Greenscape Gardens Green Blog

CHESTNUT BLIGHT

Prior to the chestnut blight, one in four hardwood trees in Pennsylvania was a chestnut, according to the American Chestnut Foundation. Mature chestnuts grew to 100 feet tall, and many specimens reached 8-10 feet in diameter. Wildlife including birds, bears, squirrels and deer depend on the tree's abundant crop of nutritious nuts.

Tree expert Tim Phelps is confident that blight-resistant chestnuts are not only possible, but almost here. Blight wiped out virtually all American chestnut trees in North America after it showed up in New York in 1904. Now, seven decades of crossing blight-resistant Chinese chestnut trees with American chestnut trees, and then repeatedly back-crossing the progeny with other American chestnuts, has created 200 hybrids. The trees are now being tested in the Arboretum at Penn State with inoculations of the fungus that causes chestnut blight—with promising results.

Phelps, of the College of Agricultural Sciences and president of the Pennsylvania Chapter of the American Chestnut Foundation, is supervising the project. He explained how the years-long process works. “After a thorough screening process, the trees that show total resistance to the blight 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 said. “All the progeny of the trees selected after inoculation will be blight resistant. We are that close.”

The process starts with small wounds made on the test trees, using a spatula to apply blight-causing fungus from a Petri dish. The wounds are then taped to be sure the fungus stays moist and active. Young trees that are not blight resistant will begin exhibiting signs of decline in a month or so.

Final tree selection at the arboretum will occur in May. After five generations, one of every 64 young trees at the arboretum exposed to the blight should be highly blight resistant. 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 30,000 hybrid chestnut trees.

These trees are the direct descendants of a 1935 cross between a Chinese and an American chestnut. The first-generation back-cross to American chestnut was made in 1946.
The chestnut was a superb timber tree. It grew straight and often branch-free for 50 feet or more. 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.

In North America, pollen records from the latest interglacial period show that the American chestnut tree, Castanea dentata, was present on Long Island 30,000 to 50,000 years ago. American chestnut trees were once found all along the Appalachian mountain range, from Portland, Maine to northern Georgia. In the last 150 years it has been planted outside its range in favorable spots (Michigan, Wisconsin) where it has become a forest tree, protected from chestnut blight disease by geography until only recently.