Forest Service moves American elm tree a big step closer to landscape restoration
Prior to the outbreak of Dutch elm disease (DED) fungal pathogens, American elm trees were widely dispersed across the eastern United States, thriving in a variety of different forest habitats. Over the last several decades, considerable progress has been made cultivating new genotypes of American elm trees that are tolerant to DED. Yet, from an operational standpoint the existing DED-tolerant cultivars lack the genetic diversity necessary for large-scale landscape restoration and are not regionally adapted. In June 2016, Forest Service scientists inoculated more than 850 American elm trees with DED to assess tolerance levels. The American elm material was derived from crosses between DED-tolerant individuals as well as material from large survivor trees. DED-induced canopy decline was assessed at eight weeks and one year after inoculation. At one year post-inoculation, 18 selections have exhibited tolerance (less than 20 percent DED symptoms) to the disease. These varieties will continue to be assessed for tolerance and will be incorporated into restoration plantings across the urban to rural gradient.