First outbreak of Phytophthora ramorum in England, on Viburnum tinus

Phytophthora ramorum is a recently described pathogen causing oak mortality in California, USA, and is commonly known as sudden oak death (Werres et al., 2001; Rizzo et al., 2002). The disease has reached epidemic proportions on native oaks in the central coast area, as well as damage to a range of other native plants. In Europe it has not been recorded on oaks, but has been found causing twig blight of species of Rhododendron, and occasionally stem base decay of Viburnum, in Germany and the Netherlands (Werres et al., 2001). In 2002, emergency phytosanitary measures were implemented to prevent spread within the European Community. In February 2002, DEFRA's Plant Health & Seeds Inspectors submitted one plant from a batch of five container-grown plants of Viburnum tinus cv. Eve Price, from a garden centre in southern England, showing severe aerial dieback, stem base discoloration and partial root decay, to the Central Science Laboratory (CSL) for diagnosis. The plants had recently been obtained from another English nursery. Samples from the basal region were excised, then surface-decontaminated by washing in running tap water, flowing into quarantine drainage, for 12 h. They were then transferred to a semiselective medium (P5ARP[H]) and floated in Petri's mineral solution (Jeffers & Martin, 1986). Following 5 days’ incubation, a Phytophthora sp. was consistently isolated with features typical of P. ramorum (Werres et al., 2001). The ITS sequence was identical to P. ramorum (http://www.ncbi.nlm.nih.gov) and reference to type cultures determined the mating type as A1. To date, the A1 mating type has only been found in Europe, whilst the A2 has only been found in the USA. Pathogenicity of the isolated fungus was confirmed using the twig dipping method with Rhododendron cv. ‘Catawbiense Grandiflorum’ as described by Werres et al. (2001); re-isolation of the fungus satisfied Koch's postulates. Using statutory plant health procedures, all five plants and associated growing media were destroyed, contaminated surfaces disinfected and other susceptible hosts inspected. Additional inspection and testing at the garden centre found no further evidence of the pathogen. The nursery that supplied the plants was intensively inspected and this revealed the presence of one block of 100 container-grown plants of V. tinus cv. Eve Price with two plants infected with P. ramorum. The source of the infection at this nursery is unknown. Statutory plant health action, as described previously, was taken, and no further symptoms have been observed on either of the premises. This is the first report of Phytophthora ramorum causing dieback of Viburnum tinus and the first record of the pathogen for England. The authors wish to thanks Jans De Gruyter, Plantenziektenkundige Dienst, Wageningen, the Netherlands, and Sabine Werres, Institute of Plant Protection in Horticulture, Braunschweig, Germany, for provision of information and cultures.