Antibacterial activity of Thuja orientalis essential oil against some tomato pathogens and determination of inhibitory properties of major compounds by molecular docking

The aim of this study was to determine the in vitro antibacterial activity and minimum inhibitory concentration (MIC) of Thuja orientalis essential oil (EO) against two important agricultural tomato pathogens: Clavibacter michiganensis subsp. michiganensis and Xanthomonas euvesicatoria pv. vesicatoria. The chemical composition of the EO was analysed using GC-MS/MS. The inhibitory properties of the volatile oil’s main components were investigated via molecular docking and molecular dynamics (MD) with the D78N mutant apo form of C. michiganensis expansin and the XopD effector protein of X. campestris. The antibacterial activity of the essential oil was evaluated using the agar disc diffusion method. Inhibition zones measuring 66.67 mm, 65.0 mm and 55.0 mm were formed against the Cmm 8, Cmm 10 and XCVOZ1 strains, respectively. By contrast, netilmicin produced inhibition zones of only 7–11 mm against the pathogenic strains, clearly demonstrating the oil’s much stronger effect. The MIC values at which T. orientalis oil inhibited pathogen growth were found to be between 10.0 and 16.0 mg/mL. GC-MS/MS analysis revealed the main components of T. orientalis essential oil to be 3-carene (16.52%), α-pinene (11.28%), limonene (10.16%), sabinene (8.91%), oleic acid (8.5%), cedrol (7.81%), bornyl acetate (5.78%), 4-terpineol (3.72%), β-myrcene (3.2%), and terpinolene (2.8%). According to the results of the molecular docking study, cedrol exhibited the highest binding affinity for XopD (-7.7 kcal/mol) and the D78N mutant apo form (-7.5 kcal/mol), with these results being confirmed by MD. It can therefore be suggested that T. orientalis EO could be used to control the bacteria C. michiganensis and X. euvesicatoria, which cause bacterial spot disease in tomatoes.