Abstract
We investigated Solanum nigrum (seeds) and Datura stramonium (shoots) against root-knot nematodes in terms of J2 paralysis and egg hatch inhibition (methanol extract), as well as inhibition of nematode development in host roots (soil amending with either S. nigrum seeds' or D . stramonium shoots' meal). Datura stramonium was found equally effective at inhibiting motility of Meloidogyne incognita and Meloidogyne javanica (both EC 50 = 427 μg mL -1 at 3 day), but inhibition occurred more quickly for M. incognita (1 day). Solanum nigrum was faster and more effective at inhibiting motility of M. incognita than M. javanica (EC 50 = 481 and 954 μg mL -1 at 3 day, respectively). Datura stramonium was slower, but eventually more potent in decreasing egg hatch and cell division in M. incognita eggs, than S. nigrum . Specifically, D. stramonium significantly inhibited cell division in eggs immersed in at least 100 and 1 μg mL -1 at Day 6 and 10, respectively. Solanum nigrum impeded cell division in un-differentiated eggs immersed in not less than 10 and 100 μg mL -1 after days 2 and 6, respectively. Both extracts were similar in suppressing J2 exclosure but D. stramonium was effective in smaller test concentrations. Specifically, D. stramonium suppressed J2 emerging from eggs immersed in 10 μg mL -1 at day2, and in at least 1 μg mL -1 at day 6. Solanum nigrum significantly reduced J2 hatch from eggs immersed in a minimum of 100 μg mL -1 at day 2 and not less than 1,000 μg mL -1 at day 6. In pots, powdered S. nigrum seeds meal was more active than D. stramonium and the respective EC 50 females/ g values for M. incognita were 1.13 and 11.4 mg g -1 of soil, respectively. The chemical composition of active extracts was determined after derivatization by GC-MS. Chemical analysis of active extracts showed the presence of fatty acids with known nematicidal activity.
Highlights
Weeds compete with crop plants and soil organisms for resourses through the production of allelochemicals like phenolic acids, terpenes, terpenoids, glycosides, alkaloids, and flavonoids (Whittaker and Feeny, 1971; Blum, 1996; Keating, 1999)
Saponins like solanigroside A and solanigroside B (Zhou et al, 2007) as well as oleanane-type triterpenoid saponins exhibit LC50 values against M. incognita ranging from 70.1 to 94.7 μ g ml-1 after 48 h (Li et al, 2013); while a saponin based commercial nematicide from Quillaja saponaria has been registered for nematode control in Europe (Giannakou, 2011). 4-methylphenol is of significant in vitro activity against M. javanica (Yang et al, 2015) while Zhang and co-workers have demonstrated that fatty acids like caproic, caprylic, capric, lauric, myristic, and palmitic cause significantly high mortality to M. incognita J2 (Zhang et al, 2012)
Meloidogyne incognita development in artificially inoculated tomato plants treated with the weed powders was reduced with EC50 values for female per gram root counts calculated for S. nigrum and D. stramonium of 1.13 and 11.40 mg g-1, respectively
Summary
Populations of M. incognita and M. javanica both of Greek origin were reared on tomato (Solanum lycopersicum Mill.) cv. Data were fit to the log-logistic model (Seefeldt et al, 1995) to estimate the concentration that caused a 50% decrease in females and galls per gram of root (EC50 value) In this regression equation, the test compounds (% w/w) were the independent variables (x) and the female nematodes, or galls, (as the percentage decrease over the water control) was the dependent variable (y). Corrected % = {(Mortality percent in treatment - Mortality percent in control)/(100 - Mortality percent in Paralysis activity of M. incognita was more affected control)} × 100 and they were analysed (ANOVA) after by D. stramonium and S. nigrum extracts than M. jabeing combined over time. Meloidogyne incognita development in artificially inoculated tomato plants treated with the weed powders was reduced with EC50 values for female per gram root counts calculated for S. nigrum and D. stramonium of 1.13 and 11.40 mg g-1, respectively. When the alkaloid rich extract was tested against J2, no paralysis was evidenced at the concentration range of 100 to 1,000 μ g ml-1 (data not shown)
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