Chemical composition and phytotoxic activity of Lippia origanoides essential oil on weeds

Studies in the area of allelopathy in agriculture have increased due to search on alternative methods of weed control compared to conventional herbicides. Thus, the objective of this work was to evaluate the chemical composition and phytotoxicity of the Lippia origanoides essential oil on weeds of the species Bidens subalternans, Euphorbia heterophylla and Macroptilium lathyroides. The essential oil was extracted from the leaves of L. origanoides by means of hydrodistillation and diluted in the concentrations of 0.01 to 1%. The chemistry composition was determined by a gas chromatograph coupled with a mass spectrometry. Phytotoxic activity was evaluated in pre and post-emergence by tests of germination, seedling growth, chlorophyll content and cellular respiration. The results demonstrated an essential oil rich in monoterpenes, mainly oxygenated, with camphor as the major compound. In general, both germination and seedling development were entirely inhibited by essential oil, decreasing with increasing concentrations. The concentrations 0.5 and 1.0% totally inhibited the germination of B. subalternans, but did not affect the germination of M. lathyroides. The essential oil sprayed on the weed leaves had no effect on chlorophyll content but was able to induce visible injuries such as necrosis and chlorosis. Only the cellular respiration of E. heterophylla was affected by the essential oil. All the phytotoxic effects observed are due to the high content of monoterpenes in the essential oil, mainly the oxygenates, and also the concentration used. Therefore, the L. origanoides essential oil have bioherbicidal potential for the tested species.