Nematicidal activity of volatile organic compounds emitted by Brassica juncea, Azadirachta indica, Canavalia ensiformis, Mucuna pruriens and Cajanus cajan against Meloidogyne incognita

• Novel technique for plant volatile organic compounds (VOCs) test.
• Exposed water to plant VOCs lead it to acquire molecules.
• Plant VOC damage to Meloidogyne incognita J2 affect nematode pathogenicity and growth.
• Analyses by GC/MS revealed molecules, once soluble in water, may affect nematodes.
• Retaintion of VOCs in water avoids them from escaping to the air.

Understanding the effect of plant volatile organic compounds (VOCs) on soil nematodes and water may explain plant damage in the field and how some nematode management strategies reduce soil nematode populations. M. incognita is a damaging plant pathogenic nematode that affects crops worldwide. The aims of this study were to evaluate the effect of the VOCs emitted by five common crops used for soil incorporation to control the second-stage juveniles (J2) of Meloidogyne incognita. To investigate the “in vitro” role of water in the relationship between nematodes and plant VOCs. And to identify the volatile molecules by gas chromatography (GC/MS). The method used permitted the volatile molecules from macerated plant organs to only contact the J2 nematodes by air. Plants organs from all plants macerated with and without water emitted VOCs that immobilized J2 nematodes, with higher levels emitted when the plant organs were macerated without water. Only water exposed to VOCs from neem and mustard leaves were capable of immobilizing M. incognita J2. The M. incognita J2 exposed to neem and mustard VOCs and inoculated in tomato seedlings resulted in reduced gall formation and nematode reproduction, showing the nematicidal effect of the plant-emitted VOCs. GC/MS analysis revealed the presence of 58 and 32 molecules in the VOCs emitted from neem and mustard macerates, respectively. Alcohols were found in both the neem and mustard VOCs. Esters were found in the neem VOCs, and sulfur-containing compounds, mostly isothiocyanates, were found in mustard. Our results demonstrate that plant VOCs contain diversified molecules that affect M. incognita mobility, pathogenicity and reproduction. Nematode toxic VOCs may be retained in water, which prevents the VOCs from escaping into the air and causing the water to become toxic to nematodes. These data may explain part of the role of VOCs in the biofumigation process, through plant incorporation with the soil, and suggests that irrigation performed directly after incorporation may trap the VOCs in soil water and thereafter retain nematode toxicity longer than incorporation that is performed later.