Dissemination of aerial and root infecting Phytophthoras by human vectors

Abstract

Two new Phytophthora pathogens, Phytophthora kernoviae and P. ramorum, have recently established in parts of the U.K. They are most prevalent in the south west of England where they cause intense episodes of foliar blight and dieback on both ornamental and naturalised rhododendron such as Rhododendron ponticum, but both also cause lethal stem cankers on a range of broadleaved trees. Patterns of disease spread suggest hat both pathogens could be spread over longer distances by vertebrate movement. People and animals frequently walk through these contaminated areas and may pick up infested soil or litter on their feet and transfer it o new sites. A study was therefore set up to analyse how frequently Phytophthora could be isolated from the soil or litter attached to people?s boots, particularly those walking in woodlands and gardens known to be infested with P. kernoviae and/or P. ramorum. The study, which started in July 2004, has shown that in total more than 30 percent of samples collected from walker?s boots were contaminated with Phytophthora. The most commonly occurring species was P. citricola, but 10 to 15 percent of the Phytophthora positive samples contained either P. ramorum or P. kernoviae. The source of inoculum could be fragments of the infected leaves which are shed from infected Rhododendron and rapidly break down as they incorporate into the litter layer in affected woodlands. Tests have shown that P. kernoviae can survive in both air-exposed and litter-embedded infected leaves for more than a year, although there is a decline in the amount of inoculum that survives, indicated by the success of isolation. In air-exposed leaves isolation success dropped from 60 percent to 15 percent over 12 months, and from 78 percent to 18 percent for litter embedded leaves over the same time.

Parent Publication

• Proceedings of the sudden oak death third science symposium

Citation

Webber, J.F.; Rose, J. 2008. Dissemination of aerial and root infecting Phytophthoras by human vectors. 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. 195-198