Synthesis of new Blended Formulations of Oregano-Sage Essential Oils: Chemical Characterization, Antimicrobial and Phytotoxic Activities

There is a growing interest in a potential use of essential oils (EOs) as a possible alternative for chemical pesticides. The formulation between different EOs could maximize the single biological efficacy by synergic mechanism. The aim of the current study was to evaluate the biological activity of three prepared blended oil formulations (BOFs) derived from Origanum vulgare L. (oregano) and Salvia officinalis L. (sage) compared to each parent EO. The chemical composition of each single studied EO has been revealed using GC-MS analysis. The three BOFs have been prepared as following: i) 25% oregano EO + 25% sage EO (BOF-I); ii) 25% oregano EO + 5% sage EO (BOF-II); iii) 5% oregano EO + 25% sage EO (BOF-III). The antibacterial activity of the new BOFs has been evaluated against Bacillus megaterium, B. cereus and Xanthomonas campestris, whereas, the antifungal activity has been carried out against Botrytis cinerea, Penicillium italicum and Fusarium oxysporum. The possible phytotoxic effect of the new BOFs has been evaluated on Lepidium sativum (garden cress), Solanum lycopersicum (tomato) and Lactuca sativa (lettuce) following the seed germination and radicle elongation assay. GC-MS analysis revealed that the oregano EO composed mainly from thymol, p-cymene and carvacrol with 76.0, 5.7 and 3.2 %, respectively. Whereas, salvia EO, the GC-MS analysis showed that the relevant predominant constituents were trans-thujone and camphor with 37,9 and 13,9 %, respectively. Results demonstrated that the tested BOFs possess antimicrobial effect higher than each parent EO. In particular, BOF-II showed the highest effect against all tested bacteria. Regarding the antifungal activity, BOF-II showed the highest significant antifungal effect against all tested fungi. Results showed also that both BOF-I and BOF-III explicated a moderate effect against B. cereus and all tested fungi compared to single EOs. In addition, the three BOFs showed notable phytotoxic effect against all three tested plants, particularly BOF-I. Whereas, the single sage EO at 25% showed the lowest significant phototoxic effect indicating its possible using as natural herbicides.