Thyme and Savory Essential Oil Efficacy and Induction of Resistance against Botrytis cinerea through Priming of Defense Responses in Apple

Challenges and Opportunities Arising from Host-Botrytis cinerea Interactions to Outline Novel and Sustainable Control Strategies: The Key Role of RNA Interference

The necrotrophic plant pathogenic fungus Botrytis cinerea (Pers., 1794), the causative agent of gray mold disease, causes significant losses in agricultural production. Control of this fungal pathogen is quite difficult due to its wide host range and environmental persistence. Currently, the management of the disease is still mainly based on chemicals, which can have harmful effects not only on the environment and on human health but also because they favor the development of strains resistant to fungicides. The flexibility and plasticity of B. cinerea in challenging plant defense mechanisms and its ability to evolve strategies to escape chemicals require the development of new control strategies for successful disease management. In this review, some aspects of the host-pathogen interactions from which novel and sustainable control strategies could be developed (e.g., signaling pathways, molecules involved in plant immune mechanisms, hormones, post-transcriptional gene silencing) were analyzed. New biotechnological tools based on the use of RNA interference (RNAi) are emerging in the crop protection scenario as versatile, sustainable, effective, and environmentally friendly alternatives to the use of chemicals. RNAi-based fungicides are expected to be approved soon, although they will face several challenges before reaching the market.

Impacts of a Commercially Available Horticultural Oil Biopesticide (EF-400) on the Tomato-Phytophthora infestans Pathosystem

Biopesticide fungicides are naturally derived compounds that offer protection from plant diseases through various modes of action, including antimicrobial activity and upregulation of defense responses in host plants. These plant protectants provide a sustainable and safe alternative to conventional pesticides in integrated disease management programs and are especially salient in the management of high-risk and economically important diseases such as late blight of tomato and potato, for which host resistance options are limited. In this study, a commercially available biopesticide, EF400 comprised of clove (8.2%), rosemary (8.1%), and peppermint oils (6.7%) (Anjon AG, Corcoran, CA), was investigated for its effects on the Phytophthora infestans-tomato pathosystem. Specifically, we evaluated the impact of EF400 on P. infestans growth in culture, disease symptoms in planta, and activation of host defenses through monitoring transcript accumulation of defense-related genes. The application timing and use rate of EF400 were further investigated for managing tomato late blight. EF400 delayed the onset of tomato late blight symptoms, although not as effectively as the copper hydroxide fungicide Champ WG (Nufarm Americas Inc., Alsip, IL). Pathogen mycelial growth and sporangial quantity on late blight-susceptible tomato leaves were significantly reduced with EF400. The biopesticide also had an enhancing or suppressing effect on the transcript accumulation of three defense-related genes: Pin2, PR1a, and PR1b. Our work in exploring a commercially available horticultural oil biopesticide meaningfully contributed to the essential knowledge base for optimizing recommendations for the management of tomato late blight.

Composite Coating of Oleaster Gum Containing Cuminal Keeps Postharvest Quality of Cherry Tomatoes by Reducing Respiration and Potentiating Antioxidant System

Exploring the green and affordable protection of perishable cherry tomato fruits during storage, herein, the protective efficacy, and its underpinning mechanisms, of a coating of oleaster gum, alone or incorporated with cuminal, on cherry tomatoes stored at ambient temperature was investigated. The composite coating of oleaster gum with 0.1% cuminal reduced the decay, respiration rate, weight loss, and softening of the fruits and decelerated the decreases in their total soluble solid, titratable acidity, and soluble protein levels, and therefore maintained their marketability. Furthermore, it reduced the accumulation of O2·- and H2O2 in the fruits and mitigated cell membrane lipid oxidation and permeabilization, thereby retarding their senescence. Instrumentally, it elevated the activities of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase and the levels of ascorbic acid and glutathione. This potentiation of the fruits' antioxidant system makes this composite coating a promising approach to keeping the postharvest quality of perishable fruits.

Efficacy of Essential Oil Vapours in Reducing Postharvest Rots and Effect on the Fruit Mycobiome of Nectarines

Nectarines can be affected by many diseases, resulting in significant production losses. Natural products, such as essential oils (EOs), are promising alternatives to pesticides to control storage rots. This work aimed to test the efficacy of biofumigation with EOs in the control of nectarine postharvest diseases while also evaluating the effect on the quality parameters (firmness, total soluble solids, and titratable acidity) and on the fruit fungal microbiome. Basil, fennel, lemon, oregano, and thyme EOs were first tested in vitro at 0.1, 0.5, and 1.0% concentrations to evaluate their inhibition activity against Monilinia fructicola. Subsequently, an in vivo screening trial was performed by treating nectarines inoculated with M. fructicola, with the five EOs at 2.0% concentration by biofumigation, performed using slow-release diffusers placed inside the storage cabinets. Fennel, lemon, and basil EOs were the most effective after storage and were selected to be tested in efficacy trials using naturally infected nectarines. After 28 days of storage, all treatments showed a significant rot reduction compared to the untreated control. Additionally, no evident phytotoxic effects were observed on the treated fruits. EO vapors did not affect the overall quality of the fruits but showed a positive effect in reducing firmness loss. Metabarcoding analysis showed a significant impact of tissue, treatment, and sampling time on the fruit microbiome composition. Treatments were able to reduce the abundance of Monilinia spp., but basil EO favored a significant increase in Penicillium spp. Moreover, the abundance of other fungal genera was found to be modified.

Antifungal Activities of L-Methionine and L-Arginine Treatment In Vitro and In Vivo against Botrytis cinerea

Gray mold caused by Botrytis cinerea is a common postharvest fungal disease in fruit and vegetables. The prevention and treatment of postharvest gray mold has been one of the hot research issues addressed by researchers. This study aimed to investigate the effect of L-methionine and L-arginine on Botrytis cinerea in vitro and on cherry tomato fruit. The results of the in vitro experiment showed that L-methionine and L-arginine had significant inhibitory effects on the mycelial growth and spore germination of Botrytis cinerea, and the inhibitory effects were enhanced with increasing L-methionine or L-arginine concentration. In addition, L-methionine and L-arginine treatment increased the leakage of Botrytis cinerea electrolytes, proteins and nucleic acids. The experiment involving propidium iodide staining and malondialdehyde content assay also confirmed that L-methionine and L-arginine treatment could lead to cell membrane rupture and lipid peroxidation. The results of scanning electron microscopy further verified that the morphology of hyphae was damaged, deformed, dented and wrinkled after treatment with L-methionine or L-arginine. Fruit inoculation experiments displayed that L-methionine and L-arginine treatments significantly inhibited the occurrence and development of gray mold in postharvest cherry tomato. Therefore, treatment with L-methionine or L-arginine might be an effective means to control postharvest gray mold in fruit and vegetables.

Tetraclinis articulata essential oil emulsion use as alternative to chemical fungicide to control tomato grey mould disease

Tetraclinis articulata essential oil proved to be effective in controlling tomato grey mould, so we would investigate its effect on some tomato defense mechanisms. The pretreatment of Botrytis cinerea infected tomato plants with TAEO emulsion enhanced the activity of antioxidant enzymes activity SOD, CAT, APX, and GPX, and total polyphenols content and it decreased IC50 of free radical-scavenging activity and H2O2 content. Results showed amelioration in antioxidant status in TAEO emulsion treated and B. cinerea infected plants indicating that treatment decreased infection in tomato plants. The qRT-PCR analysis of defense genes expression Chitinase SlChi, transcription factors SlWRKY and SlAP2/ERF, Lipoxygenase SlLOX, and Thioredoxin SlTRX showed that they were up-regulated as early as 12 hpi sustained with a second increase at 48 hpi in TAEO emulsion pretreated and infected plants. These results suggest the potential use of TAEO emulsion as natural product to induce tomato antioxidant status and activate defense genes.

Defense Mechanisms Induced by Celery Seed Essential Oil against Powdery Mildew Incited by Podosphaera fusca in Cucumber

This study aimed to evaluate the effectiveness of essential oil extracted from celery (Apium graveolens) seeds (CSEO) for the control of powdery mildew of cucumber (Cucumis sativus) incited by Podosphaera fusca and to investigate the metabolic and genetic defense mechanisms triggered by the treatment with this essential oil in cucumber seedlings. The main compounds in the CSEO as determined by gas chromatography-mass spectrometry (GC-MS) analysis were d-limonene, 3-butyl phthalide, β-selinene, and mandelic acid. The treatment with CSEO led to an increase in the content of both chlorophyll and phenolic/flavonoid compounds in cucumber leaves. In greenhouse tests, the application of CSEO reduced by 60% the disease severity on leaves of cucumber plants and stimulated the activity of defense-related enzymes such as β-1,3-glucanase, chitinase, phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase. Moreover, treatment with CSEO induced overexpression of β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase genes. A highly significant correlation was found between the β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase enzymatic activities and the relative expression of the corresponding encoding genes in both inoculated and non-inoculated cucumber seedlings treated with the essential oil. Overall, this study showed that CSEO is a promising eco-friendly candidate fungicide that can be exploited to control cucumber powdery mildew.

Satureja montana and Mentha pulegium essential oils' antimicrobial properties against Pseudomonas syringae pv. actinidiae and elicitor potential through the modulation of kiwifruit hormonal defenses

Pseudomonas syringae pv. actinidiae (Psa) is responsible for the kiwifruit bacterial canker, the most severe disease of Actinidia spp. The use in agriculture of antibiotics and cooper-based compounds is increasingly being restricted, demanding for new sustainable alternatives to current agrochemicals. We aimed to characterize the anti-Psa potential of essential oils (EOs) of Mentha pulegium and Satureja montana and investigate if they elicit the plant-host hormonal defenses. The EOs were characterized through gas-chromatography with flame ionization detector (GC-FID) and mass spectrometry (MS). Pulegone (78.6%) and carvacrol (43.5%) were the major constituents of M. pulegium and S. montana EO, respectively. Only S. montana EO showed relevant anti-Psa activity in vitro. To evaluate if the EOs also elicited host defenses, in vitro shoots were treated with 2 mg shoot-1 of EO-solution and subsequently inoculated with Psa three days later. Shoots were analyzed 10 min, three days (and 10 min after Psa-inoculation), four and ten days after EO application. The up/down regulation of RNA-transcripts for hormone biosynthesis, Psa biofilm production and virulence genes were quantified by real-time quantitative PCR (RT-qPCR). Phytohormones were quantified by High-Performance Liquid Chromatography (HPLC). S. montana EO showed the most promising results as a defense elicitor, increasing 6-benzylaminopurine (BAP) by 131.07% and reducing indole-3-acetic acid (IAA) levels by 49.19%. Decreases of salicylic acid (SA), and gibberellic acid 3 (GA3) levels by 32.55% and 33.09% respectively and an increase of abscisic acid (ABA) by 85.03%, in M. pulegium EO-treated shoots, revealed some protective post-infection effect. This is the most comprehensive research on the Psa's impact on phytohormones. It also unveils the protective influence of prior EO exposure, clarifying the plant hormonal response to subsequent infections. The results reinforce the hypothesis that carvacrol-rich S. montana EO can be a suitable disease control agent against Psa infection. Its dual action against pathogens and elicitation of host plant defenses make it a promising candidate for incorporation into environmentally friendly disease management approaches. Nonetheless, to fully leverage these promising results, further research is imperative to elucidate the EO mode of action and evaluate the long-term efficacy of this approach.

Biotechnological and Biocontrol Approaches for Mitigating Postharvest Diseases Caused by Fungal Pathogens and Their Mycotoxins in Fruits: A Review

Postharvest diseases caused by fungal pathogens are significant contributors to the postharvest losses of fruits. Moreover, some fungal pathogens produce mycotoxins, which further compromise the safety and quality of fruits. In this review, the potential of biotechnological and biocontrol approaches for mitigating postharvest diseases and mycotoxins in fruits is explored. The review begins by discussing the impact of postharvest diseases on fruit quality and postharvest losses. Next, it provides an overview of major postharvest diseases caused by fungal pathogens. Subsequently, it delves into the role of biotechnological approaches in controlling these diseases. The review also explored the application of biocontrol agents, such as antagonistic yeasts, bacteria, and fungi, which can suppress pathogen growth. Furthermore, future trends and challenges in these two approaches are discussed in detail. Overall, this review can provide insights into promising biotechnological and biocontrol strategies for managing postharvest diseases and mycotoxins in fruits.

Seed priming with essential oils for sustainable wheat agriculture in semi-arid region

Drought is one of the major constraints to global crop production. A number of sustainable systems have focused on the development of environmentally friendly innovative biotechnological interventions to prevent yield losses. The use of essential oils as a seed priming agent can make an important contribution as a natural stimulant in increasing drought stress tolerance. This study focuses on the effects of seeds coated with different doses (D0 (0%), D1 (0.01%), D2 (0.05%), D3 (0.10%) and D4 (0.25%)) of sage, rosemary and lavender essential oils on wheat germination, seedling establishment and yield parameters. Turkey’s local wheat genotype Köse was used as plant material. The impact of the seed priming on germination rate, coleoptile length, shoot length, root length, shoot fresh and dry weight, root fresh and dry weight, relative water content (RWC), proline, and chlorophyll contents was assessed in laboratory experiments. In addition, the effect of essential oil types on yield parameters and agronomic components (plant height, spike height, number of grains per spike, grain yield per spike, grain yield per unit area, thousand-grain weight) was evaluated in a field experiment during the 2019–2020 crop seasons in a semi-arid climate. According to laboratory results, the highest germination rate among all treatment doses was determined in the D2 treatment (rosemary 93.30%, sage 94.00% and lavender 92.50%), while the lowest germination rates for all essential oil types were determined in the D4 treatment (rosemary 41.70%, sage 40.90% and lavender 40.90%). Increasing treatment doses showed a similar suppressive effect on the other parameters. In the field experiment, the highest grain yield (256.52 kg/da) and thousand-grain weight (43.30 g) were determined in the rosemary treatment. However, the priming treatment has an insignificant on the number of grains per spike and the spike length. The light of these results, the effects of essential oil types and doses on yield parameters were discussed. The findings highlight the importance of using essential oils in seed priming methods for sustainable agricultural practices.

Vapours from plant essential oils to manage tomato grey mould caused by Botrytis cinerea

Tomato grey mould has been a great concern during tomato production. The in vitro antifungal activity of vapours emitted from four plant essential oils (EOs) (cinnamon oil, fennel oil, origanum oil, and thyme oil) were evaluated during in vitro conidial germination and mycelial growth of Botrytis cinerea, the causal agent of grey mould. Cinnamon oil vapour was the most effective in suppressing conidial germination, whereas the four EOs showed similar activities regarding inhibiting mycelial growth in dose-dependent manners. The in planta protection effect of the four EO vapours was also investigated by measuring necrotic lesions on tomato leaves inoculated by B. cinerea. Grey mould lesions on the inoculated leaves were reduced by the vapours from cinnamon oil, origanum oil and thyme oil at different levels, but fennel oil did not limit the spread of the necrotic lesions. Decreases in cuticle defect, lipid peroxidation, and hydrogen peroxide production in the B. cinerea-inoculated leaves were correlated with reduced lesions by the cinnamon oil vapours. The reduced lesions by the cinnamon oil vapour were well matched with arrested fungal proliferation on the inoculated leaves. The cinnamon oil vapour regulated tomato defence-related gene expression in the leaves with or without fungal inoculation. These results suggest that the plant essential oil vapours, notably cinnamon oil vapour, can provide eco-friendly alternatives to manage grey mould during tomato production.

A Review of Regulatory Standards and Advances in Essential Oils as Antimicrobials in Foods

As essential oils (EOs) possess GRAS status, there is a strong interest in their application to food preservation. Trends in the food industry suggest consumers are drawn to environmentally friendly alternatives and less synthetic chemical preservatives. Although the use of EOs has increased over the years, adverse effects have limited their use. This review aims to address the regulatory standards for EO usage in food, techniques for delivery of EOs, essential oils commonly used to control pathogens and molds, and advances with new active compounds that overcome sensory effects for meat products, fresh fruits and vegetables, fruit and vegetable juices, seafood, dairy products, and other products. This review will show adverse sensory effects can be overcome in various products by the use of edible coatings containing encapsulated EOs to facilitate the controlled release of EOs. Depending on the method of cooking, the food product has been shown to mask flavors associated with EOs. In addition, using active packaging materials can decrease the diffusion rate of the EOs, thus controlling undesirable flavor characteristics while still preserving or prolonging the shelf life of food. The use of encapsulation in packaging film can control the release of volatile or active ingredients. Further, use of EOs in the vapor phase allows for contact indirectly, and use of nanoemulsion, coating, and film wrap allows for the controlled release of the EOs. Research has also shown that combining EOs can prevent adverse sensory effects. Essential oils continue to serve as a very beneficial way of controlling undesirable microorganisms in food systems.

Essential Oils Reduce Grey Mould Rot of Apples and Modify the Fruit Microbiome during Postharvest Storage

Botrytis cinerea is the causal agent of grey mould rot of apples. The efficacy of biofumigation with thyme (Thymus vulgaris), savoury (Satureja montana), and basil (Ocimum basilicum) essential oils (EOs) at 1%, 0.5%, and 0.1% concentrations were tested against B. cinerea. In vitro, the results showed 100% growth inhibition at 1% concentration for all oils. Subsequent biofumigation experiments on apples of cultivar 'Opal' with 1% EOs showed that, after 60 d storage, thyme and savoury EOs significantly reduced grey mould rot incidence (average incidence 2% for both treatments) compared to the control (7%). Analyses of quality indicated slightly higher fruit firmness for 1% thyme at 30 d and slightly higher titratable acidity for 1% thyme and savoury at 60 d. Sampling of the atmosphere inside the cabinets was performed to characterize and quantify the volatile components of EOs released through biofumigation. Though thymol and p-cymene were the main components of thyme EO, the antimicrobial activity was mainly due to the presence of thymol and, to a lower extent, of carvacrol. In savoury EO, carvacrol and p-cymene were the main components, whereas in basil EO, linalool and estragole were mainly present. Metabarcoding analyses showed that the epiphytic microbiome had higher richness and evenness compared to their endophytic counterpart. By the end of shelf-life, treatments with thyme EO reduced B. cinerea abundance compared to the inoculated control for both endophytes (from 36.5% to 1.5%) and epiphytes (from 7.0% to 0.7%), while favouring a significant increase in Penicillium species both in endophytes (from 0.2% to 21.5%) and epiphytes (from 0.5% to 18.6%). Results indicate that thyme EO (1%) and savoury EO (1%) are equally effective in hampering grey mould rot development in vivo.

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.

Direct and Indirect Effects of Essential Oils for Sustainable Crop Protection

Plant essential oils (EOs) are gaining interest as biopesticides for crop protection. EOs have been recognized as important ingredients of plant protection products including insecticidal, acaricidal, fungicidal, and nematicidal agents. Considering the growing importance of EOs as active ingredients, the domestication and cultivation of Medicinal and Aromatic Plants (MAPs) to produce chemically stable EOs contributes to species conservation, provides the sustainability of production, and decreases the variations in the active ingredients. In addition to these direct effects on plant pests and diseases, EOs can induce plant defenses (priming effects) resulting in better protection. This aspect is of relevance considering that the EU framework aims to achieve the sustainable use of new plant protection products (PPPs), and since 2020, the use of contaminant PPPs has been prohibited. In this paper, we review the most updated information on the direct plant protection effects of EOs, focusing on their modes of action against insects, fungi, and nematodes, as well as the information available on EOs with plant defense priming effects.

"An apple a day keeps the doctor away": The potentials of apple bioactive constituents for chronic disease prevention

Apples are rich sources of selected micronutrients (e.g., iron, zinc, vitamins C and E) and polyphenols (e.g., procyanidins, phloridzin, 5′‐caffeoylquinic acid) that can help in mitigating micronutrient deficiencies (MNDs) and chronic diseases. This review provides an up‐to‐date overview of the significant bioactive compounds in apples together with their reported pharmacological actions against chronic diseases such as diabetes, cancer, and cardiovascular diseases. For consumers to fully gain these health benefits, it is important to ensure an all‐year‐round supply of highly nutritious and good‐quality apples. Therefore, after harvest, the physicochemical and nutritional quality attributes of apples are maintained by applying various postharvest treatments and hurdle techniques. The impact of these postharvest practices on the safety of apples during storage is also highlighted. This review emphasizes that advancements in postharvest management strategies that extend the storage life of apples should be optimized to better preserve the bioactive components crucial to daily dietary needs and this can help improve the overall health of consumers.

Essential Oils and Hydrolates: Potential Tools for Defense against Bacterial Plant Pathogens

The essential oils (EOs) of Origanum compactum and Satureja montana chemotyped (CT) at carvacrol, two Thymus vulgaris CT at thujanol and thymol, and Hydrolates (Hys) of S. montana and Citrus aurantium var. amara were chosen for studying their bactericidal efficacy against few phytobacterial pathogens. The Minimal Inhibitory Concentration (MIC) and Bactericidal Concentration (MBC) were found by microdilution assay. The essential oils of O. compactum (MBC 0.06% v/v), T. vulgaris CT thymol (MBC 0.06% v/v), and Hy of C. aurantium (MBC 6.25% v/v) resulted in being the most effective against Erwinia amylovora; thus, they were used as starting concentrations for ex vivo assays. Despite the great in vitro effectiveness, the disease incidence and the population dynamic ex vivo assays showed no significant results. On the other hand, EO of O. compactum and Hy of C. aurantium (at 0.03% and 4.5% v/v, respectively) showed resistance induction in tomato plants against Xanthomonas vesicatoria infections; both treatments resulted in approximately 50% protection. In conclusion, EOs and Hys could be promising tools for agricultural defense, but further studies will be necessary to stabilize the EOs emulsions, while Hys application could be an effective method to prevent bacterial diseases when used as resistance inducer by pre-transplantation treatment at roots.

Biocontrol Potential of Essential Oils in Organic Horticulture Systems: From Farm to Fork

In recent decades, increasing attention has been paid to food safety and organic horticulture. Thus, people are looking for natural products to manage plant diseases, pests, and weeds. Essential oils (EOs) or EO-based products are potentially promising candidates for biocontrol agents due to their safe, bioactive, biodegradable, ecologically, and economically viable properties. Born of necessity or commercial interest to satisfy market demand for natural products, this emerging technology is highly anticipated, but its application has been limited without the benefit of a thorough analysis of the scientific evidence on efficacy, scope, and mechanism of action. This review covers the uses of EOs as broad-spectrum biocontrol agents in both preharvest and postharvest systems. The known functions of EOs in suppressing fungi, bacteria, viruses, pests, and weeds are briefly summarized. Related results and possible modes of action from recent research are listed. The weaknesses of applying EOs are also discussed, such as high volatility and low stability, low water solubility, strong influence on organoleptic properties, and phytotoxic effects. Therefore, EO formulations and methods of incorporation to enhance the strengths and compensate for the shortages are outlined. This review also concludes with research directions needed to better understand and fully evaluate EOs and provides an outlook on the prospects for future applications of EOs in organic horticulture production.

Recent advances and future perspective of essential oils in control Colletotrichum spp.: A sustainable alternative in postharvest treatment of fruits

The world population growth has raised concerns about food security. Agricultural systems are asked to satisfy a growing demand for food with increasingly limited resources, and simultaneously still must reduce the impacts on the environment. This scenario encourages the search for safe and sustainable production strategies. Reducing losses in the production process can be one of the main ways to guarantee food safety. In fruticulture, it is estimated that more than 50% of the production can be lost between harvest and the final consumer due to postharvest diseases caused by phytopathogenic fungi. The fungi of the genus Colletotrichum are opportunistic and are associated with several diseases, being the anthracnose the most relevant in terms of the quality and yield losses in fruit species around worldwide. To control these diseases, the use of synthetic fungicides has been the main instrument utilized, however, because of their phytotoxicity to human health, the environment, and strong selection pressure imposed by continuous applications, the fungicides have caused resistance in the pathogen populations. So reducing the excessive application of these products is indispensable for human health and for sustainable Agriculture. Towards this purpose, research has been carried out to identify the phytopathological potentiality of essential oils (EOs) extracted from plants. Therefore, this review aims to contribute to the formation of knowledge bases, about the discoveries, recent advances, and the use of EOs as a strategy to alternatively control fungal disease caused by Colletotrichum spp. in postharvest fruits. Here, we provide valuable information exploring the application potential of essential oils as commercially useful biorational pesticides for food preservation, contributing to sustainable production and global food security.

Chitosan Coating Enriched With Ruta graveolens L. Essential Oil Reduces Postharvest Anthracnose of Papaya (Carica papaya L.) and Modulates Defense-Related Gene Expression

Anthracnose of papaya (Carica papaya L.) caused by the fungus Colletotrichum spp. is one of the most economically important postharvest diseases. Coating with chitosan (CS) and Ruta graveolens essential oil (REO) might represent a novel eco-friendly method to prevent postharvest anthracnose infection. These compounds show both antimicrobial and eliciting activities, although the molecular mechanisms in papaya have not been investigated to date. In this study, the effectiveness of CS and REO alone and combined (CS-REO) on postharvest anthracnose of papaya fruit during storage were investigated, along with the expression of selected genes involved in plant defense mechanisms. Anthracnose incidence was reduced with CS, REO, and CS-REO emulsions after 9 days storage at 25°C, by 8, 21, and 37%, respectively, with disease severity reduced by 22, 29, and 44%, respectively. Thus, McKinney's decay index was reduced by 22, 30, and 44%, respectively. A protocol based on reverse transcription quantitative real-time PCR (RT-qPCR) was validated for 17 papaya target genes linked to signaling pathways that regulate plant defense, pathogenesis-related protein, cell wall-degrading enzymes, oxidative stress, abiotic stress, and the phenylpropanoid pathway. CS induced gene upregulation mainly at 6 h posttreatment (hpt) and 48 hpt, while REO induced the highest upregulation at 0.5 hpt, which then decreased over time. Furthermore, CS-REO treatment delayed gene upregulation by REO alone, from 0.5 to 6 hpt, and kept that longer over time. This study suggests that CS stabilizes the volatile and/or hydrophobic substances of highly reactive essential oils. The additive effects of CS and REO were able to reduce postharvest decay and affect gene expression in papaya fruit.

Hormesis-Inducing Essential Oil Nanodelivery System Protects Plants against Broad Host-Range Necrotrophs

Botrytis cinerea, a broad host-range necrotrophic (BHN) phytopathogen, establishes compatible interactions with hosts by deploying multigene infection strategies, rendering simply inherited resistance ineffective to fight off this pathogen. Since essential oils (EOs) serve as intermediators during phytobiome communication, we hypothesize that they have the potential to enhance the quantitative disease resistance against BHN by eliciting the adaptive stress response (hormesis) in plants. However, using EOs is challenging due to their poor solubility in water. Nanoemulsification of EOs enhances not only the solubility of EOs but also their potency and stability. Here, we demonstrate the potential use of essential oil nanoemulsions (EONEs) to control infections caused by BHN. Using basic engineering principles of nanocarrier design, we demonstrate the efficacy of a robust EONEs design for controlling B. cinerea infection in a model plant, Arabidopsis thaliana. Our nanoemulsion delivery system significantly enhanced the disease resistance of the host by reducing the necrotic area by up to 50% compared to untreated plants. RNA-seq analysis indicated that successful treatments upregulated autophagy, ROS scavenging, and activation of the jasmonic acid signaling pathway.

Unraveling Interactions of the Necrotrophic Fungal Species Botrytis cinerea With 1-Methylcyclopropene or Ozone-Treated Apple Fruit Using Proteomic Analysis

Gray mold caused by the necrotrophic fungus Botrytis cinerea is one of the major postharvest diseases of apple fruit. The exogenous application of 1-methylcyclopropene (1-MCP) and gaseous ozone (O 3) is commonly used to ensure postharvest fruit quality. However, the effect of these treatments on the susceptibility of apple fruit to postharvest pathogens remains largely unknown. Herein, the effect of O 3 and 1-MCP treatments on the development of gray mold on apple fruit (cv. "Granny Smith") was investigated. Artificially inoculated apple fruits, treated or not with 1-MCP, were subjected for 2 months to cold storage [0°C, relative humidity (RH) 95%] either in an O3-enriched atmosphere or in a conventional cold chamber. Minor differences between 1-MCP-treated and control fruits were found in terms of disease expression; however, exposure to ozone resulted in a decrease of disease severity by more than 50% compared with 1-MCP-treated and untreated fruits. Proteomic analysis was conducted to determine proteome changes in the mesocarp tissue of control and 1-MCP- or O3-treated fruits in the absence or in the presence of inoculation with B. cinerea. In the non-inoculated fruits, 26 proteins were affected by 1-MCP, while 51 proteins were altered by ozone. Dynamic changes in fruit proteome were also observed in response to B. cinerea. In O3-treated fruits, a significant number of disease/defense-related proteins were increased in comparison with control fruit. Among these proteins, higher accumulation levels were observed for allergen, major allergen, ACC oxidase, putative NBS-LRR disease resistance protein, major latex protein (MLP)-like protein, or 2-Cys peroxiredoxin. In contrast, most of these proteins were down-accumulated in 1-MCP-treated fruits that were challenged with B. cinerea. These results suggest that ozone exposure may contribute to the reduction of gray mold in apple fruits, while 1-MCP was not effective in affecting this disease. This is the first study deciphering differential regulations of apple fruit proteome upon B. cinerea infection and postharvest storage treatments, underlying aspects of host response related to the gray mold disease.

Antifungal Polyvinyl Alcohol Coatings Incorporating Carvacrol for the Postharvest Preservation of Golden Delicious Apple

Different polyvinyl alcohol (PVA) coating formulations incorporating starch (S) and carvacrol (C) as the active agent were applied to Golden Delicious apples to evaluate their effectiveness at controlling weight loss, respiration rate, fruit firmness, and fungal decay against B. cinerea and P. expansum throughout storage time. Moreover, the impact of these coatings on the sensory attributes of the fruit was also analyzed. The application of the coatings did not notably affect the weight loss, firmness changes, or respiration pathway of apples, probably due to the low solid surface density of the coatings. Nevertheless, they exhibited a highly efficient disease control against both black and green mold growths, as a function of the carvacrol content and distribution in the films. The sensory analysis revealed the great persistence of the carvacrol aroma and flavor in the coated samples, which negatively impact the acceptability of the coated products.

Application of Plant Extracts to Control Postharvest Gray Mold and Susceptibility of Apple Fruits to B. cinerea from Different Plant Hosts

Sustainable plant protection can be applied on apples against fungal pathogens such as Botrytis cinerea (which is responsible for gray mold)-a significant global postharvest disease. This pathogen can affect a wide range of hosts; and fruits may have variable susceptibilities to B. cinerea from different plant hosts. New possibilities to control gray mold in food production are under demand due to the emergence of resistance against antifungal agents in fungal pathogens. Cinnamon, pimento, and laurel extracts were previously assessed for antifungal activities under in vitro conditions and were found to have the potential to be effective against postharvest gray mold. Therefore, this study aimed to investigate the antifungal activity of cinnamon, pimento, and laurel extracts in vitro and against postharvest gray mold on apples to determine the susceptibility of apple fruits to B. cinerea from different plant hosts, and to analyze the chemical composition of the extracts. Apples (cv. "Connell Red") were treated with different concentrations of extracts and inoculated with B. cinerea isolates from apple and strawberry followed by evaluation of in vitro antifungal activity. The results reveal that most of the concentrations of the extracts that were investigated were not efficient enough when assessed in the postharvest assay, despite having demonstrated a high in vitro antifungal effect. Apples were less susceptible to B. cinerea isolated from strawberry. To conclude, cinnamon extract was found to be the most effective against apple gray mold; however, higher concentrations of the extracts are required for the efficient inhibition of B. cinerea in fruits during storage.

Phytotoxicity of Essential Oils: Opportunities and Constraints for the Development of Biopesticides. A Review

The extensive use of chemical pesticides leads to risks for both the environment and human health due to the toxicity and poor biodegradability that they may present. Farmers therefore need alternative agricultural practices including the use of natural molecules to achieve more sustainable production methods to meet consumer and societal expectations. Numerous studies have reported the potential of essential oils as biopesticides for integrated weed or pest management. However, their phytotoxic properties have long been a major drawback for their potential applicability (apart from herbicidal application). Therefore, deciphering the mode of action of essential oils exogenously applied in regards to their potential phytotoxicity will help in the development of biopesticides for sustainable agriculture. Nowadays, plant physiologists are attempting to understand the mechanisms underlying their phytotoxicity at both cellular and molecular levels using transcriptomic and metabolomic tools. This review systematically discusses the functional and cellular impacts of essential oils applied in the agronomic context. Putative molecular targets and resulting physiological disturbances are described. New opportunities regarding the development of biopesticides are discussed including biostimulation and defense elicitation or priming properties of essential oils.

Essential Oils and Their Natural Active Compounds Presenting Antifungal Properties

The current rise in invasive fungal infections due to the increase in immunosuppressive therapies is a real concern. Moreover, the emergence of resistant strains induces therapeutic failures. In light of these issues, new classes of antifungals are anticipated. Therefore, the plant kingdom represents an immense potential of natural resources to exploit for these purposes. The aim of this review is to provide information about the antifungal effect of some important essential oils, and to describe the advances made in determining the mechanism of action more precisely. Finally, the issues of toxicity and resistance of fungi to essential oils will be discussed.

Clove Essential Oil as an Alternative Approach to Control Postharvest Blue Mold Caused by Penicillium italicum in Citrus Fruit

Penicillium italicum causes blue mold disease and leads to huge economic losses in citrus production. As a natural antifungal agent, clove essential oil (CEO), which is a generally recognized as safe (GRAS) substance, shows strong in vitro activity against fungal pathogens. However, few studies on CEO for controlling postharvest blue mold disease caused by P. italicum in citrus fruit have been reported. Our aims were to investigate the control efficacy and possible mechanisms involved of CEO against P. italicum. In the present study, CEO treatment inhibited the disease development of blue mold when applied at 0.05% to 0.8% (v/v), and with the effective concentration being obtained as 0.4% (v/v). Besides its direct antifungal activity, CEO treatment also spurred a rapid accumulation of H₂O₂ compared with untreated fruits, which might contribute to enhancing an increase in the activities of defense-related enzymes, such as β-1,3-glucanase (β-Glu), chitinase (CHI), phenylalanine ammonia-lyase (PAL), peroxidase (POD), polyphenol oxidase (PPO), and lipoxygenase (LOX) in citrus fruit. Results of real time-quantitative polymerase chain reaction (RT-qPCR) showed that the gene expressions of β-Glu, CHI, PAL, POD and PPO were up-regulated in CEO-treated fruits. At the same time, CEO treatment led to down-regulated expression of the LOX gene in citrus fruit. Clove essential oil effectively control the disease incidence of blue mold decay in citrus fruit by motivating the host-defense responses, suppressing the malondialdehyde (MDA) accumulation while enhancing the activities and gene expressions of defense-related enzymes. Our study provides an alternative preservative applying CEO to reduce postharvest fungal decay in citrus fruit.

Introduction to the Special Issue: Application of Essential Oils in Food Systems

Essential oils have received increasing attention as natural additives for the shelf-life extension of food products due to the risk in using synthetic preservatives. Synthetic additives can reduce food spoilage, but the present generation is very health conscious and believes in natural products rather than synthetic ones due to their potential toxicity and other concerns. Therefore, one of the major emerging technologies is the extraction of essential oils from several plant organs and their application to foods. Essential oils are a good source of several bioactive compounds, which possess antioxidative and antimicrobial properties, so their use can be very useful to extend shelf-life in food products. Although essential oils have been shown to be promising alternative to chemical preservatives, they present special limitations that must be solved before their application in food systems. Low water solubility, high volatility, and strong odor are the main properties that make it difficult for food applications. Recent advances that refer to new forms of application to avoid these problems are currently under study. Their application into packaging materials and coated films but also directly into the food matrix as emulsions, nanoemulsions, and coating are some of their new applications among others.