Potencial Bio-herbicida de Vanillosmopsis arborea Baker

Abstract

The indiscriminate use of synthetic herbicides to control weeds can result in severe damage to the environment. An alternative is the use of bioherbicides produced from secondary plant metabolites, which compounds have allelochemical potential. Essential oils contain allelochemicals that affect the growth of target plants, through the modification of physiological processes that are essential for their germination and growth. The allelopathic potential of the essential oil from Vanillosmopsis arborea Baker (“candeeiro”), an endemic plant from Chapada of Araripe, Crato, Ceará, Brazil, has been reported in suppressing the germination of model species; and it is therefore a candidate for prospecting for bioherbicide. However, the action of this essential oil in the pre and post-emergence of weeds and crops is unknown. This potential may be related to its major component, the sesquiterpene α-bisabolol, or to the synergy of all its components. Thus, it is necessary to know the action of the essential oil and the isolated action of α-bisabolol on weeds and crops. Hence, this work aimed to investigate if and how the essential oil of V. arborea and α-bisabolol affect pre and post-emergence in different species. The essential oil of V. arborea was extracted from its wood by the hydrodistillation process and the α-bisabolol molecule was obtained commercially from Sigma-Aldrich-Merck®. Both were diluted in deionized water to obtain the concentrations (0.125; 0.25; 0.5; 0.75; and 1%). In chapter 1, the essential oil was applied to the seeds of target (Bidens pilosa L., Cenchrus echinatus L., Cyperus disfformis L., Desmodium tortuosum (Sw.) DC. and Senna occidentalis (L.) Link) and non-target species (Lactuca sativa L. and Oryza sativa L.). The germination percentage (GP), germination speed index (GSI), and shoot and root length of different species were significantly affected by the treatments. The species showed different levels of sensitivity to the essential oil, B. pilosa, C. echinatus, and C. disfformis were the most sensitive and the cultivated species O. sativa the least sensitive. The mitotic index of cells from roots meristem of L. sativa was reduced by the action of the essential oil of V. arborea. In the chapter II, different concentrations of essential oil or α-bisabolol were applied to the seeds of two species selected in the previous experiment. The essential oil reduced the GP, GSI and α-amylase activity and induced a redox imbalance in seeds of the weed species Senna occidentalis. α-bisabolol induced oxidative stress in S. occidentalis seedlings, reducing growth and inducing necrosis. The seeds and seedlings of the cultivated species O. sativa showed a redox imbalance, but with a lesser extent than the weed species. In the chapter III, the 0.5% concentration of oil or α-bisabolol was applied to the species selected in experiment 1. The treatments induced a reduction in photosynthesis in S. occidentalis plants. However, O. sativa plants were minimally influenced by the treatments. It is concluded, that the essential oil of V. arborea and α-bisabolol showed a selective and promising action for its use as a bioherbicide.