After 2 months from the infestation of tomato plants with the root-knot nematode (RKN) Meloidogyne incognita, we performed a gas chromatography-mass spectrometry untargeted fingerprint analysis for the identification of characteristic metabolites and biomarkers. Principal component analysis, and orthogonal projections to latent structures discriminant analysis suggested dramatic local changes of the plant metabolome. In the case of tomato leaves, β-alanine, phenylalanine, and melibiose were induced in response to RKN stimuli, while ribose, glycerol, myristic acid, and palmitic acid were reduced. For tomato stems, upregulated metabolites were ribose, sucrose, fructose, and glucose, while fumaric acid and glycine were downregulated. The variation in molecular strategies to the infestation of RKNs may play an important role in how Solanum lycopersicum and other plants adapt to nematode parasitic stress.

Research on new pesticides based on plant extracts, aimed at the development of nontoxic formulates, has recently gained increased interest. This study investigated the use of the volatilome of rucola (Eruca sativa) as a powerful natural nematicidal agent against the root-knot nematode, Meloidogyne incognita. Analysis of the composition of the volatilome, using GC-MS-SPME, showed that the compound (Z)-3-hexenyl acetate was the most abundant, followed by (Z)-3-hexen-1-ol and erucin, with relative percentages of 22.7 ± 1.6, 15.9 ± 2.3, and 8.6 ± 1.3, respectively. Testing of the nematicidal activity of rucola volatile compounds revealed that erucin, pentyl isothiocyanate, hexyl isothiocyanate, (E)-2-hexenal, 2-ethylfuran, and methyl thiocyanate were the most active with EC50 values of 3.2 ± 1.7, 11.1 ± 5.0, 11.3 ± 2.6, 15.0 ± 3.3, 16.0 ± 5.0, and 18.1 ± 0.6 mg/L, respectively, after 24 h of incubation. Moreover, the nematicidal activity of fresh rucola used as soil amendant in a containerized culture of tomato decreased the nematode infection in a dose-response manner (EC50 = 20.03 mg/g) and plant growth was improved. On the basis of these results, E. sativa can be considered as a promising companion plant in intercropping strategies for tomato growers to control root-knot nematodes.

Different maleimide derivatives were synthesized and assayed for their in vitro activity on the soil inhabiting, plant-parasitic nematode Meloidogyne incognita, also known as root-knot nematode. The compounds maleimide, N-ethylmaleimide, N-isopropylmaleimide, and N-isobutylmaleimide showed the strongest nematicidal activity on the second stage juveniles of the root-knot nematode with EC50/72h values of 2.6 ± 1.3, 5.1 ± 3.4, 16.2 ± 5.4, and 19.0 ± 9.0 mg/L, respectively. We also determined the nematicidal activity of copper sulfate, finding an EC50 value of 48.6 ± 29.8 mg/L. When maleimide at 1 mg/L was tested in combination with copper sulfate at 50 mg/L, we observed 100% mortality of the nematodes. We performed a GC-MS metabolomics analysis after treating nematodes with maleimide at 8 mg/L for 24 h. This analysis revealed altered fatty acids and diglyceride metabolites such as oleic acid, palmitic acid, and 1-monopalmitin. Our results suggest that maleimide may be used as a new interesting building block for developing new nematicides in combination with copper salts.

No abstract

Maize is cultivated worldwide and used as food and for fuel production. It is usually attacked and destroyed during storage by Sitophilus zeamais. With inaccessibility to synthetic pesticides, farmers are left with the choice of using locally available plant based pesticides. For this reason, we tested the insecticidal potentials of essential oils (EOs) of Chenopodium ambrosioides and Cupressus sempervirens and their binary combinations against S. zeamais on stored maize. Mortality, progeny inhibition, repellence and damage were tested. Pesticide characteristics of both essential oils were dose-dependent, 200 μL/kg of all the combinations caused at least 80% mortality within 14 days of storage while the 50:50 combination completely inhibited progeny production. Moreover, 8 μL of all the EO were repellent to the weevils. The 50:50 binary combination was the most active in all the tests carried out. Pesticidal interactions between the oils in combination were mostly additive and synergistic. There was also a good control of insect population increase and grain damage after six months of storage. Therefore both EOs can be recommended for the control of S. zeamais.

A series of aryl hydrazones were synthesized and in vitro assayed for their activity on the root-knot nematode Meloidogyne incognita. The phenylhydrazones of thiophene-2-carboxyaldehyde 5, 3-methyl-2-thiophenecarboxyaldehyde, 6, and salicylaldehyde, 2, were the most potent with EC50/48h values of 16.6 ± 2.2, 23.2 ± 2.7, and 24.3 ± 1.4 mg/L, respectively. A GC-MS metabolomics analysis, after in vitro nematode treatment with hydrazone 6 at 100 mg/L for 12 h, revealed elevated levels of fatty acids such as lauric acid, stearic acid, 2-octenoic acid, and palmitic acid. Whereas control samples showed the highest levels of monoacylglycerols such as monostearin and 2-monostearin, surprisingly, 2 h after treatment with hydrazone 6, nematodes excreted 3 times the levels of ammonia eliminated in the same conditions by controls. Thus, phenylhydrazones may represent a good scaffold in the discovery and synthesis of new nematicidal compounds, and a metabolomics approach may be helpful in understanding their mechanisms of toxicity and mode of action.

No 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 μ g 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 μ g 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 μ g 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 μ g 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 μ g mL-1 at day2, and in at least 1 μ g mL-1 at day 6. Solanum nigrum significantly reduced J2 hatch from eggs immersed in a minimum of 100 μ g mL-1 at day 2 and not less than 1,000 μ g 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.