First report of olive knot caused by Pseudomonas savastanoi pv. savastanoi in Nepal

During 2006-2008, a phytobacteriological investigation on olive plants (Olea europea) was carried out in Nepal. In commercial olive orchards in Bissingkhel locality, Makwanpur district, knots (0.5-3 cm in diameter) resembling those caused by Pseudomonas savastanoi pv. savastanoi (Gardan et al., 1992) on olive trees, were observed on twigs and branches of 12 year old olive plants cv. Frantoio. From knots, bacterial cells were isolated on nutrient agar medium supplemented by 5% sucrose (NAS). The isolates were positive for oxidase, pectinolytic and arginine dihydrolase activity, tobacco hypersensitivity; production of fluorescent pigments and of indole on KB and on MM media, respectively, and negative in the production of levan (Lelliot & Stead, 1987). In greenhouse studies, ten potted olive plants cv. Frantoio, two years old, were inoculated during spring by pricking two stems per plants at two sites with a hypodermic needle containing bacterial suspension (10⁸ CFU per ml). Characteristic knot symptoms were observed on all inoculated plants within six months after inoculation. Bacterial cultures with identical characteristics to the original strain used for inoculations were reisolated from all olive knots that developed. Molecular identification was achieved by sequencing the 16S rDNA region (GenBank Accession No. EU882164) and searching with BlastN (Zhang et al., 2000) for similar sequences in nucleotide databases (GenBank, EMBL and DDBJ). The sequences shared between 99.86% (1404/1406 bp) and 100% identity with the analogous sequences of P. savastanoi pv. savastanoi available in the databases. This is the first record of olive knot disease on olive trees (Olea europea) in Nepal.