Efeito dos extratos e substâncias isoladas de Sphagneticola trilobata (L.) Prusk (Asteraceae) sobre a germinação da corda-de-viola (Ipomoea triloba L., Convolvulaceae)

Abstract

The agricultural sector has invested in new technologies to better yields in crops productivity. However, weeds still cause economic losses. Herbicides application is the most used method for the control of weed plants. But its large-scale use has generated plant resistance and environmental problems. Thus, alternatives more effective to the weed control, which minor harmful to the environment, have been investigated worldwide. The use of species that release allelochemicals, like some species of the family Asteraceae, are an alternative to synthetic herbicides. The aims of this work were to evaluate the effect of the aerial parts extract, as well as of their fractions and substances isolated, from wedelia [Sphagneticola trilobata (L.) Prusk] on the germination of the morning glory (Ipomoea triloba L.), a weed that infests different types of crops. The experiments were carried out with the extract and their hexane, ethyl acetate and aqueous fractions at concentrations of 0.25, 0.5 and 1.0 mg/ml. The major substance of the ethyl acetate fraction too was tested in the concentrations 0.125, 0.25, 0.5 and 1.0 mg/ml. Distilled water was used as a negative control and glyphosate as positive control. Three replicates with 20 morning glory seeds were used for each treatment in the in vitro germination test performed in BOD with temperature at 35 ° C, 70% humidity and 12h light-dark cycle. The evaluations were carried out daily, for seven days, to obtain the percentage of germination (% G), radicle and hypocotyl length. Data were submitted to one-way ANOVA statistical test, followed by Dunnet's post-test. The results did not indicate statistical differences in the number of germinated seeds of morning glory seeds in any of the treatments. The aqueous fraction reduced significantly the radicule growth at concentrations of 1.0 and 0.5 mg/ml, whereas the ethyl acetate fraction reduced the length of the hypocotyl at the concentration of 1.0 mg/ml, and the length of the radicle in all concentrations. The ST01 compounds was isolated from ethyl acetate fraction and was identified as the sesquiterpene lactone trilobolide-6-O-isobutyrate. ST01 reduced the initial growth of the radicle at 0.125mg/ml, 0.25mg/ml, 0.5mg/ml, 1mg/ml, similarly to treatment with the glyphosate. The obtained results suggest that the isolated substance affects the initial development of the morning glory weed.