POnTE Project: Phytophthora spp. on trees in Britain through the Tree Health Diagnostic and Advisory Service at Forest Research

Diseases caused by Phytophthora species have consistently been in the top ten reported problems on trees at the Tree Health Diagnostic and Advisory Service (THDAS) at Forest Research. A total of 227 Phytophthora reports have been submitted to THDAS since 2015 on 26 different tree genera. Phytophthora was isolated from these hosts and where possible was identified to species level by sequencing their ITS region with the primers TS4-ITS6. In 195 cases Phytophthora was identified to species level and in 32 cases confirmation was only based on the positive result of a lateral flow device (LFD). In total 19 different Phytophthora species were identified of which three were first records for Britain, P. foliorum on Rhododendron, P. siskiyouensis on Alnus incana and the hybrid P. gonapodyides x P. chlamydospora on Fagus sylvatica. The five most common identified species were P. plurivora followed by P. austrocedri, P. cinnamomi, P. pseudosyringae and P. cambivora. Phytophthora plurivora was recorded in 48 cases, 24 of which were identified on bleeding lesions on Tilia; P. austrocedri was mainly recorded on roots of Juniper; P.  cinnamomi was mainly detected on roots/soil of Castanea sativa and P. pseudosyringae was primarily detected on bleeding lesions of Fagus and Nothofagus. Pathogenicity tests were carried out and Koch’s Postulates were confirmed for the species that were detected for the first time in Britain. Furthermore, the susceptibility of different hosts to P. foliorum and of five different Alnus species to P. siskiyouensis was tested under laboratory conditions to assess their potential threat to British trees. Results on the species detected, the main hosts affected, and the value of the reports received at THDAS will be discussed.