Identification of Key Root Volatiles Signaling Preference of Tomato Over Spinach by the Root Knot Nematode Meloidogyne incognita

Authors: MURUNGI, LUCY - Jomo Kenyatta University; KIRWA, HILLARY - International Centre Of Insect Physiology And Ecology; COYNE, DANNY - International Institute Of Tropical Agriculture (IITA); Teal, Peter; Beck, John; TORTO, BALDWYN - International Centre Of Insect Physiology And Ecology

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2018
Publication Date: 6/25/2018
Citation: Murungi, L.K., Kirwa, H., Coyne, D., Teal, P.E., Beck, J.J., Torto, B. 2018. Identification of Key Root Volatiles Signaling Preference of Tomato Over Spinach by the Root Knot Nematode Meloidogyne incognita. Journal of Agricultural and Food Chemistry. 66:7328-7336. doi:10.1021/acs.jafc.8b03257.
DOI: https://doi.org/10.1021/acs.jafc.8b03257

Interpretive Summary: Nematodes are serious pests of vegetable crops worldwide. For example, the root-knot nematode (RKN, Meloidogyne incognita) is a plant root parasite of many crops, including tomato and spinach in sub-Saharan Africa. In East Africa these two crops are economically important and are commonly planted together if fields of smallholder farmers. The odors emitted by plants (host plant volatiles) are known to influence the behavior of nematodes and the role of these odors for the interactions of M. incognita and these two commodities is currently unknown. Researchers from the ARS Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, and the International Centre of Insect Physiology and Ecology, Nairobi, Kenya investigated the odors from tomato and spinach roots and their role in attraction of RKN. In assays, RKNs were attracted to root odors from both crops, and in subsequent choice tests between the two host plants, odors of tomato roots were more attractive than those released by spinach. Instrumental analysis of the host root odors identified compounds that were common to both host plants, but also specific to tomato root odors. Subsequent assays determined that some of these compounds attracted the RKN. The results indicate that since both tomato and spinach roots are attractive to the RKN, future identification of cultivars of these two host plants that do not release these attractive compounds could be helpful in the management of root knot nematodes.

Technical Abstract: The root knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, is a serious pest of tomato and spinach in sub-Saharan Africa. In East Africa these two crops are economically important and are commonly intercropped by smallholder farmers. The role of host plant volatiles in M. incognita interactions with these two commodities is currently unknown. Here, we investigate the olfactory basis of attraction of tomato and spinach roots by the infective second stage juveniles (J2s) of M. incognita. In olfactometer assays, J2s were attracted to root volatiles from both crops over moist sand (control), but in choice tests using the two host plants, volatiles of tomato roots were more attractive than those released by spinach. Gas chromatography/mass spectrometric (GC/MS) analysis identified a total of eight components, of which five (2-isopropyl-3-methoxypyrazine, 2-(methoxy)-3-(1-methylpropyl)pyrazine, tridecane, and a- and ß-cedrene) occurred in the root-emitted volatiles of both plants, with three (d-carene, sabinene and methyl salicylate) being specific to tomato root volatiles. In a series of bioassays, methyl salicylate contributed strongly to the attractiveness of tomato, whereas 2-isopropyl-3-methoxypyrazine and tridecane contributed to the attractiveness of spinach. M. incognita J2s were also more attracted to natural spinach root volatiles when methyl salicylate was combined, than to spinach volatiles alone, indicating that the presence of methyl salicylate in tomato volatiles strongly contributes to its preference over spinach. Our results indicate that since both tomato and spinach roots are attractive to M. incognita, identifying cultivars of these two plant species that are chemically less attractive can be helpful in the management of root knot nematodes.