Effect of 4-Ethylbenzaldehyde from the Volatilome of Annona muricata on Meloidogyne incognita.

The demand for new soil fumigants has increased as a result of more restrictive legislation regarding the use of pesticides. In the present study, the potent nematicidal activity of volatile organic compounds released by the Annona muricata leaf macerate was demonstrated. In addition, we searched in the A. muricata volatilome for a molecule with potential to be developed as a new fumigant nematicide. In the greenhouse, even the lowest concentration of soursop leaf macerate tested (1.0%) as a biofumigant caused a significant (P < 0.05) reduction in Meloidogyne incognita infectivity and reproduction when compared with the nontreated control (0%). Forty-one compounds were identified through gas chromatography-mass spectrometry analysis, of which three (sabinene, caryophyllene oxide, and 4-ethylbenzaldehyde) were selected for studies against the nematode. Among these compounds, in in vitro trails, only 4-ethylbenzaldehyde showed nematicidal activity at 250 µg ml-1. The effective doses of 4-ethylbenzaldehyde predicted to kill 50 and 95% of the M. incognita second-stage juvenile population after 48 h of exposure were 35 and 88 µg ml-1, respectively. In in vitro tests, 4-ethylbenzaldehyde at 150 µg ml-1 reduced M. incognita egg hatching to values similar (P > 0.05) to those of the commercial nematicide fluensulfone at a concentration of 200 µg ml-1. In plant experiments, as a soil fumigant, 4-ethylbenzaldehyde at a dose of 1 ml/liter of substrate had an effect similar (P > 0.05) to that of the commercial fumigant Dazomet (250 µg ml-1). Therefore, 4-ethylbenzaldehyde shows potential for development as a new nematicide.

Slight induction and strong inhibition of Heterodera glycines hatching by short-chain molecules released by different plant species.

New management tools are necessary to reduce the damage caused by the soybean cyst nematode (SCN), Heterodera glycines. Identification of molecules that can stimulate second-stage juveniles (J2) hatching in an environment without food may contribute to that. In in vitro experiments, we evaluate the effect of volatile organic compounds (VOCs) released by soybean (Glycine max), bean (Phaseolus vulgaris), ryegrass (Lolium multiflorum), and alfalfa (Medicago sativa) on H. glycines egg hatching. VOCs released by all plant species significantly (p < 0.05) increased egg hatching. Short-chain molecules released by leaves and roots of soybean and bean increased the hatching up to 71.4%. The analysis of the volatilome done by gas chromatography coupled with mass spectrometry revealed 44 compounds in the plant emissions. Four of them, namely 3-octanol, 1-hexanol, hexanal and linalool were tested individually as hatching inductors. Under concentrations of 200, 600, and 1,000 µg/ml there was no hatching induction of H. glycines J2 by these compounds. On the other hand, in these concentrations, the compounds 3-octanol and 1-hexanol caused hatching reduction with values similar to the commercial nematicide carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methyl carbamate). In subsequent tests, the compounds 1-hexanol and 3-octanol showed lethal concentration values required to kill 50% of thenematode population (LC50) of 210 and 228 µg/ml, respectively, in the first experiment and, 230 and 124 µg/mlin the second one. Although we have not identified any molecules acting as hatching factor (HF), here we present a list (44 candidate molecules) that can be explored in future studies to find an efficient HF.

Volatile emissions of watercress (Nasturtium officinale) leaves and passion fruit (Passiflora edulis) seeds against Meloidogyne incognita.

Watercress leaf and passion fruit seed macerates produce volatile organic compounds toxic to Meloidogyne incognita and 1-octanol, found in volatile emissions of watercress leaves, shows nematicidal activity against M. incognita.

BACKGROUND: Plants emit volatile organic compounds (VOCs) with several functions, including toxicity to plant-parasitic nematodes (PPNs). However, the toxicity of VOCs from watercress leaves (Nasturtium officinale) and passion fruit seeds (Passiflora edulis) against PPNs has not yet been studied. RESULTS: Biofumigation with watercress leaves and passion fruit seeds reduced the infectivity and reproduction of Meloidogyne incognita in tomato plants. The VOCs emitted by watercress leaves and passion fruit seeds caused immobility of M. incognita second-stage juveniles (J2 ). The reduction in infectivity and reproduction of M. incognita reached 89% and 99%, respectively, when J2 were exposed to watercress VOCs. Additionally, water exposed to VOCs emitted by watercress caused 79% M. incognita J2 mortality. The volatilome of the toxic water contained 12 compounds, mainly alcohols. The emissions from watercress leaves and passion fruit seeds contained 26 and 12 compounds, respectively, according to gas chromatography-mass spectrometry analysis. The 1-octanol occurring in watercress emissions demonstrated in vitro and in vivo nematicidal activity against M. incognita, with a lethal dose necessary to cause 50% mortality (LC50 ) of 382.5 µg mL−1 . CONCLUSIONS: Watercress leaf and passion fruit seed macerates emitted VOCs with nematicidal activity against M. incognita. The compound 1-octanol identified in watercress emissions may be useful for the nematicide-producing industry.

Volatile organic compounds produced by castor bean cake incorporated into the soil exhibit toxic activity against Meloidogyne incognita.

BACKGROUND: This study showed, for the first time, the effect of volatile organic compounds (VOCs) emitted by castor bean cake added to soil on the plant-parasitic nematode Meloidogyne incognita. Identification of nematotoxic volatiles increases the chance of identifying molecules for use in commercial nematicides. RESULTS: VOCs produced after the incorporation of castor bean cake in the soil resulted in immobility (>97.3%) and death (>96.9%) of M. incognita second-stage juveniles (J2) and reduction in M. incognita egg-hatch (>74.3%) at all concentrations of cake tested (1.5-6.0%). A similar reduction in M. incognita infectivity and reproduction was observed when nematodes were exposed to these VOCs and inoculated into tomato plants or exposed directly upon contact with the soil. We identified 32 VOCs produced by castor bean cake when incorporated into soil by using solid phase micro-extraction gas chromatography coupled with mass spectrometry (SPME-GC-MS). Four of the most intense peaks in the chromatogram represented the compounds phenol, 4-methylphenol, γ-decalactone, and skatole. When M. incognita J2 were exposed to these compounds, all of the compounds demonstrated nematicidal activity with low median lethal concentration (LC50 ) values. CONCLUSION: Castor bean cake incorporated into the soil produces volatile compounds which are toxic to M. incognita. These substances show potential for application in the nematicide-producing industry. © 2018 Society of Chemical Industry.

Plant Volatiles Reduce the Viability of the Root-Knot Nematode Meloidogyne incognita Either Directly or When Retained in Water.

Volatile organic compounds (VOC) produced by green residues for the management of plant-parasitic nematodes are poorly studied for oilseed plants and some Brassica spp. To investigate the activity of VOC in vitro and as biofumigants, dry and aqueous macerates of broccoli (Brassica oleracea var. italica) shoots and sunflower (Helianthus annuus) seed were used against the root-knot nematode Meloidogyne incognita. VOC produced by sunflower seed caused higher mortality of M. incognita second-stage juveniles (J2) than VOC produced by broccoli shoots but both plant species were equally effective in decreasing the infectivity and reproduction of this nematode. The number of galls and eggs produced by the nematode in tomato roots was reduced by 89 and 95%, respectively, on average, at the highest concentrations of broccoli and sunflower seed macerates tested as biofumigants. When nematodes were placed in water exposed to broccoli VOC, J2 immobility increased and the number of galls and eggs produced by the nematode in tomato roots decreased 80 and 96%, respectively. Water exposed to sunflower seed VOC had no effect on the viability of the nematode. Gas chromatography was used to identify five and six chemical groups in broccoli and in sunflower seed macerates, respectively, but only alcohols, sulfurated VOC, and terpenes were detected in the water exposed to these plant macerates. Sulfurated VOC from the water exposed to broccoli macerates were found to be involved in its activity against M. incognita. The purified VOC dimethyl disulfide (DMDS) and 3-pentanol were tested directly against J2 and showed a lethal concentration of 176 and 918 µg/ml (ppm), respectively, whereas dimethyl sulfide had no effect against M. incognita. Furthermore, DMDS and 3-pentanol retained in water killed J2 and reduced gall formation and the number of eggs of M. incognita on tomato roots. Both these plant species produced toxic VOC to M. incognita, whereas only VOC retained in water exposed to broccoli had activity against M. incognita.