Since the 50’s, the massive and “environmental naïve” use of synthetic chemistry has revolutionized the farming community facing the dramatic growth of demography. However, nowadays, the controversy grows regarding the long-term harmful effects of these products on human health and the environment. In this context, the use of essential oils (EOs) could be an alternative to chemical products and a better understanding of their mode of biological action for new and optimal applications is of importance. Indeed, if the biocidal effects of some EOs or their components have been at least partly elucidated at the molecular level, very little is currently known regarding their mechanism of action as herbicides at the molecular level. Here, we showed that cinnamon and Java citronella essential oils and some of their main components, i.e.,, cinnamaldehyde (CIN), citronellal (CitA), and citronellol (CitO) could act as efficient herbicides when spread on A. thaliana leaves. The individual EO molecules are small amphiphiles, allowing for them to cross the mesh of cell wall and directly interact with the plant plasma membrane (PPM), which is one of the potential cellular targets of EOs. Hence, we investigated and characterized their interaction with biomimetic PPM while using an integrative biophysical approach. If CitO and CitA, maintaining a similar chemical structure, are able to interact with the model membranes without permeabilizing effect, CIN belonging to the phenylpropanoid family, is not. We suggested that different mechanisms of action for the two types of molecules can occur: while the monoterpenes could disturb the lipid organization and/or domain formation, the phenylpropanoid CIN could interact with membrane receptors.
Nowadays, the demand for a reduction of chemical pesticides use is growing. In parallel, the development of alternative methods to protect crops from pathogens and pests is also increasing. Essential oil (EO) properties against plant pathogens are well known, and they are recognized as having an interesting potential as alternative plant protection products. In this study, 90 commercially available essential oils have been screened in vitro for antifungal and antibacterial activity against 10 plant pathogens of agronomical importance. EOs have been tested at 500 and 1000 ppm, and measures have been made at three time points for fungi (24, 72 and 120 h of contact) and every two hours for 12 h for bacteria, using Elisa microplates. Among the EOs tested, the ones from Allium sativum, Corydothymus capitatus, Cinnamomum cassia, Cinnamomum zeylanicum, Cymbopogon citratus, Cymbopogon flexuosus, Eugenia caryophyllus, and Litsea citrata were particularly efficient and showed activity on a large panel of pathogens. Among the pathogens tested, Botrytis cinerea, Fusarium culmorum, and Fusarium graminearum were the most sensitive, while Colletotrichum lindemuthianum and Phytophthora infestans were the less sensitive. Some EOs, such as the ones from A. sativum, C. capitatus, C. cassia, C. zeylanicum, C. citratus, C. flexuosus, E. caryophyllus, and L. citrata, have a generalist effect, and are active on several pathogens (7 to 10). These oils are rich in phenols, phenylpropanoids, organosulfur compounds, and/or aldehydes. Others, such as EOs from Citrus sinensis, Melaleucacajputii, and Vanilla fragrans, seem more specific, and are only active on one to three pathogens. These oils are rich in terpenes and aldehydes.
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