Allelopathic activity and identification of allelochemicals from Rumex japonicus Houtt.

Unlike phenolics from other plant species, phenolics from Rumex japonicus have not been documented. The aims of this work were to analyze the phenolic compounds in the aerial parts and roots of Rumex japonicus and study their allelopathic activity. HPLC and GC-MS analyses showed the presence of protocatechuic, p-hydroxybenzoic, syringic and ferulic acids, vanillin and pyrocatechin in aerial parts. Besides these six compounds, caffeic acid was detected in roots. In bioassay, the extracts from aerial parts and roots significantly decreased the seedling growth of lettuce and barnyardgrass and the inhibition of roots was greater than shoots. The pyrocatechin was present in large amounts in the aerial parts and appeared to be responsible for the activity of the aerial parts, while the phytotoxicity of roots may be due to the presence of protocatechuic, p-hydroxybenzoic and ferulic acids as well as pyrocatechin.