Chemical composition and antibacterial activity of essential oil of Ocimum ciliatum, as a new source of methyl chavicol, against ten phytopathogens

This study was designed to examine the chemical composition and the in vitro antibacterial activity of essential oil of Ocimum ciliatum Hornem. The inhibitory effects of the essential oil were tested against ten phytopathogenic strains, including Ralstonia solanacearum, Pseudomonas syringae pv. lachrymans, P. syringae pv. syringae, P. tolaasii, Xanthomonas oryzae pv. oryzae, Xanthomonas citri, Brenneria nigrifluens, Pantoea stewartii subsp. indologenes, Agrobacterium vitis, and Rhodococcus fascians using disk diffusion assay. GC and GC-MS analysis revealed that the essential oil predominantly contains methyl chavicol (87.6%), methyl eugenol (2.6%), and 1,8-cineole (1.7%) that making this plant as a good source of methyl chavicol or estragole. The antibacterial test results indicated the oil had antibacterial activity against all of the tested bacteria. According to the width of the inhibition zone, the most susceptible bacterium was B. nigrifluens and the most resistant bacterium was Pseudomonas tolaasii. Furthermore, the lowest MIC values were obtained from the essential oil of the plant against R. solanacearum. In addition, the most bactericidal property of the essential oil from O. ciliatum with the lowest MBC was observed against X. citri strain.