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.
References:
Ben-Jabeur, M., Ghabri, E., Myriam, M. and Hamada, W. 2015 Thyme Essential Oil as a Defense Inducer of Tomato against Gray Mold and Fusarium Wilt. Plant Physiol. Biochem. 94: 35 – 40
doi.org/10.1016/j.plaphy.2015.05.006
Butnariu, M. and Sarac, I. 2018 Essential Oils from Plants. J. Biotechnol. Biomed. Sci. 1(4): 35 – 43
doi: 10.14302/issn.2576-6694.jbbs-18-2489
Chouhan, S., Sharma, K. and Guleria, S. 2017 Antimicrobial Activity of Some Essential Oils- Present Status and Future Perspectives. Med (Basel) 4(3): 58
doi: 10.3390/medicines4030058
Colpas, F. T., Schwan-Estrada, K. R. F., Stangarlin, J. R., Ferrarese, M. L., Scapim, C. A. and Bonaldo, S. M. 2009 Induction of Plant Defense Responses by Ocimum gratissimum L. (Lamiaceae) Leaf Extracts. Summa Phytopathologica 35(3): 191 – 195
Devi, K. P., Nisha, S. A., Sakthivel, R. and Pandian, S. K. 2010 Eugenol (An Essential Oil of Clove) Acts as an Antibacterial Agent against Salmonella typhi by Disrupting the Cellular Membrane. J. Ethnopharmacol. 130(1): 107 – 115
doi: 10.1016/j.jep.2010.04.025
Gallucci, M. N., Oliva, M., Casero, C., Dambolena, J., Luna, A., Zygadlo, J. and Demo, M. 2009 Antimicrobial Combined Action of Terpenes against the Food-borne Microorganisms Escherichia coli, Staphylococcus aureus and Bacillus cereus. Flavour and Fragrance Journal 24(6): 348 – 354
doi.org/10.1002/ffj.1948
Liu, W-R., Qiao, W-L., Liu, Z-Z., Wang, X-H., Jiang, R., Li, S-Y., Shi, R-B. and She, G-M. 2013 Gaultheria: Phytochemical and Pharmacological Characteristics. Molecules 18(10): 12071 – 12108
doi.org/10.3390/molecules181012071
Masyita, A., Sari, R. M, Astuti, A. D., Yasir, B., Rumata, N. R., Emran, T. B., Nainu, F. and Simal-Gandara, J. 2022 Terpenes and Terpenoids as Main Bioactive Compounds of Essential Oils their Roles in Human Health and Potential Application as Natural Food Preservatives. Food Chem. X. 13: 100217
doi: 10.1016/j.fochx.2022.100217
Nazzaro, F., Fratianni, F., Coppola, R. and De Feo, V. 2017 Essential Oils and Antifungal Activity. Pharmaceuticals (Basel) 10(4): 86
doi: 10.3390/ph10040086
Nazzaro, F., Fratianni, F., De Martino, L., Coppola, R. and De Feo, V. 2013 Effect of Essential Oils on Pathogenic Bacteria. Pharma. (Basel) 6(12): 1451 – 1474
doi: 10.3390/ph6121451
Nikolic, M., Markovic, T., Mojovic, M., Pejin, B., Savic, A., Peric, T., Markovic, D., Stevic, T. and Sokovic, M. 2013 Chemical Composition and Biological Activity of Gaultheria procumbens L. Essential Oil. Industrial Crops and Products 49: 561 – 567
doi.org/10.1016/j.indcrop.2013.06.002
Park, S-W., Kaimoyo, E., Kumar, D., Mosher, S. and Klessig, D. F. 2007 Methyl Salicylate is a Critical Mobile Signal for Plant Systemic Acquired Resistance. Sci. 318(5847): 113 – 116
doi: 10.1126/science.1147113
Proto, M. R., Biondi, E., Baldo, D., Levoni, M., Filippini, G., Modesto, M., Di Vito, M., Bugli, F., Ratti, C., Minardi, P. and Mattarelli, P. 2022 Essential Oils and Hydrolates: Potential Tools for Defense against Bacterial Plant Pathogens. Microorganisms 10: 702
doi.org/10.3390/microorganisms10040702
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
doi.org/10.1038/s41598-022-04903-x
Raveau, R., Fontaine, J. and Sahraoui, A. L-H. 2020 Essential Oils as Potential Alternative Biocontrol Products against Plant Pathogens and Weeds: A Review. Foods 9(3): 365
doi: 10.3390/foods9030365
Rienth, M., Crovadore, J., Ghaffari, S. and Lefort, F. 2019 Oregano Essential Oil Vapour Prevents Plasmopara viticola Infection in Grapevine (Vitis vinifera) and Primes Plant Immunity Mechanisms. PLoS ONE 14(9): e0222854
doi.org/10.1371/journal.pone.0222854
Stringaro, A., Colone, M and Angiolella, L. 2018 Antioxidant Antifungal Antibiofilm and Cytotoxic Activities of Mentha spp. Essential Oils. Medicines (Basel) 5(4): 112
doi: 10.3390/medicines5040112
Tian, J., Ban, X., Zeng, H., He, J., Chen, Y. and Wang, Y. 2012 The Mechanism of Antifungal Action of Essential Oil from Dill (Anethum graveolens L.) on Aspergillus flavus. PLoS 7(1): e30147
doi: 10.1371/journal.pone.0030147
Tworkoski, T. 2002 Herbicide Effects of Essential Oils. Weed Sci. 50(4): 425 – 431
doi: 10.1614/0043-1745(2002)050[0425:HEOEO]2.0.CO;2
Tzakou, O., Loukis, A. and Said, A. 2007 Essential Oil from the Flower and Leaves of Cassia fistula L. J. Essential Oil Res. 19(4): 360 – 361
doi: 10.1080/10412905.2007.9699305
Vergnes, S., Ladouce, N., Fournier, S., Ferhout, H., Attia, F. and Dumas, B. 2014 Foliar Treatments with Gaultheria procumbens Essential Oil Induce Defense Responses and Resistance against a Fungal Pathogen in Arabidopsis. Front. Plant Sci. 5: 477
doi: 10.3389/fpls. 2014.00477
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
doi: 10.3390/molecules24234418
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
doi.org/10.3390/jof7060432
BIOLOGICAL PROCESSES- A NATURE'S GIFT 