Avaliação da bioatividade de extratos de espécies vegetais, enquanto excipientes de aleloquímicos

Abstract

Periodically humanity is challenged to discovering new ways to progress, since conventional technologies fatally lose their function at the frontier of a new age. In agriculture the new challenger is get more productivity in less area, with less environment and social impact. The necessity of discovering new efficient and socially acceptable biocide molecules is the main goal in the modern and sustainable agriculture. Aiming to screen plant species as source of secondary metabolic with allelopathic effects and potentially useful, bioassays of allelopathy were performed, during the period from November 2002 to April 2004, at Universidade Federal de Santa Maria, RS, Brazil. Extracts from 56 species were tested at laboratory (fotofase14, 25 ± 0,5°C) on seeds and seedlings of Lactuca sativa, Bidens pilosa and Triticum aestivum.and from 21 were applied on Spodoptera frugiperda and Ascia monuste orseis (natural fotofase, 25 ± 1°C, UR 65 ± 10%). Also aiming to develop efficient methodology, this work was organized by phases. In the six basic bioassays (screening) extracts of 56 species (dose 1/3, p/v) were tested on seeds and seedlings of L. sativa. The more promising extracts, with more drastic allelopathic effects (negative and positive) passed to new phase, where doses of extracts were applied on seeds and seedlings of L. sativa, B. pilosa and T. aestivum. On this way, extract of Cymbopogum citratus, that shows drastic inhibitory effects, resulted in nine bioassays of doses. Similarly, doses of extract of Achyrocline satureioides, that shows positives effects, were tested in 11 experiments. In Four basic bioassays, extracts of 21 species were tested for S. frugiperda. The more promising extracts composed specific experiments with S. frugiperda and A. monuste orseis. The extracts were applied on larvae of S. frugiperda and included on artificial diets. On A. monuste orseis the extracts were applied on larvae and leaves of Brassica oleracea. Therefore, three set of bioassays were carried out: Rollinia silvatica was tried in four and three assays to S.frugiperda and A. monuste orseis, respectively. Melia azedarach, other promising source of insecticide, was tested on S. frugiperda in three experiments. The experimental design adopted was the randomized complete block, and the methodology used shows to be efficient to select promising species as source of bioactive agents. The advanced experiments permitted to study bioactivity by curves (equations) doseresponses and resulted on valuable information to go forward on procedures to identify molecules of biocide and stimulatory agents. C. citrates showed to be a powerful biocide, with herbicidal characteristics, including demonstrating occurrence of hormetic effects. R. silvatica, through their extracts, demonstrated to be source of powerfull insecticides, including agents with neurotoxic action. M. azedarach, by extracts of leaves, showed to be an efficient insecticide by ingestion. On the other side, extract of A. satureioides, presented inhibitory, stimulatory and protective action on growing and development of reagent material. Finally, the results obtained with a relatively small number of vegetal species allow to conclude there is a practically inexhaustible potential in plants on research of new molecules for the central goal: a more sustainable agriculture.