Determinação do potencial alelopático e composição química de extratos vegetais da espécie Croton heliotropiifolius Kunth no controle de Bidens pilosa (L.) e Digitaria insulares (L.) Fedde

Abstract

The expansion of weeds in different agricultural areas has interfered in the development of the cultivars, leading to decrease of production and economic losses. One of the forms of cultural management of these species occurs through allelopathy. This management occurs through the mechanism in which the plants according to their chemical composition from certain plants apply positive and / or negative effects on other plants, playing an important role by minimizing impacts in agriculture. This work aims to evaluate the allelopathic potential and chemical composition of Croton heliotropiifolius Kunth extracts in the control of Bidens pilosa (L.) and Digitaria insularis (L.) Fedde. The vegetal material was collected, dried, crushed and used for the preparation of the crude extracts by maceration with ethanol and decoction. The determination of the compounds was performed quantitatively, respectively, by the Folin Ciocalteau test, flavonoid content in UV-Vis spectrophotometer, preliminary phytochemical screening and High Performance Liquid Chromatography (HPLC). The extract solutions were prepared at 1mg / mL (100%), from which test solutions were obtained at the concentrations of 0,10;0,25;0,5 and 1 mg/mL, having distilled water as control. After preparation of the solutions, pH was checked and the osmotic potential was evaluated in aliquots of 10μL of these solutions.7 mL of each stock solution were applied in four replicates and 25 seeds of the target plants were distributed ; these were kept in a BOD type chamber with alternating photoperiod (12L: 12E) for 10 days. The experiment was set up in a completely randomized design and the data were submitted to the Dunnett test at 5% probability, to compare each treatment with the control. The pH values ranged from 5.70 to 7.62 (aqueous extract) and 4.60 to 5.70 (ethanolic extract), and the osmotic potential between -0,000 to -0,0244 (aqueous extract) and -0,000 to -0 , 0244 (ethanolic extract). The total phenol content ranged from 216.06 mg GAE / g for the aqueous extract to 342.22499243 mg GAE / g for the ethanolic extract. It was also observed the presence of metabolites such as flobafenic tannins, flavones, flavonols, xanthones, catechins and saponins. The results of the allelopathic test showed a reduction in the percentage of germination, a reduction in the rate of germination, a reduction in the percentage of seedlings with abnormalities and a decrease in root and shoot length from the 0,25; 0,5 and 1mg/mL concentrations for B. pilosa and Digitaria insularis, when submitted to the ethanolic and aqueous extract, evidencing the allelopathic effect of C. heliotropiifolus extracts by reducing the percentage of germination and root length, which are considered determinant parameters for the germination bioassay.Therefore, a greater sensitivity of the species Bidens pilosa and D. insularis when submitted to the aqueous extract from the concentrations of 0,25; 0,5 and 1 mg/mL, due to the presence of compounds like phenolic acids and flavonoids in the aqueous extract and that the species D. insularis revealed be more sensitive to extracts than B. pilosa, characterizing the strong potential of C. heliotropiifolius.