This article was originally published in Nature, 4 October 2012.
“They’re hard to breed and easy to kill,” says plant pathologist Fred Hebard as he attacks a 2-metre-tall chestnut tree in southwest Virginia. Hebard bores a hole in the bark and squeezes a mash of orange fungus into the wood. The tree is a hybrid of the Chinese and American chestnut species, and Hebard hopes that it has enough resistance genes to keep the fungus — called chestnut blight — at bay. If so, the hybrid could help to resurrect a long-gone icon.
Until a century ago, the American chestnut (Castanea dentata) was the cornerstone tree species of eastern North America. With long, straight trunks and bushy crowns, it carpeted the forest floor each autumn with prickly brown nuts. But the arrival of chestnut blight (Cryphonectria parasitica) from Asia wiped out almost all the stately trees, leaving only a few, isolated stands. Since then, a faithful fan club of scientists and citizens has sought to tame the blight.
As chief scientist of the American Chestnut Foundation (ACF), a group of chestnut enthusiasts and scientists, Hebard has bred thousands of hybrids at the organization’s research farm in Meadowview, Virginia. He crosses descendants of the original American chestnut with the much smaller Chinese variety (Castanea mollissima), which has some natural immunity to the Asian fungus. And after decades of work, he is within reach of his goal, a tall American tree with enough Chinese traits to keep it healthy.
Other researchers are trying to attack the blight with viruses or are creating trees that are genetically modified (GM) to resist the fungus, and could be the first GM forest trees released in the wild in the United States. Progress with all three approaches is raising hopes that chestnuts will soon start to flourish again in the forests of the American east. “We’re starting to pull the American chestnut tree back from the brink of extinction,” says Hebard.
The work is also offering lessons that could help to save other trees, such as elm and ash, which face similar threats in America and abroad.