Chemical Composition, Nematicidal and Fungicidal Activities of the Essential Oil of <i>Mentha spicata</i> Against <i>Meloidogyne incognita</i> and <i>Fusarium oxysporum</i> f.sp. <i>lycopersici</i>

Mentha spicata is commercially grown in India for the production of spearmint oil, used in flavouring and medicinal purposes, but never used to develop crop protection products against pathogens of disease complex as an alternative to synthetic pesticides. This study aimed to determine the quantitative variation in the yield and chemical composition of M. spicata essential oil (MESO) at three main harvesting months and its nematicidal and fungicidal activities against Meloidogyne incognita (root knot nematode) and Fusarium oxysporum f.sp. lycopersici, the two soil-borne pathogens of a disease complex, are responsible for massive economic losses to various agricultural crops. The bioactivity of the major compounds of the oil was further described by in silico molecular docking studies. Analysis of the MESO of its three harvests showed the presence of a high amount of essential oil, which varies from 1.61% to 1.76% and is rich in carvone (79.0 ± 1.36%-83.19 ± 2.16%) and limonene (4.82 ± 0.72%-7.56 ± 0.35%) contents. Chemometric analysis showed that the minor components of MSEO, such as elemene, sabinene, germacrene D and terpinolene, were the main distinctive compounds of the harvests compared to carvone and limonene. The results showed that MSEO and carvone exhibited promising nematicidal activity against M. incognita (LC₅₀ = 212.58 and 117.76 µg/mL) and fungicidal activity against F. oxysporum f.sp. lycopersici, with complete inhibition of its growth at 200 µg/mL. In silico molecular docking studies suggested the strong interaction of germacrene D and carvone with acetylcholinesterase of M. incognita (binding affinity = -6.8 and -5.5 kcal/mol) and cutinase of F. oxysporum f.sp. lycopersici (binding affinity of -8.0 and -6.7 kcal/mol), facilitated by hydrogen bonding and hydrophobic interactions. This study showed the potential of both MSEO and carvone as nematicidal and fungicidal products for controlling the pathogens of disease complex under in vitro conditions, but further investigation under pot and field conditions needs to be explored for their utilisation as crop protection products.