Óleo essencial de Hesperozygis ringens (Benth.) Epling: variabilidade do rendimento, composição química e atividades biológicas

Abstract

Researches involving plant derived products aiming to discover extractives useful for different purposes have been growing, and among them, essential oils (EO) are noteworthy. One of the main sources of EO is the Lamiaceae family. Belonging to this family, Hesperozygis ringens (Benth.) Epling is a native species from the Pampa biome, popularly known as espanta-pulga . This study aimed to evaluate the biological potential of EO from its leaves as allelopathic and larvicidal, as well as to check the seasonal and individual variability of yield and chemical composition of this oil. EO of four specimens were obtained from leaves collected in different seasons of a year and had their yield (% m/m) and chemical compositions determined. EO were extracted by hidrodestillation in Clevenger apparatus and analyzed by gas chromatography coupled to mass spectrometry (GC-MS) and gas chromatography with flame ionization detector (GC-FID). The allelopathic potential of the EO was tested against seeds of Dicots and Monocots classified as bioindicators [Avena strigosa Schreb. and Lactuca sativa L.], weeds [Lolium multiflorum Lam and Bidens pilosa L.] and crops [Oryza sativa L. and Glycine max (L.) Merr.] by observing the following variables: germination, emergence velocity index, root length, shoot lenght and total length of seedlings. The tested concentrations were 0.25, 0.50, 1.00, 2.50 and 5.00%.The EO of H. ringens had also its larvicidal activity tested against larvae of Odonata in order to determine its 50% lethal concentration (LC50). Regarding the allelopathic tests on Dicotyledons, EO with 82.02% of pulegone inhibited completely the germination of B. pilosa at 5.00%, without affecting significantly L. sativa, but slowing the emergence and damaging root lengths and seedlings of G. max. Regarding the monocots, the same concentration strongly impaired L. multiflorum, without affecting the germination of O. sativa, but it influenced negatively the other evaluated parameters. In addition, the development of the seeds of A. strigosa was completely inhibited at the concentration of 2.50%. The yield of EO proved to be influenced by seasonality, being higher in spring, summer, and autumn. The yield also showed individual variability (1.15 a 4.38%), proving to be higher in specimen 4. The chemical composition of EO obtained from leaves collected in autumn, spring, and summer showed similar results. The production of the major constituent (pulegone) and the predominant class (oxygenated monoterpenoids) were favored in spring, summer, and autumn. These seasons proved to be more indicated for the EO extraction, since they enabled concomitantly higher yields and higher contents of oxygenated monoterpenoids and pulegone. Regarding the larvicidal activity, EO containing 95.18% of pulegone showed a LC50 of 69.05 µL L-1 against the Odonata larvae.