In vitro nematicidal activity of naphthoquinones against the root-lesion nematode <em>Pratylenchus thornei</em>

Abstract

The root-lesion nematode Pratylenchus thornei is a widely distributed and important parasite of cereals and legumes. As migratory endoparasites, P. thornei are difficult to manage  because they enter and leave host roots and may remain quiescent inside roots or in soil when conditions are unfavourable for plant growth. The number of available nematicides to manage these nematodes is restricted, so new, effective and eco-friendly sustainable management strategies are needed. The effects of naphthoquinones (juglone, 1,4-naphtoquinone and plumbagin) produced by some plants species, including walnut (Juglandaceae), were assessed against P. thornei. An additional treatment of a mixture of juglone and 1,4-naphtoquinone (2:1, w/w), was included because these compounds are frequently found at these propotion in walnut extracts. Juveniles and adult nematodes were exposed to different concentrations of each naphthoquinone and nematode mortality was assessed. Juglone and 1,4-naphthoquinone (at 500 ppm) were more effective than plumbagin, and gave 100% mortality after 24 h of exposure. A synergistic effect was not detected when juglone and 1,4-naphthoquinone (2:1, w/w) were combined. Estimated lethal concentrations causing 50% P. thornei mortality (LC₅₀s) (72 h exposure) were: 134.7 ppm for juglone, 161.2 ppm for 1,4-naphthoquinone, 207.6 ppm for juglone + 1,4-naphthoquinone (2:1, w/w), and 178.8 ppm for plumbagin. This study has demonstrated the nematicidal potential of these naphthoquinones against P. thornei, and has shown that walnut residues may be valuable sources for extraction of these compounds.