Chestnut Blight - Hybrid Chestnut Trees

Hybrid Chestnut Trees

In the years since the chestnut blight, many scientists and botanists have worked to create a resistant hybrid chestnut tree that retains the main characteristics of the American chestnut tree. In the early 1950s, James Carpenter discovered a large living American chestnut in a grove of dead and dying trees in Salem, Ohio that showed no evidence of blight infection. Carpenter sent budwood to Dr. Robert T. Dunstan, a plant breeder in Greensboro, North Carolina. Dunstan grafted the scions onto chestnut rootstock and the trees grew well. He cross-pollinated one with a mixture of 3 Chinese chestnut selections: "Kuling", "Meiling", and "Nanking". The resulting fruit-producing hybrid was named the Dunstan Chestnut. The trade off for resistance to the chestnut blight is that the Dunstan hybrid grew to a height of only twenty-five feet or 7.6 meters.

Current efforts are under way by the Forest Health Initiative to use modern breeding techniques and genetic engineering to create resistant tree strains, with contributions from SUNY College of Environmental Science and Forestry, Penn State, UGA, and the US Forest Service. One of the most successful methods of breeding is to create a back cross of a resistant species (such as one from China or Japan) and American Chestnut. The two species are first bred to create a 50/50 hybrid. After three back crosses with American Chestnut, the remaining genome is approximate 1/16 that of the resistant tree, and 15/16 American. The strategy is to select blight-resistance genes during the back crossing, while preserving the more wild-type traits of American Chestnut as the dominant phenotype. Thus, the newly bred hybrid chestnut trees should reach the same heights as the original American chestnut. Research is also being conducted at the State University of New York College of Environmental Science and Forestry, by using the bacterial vector, Agrobacterium tumefaciens, to insert resistance genes from the Asian chestnuts into American chestnut. The inserted genes are present only in the resistant strain, and not in the native American chestnut, and are tested for their potential to produce blight-resistant trees. Currently, SUNY ESF has over 100 individual events being tested, with more than 400 slated to be in the field or in the lab for various assay tests in the next several years.