Antifungal Activities and Mode of Action of Cymbopogon citratus, Thymus vulgraris, and Origanum heracleoticum Essential Oil Vapors against Botrytis cinerea and Their Potential Application to Control Postharvest Strawberry Gray Mold

The mechanistic insights of essential oil of Mentha piperita to control Botrytis cinerea and the prospection of lipid nanoparticles to its application

Botrytis cinerea is the phytopathogenic fungus responsible for the gray mold disease that affects crops worldwide. Essential oils (EOs) have emerged as a sustainable tool to reduce the adverse impact of synthetic fungicides. Nevertheless, the scarce information about the physiological mechanism action and the limitations to applying EOs has restricted its use. This study focused on elucidating the physiological action mechanisms and prospection of lipid nanoparticles to apply EO of Mentha piperita. The results showed that the EO of M. piperita at 500, 700, and 900 μL L-1 inhibited the mycelial growth at 100 %. The inhibition of spore germination of B. cinerea reached 31.43 % at 900 μL L-1. The EO of M. piperita decreased the dry weight and increased pH, electrical conductivity, and cellular material absorbing OD260 nm of cultures of B. cinerea. The fluorescence technique revealed that EO reduced hyphae width, mitochondrial activity, and viability, and increased ROS production. The formulation of EO of M. piperita loaded- solid lipid nanoparticles (SLN) at 500, 700, and 900 μL L-1 had particle size ∼ 200 nm, polydispersity index < 0.2, and stability. Also, the thermogravimetric analysis indicated that the EO of M. piperita-loaded SLN has great thermal stability at 50 °C. EO of M. piperita-loaded SLN reduced the mycelial growth of B. cinerea by 70 %, while SLN formulation (without EO) reached 42 % inhibition. These results supported that EO of M. piperita-loaded SLN is a sustainable tool for reducing the disease produced by B. cinerea.

Essential oils on the control of fungi causing postharvest diseases in mango

The use of fungicides in the postharvest treatment of mangoes has been widespread due to the incidence of pathogens, but awareness of the health risks arising from their use has increased, driving the search for more sustainable treatments. This study aimed to evaluate the activity of antifungal treatment of seven essential oils (EO) against four fungi that cause postharvest diseases in mangoes and define the minimum inhibitory concentration (MIC) and chemical composition, analyzed by gas chromatography (GC-MS). The results showed that the EOs of oregano, rosemary pepper, cinnamon bark, and clove inhibited 100% of the mycelial growth of the studied pathogens, with MIC ranging from 250 to 2000 μL.L-1. The main compound found in oregano was carvacrol (69.1%); in rosemary and pepper oil, it was thymol (77.2%); cinnamaldehyde (85.1%) was the main constituent of cinnamon bark, and the eugenol (84.84%) in cloves. When evaluating the antifungal activity of these compounds, thymol and carvacrol showed greater inhibitory activity against fungi. Therefore, this study showed the great potential of oregano, clove, rosemary pepper, and cinnamon bark essential oil as alternative treatments to synthetic fungicides in controlling postharvest diseases in mangoes.

Antifungal activity of volatile organic compounds from essential oils against the postharvest pathogens Botrytis cinerea, Monilinia fructicola, Monilinia fructigena, and Monilinia laxa

Gray mold and brown rot, caused respectively by Botrytis cinerea and Monilinia spp., are fungal diseases responsible for significant losses during the storage of fruit and vegetables. Nowadays, the control of postharvest diseases is shifting towards more sustainable strategies, including the use of plant secondary metabolites. In this study, the antifungal activity of Origanum vulgare, Thymus vulgaris, Thymus serpyllum, Melaleuca alternifolia, Lavandula officinalis, Lavandula hybrida, Citrus bergamia, Rosmarinus officinalis, Cinnamomum zeylanicum essential oils (EOs) in vapor phase was tested in vitro against B. cinerea, Monilinia fructicola, Monilinia fructigena, and Monilinia laxa. For the experiments, a protocol using a volatile organic compounds (VOC) chamber was designed. Results indicate a dose-dependent inhibitory activity of all the tested EOs, with O. vulgare, T. vulgaris, and T. serpyllum being the most active ones, with minimum inhibitory concentrations (MIC) of 22.73, 45.45, and 22.73 µl/L, respectively, against B. cinerea and a range between 5.64 and 22.73 µl/L against the three Monilinia spp. Overall, B. cinerea presented lower sensitivity to vapor-phase EOs than any of the Monilinia strains, except for the C. zeylanicum EO, which consistently showed higher inhibition against B. cinerea. Among the three Monilinia spp., M. fructicola was the least sensitive, while M. fructigena was the most sensitive. The use of VOC chambers proved to be a reliable protocol for the assessment of antimicrobial activities of EOs. These results suggest that the VOC emitted by the tested EOs are effective towards important decay-causing fungi, and that they could be used for the control of gray mold and brown rot in in vivo trials.

Antifungal activity of star anise extract against Penicillium roqueforti and Aspergillus niger for bread shelf life

Because star anise is underutilized in the baking sector and the antifungal targets are unclear, this study aimed to investigate the antifungal effect and mechanism of star anise extract (SAE) on spoilage fungi in bread. SAE was prepared by ethanol extraction and 31 substances were identified by GC-MS, among which trans-anethole (62.62%), estragole (7.82%) and linalool (4.66%) were the major components. The antifungal activity of SAE and the three main components against Penicillium roqueforti and Aspergillus niger were determined by using the Oxford cup method and the sesqui-dilution method. The inhibition zones were 9.88 mm and 15.09 mm, while the minimum inhibitory concentrations were 125.00 μL/mL and 31.25 μL/mL. Trans-anethole and estragole both showed antifungal activity against Penicillium roqueforti and Aspergillus niger, while linalool only showed antifungal activity against Aspergillus niger. Propidium iodide and fluorescein diacetate staining analysis, leakage of cellular components (nucleic acids and proteins) and rise in ergosterol content indicated that SAE disrupted the integrity and permeability of the cell membrane. Malondialdehyde was increased after SAE treatment, indicating that SAE caused lipid peroxidation in the cell membrane, further confirming that it disrupted the cell membrane. At the same time, SAE interacted with membrane proteins and altered their conformation, resulting in cell membrane dysfunction. Finally, the shelf life test showed that SAE extended the shelf life of the bread by up to 6 days. In general, this study highlights the antifungal effect of SAE against Penicillium roqueforti and Aspergillus niger, which indicated that SAE can be used as an antifungal agent to extend the shelf life of bread.

Protection of postharvest grains from fungal spoilage by biogenic volatiles

Fungal spoilage of postharvest grains poses serious problems with respect to food safety, human health, and the economic value of grains. The protection of cereal grains from deleterious fungi is a critical aim in postharvest grain management. Considering the bulk volume of grain piles in warehouses or bins and food safety, fumigation with natural gaseous fungicides is a promising strategy to control fungal contamination on postharvest grains. Increasing research has focused on the antifungal properties of biogenic volatiles. This review summarizes the literature related to the effects of biogenic volatiles from microbes and plants on spoilage fungi on postharvest grains and highlights the underlying antifungal mechanisms. Key areas for additional research on fumigation with biogenic volatiles in postharvest grains are noted. The research described in this review supports the protective effects of biogenic volatiles against grain spoilage by fungi, providing a basis for their expanded application in the management of postharvest grains.

Production of New Biopesticides from Cymbopogon citratus for the Control of Coffee Rust (Hemileia vastatrix) under Laboratory and Field Conditions

One of the diseases with the greatest economic impact on coffee cultivation worldwide and particularly in Peru is coffee rust (Hemileia vastatrix). The search for sustainable control methods as disease management strategies in coffee cultivation is necessary. The objective of this research was to determine the effectiveness of five biopesticides based on lemon verbena (Cymbopogon citratus) for the control of rust applied in laboratory and field conditions to allow the recovery of coffee (Coffea arabica L. var. typica) in La Convención, Cusco, Peru. Five biopesticides (oil, macerate, infusion, hydrolate and Biol) and four concentrations (0, 15, 20 and 25%) were evaluated. The biopesticides were evaluated under laboratory conditions (light and dark) at different concentrations. The design used was completely randomized in a factorial scheme. The biopesticides were incorporated into the culture medium and inoculated with 400 uredospores of rust, and the germination percentage was evaluated. Under field conditions, the biopesticides at the same concentrations were evaluated for 4 weeks after application. Under these field conditions, the incidence, severity and area under the disease progress curve (AUDPC) of selected plants with a natural degree of infection were evaluated. In the laboratory, the results showed that all biopesticides were effective in reducing the germination of rust uredospores to values <1% of germination in relation to the control, which showed values of 61% and 75% in the light and dark, respectively, independent of the concentration used, with no significant differences between them. In the field, 25% oil promoted the best response with values <1% and 0% incidence and severity, respectively, in the first two weeks after application. The AUDPC for this same treatment showed values of 7 in relation to 1595 of the control. Cymbopogon citratus oil is an excellent biopesticide that can be used to control coffee rust.

Origanum heracleoticum Essential Oils: Chemical Composition, Phytotoxic and Alpha-Amylase Inhibitory Activities

Many studies have demonstrated the herbicidal effects of several essential oils and their possible use as substitutes for chemical herbicides. Several enzymes play a very significant role in seed germination: among these, α-amylase could be involved in essential oil phytotoxic processes. The aims of this study were to compare the chemical composition of the essential oils of two ecotypes of O. heracleoticum growing in Cilento (Southern Italy) and to study their possible use as natural herbicide using Raphanus sativus, Sinapis arvensis and Lolium multiflorum seeds. Moreover, a possible inhibitory activity on the α-amylase enzyme extracted from germinating seeds was evaluated as a possible mechanism of action. Both oils, characterized by GC-MS, belonged to a carvacrol chemotype. The alpha-amylase activity was determined using DNSA (dinitrosalicylic acid) assay quantifying the reducing sugar produced. Furthermore, the essential oils demonstrated phytotoxicity at the highest dose tested, and an inhibitory effect on α-amylase, probably correlated with the phytotoxic effects, was registered. The oils showed interesting phytotoxic and alpha-amylase inhibitory activities, which deserve to be further investigated.

Inhibitory effect of (E)-2-heptenal on Aspergillus flavus growth revealed by metabolomics and biochemical analyses

The prevention of fungal proliferation in postharvest grains is critical for maintaining grain quality and reducing mycotoxin contamination. Fumigation with natural gaseous fungicides is a promising and sustainable approach to protect grains from fungal spoilage. In this study, the antifungal activities of (E)-2-alkenals (C₅-C₁₀) on Aspergillus flavus were tested in the vapor phase, and (E)-2-heptenal showed the highest antifungal activity against A. flavus. (E)-2-Heptenal completely inhibited A. flavus growth at 0.0125 µL/mL and 0.2 µL/mL in the vapor phase and liquid contact, respectively. (E)-2-Heptenal can disrupt the plasma membrane integrity of A. flavus via leakage of intracellular electrolytes. Scanning electron microscopy indicated that the mycelial morphology of A. flavus was remarkably affected by (E)-2-heptenal. Metabolomic analyses indicated that 49 metabolites were significantly differentially expressed in A. flavus mycelia exposed to 0.2 µL/mL (E)-2-heptenal; these metabolites were mainly involved in galactose metabolism, starch and sucrose metabolism, the phosphotransferase system, and ATP-binding cassette transporters. ATP production was reduced in (E)-2-heptenal-treated A. flavus, and Janus Green B staining showed reduced cytochrome c oxidase activity. (E)-2-Heptenal treatment induced oxidative stress in A. flavus mycelia with an accumulation of superoxide anions and hydrogen peroxide and increased activities of superoxide dismutase and catalase. Simulated storage experiments showed that fumigation with 400 µL/L of (E)-2-heptenal vapor could completely inhibit A. flavus growth in wheat grains with 20% moisture; this demonstrates its potential use in preventing grain spoilage. This study provides valuable insights into understanding the antifungal effects of (E)-2-heptenal on A. flavus. KEY POINTS : • (E)-2-Heptenal vapor showed the highest antifungal activity against A. flavus among (C₅-C₁₀) (E)-2-alkenals. • The antifungal effects of (E)-2-heptenal against A. flavus were determined. • The antifungal actions of (E)-2-heptenal on A. flavus were revealed by metabolomics and biochemical analyses.

Antifungal Activities of Essential Oils in Vapor Phase against Botrytis cinerea and Their Potential to Control Postharvest Strawberry Gray Mold

Essential oils (EOs) from aromatic plants seem to have the potential to control several fungal pathogens and food contaminants. Botrytis cinerea is the main strawberry fruit contaminant causing high losses during storage. Here, thirteen EOs applied in the vapor phase were evaluated for their potential to inhibit the growth of three different strains of B. cinerea isolated from strawberry fruits. Eight EOs (lemongrass, litsea, lavender, peppermint, mint, petitgrain, sage, and thyme) were able to completely inhibit the growth of B. cinerea for 7 days when applied at a concentration of 625 μL·L⁻¹. Four EOs with the lowest minimal inhibition concentrations (thyme, peppermint, lemongrass, and litsea) have been tested on strawberry fruits intentionally inoculated by B. cinerea. All four EOs showed high inhibition at a concentration of 250 or 500 μL·L⁻¹, but only peppermint EO was able to completely inhibit B. cinerea lesion development at a concentration of 125 μL·L⁻¹. The sensory evaluation of strawberries treated by EOs at a concentration 125 μL·L⁻¹ resulted in a statistically significant decrease in taste, aftertaste, aroma, and overall quality. Lemongrass and litsea EOs scored better than thyme and peppermint ones, thus forming two viable methods for B. cinerea suppression and the extension of packed strawberries’ shelf life.