Comparative Susceptibility of Plants Native to the Appalachian Range of the United States to Inoculation with Phytophthora ramorum

Abstract

Phytophthora ramorum, cause of sudden oak death of trees or ramorum blight of other plant species, has an ever-increasing host range. Some geographic regions are considered to be at high risk of becoming infested with the pathogen, possibly causing plant mortality such as seen in native habitats of California and Oregon. One such region is the Appalachian range of the eastern United States, where known susceptible plants occur and climatic characteristics appear favorable for infections by this pathogen. We collected foliage of a range of plant species native to Appalachia in Kentucky during two summer seasons, and the foliage was shipped to Oregon for inoculation with P. ramorum to determine relative susceptibility. Leaves were needle-wounded and inoculated with either mycelium agar plugs or sporangia of a North American (A2 mating type) or European (A1 mating type) isolate. After 14 days incubation at 20°C in moist boxes, lesions caused by either inoculum type or isolate generally were comparable using digital photos and ASSESS software. Some genera, species, and cultivars within species were highly susceptible, while others were moderately susceptible or not susceptible. These results provide a basis for regional surveyors to select target hosts and to generate survey and management practices for nursery and forest areas. Accepted for publication 24 April 2007. Published 17 September 2007.