In target, scope, and sheer lethal speed, the obliteration of the American chestnut is an ecological disaster without precedent.

The towering trees — redwoods of the east, some called them — were a foundational species in the forests that stretched from southwestern Ontario to Georgia. In some parts, one in four trees was an American chestnut. The trees were a refuge for hundreds of species and a thrumming industry: its wood was so hardy that chestnut fences still stake Ontario fields.

Then, in less than 50 years, the trees were gone. An exotic blight, accidentally carried over on an Asian chestnut variety, began infecting American chestnuts as the 20th century dawned. By 1950, up to four billion trees had died, two million of them in Ontario, wiping out 99.9 per cent of the species and radically reshaping the forests it once dominated.

Now, a century later, an American research team has an equally unprecedented solution: a genetically modified American chestnut. By splicing a single gene from wheat into the tree’s genome, scientists from the State University of New York’s College of Environmental Science and Forestry (SUNY-ESF) have engineered blight-resistant saplings.

This year, the team plans to apply for approval from U.S. and Canadian regulators to distribute the plant. If they are successful, the tree would be the first genetically modified organism released with the goal of reintroducing an endangered species to the wild, rather than producing a commercial agricultural crop.

The SUNY-ESF team, led by William Powell, a professor and director of the American Chestnut Research and Restoration Project, expects the regulatory review to take between two and four years. But because no one has ever done this before, there could be unexpected hurdles or accelerants — including the response of the public.

“I think many of the values and perceptions of people about genetically modified organisms are based around issues of commercial interest,” like profits and patents, says Sally Aitken, a professor who studies forest and conservation genetics at the University of British Columbia, who is not involved in the research.

“The case of the chestnut and chestnut blight really makes us reconsider some of the concerns, perhaps, but it also raises additional concerns about working with genetic manipulations of native wild species.”

Aitken and other researchers are monitoring Powell’s progress, because so many other tree species, from the Elm to the Butternut, are being ravaged by disease.

“Really, the chestnut has a chance to pave the way,” says Aitken.

The blight, a fungus, was first observed at the Bronx Zoo in 1904, in an era when importing exotic botanical specimens was popular. By 1906, it was discovered in Maryland, Virginia, New Jersey, and D.C. Within 20 years, it had reached Ontario, the northerly edge of its range.

Researchers discovered the fungus on chestnuts in China and Japan, but found fewer symptoms: the pathogen and the trees had co-evolved. The American species, however, bore no natural resistance.

It’s hard to overstate the consequences of the loss of the American chestnut, ecologically, commercially and culturally. The trees dominated the forest canopy, produced massive volumes of nuts, and shed a particularly protein-rich leaf litter, providing shelter and nourishment for other species.

When the tree was wiped out, multiple species of insects went extinct almost immediately, and many other animals, from deer to bears to wild turkeys, were impacted. Some scientists wonder whether the loss of the American chestnut contributed to the extinction of the passenger pigeon, since the soaring, 35-metre-high trees provided roosts for birds and both died out around the same time.

As commercial timber, Americans “called it the cradle to grave wood, since almost all everyday items were made of chestnut,” says Ron Casier, chair of the Canadian Chestnut Council, a conservation group. Its supreme rot resistance made it a favourite for log cabins, flooring, and railroad ties. Nuts from the tree were a common food, as North American holiday traditions still suggest.

In a single human generation, a geological wink, the tree disappeared.

“That’s pretty much the most important wipeout of a species by a pathogen — I can’t think of anything else on that scale,” says Richard Hamelin, a professor of forest pathology at the University of British Columbia.

Because the tree is so “iconic,” says Hamelin, “ever since I did my PhD — and before that, of course — people have been interested in its restoration.”

The fungus creates cankers that girdle the trunk and branches, but it does not affect the roots. Decades after the trees died off, stump rings still pock the countryside, sending up shoots that then become infected and die. This cycle gives researchers hope — and more importantly, if the trees survive long enough to flower, seeds.

For decades, researchers have been trying to crossbreed the naturally resistant Asian chestnut species with the American. But the offspring of these trees are smaller hybrids, so the ones with blight resistance are then selected and “back-crossed” with another American chestnut tree to create offspring that are genetically truer to the endangered species.

Through enough generations of crossing and back-crossing, a tree that is blight-resistant and mostly American chestnut would be created. But the tree takes years to reach sexual maturity, so this research has been painstakingly slow, and has not yet produced trees with high levels of resistance.

Researchers also tried a tactic called hypovirulence, which uses a virus to infect the fungus, making it less potent. It didn’t pan out, but it gave researchers a clue. The weaker strains of fungus produced less of a substance called oxalic acid — a hint that this was the fungus’ weapon.

Powell and his colleagues noted that wheat and other grasses carry a gene that produces an enzyme that defangs oxalic acid, transforming it into two harmless byproducts, carbon dioxide and hydrogen peroxide. By splicing this gene into the American chestnut genome, the SUNY-ESF team theorized they could create a blight-resistant tree.

It sounds simple. It took Powell and his colleagues 27 years. “We started off when no one was doing this stuff,” he says.

The lab planted their first transgenic American chestnut trees in an outdoor research plot in 2006, ones with “intermediate” levels of blight resistance. Recent tests have shown even better defences, matching or surpassing the Asian trees; these highly resistant trees will be planted in the New York Botanical Garden this year.

As early as summer, Powell and his team will begin applying to U.S. federal agencies for approval to distribute the plant to the public. As soon as those reviews are initiated, they will reformat their documents and submit to Environment Canada and the Canadian Food Inspection Agency.

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“What we want to do is quickly get their approval too so we can plant up there. We want them planted throughout their range,” says Powell.

The lab has already been in discussion with regulators on both sides of the border, and initiated experiments to determine whether the transgenic tree is a benign presence in its ecosystem (which so far, Powell says, have been reassuring — he emphasizes that the transgenic approach alters far less of the species’ genome than conventional crossbreeding, which mixes thousands of genes). Each agency has a different package of requirements.

“It’s always harder to be the first,” Powell says, adding that he hopes this sets a precedent for other researchers trying to save wild plants threatened by invasive pests and pathogens.

With any intervention into nature, there are unknowns. “There’s always a risk because it’s biology,” says Hamelin, the forest pathology researcher.

Horizontal gene transfer, the transmission of DNA between species, is far less common in multicellular organisms like plants than in bacteria, but scientists are discovering more and more instances of it. Powell doesn’t believe this is an overwhelming concern, in part because the oxalic acid neutralizing enzyme is found in so many plants, including bananas and strawberries.

A more pressing scenario, one often encountered by agricultural biotechnologists, is a genetic arms race between the transgenic tree and the fungus. The tree would carry a single gene conferring resistance and takes years to mature. The pathogen produces billions of spores in that time, and each is an opportunity to mutate — an “unfair advantage,” Hamelin notes. In a discussion of the transgenic tree, “this issue has to be addressed.”

Powell says that his team’s approach, which doesn’t attack the fungus itself, lessens the selective pressure to beat the tree’s gene. The lab is also working with groups that are crossing and back-crossing the Asian and American chestnuts, exploring ways to “stack” resistance genes — a platoon approach.

UBC’s Aitken says Powell is “doing great work,” in part because his lab has taken pains to keep their work transparent — a chance for fruitful dialogue.

“In addition to having great potential for getting American chestnut back out on the landscape and increasing the diversity of species in the forest and providing food for all those creatures that eat chestnuts and all those good things, it also provides us with a good example of one use of genetic modification that isn’t tangled up with profit and patent and genetic control of resources,” Aitken says. In a survey that was part of a larger project Aitken led, researchers found that approximately half of respondents would accept planting genetically modified seedlings as a strategy to help western Canada’s forests adapt to climate change.

“Really, the number of American chestnuts they’re going to have if they don’t do this is zero.”

Hamelin says the greater concern in the forestry research community is not that the approach is risky, but that it will fail because the pathogen will adapt.

“Among the people who care about chestnuts and the people who care about trees and forest protection, I think most people, because of the fact that it’s an endangered species decimated by a foreign invader, that justifies going to this level.”

Others have reservations. The Canadian Chestnut Council is pursuing a conventional breeding program. “We are not interested at this point, nor do I see it in the future, in bringing in any genetically modified trees,” says Casier, chair of the council and a retired secondary school science teacher.

Casier says the group is “not anti-GMO” and “not opposed to what they’re doing in the States. We just have concerns,” chiefly about the ability of the pathogen to overwhelm the new tree’s single resistant gene, and whether transgenic trees will contaminate the wild tree gene pool.

“Once that pollen is genetically modified and is released into environment, there’s no way of going back and putting the genie in the bottle.” (Powell’s group has developed a way to identify the transgenic trees with a test that shows results in 30 minutes.)

A recent survey found 800 surviving American chestnuts in Ontario, though most were immature saplings. Casier says there is reason to think some Canadian trees carry blight resistance, in part because some trees scarred with the blight remain standing for years, perhaps decades.

The Canadian Chestnut Council’s program is breeding trees from Ontario with each other, with the goal of producing trees that carry native blight resistance genes and are adapted to the colder climate. But it is not clear how many generations will be needed to produce a viable resistant tree, if the program is successful at all. No matter what it will be an important pool of genetic diversity from the fringe of the species’ range.

While the species is wind-pollinated, a reproductive strategy that doesn’t care much for national borders, Powell notes that the natural spread of the tree is incredibly slow, a few kilometres every hundred years.

“We always call it a century project,” he adds. “This is something for our grandchildren — that’s the way I look at it.”

Correction – March 22, 2017: This article was edited from a previous version that mistakenly referred to Elm trees as Dutch Elms. In fact, Dutch elm is the name of a disease that affects Elm trees.