the legacy left behind by his predecessor, William MacDonald, who was nationally renowned for his three decades of work preserving the American chestnut tree.
At the WVU Agronomy Farm, blight is present in six plots of chestnut trees. For one
study, Matt Kasson is evaluating how a virus-treated fungus performs there in an
orchard setting.
MacDonald, now a professor emeritus, also used hypoviruses that diminished the virulence of chestnut blight fungus, leading to saving the American chestnut from near extinction. In 1982, MacDonald helped spearhead a multistate project, now known as NE-1833, addressing chestnut management. Scholars from 16 universities, the American Chestnut Foundation, the Ontario Horticultural Research Institute and the USDA Forest Service now collaborate on the project.
His research has led to the development of blight-resistant chestnut varieties as both timber crops and orchard trees for nuts, new strategies for planting chestnuts in harvested and disturbed ecosystems, and a program that reintroduces domestically grown chestnuts as a diversely used food source for common consumption.
While American chestnut trees have persisted, they don’t grow the same way they did before the 1900s. The disease itself does not kill the root system; it only kills above- ground stems. The most visible symptom of infection is a canker on the bark, much like an open sore on your arm, Kasson explained.
“The canker disease restricts the flow of sugars from the crown and the flow of nutrients and water up the stem, rendering that stem dead,” Kasson said. “As the tree dies, new shoots sprout out of the surviving roots.”
In the early 1900s, an exotic fungus, Cryphonectria parasitica, was accidentally introduced into the United States from Japanese nursery stock, causing chestnut blight.
Instead of towering trees that bloom straight into the sky, you’ve got skinny, wayward shrubs that succumb to disease before they can even produce nuts. Blight has reduced these once giants to feeble “trash trees” with diminished economic and ecological value.
This makes restoring the American chestnut a matter of improving quality over quantity.
Over the years, researchers sought solutions to revive the tree. Simply removing blighted trees to control the disease proved to be ineffective, and the use of fungicide is impractical over large, vast swaths of forests and acreage.
Scientists eventually identified a virus capable of infecting the chestnut blight fungus, which was used deliberately in an attempt to weaken chestnut blight’s wrath. Success was limited.
“It’s hard to introduce a virus when there’s a lot of genetic diversity,” Kasson said. “In order for the virus to pass from fungal strain to fungal strain, they have to be compatible in six genes.”
A few years ago, Donald Nuss, founding director of the Institute for Bioscience and Biotechnology Research at the University of Maryland, developed a genetically engineered strain of the fungus by removing the incompatibility genes. Nuss retired, became an adjunct professor at the Davis College of Agriculture, Natural Resources and Design, and brought his concept with him to WVU.
In 2016, Kasson and fellow researchers put the new strain, which they dubbed “super donor 1.0,” to the test at Savage River State Forest in western Maryland.
They found that the strain was effective on 94 percent of cankers to which they applied the virus. That is up from around 50 percent in research studies using previous virus-containing strains. Kasson’s findings, led by his PhD student Cameron Stauder, were recently published in the scientific journal Virology.
“We saw a significant reduction in canker expansion,” Kasson said. “If we hadn’t treated the cankers, they’d keep growing until they girdled the stem.”
Halting canker growth won’t instantly restore the American chestnut to prosperity. But it will lead to more studies, in which perhaps the strain can be tweaked or combined with other viruses to battle blight. Kasson’s team is already working on more experiments.
“We can’t be naïve and assume that one in four trees will be American chestnuts,” Kasson said. “But as forest health professionals and land managers, we can work to make the American chestnut strong and relevant again.
“It would take 150 to 250 years for the trees to get that big again. It’s nothing we’ll see in our lifetime, but generations out may be able to see it. Knowing that’s a possibility is a strong motivation.”