Phytotoxic and Antimicrobial Activities of Teucrium polium and Thymus decussatus Essential Oils Extracted Using Hydrodistillation and Microwave-Assisted Techniques

Abstract

Essential oils (EOs) have been described as promising eco-friendly secondary products of aromatic plants with several biological activities. The present study aimed to characterize the chemical composition and explore phytotoxic and antimicrobial activities of Teucrium polium and Thymus decussatus EOs extracted using hydrodistillation (HD) and microwave-assisted extraction (MAE) methods. Twenty-seven and twenty-eight compounds were identified from HD and MAE extracted EOs of T. polium, respectively. The oxygenated sesquiterpenes (57.68%) were characterized as the main components of the hydrodistilled EO with a prominence of 6-epi-shyobunol (33.00%), while sesquiterpene hydrocarbons (54.48%) were the main components of the MAE method, with a prominence of delta-cadinene (25.13%). Eighteen and nineteen compounds, were characterized in T. decussatus EOs extracted using HD and MAE methods, respectively, and oxygenated monoterpenes represented the main components of both EOs with carvacrol (94.40% and 75.91%, respectively) as the main compound. The EOs extracted using the MAE method were slightly more phytotoxic than those extracted using the HD method. The T. decussatus EO extracted using the MAE method showed a higher inhibitory effect than T. polium by 16-, 32-, and 24-fold, regarding seed germination, shoot, and root growth of lettuce, respectively. Moreover, EOs extracted by HD method showed a similar pattern with 16-, 28-, and 14-fold effects. Both T. decussatus EOs exhibited potent inhibitory effect against all tested bacteria with an inhibition zone of 34–39 mm and the lowest minimum inhibitory concentration (MIC) of 0.49, 0.98, and 1.95 μg/mL against Aspergillus niger, Escherichia coli, and Staphylococcus aureus, respectively. However, the EOs of T. polium showed weak antibacterial activity and no antifungal effect. Further studies are needed for the characterization of bioactive major compounds, either singular or synergistic, at field scale and to determine their modes of action and safety.

Essential Oil Enriched with Oxygenated Constituents from Invasive Plant Argemone ochroleuca Exhibited Potent Phytotoxic Effects

“…These compounds may act individually or in synergy as phytotoxic agents (allelochemicals). Compared to other reported EOs, the A. ochroleuca EO is more phytotoxic against lettuce (plant model) than the EO of Teucrium polium [ 50 ], Eucalyptus grandis and E. citriodora [ 51 ], Acacia cyanophylla [ 52 ], and Eremanthus erythropappus [ 53 ]. The most abundant compound, trans -chrysanthenyl acetate, has been reported as the main compound of other plants’ EO, with phytotoxic activity, such as Artemisia herba-alba [ 28 ] and Chrysanthemum coronarium [ 29 ].…”

Comparative Study on the Essential Oils from Five Wild Egyptian Centaurea Species: Effective Extraction Techniques, Antimicrobial Activity and In-Silico Analyses

“…The dried aerial parts (250 g) of investigated Centaurea species were extracted for 3 h over a Clevenger-type apparatus using our previous protocol [ 53 ]. The EO samples kept were stored in sealed air-tight glass vials at 4 °C for analyses.…”

“…A microwave apparatus working at 2450 MHz and 1600 W maximum power (CEM Corporation, Matthews, NC, USA) was used to examine the plant species (250 g) under study using our previously reported protocol [ 53 ]. Extraction parameters: power, time and temperature were 800 W, 60 min and 100 °C respectively.…”

Essential Oil of Deverra tortuosa Aerial Parts: Detailed Chemical Profile, Allelopathic, Antimicrobial, and Antioxidant Activities

“…Recently, there is an increasing trend by researchers, scientists, and policymakers to integrate natural, eco‐friendly, and safer compounds such as EOs. The EOs were reported as a green eco‐friendly natural product that used as antimicrobial agents [7–13] . Also, the EOs were integrated as safe and powerful antioxidant compounds used in pharmaceutical and industrial applications as well as food preservation [2,10,14–22] …”