The aim of this present study is to evaluate the antimicrobial activities of three plants essential oils, Nigella (Nigella sativa), Eucalyptus (Cinnamomum camphora) and clove (Syzygium aromaticum) against plant pathogenic bacteria Xanthomonas vesicatoria and their influences on controlling the bacterial spot disease of tomato plants. The chemical composition of the oils was calculated by gas chromatograph/mass spectrometer (GC/MS) analysis. The results revealed that the major constituents of Nigella oil were fatty acid i.e. oleic acid (4.09%%), Fumaric acid (0.13%), Palmitic acid (4.95-1.65 %), Octadec-9-enoic acid (0.53%), myristic acid (0.78%), Cyclohexadecane (0.01%) and Hexanedioic acid bis (2-ethylhexyl) ester (75.02%). In addition, the main components of Eucalyptus oil were D-camphor (40.01%), linalool (20.57%), and cineole (10.86%). The chemical analysis showed also that clove oil contained eugenol (22.94%), eugenyl acetate (16.65%), caryophyllene (10.37 %) and 2-Pyridineethanol (6.08 %). In in vitro bioassay against X.anthomonas vesicatoria, the results demonstrated that among the three tested plant oils, Eucalyptus oil (10 %) recorded the maximum value was (1.73 cm) bacterial inhibition zone followed by Clove oil (1.50 cm). Results also showed spraying plants with the tested essential oils two days before bacterial inoculation recorded the lowest disease index comparing to the treatment where plants were treating with essential oils two days after bacterial inoculation. The obtained results also clearly illustrated that, Peroxidase (PO), polyphenoloxidase PPO and chitinase activities increased as a result of spraying tomato plants with the tested oils. Moreover, protein analysis confirmed that new protein bands with low molecular weight had a progressive relationship with reduction of bacterial spot disease severity on plants treated with the tested oils. |
