Thymol Chemotype Origanum vulgare L. Essential Oil as a Potential Selective Bio-Based Herbicide on Monocot Plant Species

Abstract

Searching for new bio-based herbicides is crucial for decreasing chemical pollution, protecting the environment, and sustaining biodiversity. Origanum vulgare is considered a promising source of essential oil with herbicidal effect. The mode of action is not known. The present study focused on (1) comparison of phytotoxic activity of Origanum vulgare EO on monocot (Triticum aestivum and Hordeum vulgare) and dicot species (Lepidium sativum and Sinapis alba); (2) and evaluating other antimicrobial biological activities against phytopatogen bacteria (Clavibacter michiganensis, Pseudomonas syringae pv. phaseolicola, Pseudomonas savastanoi, and Xanthomonas campestris); antifungal activity against Monilinia fructicola, Aspergillus niger, Penicillium expansum, and Botrytis cinerea; cytotoxic activity and antioxidant activity. According to the GC/MS analyses, the EO belongs to the thymol chemotype O. vulgare with its high content of thymol (76%). Germination of all four species was not influenced by EO. The phytotoxic effect was statistically significant in the monocot species, while in the dicot species the opposite was observed-a stimulation effect, which was also statistically significant. Strong biological activity of O. vulgare EO was noted on all phytopatogen bacteria and fungi in the highest dose. Cytotoxic activity showed an IC₅₀ = 50.5 μg/mL. Antioxidant activity showed an IC₅₀ = 106.6 μg/mL after 45 min experimental time. Based on the presented results, it is possible to conclude that thymol chemotype O. vulgare essential oil could be potentially used as a herbicide with selective effects on monocot plant species.

Keywords: antifungal activity; antimicrobial activity; dicots; monocots; phytotoxicity; thymol chemotype.

Figure 1

Percentage of cell viability after 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Cells were treated with different doses (800–100 µg/mL) of Origanum vulgare EO for 24 h and solvent (DMSO, 0.1%) alone. Data are the mean ± SD of three experiments **** - p < 0.0001.

Figure 2

Antibacterial activity of Origanum vulgare EO Bars with different letters for each tested EO dose indicate mean values significantly different at p < 0.05 according to Tukey (B) test. Data are expressed as mean of three replicates ± SD.

Figure 3

Antifungal activity of Origanum vulgare EO. Bars with different letters for each tested fungus indicate mean values significantly different at p < 0.05 according to Tukey B test. Data are expressed as mean of three replicates ± SD.

Figure 4

Percentage of DPPH in solution after 15, 30, and 45 min of treatment with different doses of Origanum vulgare EO.