ALLELOPATHIC EFFECT AND WEED CONTROL POTENTIAL OF Richardia brasiliensis Gomes

Abstract

The allelopathic effects of the extracts of Richardia brasiliensis Gomes were evaluated on the germination and growth inhibition of Mimosa pigra L. Dried whole plant materials were extracted by hexane, CH2Cl2, EtOAc and CH3OH, respectively. The inhibitory activity was compared using five diverse concentrations of 0.1, 0.5, 1.0, 2.5 and 5.0 g dry weight equivalent extract (gE). The CH3OH extract was completely inhibited the germination of M. pigra at ≥ 1.0 gE. Additionally, the root and shoot length were also inhibited by 43 and 48% respectively by the CH3OH extract at 1.0 gE. The CH3OH extract was further tested for the inhibition of the germination and growth on weeds and crops at 1 gE. This extract efficiently displayed the inhibition of the germination and growth on weed seeds, while it did not affect on the crop seeds. The CH3OH extract was separated by quick column to yield four fractions namely RBM-1, RBM-2, RBM-3 and RBM-4. All fractions did not inhibit the seed germination and shoot length, except for RBM-4 showing 100% inhibition at 2.5 and 5.0 gE, same as the root length. Further investigation on its constituents was performed by HPLC analysis and revealed that 4-hydroxybenzoic acid, p-coumaric acid, benzoic acid and caffeic acid were main composition. To ascertain the capability of phenolic compounds on germination and growth inhibition, all compounds exhibited the greatest inhibition on the root length of weeds at 1 mM. These results suggested that R. brasiliensis contain growth inhibitory substances, possess allelopathic potentials and be possible candidate for developing as natural herbicides. On the other hand, 3,4-dihydroxybenzoic acid and caffeic acid were found to promote the germination, shoot and root length at 1 mM.