First report of ramorum bud and leaf blight (Phytophthora ramorum) on Syringa vulgaris in the UK.

The recently described pathogen Phytophthora ramorum (Werres et al., 2001) causes tree mortality (Rizzo et al., 2002), dieback and leaf blight on various ornamentals and understory plants (Inman et al., 2003; Lane et al., 2003). Due to the potential threat to European flora from P. ramorum, EC emergency legislation was introduced in November 2002. During March 2003, a Syringa vulgaris plant originating from a nursery in Scotland was examined by SASA. The leaves had yet to develop, but the terminal bud and some axillary buds were blackened and dead. A Phytophthora sp. morphologically typical for P. ramorum was isolated (Werres et al., 2001). The culture was slow-growing with weakly coralloid mycelium. Sporangia were sympodial, semipapillate, deciduous with a short (< 5 μm) pedicel (40– 80 μm × 20–32 μm). Chlamydospores (25–72 μm) were also present. The culture tested positive for P. ramorum by TaqMan® PCR (K. J. D. Hughes, unpublished data). Subsequently, two separate samples of S. vulgaris were received at CSL during June 2003, both nursery-grown container plants from separate sites in England. Each plant had extensive greyish-brown, diffuse, water-soaked leaf lesions. Isolations once again conformed to P. ramorum and were confirmed by TaqMan® PCR. Pathogenicity was confirmed by inoculating healthy, unwounded detached leaves of S. vulgaris with a 9 mm plug from the edge of the original lilac isolate. After 1 week’s incubation (18°C in a damp chamber), typical lesions were seen. Phytophthora ramorum was re-isolated, thereby completing Koch’s postulates. No symptoms were observed on control leaves. Subsequent tests on whole lilac plants produced identical leaf lesions. Interestingly, profuse sporangia were produced from affected areas and the leaves abscised within a few days of infection. Following confirmatory diagnosis, statutory plant health action was taken to eradicate the disease. This is the first ever report of P. ramorum affecting S. vulgaris.