Natural outbreaks of Phytophthora ramorum in the U.K.—current status and monitoring update

Abstract

To date (February 2007) there have been 160 outbreaks of Phytophthora ramorum in gardens or woodlands in the U.K. Current EU policy requires that appropriate measures be taken to contain P. ramorum in such situations. In the U.K., the measures have either been aimed at eradication, through destruction of infected plants, or at containment to minimise the risk of P. ramorum being spread from the site to other areas. Of the 160 natural outbreaks recorded, 123 are ongoing, whilst the remainder are considered to have been eradicated as no further plant infections have been recorded, although in some cases the pathogen may still be detected as residual inoculum in soil or water. Monitoring of residual inoculum levels in soil/leaf debris has been carried out monthly for a period of up to three years in several sites in the south of England to investigate the extent of contamination within the gardens or woodlands and to quantify the effect of season on variation in inoculum levels. A number of the gardens were also found to be infected by P. kernoviae and in those situations the monitoring was extended to include both pathogens. A range of methods for monitoring levels of P. ramorum and P. kernoviae has been evaluated for routine use within the project. Initially samples were analysed using rhododendron leaf bait methods followed by isolation and identification on selective agar. All positive identifications were then confirmed using Real- Time Taqman PCR (polymerase chain reaction). More recently, PCR methods have replaced isolation and identification steps and have been used to develop more quantitative methodologies for monitoring seasonal changes in inoculum levels. Results have confirmed that the pathogens can survive and establish in the U.K. environment and that inoculum levels fluctuate in response to seasonal weather factors. During 2006, additional studies have been carried out to monitor inoculum movement from infected plants and has confirmed long distance (>50m) dispersal during wind-driven rain.

Parent Publication

• Proceedings of the sudden oak death third science symposium

Citation

Turner, Judith; Jennings, Philip; Humphries, Gilli; Parker, Steve; McDonough, Sam; Stonehouse, Jackie; Lockley, David; Slawson, David. 2008. Natural outbreaks of Phytophthora ramorum in the U.K.—current status and monitoring update. In: Frankel, Susan J.; Kliejunas, John T.; Palmieri, Katharine M., tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. Tech. Rep. PSW-GTR-214. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. pp. 43-48