Blight Resistant Chestnut Trees Close to Reality

Research technologist Tim Phelps, who is also president of the Pennsylvania Chapter of the American Chestnut Foundation—the group the college is working with to develop and reintroduce blight-resistant chestnut trees into Northeast forests—applies blight-causing fungus to the trunk of a small hybrid tree at the chestnut seed orchard in The Arboretum at Penn State.

As he helped administer the fungus that causes chestnut blight to more than 200 young hybrid trees in the seed orchard in The Arboretum at Penn State—a huge step in the process of developing a blight-resistant American chestnut tree—Tim Phelps admits he felt a twinge of doubt.

The research technologist in the College of Agricultural Sciences—who is also president of the Pennsylvania Chapter of the American Chestnut Foundation—knew that seven decades of crossing blight-resistant Chinese chestnut trees with American chestnut trees, and then repeatedly back-crossing the progeny with other American chestnuts, had led to this moment. After five generations, theoretically one of every 64 young trees at the arboretum exposed to the blight should be highly blight resistant.

“Scientists with the American Chestnut Foundation are confident that we are seeing blight resistance holding up across the various generations, but sure, I will feel better when we see the complete blight resistance actually express itself,” Phelps says. “And there will be varying levels. Only one out of 64 trees will show resistance on par with its great, great, great Chinese grandmother—and conversely, one out of 64 will have no resistance, similar to the native chestnut growing in our Pennsylvania forests today. The majority of the young trees will be somewhere in the middle.

“After a thorough screening process, it is the trees that showtotal resistance to this inoculation of the blight that will be selected as parents of the seed that will be used to reintroduce American chestnuts into the forests of the Mid-Atlantic region,” Phelps adds. “All the progeny of the trees selected after inoculation will be blight resistant. We are that close.

” Volunteers from around Pennsylvania—and even Ohio and Maryland—were on hand at The Arboretum at Penn State to help with the inoculation under the watchful eye of Sara Fitzsimmons, a research technician in the School of Forest Resources who provides support to the foundation’s volunteer breeding activities in the Mid-Atlantic region. She showed Phelps and the volunteers how to make small wounds on the trees, use a spatula to apply blight-causing fungus from a Petri dish and then tape the wound to be sure the fungus stays moist and deadly. It took hours to inoculate the trees.

It won’t take long to find out which of the young trees will be the chosen ones, according to Phelps, who notes that trees susceptible to the blight, which wiped out virtually all American chestnut trees in North America after it showed up in New York in 1904, should have begun exhibit ing signs of decline after about a month. But final tree selection at the arboretum will occur in May 2006.

Many Pennsylvania, Delaware, and New Jersey volunteers of the American Chestnut Foundation maintain earlier-generation hybrid chestnut trees that also will be subjected to the inoculation/screening process. Seed from trees selected after those inoculations around the Mid-Atlantic region will eventually be planted in The Arboretum at Penn State until the orchard numbers more than exhibit30,000 hybrid chestnut trees, according to Phelps.

The stakes are high for success of the chestnut program. According to the American Chestnut Foundation, prior to the chestnut blight, one in four hardwood trees in Pennsylvania was a chestnut. Mature chestnuts averaged up to 5 feet in diameter and grew to 100 feet tall, and many specimens reached 8-10 feet in diameter. Wildlife from birds and bears to squirrels and deer depended on the tree’s abundant crops of nutritious nuts.

The tree was one of the best for timber, according to the foundation. It grew straight and often branch free for 50 feet. Loggers tell of loading entire railroad cars with boards cut from just one chestnut tree.

Penn State has been a partner with the American Chestnut Foundation since 1997, according to Kim Steiner, professor of forest biology and director of The Arboretum at Penn State, who was an early proponent of locating the seed orchard there. “We do not precisely know the genetic makeup of these hybrid chestnut trees or even the mode of genetic control of blight resistance—we think three genes control blight resistance,” he says. “The inoculations that we just did at the arboretum were the final test of breeding theory and our informed conjectures.

“These trees are the direct descendants of a 1935 cross between a Chinese and an American chestnut, and the first-generation back-cross to American chestnut was made in 1946,” Steiner adds. “Naturally, we are very excited to see how these inoculations work out.”

— Jeff Mulhollem