Perfil químico, potencial alelopático e acaricida dos óleos essenciais de Piper hispidum SW (Piperaceae), coletada em Itacoatiara-AM

Abstract

The genus Piper harbors species with remarkable potential for the production of essential oils, which in turn have a wide variety of biological properties, highlighting the toxic effect against numerous agricultural pests. In this sense, essential oils have been increasingly attracting the interest of the agricultural sector, since they have been shown to be effective and safer for human health and the environment when compared to conventional chemical pesticides. The objective of this work was to evaluate the chemical profile of the essential oil of the leaves and branches of Piper hispidum SW as well as to investigate its inhibitory effect on the germination and growth of lettuce and tomato seed radicles and its fumigant acaricide potential against the mite of Suidasia pontifica Oudemans stored products in order to provide a sustainable alternative for pest control. Plant material was collected in May 2021, in the morning. The leaves and branches were separated and their respective essential oils were obtained using the hydrodistillation technique of fresh biomass in a Clevenger-type apparatus for 4 hours. At the end of the extraction, the oil yields were calculated (v/m). For the analysis of chemical composition, the essential oils were subjected to analysis by Gas Chromatography Coupled with Mass Spectrometry (GC/MS) and the identification of the constituents was based on the interpretation of their respective mass spectra, calculation of the retention index and comparison with data from the literature. The allelopathic assays consisted of daily evaluations of the development of lettuce and tomato seeds submitted to concentrations of 0.1 and 1% of essential oils from leaves (OEPHF) and branches of P. hispidum (OEPHR), being considered as parameters the percentage of germination, mean germination time, germination speed, seed vigor by the seed speed index and the length of the primary root. The acaricidal effect of essential oils was tested in fumigation tests in which adult mites were subjected to different concentrations of essential oils, with evaluations after 24, 48 and 72 h. In the essential oils of leaves and branches, 91.1 and 92.3% of their total chemical composition were identified, respectively. The main chemical class identified was sesquiterpenes and the major constituents were germacrone, curzerene, safrole, E-caryophyllene, germacrene B, in both oils, and 1,8-cineole only in OEPHR. The two essential oils tested, at all concentrations, had an inhibitory effect on the germination process of lettuce and tomato bioindicators. Both OEPHF and OEPHR exhibited toxic action against S. pontifica, with higher mortality being observed at the highest concentration tested, characterizing a dose-dependent effect. The findings in the present study are an indication that the essential oils of P. hispidum from the region of Itacoatiara-Am have promising pesticide action. From more in-depth studies that guarantee the safety of their use for humans and other non-target organisms, they may be important candidates for natural herbicides and acaricides.