Elicitation of differential responses in the root-knot nematode Meloidogyne incognita to tomato root exudate cytokinin, flavonoids, and alkaloids

Authors: KIRWA, HILLARY - International Centre Of Insect Physiology And Ecology; MURUNGI, LUCY - Jomo Kenyatta University; 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: 10/12/2018
Publication Date: 10/12/2018
Citation: Kirwa, H.K., Murungi, L.K., Beck, J.J., Torto, B. 2018. Elicitation of differential responses in the root-knot nematode Meloidogyne incognita to tomato root exudate cytokinin, flavonoids, and alkaloids. Journal of Agricultural and Food Chemistry. 66(43):11291-11300. https://doi.org/10.1021/acs.jafc.8b05101.
DOI: https://doi.org/10.1021/acs.jafc.8b05101

Interpretive Summary: Plant roots are able to secrete substances (exudates) containing chemical compounds that can mediate a wide range of interactions with a variety of organisms in the rhizosphere. Among these organisms are plant parasitic nematodes that include the root-knot nematodes (RKNs) belonging to Meloidogyne spp. Plant parasitic nematodes are major pests to agriculture worldwide and can cause significant damage to plants. Investigated were the responses of infective second stage juveniles (J2s) of M. incognita to non-volatile components identified in the root exudate of tomato. Using a bioassay-guided approach, researchers from the International Centre for Insect Physiology and Ecology (icipe), Nairobi, Kenya, in collaboration with the ARS Center for Medical, Agricultural, and Veterinary Entomology, Chemistry Research Unit in Gainesville, FL, identified specific root exudate compounds that attracted or repelled J2s of M. incognita. Chemical analysis of bioactive fractions obtained from the root exudate, revealed a high diversity of compounds. Five compounds from the exudate were found to elicit specific responses from the J2s. These results indicate that J2 root-feeding damage is influenced by root exudate chemistry. These results demonstrate that compounds such as these may have potential applications in RKN management in the U.S. and Kenya agriculture, as well as affected crops worldwide.

Technical Abstract: Root exudates of plants mediate a wide range of interactions with a variety of organisms in the rhizosphere. Among these organisms, are plant parasitic nematodes that include the root-knot nematodes (RKNs) belonging to Meloidogyne spp. Investigated were the responses of J2s of M. incognita to non-volatile components identified in the root exudate of tomato. Using a bioassay-guided approach, combining stylet thrusting and chemotaxis assays with chemical analysis, we identified specific metabolites in the root exudate that attract and repel J2s of M. incognita. Chemical analysis by LC-QTOF-MS of bioactive fractions obtained from the root exudate, revealed a high diversity of compounds, including the phytohormone zeatin (cytokinin), the flavonoids quercetin and luteolin, and the alkaloids solasodine and tomatidine. In stylet thrusting assays, these five compounds elicited positive but concentration-dependent responses in J2s relative to 2% dimethyl sulfoxide (negative control) and methyl salicylate (positive control). In chemotaxis assays, zeatin and quercetin elicited concentration-dependent positive responses in J2s, while luteolin, solasodine, and tomatidine tested as the hydrochloride derivative, elicited the opposite effect. These results indicate that J2 herbivory is influenced by root exudate chemistry, quality and concentration of specific compounds, which may have potential applications in RKN management.