Allelopathic Potential of Aqueous Extracts and Essential Oils of Rosmarinus officinalis L. and Thymus vulgaris L

Abstract

Allelopathic effects of essential oils and aqueous extracts from Rosmarinus officinalis (rosemary) and Thymus vulgaris (thyme) have been investigated as a source of new natural herbicidal compounds to suppress two weeds: Chenopodium album and Echinochloa crus-galli associated with two important economic crops, Triticum aestivum (wheat) and Oryza sativa (rice), respectively. A petri-dish experiment was performed, and 10, 20, 50, and 100% aqueous solutions, and doses of 0, 2, 4, 8, and 16 µL of essential oil per petri dish were applied. The number of germinated seeds in each Petri dish was counted daily. After 15 days, germination percentage, the coefficient of velocity of germination, speed of germination, germination energy, germination index, mean germination time, seedling shoot length, root length, shoot–root ratio, and seedling vigour index were recorded. The chemical profiles of both essential oils were identified with GC–MS analysis. Eucalyptol (1,8-cineole), α-pinene, and camphor were identified as the dominant constituents of the rosemary essential oil. The major components detected in thyme essential oil were thymol, o-cymene, caryophyllene, and gamma-terpinene. The results showed that thyme essential oils had the most negative effect by inhibiting the germination of weeds. Both rosemary and thyme essential oils had a generally reducing effect on the growth parameters of weeds. The essential oils of rosemary and thyme have allelopathic potential and should be assessed as allelopathic agents to be used for weed control.