Efeito do óleo essencial de Cymbopogon winterianus Jowitt na germinação, respiração e crescimento de plântulas de Glycine max L. Merril, Ipomoea grandifolia e Euphorbia heterophylla L

Abstract

The objective of this experiment was to study the bioherbicida effect of the essential oil of Cymbopogon winterianus Jowitt on germination, growth and respiration of Glycine max L. Merrill (soybean), and weed Ipomoea grandifolia (string-de-viola) and Euphorbia heterophylla (dairy). The three species seeds were treated with different concentrations (0, 0.03, 0.06, 0.12 and 0.25% with 2% DMSO) of essential oil of C. winterianus. Seeds were placed on plates with the corresponding concentrations of essential oil and placed in chamber at 250C with a photoperiod of 12 h for 7 days. We evaluated the following variables: germination percentage (PGER), germination average time (TMG), germination average speed (VMG), germination speed index (IVG), shoot length (CPA), length of root system (CSR), total length (CT), shoot / root system ratio (RPA/SR), shoot dry mass (MSPA), root dry mass (MSR), total dry matter (MST), shoot water content (CAPA), root water content (CAR), total water content (CAT) and respiration of embryos pretreated with essential oil. It also determined the direct effect of essential oil on mitochondrial respiration of E. heterophylla (dairy). The data were analyzed by ANOVA and the significant variables analyzed by regression at 5% probability. Essential oil of citronella inhibited germination and this effect was directly proportional to the concentration tested in all species studied. Germination variables PGER, VMG, IVG, TMG were affected drastically by presence of essential oil in the species tested. The values of CT, CPA, CSR and RPA/SR also showed significant decreases tending to zero for all species. The presence of essential oil markedly reduced the amounts of MSPA, MSR, MST, CAPA, CAR and CAT of the three species. The values of total oxygen consumption, and the inhibitor SHAM (cyanide-sensitive respiration) were affected by pretreatment of embryos with the essential oil of all species. The essential oil of C. winterianus significantly reduced mitochondrial oxidative phosphorylation measured by O2 consumption during ADP phosphorylation (state III) and for ADP/O when using NADH or malate as respiratory substrate. The other variables - basal, state IV and respiratory control did not differ significantly from control. The results demonstrate that the essential oil dramatically affects both the total respiration and the sensitive to KCN one. Soybean was among the least affected, in practically all variables when compared to the weeds. The fact of the essential oil interfere with respiration coupled with oxidative phosphorylation suggests that the oil may be interfering with the ATP synthase complex, and adenylate or supply, such as the amount of ADP that reaches the mitochondrial matrix and that is capable of being phosphorylated, as well as in the amount of carbon skeletons that come within the mitochondria. Thus, the respiratory effect may explain, at least in part the influence of essential oil on the germination variables and growth of three plants species. Thus, the essential oil of citronella has great potential to be used as bioherbicide. However, it remains to be done important detailed studies at metabolic level at the level of field so that definitive conclusions can be reached.