Phytochemical composition and allelopathic potential of three Tunisian Acacia species

•Phytochemical content of three species of Acacia was evaluated for the first time.•Allelopathic potential of Acacia seeds and pods extracts was tested.•The phytochemical content contributes significantly to the allelopathic activity.•A saponoside was isolated for the first time from extract of Acacia cyclops pods.•The isolate exhibited phytotoxicity on Lactuca sativa L.

This study was conducted to evaluate the phytochemical content and allelopathic potential of various organic extracts from seeds and pods of three Tunisian species of Acacia (Acacia cyclops, Acacia mollissima and Acacia cyanophylla) which was evaluated on lettuce germination and seedling growth. The total flavonoid contents in the organic extracts were closely ranged (3.1–24 mg RE/100 g DW), n-butanol extracts of Acacia pods were the richest ones in phenol and condensed tannin contents. For allelopathic activity, the EtOAc extract of seeds from A. cyanophylla inhibited the germination of the target seeds. The seedling growth was inhibited by all organic extracts with disproportion. The chromatographic separation methods led to isolation of a triterpenoid saponin named mollisside B from A. cyclops pods n-butanol extract. The allelopathic effect of this compound was evaluated on Lactuca sativa L. At a concentration of 200 μg/mL, the isolate has influenced on seedling growth with percentages of inhibition of 63.68% and 88.21% for shoot and root length, respectively.