First report of Pseudomonas savastanoi pv. savastanoi causing olive knot in Syria

During field surveys carried out in 2007 in the main Syrian olive (Olea europaea) growing areas, bacterial knot symptoms were observed on olive twigs and branches, with the highest incidence (70%) in the coastal region (Lattakia and Tartous). Bacterial colonies isolated from knots resembled those of Pseudomonas savastanoi pv. savastanoi. Ten selected representative bacterial strains and the reference strains LMG 2209^T, CFBP 6012 and 6013 of P. savastanoi pv. savastanoi were subjected to identification tests. All strains were Gram negative, fluorescent on King’s medium B and had oxidative but not fermentative metabolism. They were negative for levan, oxidase, potato rot and arginine dihydrolase and positive for tobacco hypersensitivity. One-year-old olive plants (cvs. Nebali and Jlot) were inoculated by introducing bacterial suspensions (10⁸ cfu/ml) into wounds made in the bark with a sterile scalpel. All strains induced knots at the site of inoculation from 20 days onwards. Bacteria with characteristics identical to the original strains were re-isolated from inoculated plants. PCR analysis using primers specific for P. savastanoi pv. savastanoi, which amplify fragments of iaaL (Penyalver et al., 2000) and ptz (Powell & Morris, 1986) genes, generated amplicons of the expected size from all strains. Using BOX-, ERIC- and REP-PCR, we demonstrated that the isolates have a similarity of 87-98.9 % between themselves and with the reference strains. Based on morphological, biochemical, physiological and pathogenicity tests as well as molecular analyses, we can conclude that the Syrian strains belongs to P. savastanoi pv. savastanoi.

Although strains from Syria have previously been characterised with respect to their ability to produce auxin (Gardan et al., 1992), this is the first authoritative report of olive knot disease symptoms in Syria caused by P. savastanoi pv. savastanoi.