Parasitic nematode Meloidogyne incognita interactions with different Capsicum annum cultivars reveal the chemical constituents modulating root herbiovry

Authors: KIHIKA, RUTH - International Centre Of Insect Physiology And Ecology; MURUNGI, LUCY - Jomo Kenyatta University; COYNE, DANNY - International Institute For Tropical Agriculture; NG'ANG'A, MARGARET - Kenyatta University; HASSANALI, AHMED - Kenyatta University; Teal, Peter; TORTO, BALDWYN - International Centre Of Insect Physiology And Ecology

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2017
Publication Date: 6/6/2017
Citation: Kihika, R., Murungi, L.K., Coyne, D., Ng'Ang'A, M., Hassanali, A., Teal, P.E., Torto, B. 2017. Parasitic nematode Meloidogyne incognita interactions with different Capsicum annum cultivars reveal the chemical constituents modulating root herbiovry. Scientific Reports. 7(2903):1-10. doi:10.1038/s41598-017-02379-8.

Interpretive Summary: Odors emitted by plants can be used by arthropod herbivores to locate suitable host plants to feed on. A scientist from the USDA-ARS Center for Medical, Agricultural and Veterinary Entomology, Gainesville FL in collaboration with scientists from the International Centre of Insect Physiology and Ecology, Nairobi, Kenya, discovered odors used by the below-ground parasitic nematodes, southern root-knot nematode (Meloidogyne incognita) to locate several varieties of pepper plant (Capsicum annum) roots. In laboratory-based bioassays, a blend of the plant odors (a-pinene, limonene, 2-methoxy-3-(1-methylpropyl)-pyrazine, methyl salicylate and tridecane) stimulated movement of the nematodes toward the source of blend odors. Also, the odor thymol released by one of the pepper plants caused the nematodes to move away from the source odor. These results offer further insight into how plant odors can be used to manipulate nematode behavior, thus providing methods for protection of agricultural commodities against this important belowground pests.

Technical Abstract: Plant volatile signatures are often used as cues by herbivores to locate their preferred hosts. Here, we report on the volatile organic compounds used by the subterranean root-knot nematode (RKN) Meloidogyne incognita for host location. We compared responses of infective second stage juveniles (J2s) to root volatiles of three cultivars and one accession of the solanaceous plant, Capsicum annum against moist sand in dual choice assays. J2s were more attracted to the three cultivars than to the accession, relative to controls. GC/MS analysis of the volatiles identified common constituents in each plant, five of which were identified as a-pinene, limonene, 2-methoxy-3-(1-methylpropyl)-pyrazine, methyl salicylate and tridecane. We additionally identified thymol as being specific to the accession. In dose-response assays, a blend of the five components elicited positive chemotaxis (71–88%), whereas individual components elicited varying responses; Methyl salicylate (MeSA) elicited the highest positive chemotaxis (70–80%), a-pinene, limonene and tridecane were intermediate (54–60%), and 2-methoxy-3-(1-methylpropyl)-pyrazine the lowest (49–55%). In contrast, thymol alone or thymol combined with either the preferred natural plant root volatiles or the five-component synthetic blend induced negative chemotaxis. Our results provide insights into RKN-host plant interactions, creating new opportunities for plant breeding programmes towards management of RKNs.