An in Vitro Attempt for Controlling Severe Phytopathogens and Human Pathogens Using Essential Oils from Mediterranean Plants of Genus Schinus

Growing concerns about food safety and environmental protection enhanced the need for new and safe plant disease control strategies. The chemical composition of the three essential oils (EOs) extracted from leaves and fruits of Schinus terebinthifolius and leaves of Schinus molle, growing in Tunisia, was studied by GC and GC-MS. In all, 12 compounds were identified. The oils were mainly composed of terpene compounds. α-Pinene, α-phellandrene, and d-limonene were the major constituents. The aim of the current study was to evaluate the in vitro antimicrobial effectiveness of three EOs derived from plants of genus Schinus and extracted from leaves and fruits of S. terebinthifolius and leaves of S. molle. Both antifungal and antibacterial activities of the EOs were examined. The antifungal activity of the studied EOs was investigated against Colletotrichum acutatum and Botrytis cinerea in comparison with the systemic fungicide azoxystrobin used at 0.8 μL mL-1. The antibacterial activity was evaluated against three strains of Gram-positive (G+ve) bacteria (Bacillus megaterium, Bacillus mojavensis and Clavibacter michiganensis) and four strains of Gram-negative (G-ve) bacteria (Escherichia coli, Xanthomonas campestris, Pseudomonas savastanoi, and Pseudomonas syringae pv. phaseolicola) compared with the synthetic antibiotic tetracycline at a concentration of 1600 μg mL-1. The minimum inhibitory concentration of the studied EOs has been evaluated against the above microorganisms using the 96-well microplate method. Tested microorganisms exhibited different levels of sensitivity to each tested EO. All investigated EOs reduced the fungal mycelial growth when used at low concentrations from 250 to 1000 ppm and from 2000 to 8000 ppm against C. acutatum and B. cinerea, respectively. Higher concentrations of the same EOs exhibited a fungicidal effect against both mitosporic fungi. The EO extracted from leaves of S. terebinthifolius significantly inhibited the growth of tested bacterial strains. Nevertheless, E. coli showed a weak resistance toward the same EO and a high resistance toward the other two tested EOs. Finally, P. savastanoi and P. syringae pv. phaseolicola showed a high resistance toward all tested EOs.