Restoring the American Chestnut: Hybridization and Genetic Modification for Fungal Resistance

The eastern forests of the United States were once home to four billion American chestnut trees, which made up a quarter of all northeastern hardwoods. These majestic trees were valued for their straight, hard, and rot-resistant wood and could reach heights of fifty feet before their first branches. However, their numbers began to dwindle after a ship carrying Japanese chestnut nursery stock infested with a fungal blight accidentally spread the disease to the American chestnut trees in 1904. By 1950, the blight had devastated the American chestnut population.

The fungal blight, Cryphonectria parasitica, enters the tree through wounds or breaks in the bark and forms a canker, which quickly kills the tree by producing oxalic acid. In recent years, two approaches have been explored to combat the chestnut blight: hybridization and genetic modification.

The American Chestnut Foundation has been working since 1940 to hybridize the Chinese chestnut, which is resistant to the fungus, with the American chestnut. The goal is to produce a hybrid tree that possesses all the desirable attributes of the American chestnut, such as hardness, cold and drought tolerance, and suitability for its natural range, while also being resistant to the fungus.

Meanwhile, researchers William A. Powell, a forest biotechnologist, and Charles A. Maynard, a geneticist, from the State University of New York College of Environmental Science and Forestry, are investigating a genetic solution. They are testing a genetically modified chestnut tree containing a wheat gene that produces an enzyme capable of inactivating oxalic acid and stopping the fungus before it can harm the tree.

Both approaches require years of evaluation to determine their success. Genetically modified trees must be grown in controlled experimental fields to prevent their pollen from fertilizing other trees.

A Century Ago, American Chestnut Trees Flourished in the Northeast US, But Now They're Nearly Extinct Due to a Devastating Fungal Blight

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