First record of Pseudomonas syringae pv. viburni in the UK

Various Pseudomonas syringae pathovars cause leaf spots and cankers of hardy nursery stock species in the UK, including P.s. pv. syringae on lilac, P.s. pv. berberidis on Berberis spp. and P.s. pv. philadelphi on Philadelphus spp. (Roberts, 1997). Leaf spots on some other hosts are attributed to P.s. pv. syringae or to P. syringae pv. undetermined. Occasionally Central Science Laboratory has received samples of Viburnum spp. with watersoaked leaf spots from which P. syringae has been isolated; one was from Viburnum tinus in 1986. The isolate, a typical LOPAT group 1 member of P. syringae (Lelliott & Stead, 1987), was placed in the National Collection of Plant Pathogenic Bacteria (NCPPB) as NCPPB 3450 and was listed under P.s. pv. viburni with a 'b' ranking; denoting authenticity not verified. More recently, plants of Viburnum sargentii with typical bacterial leaf spots were received from a Lincolnshire nursery and from which LOPAT 1 strains were isolated. Host tests confirmed pathogenicity on Viburnum sargentii. Virulence was weaker on Viburnum opulus var. 'Sterile'. Two isolates from V. sargentii on the same nursery, taken at different times (CSL 4205 and 4206), were acceded to the NCPPB as NCPPB 4265 and NCPPB 4266 respectively.

Fatty acid profiles obtained were typical of P. syringae. REP-PCR based on primers from the repetitive enterobacterial consensus sequence and BOX-PCR, based on primers from the BOX A subunit were carried out (Stead et al., 2000). Fingerprints were compared with those of reference strains of all validly-named P. syringae pathovars held in the NCPPB, including P.s . pv. viburni (NCPPB 1921, the only authentic strain). UPGMA dendrograms of both assays showed that NCPPB 3450 did not have the profile of P.s. pv. viburni but was very similar to that of P.s. pv. maculicola and P.s pv. tomato. However, NCPPB 4265 and NCPPB 4266 had profiles very similar to that of the P.s. pv. viburni type strain and were different from all other reference strains. A subset of BOX-PCR fingerprints of strains of P. syringae pathovars known to occur in the UK is shown in Fig 1. Bradbury (1986) lists the known distribution as USA and Spain, with the Spanish strains coming from a rot of tobacco. This is the first authentic record of P.s. pv. viburni in the UK. The precise taxonomic position of NCPPB 3450 remains uncertain.