For more than three decades, US farmers have been growing genetically engineered crops. Now, researchers are pushing to move the technology from farm to forest, by releasing transgenic trees, engineered to carry foreign genes that would make them resistant to pests, into the wild.

Regulatory and research challenges to such genetically modified trees could make that transition harder, according to a report released by the US National Academies of Sciences, Engineering, and Medicine on 8 January. However, the potential of genetic engineering to boost forest health is promising enough to warrant further research, the report authors say.

Unfortunately, commercial interests are already hampering scientific work on transgenic trees, says plant geneticist Steven Strauss of Oregon State University in Corvallis.

Years ago, he was able to collaborate with companies to monitor his transgenic trees in the field. Now, he says, few companies will allow him to plant his trees on their land because doing so could cause them to lose certification by organizations such as the Sustainable Forestry Initiative. Many key consumers, such as home-improvement stores, will not buy wood unless it bears such certification, which is intended to show that the wood was harvested responsibly. But some of these certifying organizations do not allow transgenic trees.

Multiplying challenges

The report comes amid growing concern about the health of forests in the face of climate change and invasive pests. Disease outbreaks and infestations are a normal part of woodland life. But climate change and increasing international commerce and travel have allowed non-native pests and diseases to infiltrate naïve forests.

The US Department of Agriculture (USDA) has estimated that about 7% of forests or land with significant numbers of trees in the United States could lose a quarter of its vegetation between 2013 and 2027 to insects and diseases.

Plant breeders have traditionally tackled such problems by breeding new stock from naturally occurring disease-resistant trees. But some researchers are developing transgenic trees that carry foreign genes that make them more tolerant of pests.

Furthest along may be plant geneticist William Powell of the State University of New York in Syracuse and his collaborators. Powell’s team is trying to bring back the American chestnut ( Castanea dentate ), a stately and beloved tree that once dominated forests in the eastern United States. The tree fell prey to the invasive ‘chestnut blight’ fungus ( Cryphonectria parasitica ) around the turn of the twentieth century, and is now nearly extinct. The fungus secretes an acid that kills plant cells.

Over the past forty years, Powell’s team has transferred a gene from wheat that enables chestnut trees to detoxify the acid. Powell has consulted with the USDA, the Environmental Protection Agency and the Food and Drug Administration about the possibility of releasing such trees into the environment. “For each of them, this is brand new,” says Powell. “And that makes it a little more challenging.”

Costs and benefits

The academies report highlights several challenges that are unique to forests. Unlike crops, which are typically harvested every few months, engineered trees would persist in the environment for decades, and they could migrate across national borders undetected. The report authors say that some modified trees could even escape regulation altogether, like some engineered crops already do , because of gaps in the rules for transgenic crops.

In 2014, regulators in Brazil came close to approving a eucalyptus tree that was engineered to grow faster than its natural counterpart . The modified tree grew 20% faster in initial tests, but those results didn’t hold up when it was tried in other locations around the country, says plant geneticist Dario Grattapaglia of EMBRAPA, a state-owned research corporation in Brasilia, who advised the government on the project. This, coupled with predicted difficulty in selling the wood from such trees, essentially felled the project, he says.

Grattapaglia is also sceptical about using genetically modified trees to combat arboreal diseases. Often, disease resistance is controlled by small contributions from hundreds or even thousands of genes, he says — too many to tackle using genetic engineering.

Given such uncertainties, the time savings created by engineering disease-resistant plants, rather than breeding them conventionally, may be overestimated, Grattapaglia says.

But Strauss argues that researchers may find a few genes with an unusually large influence on disease resistance. And Powell points to growing concerns about tree diseases, including sudden oak death. The American chestnut is not the only tree that could benefit from genetic engineering, he argues.

“There is probably going to be a wave of trees behind it,” says Powell. “There are so many problems out there.”