J.C. Bayma’s research while affiliated with Federal University of Para and other places

Essential oils are known for their several biological activities. The biodiversity of the Amazon region is rich in essential-oil producing plants.The aim of this work was to study the potentially allelopathic activity of the essential oil of Ocimum americanum and to determine its effects on seed germination and growth of two weed species. Solutions of the essential oil were tested at concentrations varying from 100 to 2,000mgL-1, considering their effects on seed germination (at 25 ºC and a photoperiod of 12hours) and radicle and hypocotyl growth (at 25 ºC and a photoperiod of 24 hours) of the weeds Mimosa pudica and Senna obtusifolia. Factors related to concentration, specificity of the receiving plants and the parameters analyzed were decisive for the effects obtained. Overall, there was a positive relation between concentration and inhibitory effect. M. pudica tended to be more sensitive to the effects than S.obtusifolia. Seed germination was more affected by the essential oil, followed by radicle elongation and hypocotyl elongation. The observed effects can be attributed to the composition of the essential oil, that includes monoterpenes, sesquiterpenes, aliphatic compounds and phenylpropanoids. The compounds limonene, camphor and linalol, found in the essential oil, are known to have allelopathic activity.

The traditional methods of weed control in cultivated pasture do not meet society's present and future needs of protecting natural resources and life quality. An alternative to this problem could be the use of secondary metabolites produced by plants. These products present few risks to the environment and meet society interests. Therefore, this research was carried out to isolate, identify and characterize the allelopathic activity of chemical compounds produced by the forage grass Brachiaria humidicola. The allelopathic effects of the extracts, fractions and compound were tested on seed germination and root elongation of the weeds Mimosa pudica, Senna obtusifolia and Senna occidentalis. Germination bioassays were developed under 25ºC and a photoperiod of 12 hours. For root elongation, the bioassay conditions were 25 ºC and photoperiod of 24 hours. Hydromethanolic extract was used as a source for isolating and identifying p-coumaric acid. The allelopathic effects were positively related to p-coumaric acid concentration, weed species and the evaluated parameter. Comparatively, S. occidentalis and M. pudica showed the greatest sensitivity to the allelopathic effects. For S. obtusifolia no allelopathic effects promoted by p-coumaric acid on seed germination or on root elongation could be detected under the concentration of 1.0 and 8.0mgL-1. Root elongation was more sensitive to p-coumaric acid allelophatic effects than seed germination.