by Lynn Hoch, Environmental Management Office
The American chestnut was once one of the dominant tree species in the eastern forests of the United States, towering over all other tree species in the forest. Due to its dominance of presence in the forest, reaching over 100 feet tall and 5-10 feet in diameter, it was commonly referred to as the “Eastern redwood.” Longevity was one of its hallmark features; some American chestnut trees were known to live as long as 600 years.
Once there were an estimated 4 billion American chestnut trees in eastern forest, representing approximately 25 percent of the total forest hardwood tree makeup. In the late 1890s, the Asian chestnut blight, a virulent fungal disease, arrived in the U.S. and spread quickly, leading to the destruction of most of the American chestnut stands by the 1950s.
Efforts have been made to bring this giant tree back, using innovative developments in genetics and plant pathology. Founded in 1983, the American Chestnut Foundation, or TACF, is a program created to coordinate breeding efforts to create blight-resistant American chestnut trees using a genetic backcross breeding strategy, with the eventual goal of developing a more disease-resistant form of the tree and beginning its reintroduction to its native range.
In 2010, the U.S. Army Garrison, Fort Detrick entered into a Memorandum of Understanding with TACF to establish a framework for cooperative research and management activities to maintain and enhance forest ecosystems by reintroduction of blight resistant seedlings of American chestnut trees on Army land. This partnership aligns with a long-standing tradition of Fort Detrick’s commitment to the environment by caring for its trees, including being recognized as Tree City USA for eleven years and a recipient of the Maryland Plant Award for fifteen years running.
The Fort Detrick orchard originally started as a one-acre demonstration orchard, containing both American and Chinese chestnut species, as well as backcrossed genetic lines of these species. Over the years, the Fort Detrick orchard has expanded and now consists of 1.5-acres and is considered a chestnut breeding orchard.
Across the eastern region of the U.S., there are some 300 volunteer-operated breeding orchards including the one located on Fort Detrick in Area B. The strategy of establishing breeding orchards over a wide geographical range helps ensure that the tree lines derived from the different breeding orchards are adaptable to a range of environmental conditions (i.e., soil types, temperatures, and rainfall amounts). Nuts planted in breeding orchards have been derived from trees pollinated using pollen from a backcrossed tree selected for resistance to the blight fungus.
To genetically transfer blight resistance, the crosses should include the first cross called “F1” that is 50 percent American and 50 percent Chinese; the 1st backcross, a “B1” that is 75 percent American; the 2nd backcross, “B2,” that is 87 percent American; and the 3rd backcross, “B3,” that is 94 percent American. The percentages represent the approximate genetic makeup that the population of American chestnut trees may have.
In the spring of 2012, Fort Detrick was selected as the only breeding orchard within the state of Maryland to receive what are considered blight-resistant seed stocks derived from genetically controlled backcrosses. Approximately 40 nuts (B3F3 seeds) were planted. Of these, over 90 percent of the seeds developed into what are commonly referred to as B3F3 seedlings, or “Restoration chestnuts.” Following one season of growth, the B3F3 seedlings are approximately 18 to 24 inches tall. This American chestnut genetic line is considered to be the most blight resistant form of the tree that is currently available. Within 5-7 years, these trees will be mature enough for seed/nut production.