Atividade fitotóxica de extratos foliares de Piptocarpha rotundifolia (candeia) (Less.) Baker – Asteraceae

Abstract

The Brazillian savanna is one of the largest vegetation with 2,036,448 km2, about 22% of the national territory. This bioma is considered a global hotspot (Mittermeier et al., 2004) and consists of three biomes: tropical fields, grasslands and dry forests (Batalha, 2011; Brasil, 2015). Cerrado flora has a high species richness with herbs, shrubs, tree and vines, totaling 12,356 species occurring spontaneously, as well as a native vascular flora (ferns and phanerogams) totaling 11,627 species (Mendonça et al., 2008) .However, the chemical potential of its plant species is still underutilized. Research plants with allelopathic activity comes against the need to introduce new alternatives in the management of agricultural pests. Studies on the biological effects of these chemical compounds represent an important tool for the development of more specific agrochemicals natural and less harmful to the environment. Piptocarpha rotundifolia (Less.) - Baker belongs to the Asteraceae family, considered the most representative of the brazilian cerrado eudicotyledons, but there are few published works that deal with potential investigations phytotoxic of this species and its secondary metabolites. Thus, the main objective of this study was to analyze the phytotoxic potential of P. rotundifolia extracts, fractions and subfractions on target species of vegetables and weeds and the mode of action of the same. In the first step of this work, an extraction in order of increasing polarity was done and the phytotoxic potential of crude extracts was evaluated on the growth of wheat coleoptile, germination and seedling growth of mono and eudicotyledons invasive and vegetable species: wild poinsettia (Euphorbia heterophylla L.), guinea grass (Megathyrsus maximus J.), onion (Allium cepa L.) and sesame (Sesamum indicum L.), respectively, as well as the evaluation of the root sesame metaxylem cell growth. The acetone extract (D) was selected for the fractionation, due the mass (2370 mg) and and the inhibitory activity on the growth of wheat coleoptile good as on the germination growth indicator target species (onion and sesame) and invasive (wild poinsettia and guinea grass). This fractions and subfractions were also tested on the growth of wheat coleoptile and those who had higher incomes and inhibitory activity (D1 and D1A) were selected for the following bioguided fractioning. After, a liquid-liquid extraction was performed using the extracts 1 (hexane), 2 (ethyl acetate) and 3 (aqueous) and, among these, the extract 2 showed inhibitory activity on the growth of wheat coleoptile and also on the germination and growth of the target species, as well as significantly reduced metaxylem cell root growth of sesame seedlings. Therefore, this extract was refractionated by a countertop chromatography column, and the fraction with the highest income was denominated (2L), then refractioned. The resulting subfractions were tested only growing wheat coleoptile. To complete the survey, a chemical profile analysis was conducted using the extracts, fractions and subfractions of P. rotundifolia from both extraction methodologies, performing the ultra efficiency liquid chromatography technique, which has found a compound identified as glaucolide b and two other compounds known to the genre. Thus, the species Piptocarpha rotundifolia shown as promissing in the search of phytotoxic compounds due to their phytotoxic activity presented by their compounds.