Laboratory and Field Evaluation of the Phytotoxic Activity of Gaertn Pulp Extract and Identification of a Phytotoxic Substance.

Interest in finding plant-based herbicides to supplement synthesized herbicides is increasing. Although the extract of Gaertn has been reported to have herbicidal activity, little is known about phytotoxic substances and their efficacy of weed control in the field. To identify phytotoxic substances, the bioassay-guided fractionation by column chromatography and high-speed counter-current chromatography (HSCCC) was carried out. The phytotoxic activity assay, performed by the agar medium method, showed that the 70% ethanol fraction exhibited strong root growth inhibition against with an 50% inhibitory concentration (IC) value of 35.13 mg/L. An active compound was isolated from the 70% ethanol fraction and identified as hederagenin 3---D-xylopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→2)-α-l-arabinopyranoside (Compound A). Compound A had an IC value of 16.64 mg/L. Finally, a new formulation was prepared based on the 70% ethanol fraction, which exhibited good efficacy against broadleaf weeds in a carrot field. The fresh weight control efficacy was 78.7% by 45 days after treatment at the dose of 1500 g a. i./ha. Hence, the extract of pulp could be a promising supplement to the synthesized herbicides. Furthermore, compound A from may be responsible for its phytotoxic activity.