UNIVERSITY PARK, Pa. – While administering a blight-causing fungus to more than 200 young hybrid trees – a huge step in the process of developing a blight-resistant American chestnut tree – researchers knew seven decades of work had led to this moment.
“These trees are the direct descendants of a 1935 cross between a (blight-resistant) Chinese and an American chestnut,” said Kim Steiner, professor of forest biology at Penn State.
Since then, the trees have been repeatedly back-crossed with other American chestnuts, said Tim Phelps, a research technologist in the university’s College of Agricultural Sciences.
Resistant trees. After five generations, theoretically one in every 64 of the university arboretum’s trees 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,” Phelps said.
“But sure, I will feel better when we see the complete blight resistance actually express itself.”
Phelps said there will be varying levels of resistance.
“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,” Phelps said.
The majority of the young trees’ resistance will fall somewhere in the middle of the two extremes, he said.
Restocking forests. Chestnut blight wiped out virtually all American chestnut trees in North America after it showed up in New York in 1904.
After thorough screening, Phelps said trees that show total resistance to the inoculation will become the parents of seed that will be used to reintroduce American chestnuts into the Mid-Atlantic forests.
“All the progeny of the trees selected after inoculation will be blight resistant. We are that close,” Phelps said.
Process. Volunteers from around Pennsylvania – and even Ohio and Maryland – helped with the inoculation under the watchful eye of Sara Fitzsimmons, a research technician who provides support to foundation’s volunteer breeding activities in the Mid-Atlantic.
She showed Phelps and the volunteers how to make small wounds on the trees, use a spatula to apply the fungus from a petri dish and then tape the wound to be sure the fungus stayed moist and deadly.
It won’t take long to discover which trees will be the chosen ones, according to Phelps, who noted that trees susceptible to the blight will begin exhibiting signs of decline about a month after inoculation.
However, final tree selection at the arboretum will occur next May.
Other sources. Many Pennsylvania, Delaware and New Jersey foundation volunteers maintain earlier-generation hybrid chestnut trees that also will be subjected to the inoculation and screening process.
Seed from trees selected after those inoculations will eventually be planted in the arboretum until the orchard numbers more than 30,000 hybrid chestnut trees, according to Phelps.
He said the foundation is using chestnuts from various sources to avoid inbreeding and provide trees adaptable to different parts of the country.
“We wouldn’t be able to reforest the entire chestnut range with only trees grown in Virginia,” Phelps explained.
“Chestnut trees from the south would likely die if we tried to grow them in Maine.”
Plentiful plant. The stakes are high for success of the chestnut program. According to the 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 to bears and squirrels to 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.
Straight-grained, lighter in weight than oak and more easily worked, chestnut was as rot resistant as redwood.
It was used for virtually everything – telegraph poles, railroad ties, shingles, paneling, fine furniture, musical instruments and even pulp and plywood.
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