Photograph by James Balog
But Powell and Maynard have struggled to get past the test-tube stage. Many commercially grown trees—fruit trees as well as timber trees such as pine, poplar, and willow—can be maintained as tissue cultures, transferred to soil, and then grown into whole plantations. “For the chestnut, it turned out to be very, very difficult,” says Maynard, who’s been working on the problem since the late 1980s. He found that the only chestnut tissue that can be cultured and replanted comes from developing nuts, and wrestling the nuts out of a thorny chestnut burr is “like taking apart a porcupine.” The SUNY scientists have harvested more than 10,000 of them, but less than one-tenth of a percent form culture growths that can then be coaxed into whole plants. Once a whole plant is established in culture—with a stem and leaves—“it’s very difficult to root, and once it’s rooted, it’s very difficult to get it growing in soil,” says Maynard.
So the biotech shortcut has turned into a lengthy detour. Even if it succeeds, some scientists are sure to protest the planting of a genetically modified organism in public forests. Griffin is hoping to avoid that scenario by breeding pure, blight-resistant American chestnuts. The first step in his project was to find the oldest, tallest, toughest trees. There was one on a dairy farm in southeast Ohio, another in a pasture just a couple of hours from Blacksburg, Virginia—trees that were alive when the blight first struck. His Blue Ridge snag was one of the biggest he’d ever seen, and the fact that it still held its bark meant it had died only recently. Although a dead tree isn’t much use in a breeding program, there were two living chestnuts of substantial girth nearby that Griffin figured were close relatives. “We felt they had to have some of the same genes,” he says. “A squirrel must’ve carried a few nuts around.”
Some plant pathologists question whether surviving American chestnuts really are genetically resistant and wonder whether interbreeding them can enhance the putative trait. Griffin says that although survivors don’t have as much resistance as Asian chestnuts, they do have some natural defenses. When their branches are grafted onto living stumps and inoculated with fungus, for example, the grafts do better than the average infected American chestnut tree. Griffin thinks that geographically distant survivors may each have unique genes for resistance. By interbreeding them he hopes to combine those different genes to yield tougher offspring. “Our ultimate goal is to get a tree with higher resistance than either of the parents,” he says. More than 100 descendants of chestnut survivors grow on a plantation not far from Griffin’s office under the auspices of the American Chestnut Cooperators Foundation, which is partly run by Griffin’s wife, Lucille. It’s too soon, he says, to tell whether his project has worked.
Meanwhile, Griffin and others are exploring a fourth strategy for saving the chestnut that involves controlling the blight fungus. In the 1950s, European chestnuts, which had been decimated by blight as well, began to rebound in Italy, where they were still cultivated. The Cryphonectria on the Italian trees had caught a virus that limited canker formation. Trees with virus-infected fungus were thriving, and the weakened fungus was spreading to other parts of Europe, reviving chestnuts as it went. Pathologists at the Connecticut Agricultural Station in New Haven gathered samples of the sickly European fungus and identified the virus. But the European fungus proved to be so weakened by the virus that it couldn’t compete against American strains. And in many trials over many years, European fungal strains have proved reluctant to transmit the virus to American Cryphonectria, even when the European fungus is injected directly into an American canker. “I still think it has the potential to work, if we can figure out how to deliver it and keep it established,” says MacDonald, who has been doing biological-control experiments on a rare stand of chestnuts in Wisconsin.
Griffin thinks the chestnut’s best bet lies in a combination of approaches. In one forest stand, for example, he and other Virginia researchers grafted branches from the largest surviving trees onto sprout clumps, then inoculated the grafts with virus-carrying fungal strains. That was in the early 1980s. Today the largest of the grafts is more than 60 feet tall and 20 inches in diameter at breast height, and there are almost no blight-killed branches. “These trees did remarkably well,” he says.
But even when the weakened fungus prospers on a single tree, it doesn’t spread to others, as it has in Europe. The trees that have been kept alive by biological control have each been hand-inoculated, one by one, sometimes canker by canker. It’s a labor of love, with results that today’s researchers probably won’t live to see. Yet no one thinks of giving up.
“Foresters like big trees,” Maynard says. “We may screw around with poplar and willow—it pays the rent. But we like the big ones: the redwoods, the grand firs. The chestnuts.”