Root-knot nematode, Meloidogyne incognita is one of the most destructive nematodes worldwide. Essential oils (EOs) are being extensively utilized as eco-benign bionematicides, although the precise mechanism of action remains unclear. Pogostemon cablin Benth. is well-known as "Patchouli". It is native to South East Asia and known for ethno-pharmacological properties. In this study, chemical composition and potential nematicidal effect of EOs hydrodistilled from the leaves of P. cablin grown at three different locations in India were comprehensively investigated to correlate their mechanism of action for target specific binding affinities toward nematode proteins. Aromatic volatile Pogostemon essential oils (PEO) from Northern India (PEO-NI), Southern India (PEO-SI) and North Eastern India (PEO-NEI) were analyzed by Gas Chromatography-Mass Spectrometry (GC/MS) to characterize forty volatile compounds. Maximum thirty-three components were identified in PEO-NEI. Sesquiterpenes were predominant with higher content of α-guaiene (2.3-24.4 %), patchoulol (6.1-32.7 %) and α-bulnesene (5.9-27.1 %). Patchoulol was the major component in PEO-SI (32.7±1.2 %) and PEO-NEI (29.2±1.1 %), while α-guaiene in PEO-NI (24.4±1.2 %). In vitro nematicidal assay revealed significant nematicidal action (LC50 44.6-87.0 μg mL-1 ) against juveniles of M. incognita within 24 h exposure. Mortality increases with increasing time to 48 h (LC50 33.6-71.6 μg mL-1 ) and 72 h (LC50 27.7-61.2 μg mL-1 ). Molecular modelling and in silico studies revealed multi-modal inhibitive action of α-bulnesene (-22 to -13 kJ mol-1 ) and α-guaiene (-22 to -12 kJ mol-1 ) against three target proteins namely, acetyl cholinesterase (AChE), odorant response gene-1 (ODR1), odorant response gene-3 (ODR3). Most preferable binding mechanism was observed against AChE due to pi-alkyl, pi-sigma, and hydrophobic interactions. Structure nematicidal activity relationship suggested the presence of hydroxy group for nematicidal activity is nonessential, rather highly depends on synergistic composition of sesquiterpene hydrocarbons.
Keywords: acetyl cholinesterase; aromatic oils; molecular modelling; patchouli; root-knot nematode; sesquiterpenes.
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