Essential oils (EOs) contain volatile molecules, including secondary metabolites which possess biological activities. EOs  are obtained from plant material such as leaves, buds, flower, fruits, herbs, twigs, bark, wood, roots and seeds (Tzakou et al., 2007; Butnariu and Sarac 2018; Wajs-Bonikowska et al., 2019) and are generally stored in secretory cells, cavities, canals, glandular trichomes or epidermic cells of the plants (Nazzaro et al., 2013). EOs are considered as potential biocontrol product (Raveau et al., 2020). They function as antifungal agents and can block cell communication mechanisms, fungal biofilm formation and mycotoxin production (Nazzaro et al., 2017). Menta spp.  EOs have antioxidant, antifungal, antibiofilm and cytotoxic properties (Stringaro et al., 2018). These antifungal activity of EO from seeds of dill (Anethum graveolens L.) results from its ability to disrupt the permeability barrier of the plasma membrane and from the mitochondrial dysfunction-induced ROS accumulation in Aspergillus flavus (Tian et al., 2012). Citronellal a terpenoid of Cymbopogan nardus EO acts as ergosterol to exhibit its antifungal activity against Penicillium digitatum. Citronellal damages the cell membrane integrity of P. digitatum by down-regulating the ergosterol gene responsible for conversion of lanosterol to ergosterol (Yang et al., 2021).

The high content of eudesmane-type sesquiterpene lactone is a common feature of EOs from Inula helenium, I. racemose and Telekia speciosa (Wajs-Bonikowska et al., 2019). Such composition of essential oils may be correlated with a presence of resin canals in roots of the plants (Wajs-Bonikowska et al., 2019). Eugenol an EO from clove has antibacterial activity and acts on the bacteria Salmonella typhi cell membrane (Devi et al., 2010). The characteristic of EOs and their component is hydrophobicity which enables them to partition with lipid present in the cell membrane of bacteria (Chouhan et al., 2017). The Gram positive bacteria cell wall allows hydrophobic molecules to easily penetrate the cells and act on both the cell wall and within the cytoplasm (Nazzaro et al., 2013). EOs are present as variable mix primarily of terpenoids especially monoterpenes (C10) and sesquiterpene (C15) as well as diterpene may also be present. Thymol, carvacrol, linalool, menthol, geraniol, linalyl acetate, citronellal and piperitone are known terpenoids (oxygen containing hydrocarbon).  The antimicrobial activity of most terpenoid is related to their functional groups, terpenes alone or in combination are effective against microorganisms (Gallucci et al., 2009; Nazzaro et al., 2013; Masyita et al., 2022). Several products from natural sources have been used as plant defense activator. The biological activity of Gaultheria essential oil is due to the composition of oil i.e. it contains methyl salicylate  (MeSA) and several derivatives of MeSA (Liu et al., 2013; Nikolic et al., 2013). Methyl salicylate is a signal for plant SAR (Park et al., 2007). Vergnes et al.(2014) demonstrated that Gaultheria essential oil is a natural source of MeSA that can substitute for synthetic SA analog for application on plants. The bioactive components in EOs such as phenol, coumarins, quinines, flavonoids, tannins and fatty acid provides multifunctional and synergistic antifungal potentialities against plant pathogenic fungi (Rashad et al., 2022). Thyme oil application controlled gray mold and Fusarium wilt inducing SAR (Ben-Jabeur et al., 2015). The peroxidase accumulation was observed as a plant response. Oregano essential oil vapour prevents Plasmopara viticola infectionin grapevines. The transcriptomic data showed treatment triggered the innate immune system with genes involved in salicylic acid, jasmonic acid and ethylene synthesis and signaling activating pathogenesis-related proteins as well as phytoalexin synthesis (Rienth et al., 2019). The antifungal efficiency of EO is mainly due to the triggering of resistance pathway inside the host plant (Rienth et al., 2019). Application of Ocimum gratissimum L. leaf extracts lead to certain defense responses in soybean, sorghum and cucumber, which may result from the combination of a direct antimicrobial activity of EOs and the elicitation of defense responses induced by the extract component (Colpas et al., 2009). The antibacterial ex vivo activity of EOs is related to concentration: doses higher than the minimum bactericidal concentration , on direct application becomes cytotoxic even for the host whereas, doses equal  or sub-Minimum bactericidal concentration used as resistance inducers can exert an inhibitory action on the bacterium without damaging plant (Proto et al., 2022). EOs from red thyme (Thymus vulgaris), summer savory (Satureja hortensis), cinnamon (Cinnamomum zeylanicum) and clove were most phytotoxic caused electrolyte leakage resulting in cell death (Tworkoski 2002). Essential oils from plants may be used as natural product to control plant pathogens.


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Rashad, Y.  M.,   Razik, E. S. A. and Darwish, D. B. 2022 Essential Oil from Lavandula angustifolia Elicits Expression of Three SbWRKY Transcription Factors and Defense-Related Genes against Sorghum   Damping- Off. Scientific Rep. 12: 857

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Wajs-Bonikowska, A., Malarz, J. and Stojakowska, A. 2019 Composition of Essential Oils from Roots and Aerial Parts of Carpesium divaricatum, A Traditional Herbal Medicine and Wild Edible Plants from South-East Asia, Grown in Poland. Molecules 24(23): 4418

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Yang, Q. O., Liu, Y., Oketch, O. R., Zhang, M., Shao, X. and Tao, N. 2021  Citronellal  Exerts its Antifungal Activity by Targeting Ergosterol Biosynthesis in Penicillium digitatum. J. Fungi 7: 432

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