CONTACT: Dr. William MacDonald, 304-293-3911
WVU researchers closing in on chestnut blight
An applesauce-like substance brewed by West Virginia University researchers could be the answer to controlling a disease that has all but wiped out the American chestnut.
The mixture in William MacDonald's lab is a genetically engineered strain of the fungus responsible for chestnut blight. The engineered strain contains a virus that prevents the fungus from killing the trees.
"If we can get the engineered strain to spread the virus more effectively, it should enable the virus to destabilize the fungus to the point where chestnut trees can survive, even though infected," said Dr. MacDonald, a forest pathology professor in the Plant and Soil Sciences Division of WVU's College of Agriculture, Forestry and Consumer Sciences.
The American chestnut was once the most abundant and versatile tree in the eastern woods. Its natural range stretched from Maine to northern Georgia, Alabama and Mississippi. The tree's rot-resistant wood was used to make furniture, construction materials, fences and utility poles. The edible chestnuts were popular with both humans and animals.
Chestnut blight changed all that. The fungus, accidentally introduced from imported Oriental chestnuts, was first recognized in New York City in 1904. It spread quickly and within 40 years had almost erased the once flourishing species from its natural habitat. The tree's roots do not become infected, so there is no immediate threat of extinction. The sprouts that emerge from the surviving roots, however, do become infected and die, and the cycle continues.
Cryphonectria parasitica, the fungus that causes chestnut blight, enters a tree through a wound. This fungus grows in and around the bark until it surrounds the tree. Symptoms of chestnut blight are cankers on the bark and yellowing of the tree's leaves as infected limbs die.
The fungus reproduces by creating asexual and sexual spores that are spread by insects, rain and wind. MacDonald and his research assistant, Mark Double, are focusing their research on this reproductive cycle of the fungus. Forest pathologists have known for some time there are naturally occurring viruses that retard the growth of the fungus. These viruses have been found to control chestnut blight in forested areas of Michigan and Italy.
"The fungus is weaker because of these virus infections," MacDonald said, adding that the viruses are only infectious when the lethal and nonlethal strains fuse.
Previous efforts to introduce virus-infected nonlethal strains of the fungus into forests where American chestnuts grow met with limited success, leading researchers to examine the compatibility between the lethal and nonlethal strains of the fungus.
"We've found we have a large number of virulent (lethal) strains," Double said.
Researchers also found that the nonlethal strains transmitted the virus to some of the lethal strains' asexual spores and none of their sexual spores.
The latest research involves copying the DNA of the virus in the nonlethal strains of the fungus and adding it to the genetic makeup of the lethal strain.
"You are gluing this whole piece of viral DNA into the DNA of the fungus," Double said.
Researchers at the University of Maryland Center for Agricultural Biotechnology have genetically engineered the virus-infected strains. MacDonald, Double and WVU graduate students are applying the engineered strains of the virus to infected chestnut sprouts in Tucker County, W.Va. The virus is also being introduced into sprouts in Connecticut.
The experiments have yielded impressive results. The virus-laden nonlethal strains have successfully transmitted the virus and permitted it to enter the sexual spores. With this technique, half of the sexual spores now contain the virus. This significantly improves the chances of spreading the nonlethal strains through the reproductive cycle.
"This is a huge breakthrough," Double said.
A huge breakthrough that has MacDonald confident the American chestnut will once again thrive in its natural environment and have positive impacts on the forest ecosystem, its wildlife and eventually the timber industry.
"The stage is set for this tree to grow again," he said.
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