First report of Ramorum dieback (Phytophthora ramorum) on container-grown English yew (Taxus baccata) in England

Phytophthora ramorum is a recently described pathogen (Werres et al., 2001) causing oak mortality in parts of North America and is commonly known as sudden oak death (Rizzo et al., 2002). In North America it also causes ramorum dieback or ramorum leaf blight on a range of woodland plants. In Europe, it is recorded as causing dieback of rhododendron and viburnum (Lane et al., 2002) but also a number of other ornamental plants e.g. Pieris (Inman et al., 2003).

In May 2003, Defra's PHSI inspected a batch of twenty young container-grown plants of Taxus baccata (English yew; Taxaceae) from a nursery in north-west England from which P. ramorum had previously been found on Viburnum tinus. The yews were showing an overall bronzing, typical of drought stress, but on half of the plants there was a more discrete shoot dieback, similar to symptoms caused by P. ramorum observed on conifers (e.g. Sequoia) in North America. A whole plant showing dieback was sent to CSL for diagnosis. Stem sections were excised from the leading edge of the shoot dieback, surface-decontaminated by rinsing in tap water then transferred to a semi-selective medium (P5ARP[H]) (Lane et al., 2002). A Phytophthora species was consistently isolated, with morphological characters typical of P. ramorum (Werres et al., 2001). The culture gave a positive reaction with both conventional and real-time PCR assays, designed to specifically detect P. ramorum (K. Hughes, unpublished). In addition, ITS sequence from the yew isolate (Genbank AY 520152) was shown to be identical to P. ramorum sequences already published on the Genbank database. The Taxus isolate was inoculated onto healthy, wounded needles of young shoots of T. baccata and infection spread from the needles to the stem, causing a dieback of the detached stem. The pathogen was re-isolated to complete Koch's postulates. No symptoms were observed with the negative control (using an uninoculated agar plug). Following the confirmatory diagnosis, statutory plant health action was taken to eradicate the disease and there were no further findings of the pathogen on the site. This is the first report of Phytophthora ramorum causing shoot dieback of Taxus baccata in England and the first occurrence of the pathogen worldwide on a member of the Taxaceae (yew family).