Seasonal variations in the chemical composition of essential oil and antifungal and larvicidal activities of Marrubium vulgare, an aromatic plant growing wild in West-Algeria

Essential oil of M. vulgare is an important natural source that can be useful in controlling the infection of tomatoes and larvicides. This work aimed to determine seasonal variations (winter, spring and summer) of the composition of M. vulgare essential oil and fungicidal and larvicidal potential of this oil. Essential oils were obtained by a Clevenger-type apparatus and analyzed by using Gas Chromatography (GC) and Gas Chromatography Mass Spectroscopy (GC/MS). The antifungal activities were tested on two strains: Penicillium expansum and Alternaria alternata, and insecticidal activity was tested against Tuta absoluta insect pest of tomatoes. The essential oil of M. vulgare, collected at the same locality throughout the three seasons (winter, spring and summer), was compared in terms of composition and yields. Mostly quantitative, rather than qualitative variation, was observed in the oil composition. Considerable changes were noted for E-β-caryophyllene (4.5-23.5 %), E-β-farnesene (3.4-22.9 %) and α-humulene (tr-14.8 %). On the other hand, essential oil of M. vulgare collected during the months of April and June (Col EO) was evaluated for its insecticidal and antifungal activity. Col EO showed good in-vitro antifungal activity against P. expansum and A. alternata with percentages of inhibition of 94 % and 100 % at 10 mL/L, respectively. Due to the promising results of in-vitro tests, the essential oil of M. vulgare was chosen to determine the protective effects in tomato fruits against infection caused by A. alternata. Observations showed that the treatment of tomato fruits with Col EO resulted in a remarkable reduction of disease severity compared with the controls. Col EO used with the concentration of 0.5 mL/L air showed a very interesting protective activity against black rot of tomatoes caused by A. alternata, up to the 15th day of storage, compared with the control. However, essential oil collected during the month of February (FEO) exhibited no effect of antifungal activity against the phytopathogens tested. On the other hand, the Col EO of M. vulgare exhibited also a good insecticidal activity. At the concentration of 20 mL/L air, the oil caused mortality up to 100% for all larval stages and adults of Tuta absoluta after 24 h of exposure. The Col EO can be used as a potential source to develop control agents to manage some of the main pests and fungal diseases of tomato.