Antibacterial activity of tulsi (Ocimum spp.) against plant pathogenic bacteria

Antimicrobial activities of two tulsi species, Ocimum sanctum L. and Ocimum canum Sim.extracts were evaluated against two bacterial plant pathogens, Ralstonia solanacearum and Xanthomonas oryzae.Agar well diffusion method was followed for antimicrobial activity assay.Extracts of methanol, n-hexane, chloroform and ethyl acetate were used with five different concentrations, viz., 10, 20, 30, 40 and 50 mg/ ml of 100% DMSO for both Ocimum species.Out of the different solvent extracts of O. sanctum, the chloroform extract showed the highest zone of inhibition (i.e., 9.66 mm) at 50 mg/ml against X. oryzae and the same concentration of methanolic extract showed the highest zone of inhibition (i.e., 7.16 mm) against R. solanacearum.Among the different solvent extracts of O. canum, the ethyl acetate extract at 50 mg/ml concentration showed the highest zone of inhibition (i.e., 12.17 mm) against X. oryzae while the same concentration of chloroform extract showed the highest zone of inhibition ( i.e., 6.84 mm) against R. solanacearum.Preliminary qualitative phytochemical studies of both the Ocimum species were done for the presence of phlobatannin, saponins, steroids, flavonoids, and tannins and for most of the cases, the results were found positive.HPLC fingerprint of the methanolic crude extracts of both the Ocimum species was done and O. sanctum showed the presence of about 38 numbers and O. canum about 34 numbers of metabolites.Thus the different solvent extracts of both the Ocimum species showed different antibacterial activities against R. solanacearum and X. oryzae, indicating their different sensitivities towards the metabolites present in the solvent extracts.Preliminary phytochemical studies of different solvent extracts and the HPLC fingerprint assay of methanolic extracts of both the Ocimum species reveal the presence of various phytoorganic constituents.