Chemo-ecological insights into use of the non-host plant vegetable black-jack to protect two susceptible solanaceous crops from root knot nematode parasitism

Authors: KIHIKA-OPANDA, RUTH - International Centre Of Insect Physiology And Ecology; TCHOUASSI, DAVID - International Centre Of Insect Physiology And Ecology; NG'ANG'A, MARGARET - 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: 5/11/2022
Publication Date: 5/25/2022
Citation: Kihika-Opanda, R., Tchouassi, D.P., Ng'Ang'A, M.M., Beck, J.J., Torto, B. 2022. Chemo-ecological insights into use of the non-host plant vegetable black-jack to protect two susceptible solanaceous crops from root knot nematode parasitism. Journal of Agricultural and Food Chemistry. https://doi.org/10.1021/acs.jafc.2c01748.
DOI: https://doi.org/10.1021/acs.jafc.2c01748

Interpretive Summary: Plant parasitic nematodes (PPNs) are small worm-like animals that can incur serious damage to agricultural commodities. Control of PPNs is difficult and can require the use of pesticides. A USDA-ARS scientists at the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, FL and collaborators at the International Centre for Insect Physiology and Ecology in Nairobi, Kenya investigated the effects of root exudates from Bidens pilosa, a plant that PPNs do not use as a host, and the ability of the root exudate to inhibit PPN infection of two known host plants of PPNs, tomato and black nightshade. Using green house and laboratory bioassays as well as chemical analysis, chemicals from the exudate were identified that inhibited egg hatching and elicited nematicidal activity against the infective juveniles (J2s) of the PPN Meloidogyne incognita, a common root knot nematode of several agricultural commodities. The identification of plants and their PPN-inhibiting exudates that can be used as crop companions can help growers protect their PPN-susceptible agricultural commodities.

Technical Abstract: Plant parasitic nematodes develop through three major stages in their life cycle; hatching, infection, and reproduction, which if interrupted will avert their growth and survival. We investigated the potential of the non-host plant vegetable black-jack (Bidens pilosa (Asteraceae)) in suppressing the infection of the plant parasitic nematode Meloidogyne incognita, a root knot nematode (RKN) in two susceptible Solanaceae host plants; tomato (Solanum lycopersicum) and black nightshade (S. nigrum). In screenhouse pot experiments combined with laboratory in-vitro hatching and mortality assays and chemical analysis, we identified metabolites from the root exudate of B. pilosa that inhibited egg hatching and elicited nematicidal activity against the infective juveniles (J2s). In intercop and drip pot experiments, B. pilosa significantly reduced the number of galls and egg masses in the RKN-suceptible host plants by ~3-9-fold compared to controls. Chemical analysis by liquid chromatography- triple quadrupole tandem mass spectrometry (LC-QQQ-MS) of the most bioactive fraction from the root exudates of B. pilosa identified several classes of compounds, including the vitamins ascorbic acid and nicotinic acid; dicarboxylic acid malic acid; amino acids tyrosine and phenylalanine; aromatic acids p-coumaric acid and 2-hydroxybenzoic acid; and flavonoid kaempferol. In in-vitro assays, the vitamins and aromatic acids elicited the highest inhibition in egg hatching. On the other hand, ascorbic acid and 2-hydroxybenzoic acid elicited strong nematicidal activity against M. incognita, with LC50/48 h values of 12 and 300 ng/µL, respectively. Our results provide insights into how certain non-host plants can be used as companion crops to disrupt plant-parasitic nematode interactions.