The Bucknell University Arboretum has partnered with the American Chestnut Foundation (ACF) to restore American chestnut trees to our campus by planting "Restoration Chestnut 1.0" that are highly resistant to the chestnut blight fungus. In April 2014 four Restoration Chestnuts were planted on the hill between the Student Health Center and Snake Road. Although they are small now, they may some day reach heights of 100 feet or more.
Until the early 20th century, the American chestnut (Castanea dentata) was a dominant forest species in the Appalachian Mountains and played a central role in the forest ecosystem, providing food and shelter to countless species. These trees were true giants, commonly growing to a height of 100 feet and a diameter of 10 feet in virgin forests, with some specimens measuring as much as 17 feet in diameter. The leaves and nuts were a very important source of food for wildlife supporting huge flocks of birds and many mammal species.
The chestnut tree was of great economic importance for the production of lumber and chemicals such as tannins (used for tanning leather). The nuts also accounted for a significant portion of the diet of Appalachian communities, and were an important source of income as the nuts were shipped by the train load to cities on the Eastern seaboard.
Chestnut blight was first discovered in 1904 in the Bronx Botanical Garden. The disease, caused by an invasive fungus from Asia (Cryphonectria parasitica), quickly spread throughout the eastern United States, killing an estimated 4 billion trees by the 1920s. While almost all of the mature trees were killed by the blight, the fungus does not kill the root system. Thus throughout the eastern woodlands one can still find root sprouts from American chestnuts. These root sprouts do not produce viable seed, but do produce pollen that is used in breeding programs.
The loss of the American chestnut resulted in a major transformation of the forest ecosystem. It not only deprived animals of a food source but also opened up huge clearings within the forests that allowed sun-loving weeds and invasive species to take hold.
Since the 1920s scientists have been working to breed a disease-resistant American chestnut. Each of these breeding programs attempted to take advantage of the fact that the Chinese chestnut (Castanea mollissima) is resistant to the blight fungus. The Chinese chestnut co-evolved for many millennia in the presence of this fungus; therefore, the blight grows on this tree but doesn’t cause serious disease symptoms. While the Chinese chestnut has good disease resistance, it does not have the fast growth, upright form and large size that characterize the American chestnut.
In the 1980s the American Chestnut Foundation began a novel breeding program that starts with a cross between the American and the Chinese chestnut. This F1 generation is then backcrossed to American chestnuts for three succeeding generations to create a tree (B3F3) that is 15/16 (93.75%). The B3F3 generation, also known as Restoration Chestnut 1.0, is highly resistant to the chestnut blight fungus but has the growth characteristics of the American chestnut.
The Backcross method (www.acf.org)
The ultimate goal of the ACF program is to produce a tree that can survive and spread in the wild so that it may evolve by natural selection to adapt to its environment. Genetic diversity of the tree is of great importance. Therefore the breeding program has used pollen from trees from across its entire range and multiple lines of Chinese chestnut.