Discovery of 2-Naphthol from the Leaves of <i>Actephila merrilliana</i> as a Natural Nematicide Candidate

Abstract

To identify natural nematicides that can replace chemical nematicides, 2-naphthol with high activity against <i>Meloidogyne incognita</i> was isolated from <i>Actephila merrilliana</i>. The nematicidal activity of 2-naphthol against <i>M. incognita</i> was 100% at 100 μg/mL with an EC₅₀ value of 38.00 μg/mL. Moreover, 2-naphthol had a significant negative effect on egg incubation. 2-Naphthol effectively inhibited the invasion of <i>M. incognita</i> into crops in both a pot experiment and field trial. In addition, the structure-activity relationship indicated that the naphthalene ring and its β-site hydroxyl group were the key pharmacophores for the nematicidal activity of 2-naphthol. Nematodes were stimulated by 2-naphthol to produce excessive reactive oxygen species, which may be the underlying mechanism of 2-naphthol nematicidal activity. A systemic evaluation of 2-naphthol in tomato plants demonstrated that 2-naphthol remained mainly fixed in the roots after being absorbed by the crop and was not transported to the stems or leaves. Thus, 2-naphthol can be developed as a natural nematicide candidate.