Inhibitory effects of essential oils of some medicinal plants on the causal agents bacteria of potato wilt and soft rot under laboratory and greenhouse conditions

Nowadays, using essential oils as natural antibacterial inhibitors to control of plant diseases has been widely investigated. In the current research, the essential oils of Coriandrum sativum L., Thymus sativum L., Cuminum cyminum L., Rosmarinus officinalis L. and Eucalyptus globulus L. were extracted by water distillation method and then the inhibitory effects were tested against Pectobacterium carotovorum (causal agent of bacterial wilt in potato) andRalstonia solanacearum (causal agent of softrot in potato) using paper disk diffusion method. The minimum inhibitory concentration and minimum bactericidal concentration were determined by twofold broth dilution method. The experiments were analyzed by a completely randomized factorial design. Duncan’s multiple range test (MSTATC software) was used for comparison of means. Thyme oil exhibited the highest antibacterial activity in cultured media for both plant pathogenic bacteria, so it was selected to be applied in greenhouse experiments. The results showed that T. vulgaris had the most inhibition zone compared to the other oils in cultured media with 34.8 mm. In the greenhouse experiments, thyme oil was used for plant spraying and soil drenching methods at concentration of 0.5 and %1, respectively. According to the results, the thyme essential oil caused a significant reduction in soft rot and bacterial wilt incidence on potato by 41 and 44%, respectively compared with the control sample. Generally, thyme oil with a suitable antibacterial potential would be considered as an inhibitory agent to management of two studied diseases on potatoes.