Abstract
Meloidogyne incognita is an obligate plant-parasitic nematode causing serious damage to agricultural crops. Major constraints in nematode management arose due to the limited availability of non-fumigant nematicides in conjunction with the considerable ill effects of fumigants on human and non-target organisms. Recently, fluensulfone has been reported to be an effective non-fumigant nematicide against plant-parasitic nematodes and the model nematode Caenorhabditis elegans. The nematicidal efficacy varies according to its concentration at the time of application, exposure timing, nematode species variability, and even across subpopulations within the same species. It interferes with the key physiological processes of nematodes, like motility, behavior, chemosensation, stylet thrusting, infectivity, metabolism, lipid consumption, tissue integrity, oviposition, egg hatching, and survival. However, the molecular basis of these multivariate physiological anomalies is still largely unknown. Quantitative real-time PCR was carried out to understand the acute transcriptional perturbation of 30 functional genes associated with key physiological and life processes in a M. incognita population, following exposure of 10, 50, and 100 ppm of fluensulfone for 5 and 10 hr. The chemical treatment resulted in significant downregulation of all the neuropeptidergic genes, with concomitant repression of majority of genes related to chemosensation, esophageal gland secretion, parasitism, fatty acid metabolism, and G-protein coupled receptors. Collectively, the parasitism genes were found to be perturbed at highest magnitude, followed by the GPCRs and neuropeptidergic genes. These results establish the wide ranging effect of fluensulfone on various metabolic and physiological pathways of nematode.
Highlights
Over 4,100 species of plant-parasitic nematodes (PPNs) pose a major threat to the present day agriculture accounting an estimated yield loss of US$ 173 billion every year (Decraemer and Hunt, 2006)
Representative genes associated with chemosensation, esophageal gland secretion, nematode parasitism, fatty acid metabolism, β -oxidation, polyunsaturated fatty acid (PUFA) fractionation, neurotransmission, and G-protein coupled receptors (GPCRs) were selected from M. incognita
Owing to the experimental integrity for quantitative real-time PCR (qRT PCR) purpose, concentration of fluensulfone and time of exposure was combined in such way so that no worm dies, and nematicidal effect was microscopically assessed by behavioral changes, immobility and mortality in the M. incognita J2s (Supplementary Table 2)
Summary
Over 4,100 species of plant-parasitic nematodes (PPNs) pose a major threat to the present day agriculture accounting an estimated yield loss of US$ 173 billion every year (Decraemer and Hunt, 2006). Fluensulfone has very low toxicity toward non-target organisms and it does not emit any volatile organic compound(s) (Ploeg et al, 2019; Waldo et al, 2019) Exposure to this chemical exerts irreversible nematicidal effects affecting the motility, chemosensory perception, stylet thrus ting, feeding, moulting, infection potential, oviposition capacity, egg hatching, behaviour, metabolism, lipid consumption, tissue integrity and survival in root-knot, cyst and other nematode species (Kearn et al, 2014, 2017; Oka and Saroya, 2019; Wram and Zasada, 2019). The effects were observed by directly treating the nematode J2s with different concentrations of fluensulfone (10, 50, and 100 ppm), followed by analysis of transcript levels of the respective genes by quantitative real-time PCR (qRT PCR) at two time points (5 and 10 hr post exposure)
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