Generation of New Dutch Elm Disease Tolerant American Elm Cultivars
One line of research on the American elm from the 1970s to the present focused on the identification of American elm cultivars that could withstand the Dutch elm disease (DED) fungal pathogen. Over 100,000 American elm trees were tested for resistance to Dutch elm disease, but no trees were found that were truly resistant to DED. However, several exhibited good levels of tolerance. Six cultivars have been developed that exhibit the necessary levels of DED tolerance to withstand the disease. These six selections are the Valley Forge, Princeton, New Harmony, R18-2, Delaware 2, and Jefferson. Recently, two additional selections— St. Croix and Prairie Expedition are undergoing final testing. While the vast majority of large American elm trees have been lost from forested areas in the eastern United States, some large trees remain. Some of these trees are those that have escaped the disease; however, after 5 to 8 decades of disease pressure, some of these trees may be survivors and hence possess DED tolerance. The New Harmony selection identified by Denny Townsend is an example of a survivor tree. Additional selections of American elm with tolerance to DED are needed to provide a broader genetic base as elms are deployed on forested and urban landscapes.
We are taking two approaches to generate and find additional elm cultivars with tolerance/resistance to DED. One approach uses known DED tolerant cultivars in controlled breeding efforts to create trees with increased tolerance or resistance. Crosses performed for this effort include Valley Forge x Princeton, New Harmony x Valley Forge, New Harmony x Delaware 2, and others. The progeny trees from these crosses were established in test plots and tested for DED tolerance. Fifteen of the best trees were clonally propagated and established in test plots and will be tested for DED tolerance in the future. The other approach is to screen large survivor American elm trees for tolerance/resistance to DED. The decades of DED pressure on the remaining American elms indicates that the remaining large trees (3-4 feet DBH) may have tolerance to DED. Screening these trees could be fruitful. Large survivor American elms identified in the Midwest are being screened for DED tolerance, and other large elms across its former range are being sought. These efforts will expand the number of elm cultivars available to the nursery industry, the National Forest System, The Nature Conservancy, and others interested in planting these "new" American elms.
Development of additional American elm cultivars with tolerance/resistance to DED.
Eshita, S.M.; Slavicek, J.M.; Kamalay, J.C. 2003. Generation of American elm trees with enhanced tolerance/resistance to Dutch elm disease through genetics. In: Gottschalk, Kurt W., ed. 2004. Proceedings, U.S. Department of Agriculture Interagency Research Forum on Gypsy Moth and Other Invasive Species, 2003. Gen. Tech. Rep. NE-315. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station. 78 p.
- James Slavicek, Research Biologist, U.S. Forest Service, Northern Research Station
- Kathleen Knight, Research Ecologist, U.S. Forest Service, Northern Research Station
- Christian Marks, The Nature Conservancy
Last Modified: 10/19/2010