Olive knot disease caused by Pseudomonas savastanoi pv. savastanoi in Egypt.

During field surveys carried out in 2008 in the entire olive districts in Egypt, bacterial knot symptoms were observed on twigs and branches of domestic olive cultivars in El-Fayoum governorate. From colonies resembling those of Pseudomonas savastanoi pv. savastanoi, isolated from olive knots on nutrient agar, 4 representative isolates were selected, purified on 5% sucrose nutrient agar medium and compared with the reference strain of P. savastanoi pv. savastanoi LMG 2209T. All isolates were gram negative, fluorescent on King’s medium B and had only oxidative metabolism. They were negative for levan, oxidase, potato rot and arginine dihydrolase and positive for tobacco hypersensitivity. When 1-year-old olive (cvs Toffahi, Agyze alshame, Picual, Manzanilla and Frantoio) and oleaster (Olea europaea subsp. oleaster) plants were inoculated with the bacterial suspensions (108 cfu ml-1) by punctured them in wounds made in the bark, all isolates induced knots in both host plants at the site of inoculation, 20-30 days after the inoculation. Bacteria re-isolated from the inoculated plants were found to be identical to the original isolates. PCR analysis revealed that all the isolates generated the expected size amplicon for P. savastanoi pv. savastanoi iaaL gene. By rep-PCR, we demonstrated that the isolates have a similarity of 95-100 % between them and with the reference strain. Based on morphological, biochemical, physiological and pathogenicity tests as well as molecular analyses, we can conclude that the Egyptian isolates are conforming with those described for P. savastanoi pv. savastanoi. This is the first record of olive knot disease on olive plants in Egypt.