Bioassay and Quantification of Causative Allelochemicals from the Extracts and Residues of Sweet Potato (Ipomoea batatas) Plant Parts

Laboratory and greenhouse experiments were conducted to determine the allelopathic potentials of aqueous or methanol extracts and ground residues of sweet potato (Ipomoea batatas cv. ‘Sinyulmi’) plant parts, leaves, stems, and roots. Aqueous leachates at 40 g dry tissue L -1 (g L -1 ) from sweet potato cultivar ‘Sinyulmi’ showed the highest inhibition against alfalfa (Medicago sativa) regardless of plant part. Alfalfa root growth was significantly inhibited by the methanol extracts of sweet potato as the concentration increased. The inhibitory effect on alfalfa root growth was greater in aqueous and methanol extracts from leaves than from stems and roots at higher concentrations. By means of HPLC analysis, methanol extracts from sweet potato leaves had the highest amount of phenolic compounds including mainly chlorognic acid and caffeic acid, and followed by those from stems and roots. Root residues showed the highest inhibition against shoot and root growth of barnyardgrass, compared to leaf and stem residues. Incorporation with root residues of above 50 g kg -1 into soil significantly inhibited shoot and root fresh weights of barnyardgrass. These results suggest that sweet potato plants had allelopathic potential, and that their activities were differential depending on plant part as well as extraction method.