Chemical Composition and Allelopathic Potential of Essential Oils from Tipuana tipu (Benth.) Kuntze Cultivated in Tunisia

In Tunisia, Tipuana tipu (Benth.) Kuntze is an exotic tree, which was introduced many years ago and planted as ornamental street, garden, and park tree. The present work reported, for the first time, the chemical composition and evaluates the allelopathic effect of the hydrodistilled essential oils of the different parts of this tree, viz., roots, stems, leaves, flowers, and pods gathered in the area of Sousse, a coastal region, in the East of Tunisia. In total, 86 compounds representing 89.9 - 94.9% of the whole oil composition, were identified in these oils by GC-FID and GC/MS analyses. The root essential oil was clearly distinguished for its high content in sesquiterpene hydrocarbons (β-caryophyllene, 1 (44); 24.1% and germacrene D, 2 (53); 20.0%), while those obtained from pods, leaves, stems, and flowers were dominated by non-terpene hydrocarbons. The most important ones were n-tetradecane (41, 16.3%, pod oil), 1,7-dimethylnaphthalene (43, 15.6%, leaf oil), and n-octadecane (77, 13.1%, stem oil). The leaf oil was rich in the apocarotene (E)-β-ionone (4 (54); 33.8%), and the oil obtained from flowers was characterized by hexahydrofarnesylacetone (5 (81); 19.9%) and methyl hexadecanoate (83, 10.2%). Principal component and hierarchical cluster analyses separated the five essential oils into three groups and two subgroups, each characterized by the major oil constituents. Contact tests showed that the germination of lettuce seeds was totally inhibited by the root essential oil tested at 1 mg/ml. The inhibitory effect on the shoot and root elongation varied from -1.6% to -32.4%, and from -2.5% to -64.4%, respectively.