🔗 The American Chestnut Tree

🔗 United States 🔗 Plants

The American chestnut (Castanea dentata) is a large deciduous tree of the beech family native to eastern North America. The American chestnut was one of the most important forest trees throughout its range and was considered the finest chestnut tree in the world.

The species was devastated by chestnut blight, a fungal disease that came from Chinese chestnut trees introduced into North America from East Asia. It is estimated that between 3 and 4 billion American chestnut trees were destroyed in the first half of the 20th century by chestnut blight after the blight's initial discovery in North America in 1904. Very few mature specimens of the tree exist within its historical range, although many small shoots of the former live trees remain. There are hundreds of large (2 to 5 ft diameter) American chestnuts outside its historical range, some in areas where less virulent strains of the pathogen are more common, such as the 600 to 800 large trees in Northern Michigan. The species is listed as endangered in the United States and Canada. American chestnuts are also susceptible to ink disease, particularly in the southern part of its native range. This susceptibility to ink disease may have contributed to the devastation of the species.

Several groups are attempting to create blight-resistant American chestnuts. Scientists at the SUNY College of Environmental Science and Forestry created the Darling 58 cultivar of American chestnut by inserting the oxalate oxidase gene from wheat into the genome of an American chestnut. When expressed in the cambium of the Darling 58 cultivar, oxalate oxidase detoxifies oxalic acid, resulting in a tree that still gets infected by the blight fungus but that resists girdling of the trunk and survives such infection. As of 2021, the researchers who developed this cultivar are working towards applying for government permission to make these trees available to the public. If approved, these chestnut trees would be the first genetically modified forest trees released into the wild in the United States. Cross-breeding of chestnut species represents an alternate approach to restoring the American chestnut. One approach has been cross-breeding among different partially blight-resistant American chestnuts, with the goal of developing a cultivar with high resistance. Another approach is to crossbreed American chestnuts with Chinese chestnut trees, which are moderately blight-resistant, and then to backcross with American chestnuts, with the goal of creating a cultivar with most of the genetic heritage of American but retaining the blight resistance of the Chinese chestnut.