Effects of Ocimum gratissimum L. extract on the germination, respiration and growth of Euphorbia heterophylla L.

We investigated the effects of O. gratissimum extract on the germination, growth, respiratory activity and survival of the weed E. heterophylla. The bioherbicidal effects of extract on adult plants were also evaluated. The gas chromatography-mass spectrometry (GC/MS) analysis detected the phenylpropanoid eugenol was the primary constituent in the extract and was 43% of the total. The increase of extract concentration inhibited the germination (%) and germination speed index. Total respiration and KCN-insensible respiration at the prominent apices treated with extract increased with increasing extract concentrations, whereas KCN-sensitive respiration was inhibited. When the extract was applied to the incubation medium the total oxygen consumption was inhibited at all concentrations tested. In adult plants, the application of extract (> 2.5%) resulted in 100% weed plants death. These results indicate that O. gratissimum extract constituents, most likely eugenol, may have modified the cell membrane permeability. In the mitochondria, the damage caused by the extract can be associated with the mitochondrial oxidative phosphorylation decoupling that reduces the energy production of the germination process and initial growth of the seedlings.