Professor William Powell with a transgenic American chestnut tree. Photo courtesy of the State University of New York's College of Environmental Science and Forestry.
In his New York Times best-seller A Walk in the Woods, author Bill Bryson mourns the loss of the “massively graceful” American chestnut: “There has never been any tree like it. Rising a hundred feet from the forest floor, its soaring boughs spread out in a canopy of incomparable lushness.” He goes on to describe the 1904 discovery of the chestnut blight at the Bronx Zoo in New York, which spread throughout the tree’s range, wiping the chestnut out within 50 years.
A Walk in the Woods was published in 1998, and little did Bryson know that scientists were already hard at work to create a blight-resistant chestnut. And it looks as if their work might be paying off. Earlier this year, 10 genetically modified American chestnuts were planted at the New York Botanical Garden (which is across the street from the zoo) in the hope that a blight-resistant, pure American chestnut will make a comeback where the tree’s demise was first documented. “This is where the blight started,” said Dr. William Powell, “and we want it to be the place where it stops.”
Powell and Dr. Charles Maynard of the State University of New York’s College of Environmental Science and Forestry have been involved with American chestnut research since the early 1980s and are the first researchers to perform field trials with transgenic chestnut trees. Their research involves growing chestnut embryos in tissue cultures, using nuts from pure American chestnut trees in New York State (trees that, although not blight-resistant, have survived by escaping the path of the blight). These trees differ from the Chinese chestnut hybrid trees that have been back-crossed with American chestnuts for years in attempts to breed a disease-resistant tree. The approach that Powell and Maynard have taken is to find a gene or combination of genes that will protect trees from the blight. The gene in the trees planted at the New York Botanical Garden is derived from wheat and contains an enzyme called oxalate oxidase, which detoxifies the lethal acid that the blight produces.
Maynard said the 10 trees planted at the botanical garden are “the most promising” of the over 600 transgenic trees growing in test sites around New York state since 2006. The researchers have already developed other trees to replace the original ten, should they fail. At age three, trees are inoculated with the blight, and their resistance is observed. Maynard said the team is trying out “lots of genes from different sources,” so that when they have successful trees ready to distribute, they “won’t be a simple clone.” In other words, the chosen trees will be genetically diverse, which will increase their resistance to disease. Nuts for the project are collected from different sources for the same reason.
Looking to the future, the trees that are finally selected as the most promising for full-scale distribution will be required to go through a USDA deregulation process, due to their transgenic status. Once that happens, private landowners in the chestnut’s home range will be invited to plant trees on their properties.
For more information, visit The American Chestnut Foundation’s New York Chapter.