ARS | Publication request: Susceptibility of sprouted oak acorns to Phytophthora ramorum zoospores

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 25, 2009
Publication Date: June 1, 2009
Citation: Widmer, T.L., Dodge, S.C. 2009. Susceptibility of sprouted oak acorns to Phytophthora ramorum zoospores. Phytopathology. 99:5205.

Technical Abstract: Phytophthora ramorum is a recently emerged pathogen, having established in Europe and several western U.S. states, including California and Oregon. It has a wide host range and is a threat to forest ecology and the nursery industry. In California, coast live oak (Quercus agrifolia) is a major host in natural settings. Although P. ramorum has not established in the eastern U.S., artificial stem and foliar inoculations have demonstrated that native eastern Quercus spp. are susceptible when inoculated with sporangia. The purpose of this study was to determine if the primary roots of different Quercus spp. native to the eastern U.S. could be infected by P. ramorum zoospores, which could be released from sporangia into natural water run-off. Sprouted acorns of Q. rubra, Q. palustrus, Q. coccinia, Q. alba, Q. michauxii and Q. prinus were exposed to motile zoospores (3000/ml) of P. ramorum for 1, 6, or 24 h, rinsed in water to remove any nonattached cysts, and transplanted to potting soil. After 4 weeks, the roots were weighed, surface sterilized, plated on PARPH+V8 selective medium and incubated for 5 to 7 days at 20 degrees C. Developing P. ramorum was identified visually based upon colony morphology and characteristic chlamydospores and sporangia. Results showed that the primary roots of all oak species tested were susceptible to P.ramorum zoospores, and that infection could occur when exposed for only 1 h to the inoculum. Root weights were not negatively impacted by exposure to P. ramorum after 4 weeks, regardless of the oak species (P = 0.952).