Phytotoxic Activity of Guapira graciliflora (Nyctaginaceae) on Weeds

The plants produce a variety of compounds that are not directly associated with their growth and are derived from their secondary metabolisms. Such compounds can be used in the formulation of bioherbicides, in the control of weeds. Among the chemical groups that most present allelopathic actions are the phenolic compounds which are present the flavonoids. A species rich in such compounds is Guapira graciliflora, which allows hypothesizing that it may present phytotoxic action. In this way, the objective of this research was to evaluate its phytotoxic action on the germination and growth of Cenchrus echinatus and Calotropis procera. For this purpose, aqueous extracts were prepared from fruits and leaves and applied to seeds of the species mentioned above. Pre and post germinative parameters were measured. Our results show that the extracts can retard the growth of the roots of C. echinatus and C. procera in a significant way (p <0.05), however it is not able to interfere in the number of germinated seeds or germinated seeds speed. The mechanisms of action of the allelochemicals may be related to inhibition of specific PSII sites or reduction of chlorophyll content. Guapira graciliflora presents allelochemicals in the constitution of its leaves and its fruits that affect the growth of the initial structures of C. echinatus and C. procera, with potential to be used as bioherbicides in the control of these weeds.