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Saving an American Icon
Page 3

Photo of chestnutsNot all experts are so circumspect. "It is obvious to me that it will work," says Sandra Anagnostakis, who oversees a much smaller backcross breeding program. She is, in many ways, Hebard's opposite: a small, sturdy, cheerful woman of 67 who bubbles with excitement. Her office is filled with chestnutabilia; the license plate on her car reads CHSNUT. An expert on plant fungi, Anagnostakis fell into chestnut work almost accidentally in 1968, when a colleague laid a blight-ridden chestnut branch on her desk, saying "Here -- you're a mycologist, why don't you do something about this."

A few years later Anagnostakis learned about a discovery in Europe that had opened a whole new avenue for fighting the chestnut blight: deploying a naturally occurring virus to defang the fungus.

The virus had first been identified in Italy in the 1950s, by which time the blight had long since reached Europe. But then a strange thing happened: Some of the trees spontaneously began to heal. French mycologist Jean Grente cultured samples from the cankers of recovering trees and found that these strains of the fungus grew more slowly than usual and were a pasty white rather than the typical vibrant orange. Later researchers established that the fungus was infected by a virus that dramatically slowed its growth. This gave the trees time to marshal their natural defenses. Grente termed the phenomenon "hypovirulence."

When Anagnostakis read about Grente's discovery she immediately fired off a letter asking for samples of his hypovirulent fungus. She and colleague Richard Jaynes then injected the strains into American chestnuts in the Connecticut Agricultural Station's greenhouse: "Sure enough," she recalls, "the cultures that had the viruses kept the blight from killing the trees."

In 1978 she and Jaynes followed up with tests on 70 young American chestnuts in one of the station's orchards. "We treated every canker we could reach for four years," she says. Then they left the trees alone. More than 20 years later, the trees are riddled with blight cankers, but they're all still alive and some continue to grow. "They're gorgeous," Anagnostakis says proudly. "Well, gorgeous in my eyes."

Truly, a mother's love is blind. These trees are a far cry from the "American classic." Many look more like bushes than trees; the best of the bunch are scraggly, limby specimens averaging no more than 35 feet tall. As another researcher joked, "They're apple trees." Could they really be signs of success?

"It depends on what you call successful," Anagnostakis says. "I'm talking about trees that survive and flower." The trees blossom abundantly each summer, and every fall produces bushels of nuts. To her the trees are proof that hypovirulence can keep the species going while she, Hebard, and others work on developing blight-resistant trees.

That's a more modest goal than the early hope that hypovirulence could be used to resuscitate entire forests. Researchers got one last chance to test that notion when some trees in West Salem, Wisconsin, started to show signs of infection. In the early 1990s, a group of scientists began inoculating the blight-stricken chestnuts with hypovirulent fungus in the hope that the virus would be transmitted to the blight strain that was already in the woods. That proved trickier than anyone expected, according to Dennis Fulbright, a plant pathologist at Michigan State University. It's believed that the first virus used was so debilitating to its fungal host that it didn't spread. After three years, the researchers tried a weaker strain. Though this spread more readily, it has not been able to keep pace with the virulent strain of fungus. By now, Fulbright concedes sadly, the epidemic is so far advanced in West Salem that the blight appears to be getting the upper hand.

Even so, hypovirulence does appear to be rescuing some individual trees. To his surprise, Fulbright, like Anagnostakis, has found that some trees are better able to take advantage of hypovirulence than others. As he puts it, "Some of the trees out there seem to 'get it,' and some of them don't."

Walking through the stand, he stops and points to a pair of trees that were inoculated seven years ago and marked with red numbers on their trunks. Number 12 is little more than an upright mass of withered sticks. Number 13, however, is exuberantly alive, flush with shiny green leaves and bunches of nut-filled prickly burrs. Fulbright suspects the difference has to do with the tree's genes: Number 13 may have "a smidgen more resistance." If the hypovirus bought the tree some time, that whisper of genetic moxie gave it a chance to heal itself. And the evidence is visible in the healing cankers that pockmark its trunk and branches.

What does Fulbright's finding mean in practical terms? If nothing else, it suggests that the century-long quest to defeat the blight is not so quixotic after all. Most researchers would now say that in the long run it will take a combination of tougher trees and a weakened fungus. As Fulbright says, "That really might be the whammy the chestnut blight needs."

Then maybe, just maybe, as the tree's devotees like to say, the American chestnut can begin to save itself.

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Photo: Forrest MacCormack

OnEarth. Spring 2006
Copyright 2006 by the Natural Resources Defense Council