Can plants with good anthelmintic activity against free-living and animal parasitic nematodes be effective against plant parasitic nematodes?

Root-knot nematodes (Meloidogyne spp.) are important pests in agricultural crops, causing more than 95% infestation in crops while livestock losses due to the animal parasitic nematode Haemonchus contortus cost tens of billions of dollars annually. Synthetic chemicals are highly effective, however increasing parasite resistance to anthelmintic drugs, environmental and health concerns have awakened interest in alternative methods of nematode control. Plants were selected on the basis of published activity against free-living (Caenorhabditis elegans) and animal parasitic (Haemonchus contortus) nematodes. Extracts of Lantana rugosa, Leonotis leonurus and Clasusena anisata were screened for corresponding efficacy against root-knot nematodes Meloidogyne incognita C. elegans and H. contortus L. leonurus and C. anisata acetone extracts had the best activity at 1 mg/mL with mortality of 100 and 92% on M. incognita juveniles after 48 hours of incubation respectively. The water extract of L. leonurus had the highest mortality of 99% on C. elegans after 24 hours of incubation but exposure indicated weaker activity. The dichloromethane/methanol extract of L. leonurus inhibited 100% of H. contortus eggs from hatching at 0.104 mg/mL, followed by acetone extracts of L. rugosa (96%) and L. leonurus (77%). Solvent-solvent fractions of L. rugosa and C. anisata had good activity against C. elegans while those of L. leonurus inhibited H. contortus eggs from hatching. In the present study, there was good translation of plant extract activity against animal and plant nematodes. Further investigations aim to identify active compounds and mechanism of action of the most promising extracts.