Chemical compositions and herbicidal (phytotoxic) activity of essential oils of three Copaifera species (Leguminosae-Caesalpinoideae) from Amazon-Brazil

The rich and diversified Amazonian flora represents an excellent resource of new chemical structures with biological activities. This study aims to contribute with information about the phytochemical profile and phytotoxic activity of the Copaifera species essential oils: Copaifera duckei (Dwyer), Copaifera martii (Hayne), and Copaifera reticulata (Ducke) (Leguminosae - Caesalpinioideae). In this study, essential oils were extracted from leaves and stems by hydrodistillation process in an adapted Clevenger type device. The identification of the essential oils chemical components was performed by gas chromatography coupled mass spectrometry (GC/MS) and gas chromatography (GC-FID). Statistical analyses of the results were obtained by the data were analyzed using F-test and the mean values were compared by the Tukey test at 5% and Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA). The phytotoxic activity of these extracted essential oils was tested against two species of invasive plants native to the Brazilian Amazon, namely, Mimosa pudica L. and Senna obtusifolia (L.) Irwin & Barneby). The essential oils effects on seed germination and elongation of the radicle and hypocotyl were observed. The compounds with the highest concentrations in the essential oils were sesquiterpene hydrocarbons, including germacrene D, beta-caryophyllene, alpha-humulene, delta-elemene, and delta-cadinene. Inhibitory effects of the essential oils were greater on root development than on seed germination. Mimosa pudica L. tended to be more sensitive to the phytotoxic effects than Senna obtusifolia (L.) Irwin & Barneby). Leaf oils presented greater inhibitory effects on root and hypocotyl development, whereas stem oils showed greater inhibition of seed germination, although in some cases, these differences were not statistically significant. The leaves essential oils had a greater number of constituents than those of the stem; this was especially observed in Copaifera martii (Hayne). These variations could justify the differences observed in the phytotoxic effects between the oils from the stems and the leaves. The recipient specie Mimosa pudica L. was most affected by the effects of essential oils.