Principal investigator: Anna Conrad, research plant pathologist, USDA Forest Service (anna.conrad@usda.gov)
Co-authors: Douglass Jacobs, Fred M. van Eck Professor of Forest Biology, Forestry and Natural Resources, Purdue University; Aziz Ebrahimi, postdoctoral research scholar, Forestry and Natural Resources, Purdue University; Mojtaba Zamani Faradonbeh, postdoctoral research associate, Forestry and Natural Resources, Purdue University.
Butternut (Juglans cinerea) is native to eastern North America and is well-known for its hard-shell nuts and timber value. A member of the walnut family, butternut is found in mixed hardwood forests and in riparian areas. Historically, the species reached as far south as northern Mississippi and northward into southeastern Canada.
Over the last half a century, butternut has been decimated by butternut canker disease. Because of this, butternut is now listed as endangered on the International Union for the Conservation of Nature Red List and in Canada under the Species at Risk Act. The disease is caused by a fungus that causes cankers (lesions) on the branches and stems of trees. These cankers, particularly when abundant and located on the main tree trunk, can lead to tree death.
Despite the disease being present across the range of butternut, not all butternut trees have died. Site conditions may influence the disease. For instance, dry, upland sites are less favorable for the disease. In addition, butternut readily hybridizes with Japanese walnut (J. ailantifolia), a non-native tree introduced into the eastern United States in the 19th century. Japanese walnut is known to have higher levels of resistance to butternut canker disease compared to butternut. Research has shown that some naturally occurring butternut/ Japanese walnut hybrids have higher levels of disease resistance, as well.
As a result, restoration of butternut has focused on identifying disease resistant trees, including both butternut and hybrids. This research project is focused on identifying the most resistant butternut and hybrid butternut families, and evaluating how resistance holds up when trees are planted in sites that are suitable for butternut restoration.
To date, researchers have screened more than 300 families for disease resistance. The most resistant families are often hybrid, but some butternut may also have acceptable levels of disease resistance. To evaluate this, the team is identifying the genetic background of the most resistant families and is using that information, as well as the geographic origin of the trees, to \select the most suitable trees for study. Sites in Connecticut, Vermont and Ohio are planned, with trees expected to go into the ground starting spring 2026.
“This research will guide butternut restoration activities in the future,” principal investigator Anna Conrad said. “To date, much of our screening for butternut resistance has occurred in plantings that are exposed to heavy levels of disease pressure. These plantings likely do not reflect disease across the broad range of butternut. Therefore, this study will be essential to determine how resistance holds up in sites where butternut may be planted in the future. In addition, these plantings can be used as a future source of butternut seed.”
Goals:
The goal of this research is to evaluate how stable resistance is in the most resistant butternut and hybrid butternut families in HTIRC’s collection. Researchers anticipate that resistance will vary depending on site locations.
Methods:
Disease incidence and severity was collected from butternut trees as part of the HTIRC butternut program. This information was used to identify the most resistant butternut families. Ongoing work to determine the genetic background of trees in HTIRC’s collection was leveraged so that knowledge of both genetic background and geographic location can be considered when selecting families for the study.
Key Findings in 2024:
Researchers identified partners to host three plantings of resistant butternut in Ohio, Vermont and Connecticut. In addition, a partner was identified to help propagate grafted trees for the study.
Currently researchers are finalizing quantitative genetic analysis to determine the most resistant families to select for grafting, which will begin in winter/spring 2025.
Future research:
This research is still in early stages, but it is anticipated that the plantings established as part of this project will serve as a germplasm resource for future studies focused on restoring butternut within the eastern United States.
Collaborators/Partners:
Jim Warren, biological scientist, USDA Forest Service, Northern Research Station
John Butnor, research plant physiologist, USDA Forest Service, Northern Research Station
Todd Hutchinson, research ecologist, USDA Forest Service, Northern Research Station
Elena Karlsen-Ayala, research plant pathologist, USDA Forest Service, Northern Research Station
Carolyn Pike, regeneration specialist, USDA Forest Service, Eastern Region — State, Private and Tribal Forestry
Nick LaBonte, regional geneticist, USDA Forest Service, National Forest System Region 9
Marcus Warwell, regional geneticist, USDA Forest Service, National Forest System Region 8
Caleb Kell, operational tree breeder, Forestry and Natural Resources, Purdue University
Carrie Fearer, assistant professor, Forest Resources and Environmental Conservation, Virginia Tech
Karl Fetter, postdoctoral researcher, Plant Computational Genomics, University of Connecticut
Martin Williams, forest genomics research scientist, Natural Resources Canada
Susanna Kerio, assistant agricultural scientist, Connecticut Agricultural Experiment Station
Jim McKenna