UGA Researchers Could Help Restore Devastated American Chestnut with Genetic Engineering

In their prime, the American chestnut trees stood a hundred feet tall and six feet wide. Now, they’re typically no bigger than shrubs, thanks to a fungal disease that spread down the East Coast decades ago, virtually wiping out the hardwood tree.

But researchers in the University of Georgia Warnell School of Forestry and Natural Resources, with support from ArborGen LLC, a leader in tree improvement and commercial production of trees, have developed a method for inserting anti-fungal genes into the tree’s DNA. They hope the new genes will fight off the fungal disease and help restore the American chestnut to its former glory. The results of Scott Merkle’s 20-year effort are detailed in a new paper published in the journal Plant Cell Reports, where he and associates Gisele Andrade and Joe Nairn describe the system they developed to insert new genes into the tree’s DNA and to propagate trees that carry the genes.

“The gene transfer system described in the new paper has already been used to produce some trees with genes that may confer resistance to the fungal disease,” said Merkle, “and ultimately could be used to help restore the tree to our eastern forests.”

The American chestnut used to grow from New England down the East Coast, abundantly through the Appalachians. It was a valuable resource for the U.S., Merkle explained, as it was a fast-growing tree that was used in construction, leather-making and as a dependable nut crop. But in the 1880s, people began to import Asian chestnuts to plant in their yards and with these trees came the fungus that attacked the American trees. The first documented instance of what became a widespread blight was in what is now the Bronx Zoo. A forester noticed the American chestnuts planted along the streets were dying. By 1904, the fungus had been identified as Endothia parasitica (eventually renamed Cryphonectria parasitica), but it was too late: The fungal disease spread rapidly, infecting Georgian trees by the 1940s.

“It happened amazingly fast,” Merkle explained. “They were actually stunned at how fast it spread.”

Merkle began researching the American chestnut blight in 1989, and has published several papers on the subject. In the past 20 years, he and his team of research associates and graduate students have been studying ways to get the chestnut trees to fight off the fungus. The disease works by attacking the chestnut after the bark has been injured, fanning out and killing the inner bark layer, eventually girdling the tree so that food and water cannot move up or down the stem.

So while the American chestnut used to grow more than a hundred feet tall, now they are usually no more than six feet tall before they are killed by the fungus, Merkle said. Most are just shrubs before they die, although larger surviving chestnuts have been found in isolated areas.

Merkle hopes to change that. After years of research, he and Andrade devised a way to grow chestnut trees from single cells and then found an effective way to separate the genetically engineered cells from the cells that did not have the inserted genes. Now, they’ve used their system to insert an anti-fungal gene, obtained from collaborator William Powell at SUNY College of Environmental Science and Forestry, into chestnut trees that are being grown in a Warnell greenhouse in preparation for testing the ability of that inserted gene to fight off the fungus.

"The way they’ll do that," Merkle said, "is by infecting the tree with the fungus and measuring how well it fights it off. It’ll be at least two years before they can take that next step in the research, however, since the trees have to grow to a certain size before they can be screened."

“It’s been a real challenge working with it,” he said. “But the potential is there.”

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Range Research, Genetic Work Spell Hope For Chestnut Comeback

Location, location, location. It’s the mantra of Realtors everywhere. But it may also be the reason a mighty tree long since gone from most of the Georgia landscape may get another chance to thrive.

Georgia Department of Natural Resources biologist Nathan Klaus made national headlines in 2006 after discovering a stand of American chestnut trees near President Franklin D. Roosevelt’s Little White House at Warm Springs, Ga. Once a fairly dominant species, the majestic chestnut was virtually wiped out by a fast-spreading fungal blight that swept through Georgia in the 1920s.

A long-time supporter of efforts to bring back the nearly extinct tree, Klaus recently began working on research that could continue to help restore the chestnut to its native range.

A few months ago, Klaus began looking at land lottery maps and using GIS (Geographic Information Systems) to plug in historic locations of American chestnuts. He hoped to develop a map showing the range and density of the trees in Georgia before the blight.

Researchers with The American Chestnut Foundation are working to develop blight-resistant chestnut sprouts, using an established program known as backcross breeding to create American chestnuts that are 1/16th Chinese chestnut, a hardier cousin. The goal is to have a tree that has enough of the Chinese species genes to resist blight but mostly is the tall, hardy American species once known and loved in the U.S.

Klaus’ research is important in helping determine the best place to plant the genetically strengthened trees. Old land lottery maps show where chestnut trees once were. Klaus scanned the paper maps into a computer-modeling program and has been able to determine which areas had a higher density of chestnuts trees and what species occurred with them.

The Georgia chapter of the American Chestnut Foundation has been working for 25 years with the national organization’s backcross-breeding program. The chapter is now using pollen found in the wild to pollinate orchard-grown chestnuts. The hope is that using the information from Klaus’ work, the American chestnut will have a higher degree of success as the seeds or seedlings are brought back to the South for planting.

Pollinating trees in the wild can be a difficult process, according to Martin Cipollini, the chapter’s breeding program coordinator.

“It relatively easy to collect the pollen from wild trees in Georgia and use it to pollinate hybrid trees in orchards. This ‘father tree’ approach is easier than trying to pollinate flowers on wild trees that are often in rather inaccessible locations on steep slopes,” Cipollini said.

“In the past 25 years, The American Chestnut Foundation has made considerable progress toward breeding blight-resistant trees. But, its ultimate goal of reintroducing these trees to the wild in large numbers requires knowledge of proper habitat requirements and planting techniques.”

The American Chestnut Foundation, working with its state chapters, has created hundreds of lines of trees that are well advanced through the backcross-breeding process. In the next few years, thousands of “final” generation nuts will be ready for testing in the wild.

So far, the Georgia chapter has created three lines using surviving Georgia trees as “fathers.” These lines are in orchard test sites. This past summer, the chapter produced four more lines using Georgia trees. These will go into test orchards next spring. The chapter wants to produce at least 20 lines using different Georgia chestnuts and including genetic diversity from throughout the tree’s historical range in the state.

But the question remains, just where is that range?

“Where do they belong and where will they thrive today? What was their true historical range? Did they grow near creeks or up on ridges, and if so, in what type of soils? These are answers we need before we begin to restore this species,” said Klaus, a senior wildlife biologist with the DNR’s Wildlife Resources Division.

Klaus is using property line records from the early 1800s to develop mathematical models that look at factors such as slope, soil composition, landforms, geology and aspect and elevation. An accurate description of the tree’s native range is needed as most institutional knowledge has been gone for several generations and the anecdotal knowledge available is not always accurate or reliable. The hope is that these new models can be applied to modern maps to show the actual historic range for the trees.

For instance, Klaus says chestnuts were not everywhere in the mountains, although anecdotally it has been suggested the trees were dominant in the Blue Ridge. An elevation map will show where best to plant the trees since they have different relationships to elevation depending on the region.

“There was definitely a well-defined niche in the world for these trees,” Klaus said. “The tree’s range extended well down into the Coastal Pain. Many people do not realize that the trees were in the Piedmont and Coastal Plain regions of Georgia.”

Hybrid trees for blight resistance testing are being planted in orchard sites around the state, including Berry College and the Georgia Mountain Research & Education Center, operated by the University of Georgia.

Georgians can help conserve rare plants such as the American chestnut as well as animals not legally hunted, fished for or trapped and their habitats, through buying wildlife license plates featuring a bald eagle or a ruby-throated hummingbird. They can also donate to the Give Wildlife a Chance state income tax checkoff. Both programs are vital to the Nongame Conservation Section, which receives no state funds.

Visit www.georgiawildlife.com for more information, or call Nongame Conservation offices in Social Circle (770-761-3035), Forsyth (478-994-1438) or Brunswick (912-264-7218).

To find out more about the Georgia chapter of The American Chestnut Foundation, visit www.gatacf.org
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