Get reliable rangeland science

The American chestnut (Castanea dentata) was an iconic tree in the eastern United States, valued for its lumber, edible mast, and tannin. The species was a common component within its 200 million acre range that stretched from southern Ontario to Mississippi. American chestnut was a keystone species, providing important dietary needs and habitat for numerous insects, birds, and mammals. The tree was ecologically extirpated by exotic pests from Asia, notably, the chestnut blight (Cryphonectria parasitica) by the early 20th century. The loss of the American chestnut probably had devastating consequences on the ecosystem, although research was not being widely conducted at the time. A backcross breeding approach that transfers resistant genes from Asian chestnut species to the American chestnut while retaining American chestnut growth characteristics was first tested in a series of experimental forest plantings from 2009 to 2014 on USDA National Forest System lands. Trees were challenged by biological factors, primarily deer browse and root rot disease (causal agent�Phytophthora cinnamomi) that limited survival and growth. Blight resistance was affected by the interaction of breeding and planting location. The breeding generation with putative blight resistance (BC3F3) exhibited better resistance than the American chestnut, but were not as resistance as the Chinese chestnut (C. mollissima) at some locations. Growth of BC3F3 seedlings was less than American chestnut seedlings at some locations, indicating a departure from desired traits. Success was affected by seedling characteristics at the time of planting, primarily size of seedlings, with larger seedlings exhibiting better growth over time. Results indicate that blight resistance is one of a multitude of interrelated factors affecting success of American chestnut restoration. A multi-disciplinary approach to research and restoration is required, but will be limited by available technological and administrative resources.