First report of Phytophthora foliorum in the United Kingdom
The NPPO of the United Kingdom recently informed the EPPO Secretariat of the first report of Phytophthora foliorum on its territory. The pathogen was found during an official survey for Phytophthora ramorum (EPPO A2 List). In March 2016, the presence of P. foliorum was confirmed in a single Rhododendron ponticum plant growing along a public road in Scotland, in an area where rhododendron clearance had been undertaken. The NPPO of the UK also noted that although P. foliorum is morphologically distinct from P. ramorum, P. lateralis and P. hibernalis, it gave a false-positive response when using the early ITS-based diagnostic PCR primers designed to screen plant material for the presence of P. ramorum. A delimiting survey has been undertaken within a 1.5 km radius around this single infected plant. Additional samples have been taken and are currently being analysed. The implementation of official control measures is awaiting the results of the delimiting survey. For the moment, the origin of this finding remains unknown. Investigations are on-going to determine the possible origin of this infection, including discussions with the landowner. It is noted that no recent plantings has occurred in this remote area.
The pest status of Phytophthora foliorum in the United Kingdom is officially declared as: Present – transient - under eradication.
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EPPO note: Phytophthora foliorum was first described in 2006 from evergreen hybrid azalea leaves collected in nurseries during surveys for P. ramorum in California and Tennessee (US). Morphologically, P. foliorum is homothallic with semi-papillate sporangia. Unlike P. lateralis and P. ramorum, P. foliorum has not been found to produce chlamydospores. During initial pathogenicity tests, P. foliorum was found to be pathogenic on both wounded and intact azalea leaves (azalea cv. ‘Pink Ruffles’). According to the available literature, no significant azalea mortality has been attributed to P. foliorum.
Sources
NPPO of the United Kingdom (2016-03).
Donahoo R, Lamour KH (2008) Characterization of Phytophthora species from leaves of nursery woody ornamentals in Tennessee. HortScience 43(6), 1833-1837 [Link].
Donahoo RCL, Blomquist CL, Thomas SL, Moulton JK, Cooke DEL, Lamour KH (2006) Phytophthora foliorum sp. nov., a new species causing leaf blight of azalea. Mycological Research 110, 1309–1322.
Widmer TL (2010) Differentiating Phytophthora ramorum and P. kernoviae from other species isolated from foliage of rhododendrons. Plant Health Progress doi:10.1094/PHP-2010-0317-01-RS [Link].