The nematicidal activity of buckwheat (Fagopyrum esculentum Moench) on the root-knot nematode Meloidogyne incognita was tested. Dried plant methanol extract presented higher nematicidal activity than fresh plant extracts with an EC50 = 62.6 ± 26.0 and 40.8 ± 26.1 μg/ml after 48 and 72 hours of immersion, respectively. GC-MS analysis showed the presence of 17 aldehydes, with salicylaldehyde (o-hydroxybenzaldehyde) being the most abundant at 16%. Nematicidal activity of the latter refers to salicylaldehyde and other aldehydes with chemical similarities was then assessed. The most active aldehyde was o-hydroxybenzaldehyde followed by m-hydroxybenzaldehyde, p-hydroxybenzaldehyde and benzeneacetaldehyde with an EC50 of about 11.0 ± 1.0, 31.0 ± 22.0, 75.0 ± 23.0 and 168.1 ± 52.3 μg/ml after 1 day of immersion, respectively. Position 2 of the hydroxyl group in the benzene ring seems to be very important for the nematicidal activity, followed by positions 3 and 4. As a complementary experiment, synergistic activity was observed when we added o-hydroxybenzaldehyde to m-hydroxybenzaldehyde and to p-hydroxybenzaldehyde with an EC50 after 24 hours of immersion of 8.0 ± 2.5 and 6.1 ± 2.3 μg/ml, respectively. Antioxidant activity assessment showed that this latter is inversely proportional to nematicidal activity. Our results showed that F. esculentum and its major compound salicylaldehyde could be integrated into the pest management system.
Keywords: DPPH; buckwheat; root knot nematodes; salicylaldehyde.