METHODS AND RESULTS:
Species of Cephalotaxus (the plum yews) produce nematotoxic compounds of unknown identity. Consequently, bioassay-guided fractionation was employed to identify the compound(s) in Cephalotaxus fortunei twigs and leaves with activity against plant-parasitic nematodes. A crude alkaloid extract, particularly Drupacine, was responsible for much of the nematotoxicity. The ED50 of Drupacine for Bursaphelenchus xylophilus was 27.1 μg mL⁻1, and for Meloidogyne incognita it was 76.3 μg mL⁻1. Immersion of M. incognita eggs in 1.0 mg mL⁻1 crude alkaloid extract (the highest tested concentration) reduced hatch by 36%; immersion of second-stage juveniles (J2) resulted in 72-98% immobility. Crude alkaloid extract and Drupacine suppressed protease activity in extracts of the microbivorous nematode Panagrellus redivivus by 50% and 80%, respectively. Application of 0.02-0.5 mg mL⁻1 crude alkaloid extract to soil with M. incognita inoculum did not significantly reduce pepper plant shoot length or weight, compared with nematode-inoculated, water-treated controls, but the number of eggs and J2 per root system respectively decreased by 69% and 73% at 0.5 mg mL⁻1.
CONCLUSIONS:
Drupacine and a crude alkaloid extract suppress nematode hatch, activity of mixed life stages, and population numbers on plant roots. This is the first demonstration of nematotoxicity of crude Cephalotaxus alkaloids and Drupacine. |
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