**4. EOs in the control of phytopathogenic fungi in agricultural crops**

In agriculture, the losses caused by plant diseases reach an average of 12% per year. Among the pathogens, fungi are considered the most important. There are around 8.000 species of fungi that attack plants, distributed in more than 64 genera of fungi [82]. Added to the importance of plant diseases caused by phytopathogenic fungi, we have two other factors that must be considered. The first concerns the constant need to produce food to feed the planet's growing population. According to the Food and Agriculture Organization of the United (FAO), global food demand in 2050 is estimated to be 60% higher than in 2006. The population living in poverty could rise from 35 to 122 million by 2030. This increase of the poor will be higher in sub-Saharan Africa, largely because of the heavy dependence of the economy of these regions on agriculture. The second factor refers to the use of pesticides. The increase in the use of pesticides is due to the increase in the cultivable area and consequently the increase in the consumption of fertilizers and pesticides. Misuse of pesticides has led to serious public and environmental health problems. The United Nations has proposed the creation of a global treaty to regulate and stop the use of pesticides in agriculture. Current patterns of production and use of pesticides are very different in each country. According to the World Health Organization (OMS), pesticides cause 200.000 deaths from poisoning each year. Almost all fatalities, or 99%, occur in developing countries. Exposure to pesticides is linked to the risk of cancer, Alzheimer's and Parkinson's disease, hormonal, developmental, and fertility problems. The rural community made up of farmers and families who live near plantations and indigenous communities is the most vulnerable. In Brazil, for example, data from the Impact of Agrochemicals on Health released in 2015 by the Brazilian Association of Collective Health (ABRASCO) show that Brazil is the largest consumer of pesticides in the world, with a 288% increase in pesticide use. The data also show that 64% of the food marketed is contaminated and that the number of poisoning by agrochemicals reaches 34.147 cases. It is believed that these statistics should be even higher due to under-reporting, i.e., subacute intoxications caused by moderate or small exposure to products of high toxicity, slow onset and subjective symptomatology, and chronic intoxications requiring months or years of exposure. Resistance of fungi to fungicides has been recorded since the 1960s. The first case of resistance was found with the use of Benomyl to control the mildew of cucurbits, caused by the fungus *Sphaerotheca fuliginea* [83] and later to control the fungus *Botrytis cinerea* in the culture of the cyclamen [84]. Since then, more than half of the known fungus species have shown some resistance to fungicides in more than 100 plant-pathogenic combinations [85]. Over the past 55 years, it has been proposed to develop agriculture under Integrated Pest Management (IPM), and this has become the main global holistic strategy for phytosanitary protection. It provides for the production of food in a sustainable agroecosystem, with the management of the soils, from the point of view of the increase in organic matter, fertility and vegetation cover, the adequate use of water for irrigation, the use of resistant varieties for different soil and climatic conditions and the use of temporal and spatial distribution of crops, the encouragement of the application of agroecology to grow food, as well as the encouragement of family agriculture, the production and preservation of creole seeds, the diversity of plant species, and reduction of pesticide use for pest and disease control as opposed to increased use of biological control. The search for biopesticides has aroused much interest from the scientific community due to the expansion of organic farming, more restrictive regulations to chemical pesticides, and the demand for healthier and safer products. Essential oils (EOs), included within the group of biopesticides of botanical origin, are complex mixtures of volatiles, mainly products of plant secondary metabolism, which comprise terpenes (mainly mono-, sesqui-, and some diterpenes) and phenolic compounds phenylpropanoids), although other groups of compounds may also occur in relevant amounts. These volatiles have aromatic components that give odor, flavor or aroma, distinct from each plant, and are part of defense mechanisms of the plant to the attack

of microorganisms. Most plant species have 1–2% EOs, but in some plant species, this value can

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The antifungal properties of EOs and their constituents have been reported in several studies, most of which are due to inhibition of fungal mycelial growth in vitro. The mycelium supports all fungal activity, from the spore germination to the formation of the fruiting body, and thus represents a good indicator of fungus survival. Studies with plants of the Lamiaceae family showed positive results in the control of several phytopathogenic fungi. The EOs of oregano (*Oreganum vulgare*) and thyme (*Thymus vulgaris*) were effective against *Aspergillus niger, A. flavus, A. ochraceus, F.oxysporum, F. solani, Penicillium* sp., *Phytophthora infestans, Sclerotinia sclerotiorum, Rhizoctonia solani, B. cinerea*, *Monilinia fructicola, Rhizopus stolonifer, Sclerotium rolfsii, Macrophomina phaseolina*, and *Pythium* sp. [87]. *R. solani*, for example, represents an important phytopathogen of agricultural crops around the world. The fungus has a host range of more than 500 species of plants, with a complex ecology and is difficult to control. Seema and Devaki [88] studied the antifungal activity of several EOs against *R. solani* and revealed that cinnamon's EO (*Cinnamomum zeylanicum Breyne*) completely inhibited the growth of the fungus at a concentration of 500 ppm. The EOs of *T. vulgaris* [89], *Salvia fruticosa* [90], *Mentha piperita* [91–94], *Monarda* spp. [95], *Calocedrus macrolepis* var. *formosana* [96], *Bunium persicum* [94] were also effective in mycelial inhibition of the fungus. In [97], it was reported that the foliar application of *Desmos chinensis* reduced the intensity of the disease caused by *R. solani* in rice. Arici and Şanlı [98] studied the EO efficiency of *Cuminum cyminum, Anethum graveolens, Salvia officinalis, Origanum onites, Rosmarinus officinalis*, and *Lavandula intermedia* against *R. solani* and *Streptomycetes scabies* on potato and found that EO of *S. officinalis* reduced *R. solani* infection in 4.2%, and oregano's EO reduced the disease severity caused by *S. scabies* to 1.8%. Fusarium species are also important phytopathogens. The EO of *Artemisia absinthium* showed effectiveness against *Fusarium moniliforme, F. oxysporum, F. solani* [99]. Other positive results have also been reported in field experiments. Citral, methyl anthranilate, and nerol tested at the concentration of 5.0 ml/L reduced 78.1 and 80% of Cercospora (*Cercospora beticola*) and Alternaria (*Alternaria tenuis)* in sugar beet, respectively [100]. El-Mohamedy and Abd-El-latif [101] tested the EO of *T. vulgaris* applied alone or in combination with humic acid and observed a 92.2% reduction in tomato blight caused by *P. infestans* when tested at the concentration of 6.0 ml/L. In postharvest, treatment with EOs of basil (*Ocimum basilicum* L.), fennel (*Foeniculum sativum* Mill.), lavender (*Lavandula officinalis* Chaix), marjoram (*O. majorana* L.), oregano (*O. vulgare* L.), mint (*Mentha piperita* L.), rosemary (*Rosmarinus officinalis* L.), sage (*Salvia officinalis* L.), savory (*Satureja montana* L.), thyme (*T. vulgaris* L.), and wild mint (*Mentha arvensis* L.) was effective against *B. cinerea* and *Penicillium expansum* [102]. Al-Reza et al. [103] tested the EO of *Cestrum nocturnum* L. at 1000 ppm concentration and showed that EO inhibited up to 80.6% growth of *B. cinerea, Colletotrichum capsici, F. oxysporum, F. solani, P. capsici, R. solani*, and *S. sclerotiorum*. The EO of *C. nocturnum* also inhibited the spore germination and reduced the disease by 82–100% in pepper seedlings. Muchembled et al. [104] studied some OEs against *Venturia inaequalis* strains of apples with different sensitivities to Tebuconazole compared to the application of copper sulfate and highlighted the effectiveness of clove EOs

reach 10%, as in *Ocimum basilicum* [86].

**4.1. Phytopathogenic fungi of agronomic interest**

of microorganisms. Most plant species have 1–2% EOs, but in some plant species, this value can reach 10%, as in *Ocimum basilicum* [86].

#### **4.1. Phytopathogenic fungi of agronomic interest**

The first concerns the constant need to produce food to feed the planet's growing population. According to the Food and Agriculture Organization of the United (FAO), global food demand in 2050 is estimated to be 60% higher than in 2006. The population living in poverty could rise from 35 to 122 million by 2030. This increase of the poor will be higher in sub-Saharan Africa, largely because of the heavy dependence of the economy of these regions on agriculture. The second factor refers to the use of pesticides. The increase in the use of pesticides is due to the increase in the cultivable area and consequently the increase in the consumption of fertilizers and pesticides. Misuse of pesticides has led to serious public and environmental health problems. The United Nations has proposed the creation of a global treaty to regulate and stop the use of pesticides in agriculture. Current patterns of production and use of pesticides are very different in each country. According to the World Health Organization (OMS), pesticides cause 200.000 deaths from poisoning each year. Almost all fatalities, or 99%, occur in developing countries. Exposure to pesticides is linked to the risk of cancer, Alzheimer's and Parkinson's disease, hormonal, developmental, and fertility problems. The rural community made up of farmers and families who live near plantations and indigenous communities is the most vulnerable. In Brazil, for example, data from the Impact of Agrochemicals on Health released in 2015 by the Brazilian Association of Collective Health (ABRASCO) show that Brazil is the largest consumer of pesticides in the world, with a 288% increase in pesticide use. The data also show that 64% of the food marketed is contaminated and that the number of poisoning by agrochemicals reaches 34.147 cases. It is believed that these statistics should be even higher due to under-reporting, i.e., subacute intoxications caused by moderate or small exposure to products of high toxicity, slow onset and subjective symptomatology, and chronic intoxications requiring months or years of exposure. Resistance of fungi to fungicides has been recorded since the 1960s. The first case of resistance was found with the use of Benomyl to control the mildew of cucurbits, caused by the fungus *Sphaerotheca fuliginea* [83] and later to control the fungus *Botrytis cinerea* in the culture of the cyclamen [84]. Since then, more than half of the known fungus species have shown some resistance to fungicides in more than 100 plant-pathogenic combinations [85]. Over the past 55 years, it has been proposed to develop agriculture under Integrated Pest Management (IPM), and this has become the main global holistic strategy for phytosanitary protection. It provides for the production of food in a sustainable agroecosystem, with the management of the soils, from the point of view of the increase in organic matter, fertility and vegetation cover, the adequate use of water for irrigation, the use of resistant varieties for different soil and climatic conditions and the use of temporal and spatial distribution of crops, the encouragement of the application of agroecology to grow food, as well as the encouragement of family agriculture, the production and preservation of creole seeds, the diversity of plant species, and reduction of pesticide use for pest and disease control as opposed to increased use of biological control. The search for biopesticides has aroused much interest from the scientific community due to the expansion of organic farming, more restrictive regulations to chemical pesticides, and the demand for healthier and safer products. Essential oils (EOs), included within the group of biopesticides of botanical origin, are complex mixtures of volatiles, mainly products of plant secondary metabolism, which comprise terpenes (mainly mono-, sesqui-, and some diterpenes) and phenolic compounds phenylpropanoids), although other groups of compounds may also occur in relevant amounts. These volatiles have aromatic components that give odor, flavor or aroma, distinct from each plant, and are part of defense mechanisms of the plant to the attack

152 Potential of Essential Oils

The antifungal properties of EOs and their constituents have been reported in several studies, most of which are due to inhibition of fungal mycelial growth in vitro. The mycelium supports all fungal activity, from the spore germination to the formation of the fruiting body, and thus represents a good indicator of fungus survival. Studies with plants of the Lamiaceae family showed positive results in the control of several phytopathogenic fungi. The EOs of oregano (*Oreganum vulgare*) and thyme (*Thymus vulgaris*) were effective against *Aspergillus niger, A. flavus, A. ochraceus, F.oxysporum, F. solani, Penicillium* sp., *Phytophthora infestans, Sclerotinia sclerotiorum, Rhizoctonia solani, B. cinerea*, *Monilinia fructicola, Rhizopus stolonifer, Sclerotium rolfsii, Macrophomina phaseolina*, and *Pythium* sp. [87]. *R. solani*, for example, represents an important phytopathogen of agricultural crops around the world. The fungus has a host range of more than 500 species of plants, with a complex ecology and is difficult to control. Seema and Devaki [88] studied the antifungal activity of several EOs against *R. solani* and revealed that cinnamon's EO (*Cinnamomum zeylanicum Breyne*) completely inhibited the growth of the fungus at a concentration of 500 ppm. The EOs of *T. vulgaris* [89], *Salvia fruticosa* [90], *Mentha piperita* [91–94], *Monarda* spp. [95], *Calocedrus macrolepis* var. *formosana* [96], *Bunium persicum* [94] were also effective in mycelial inhibition of the fungus. In [97], it was reported that the foliar application of *Desmos chinensis* reduced the intensity of the disease caused by *R. solani* in rice. Arici and Şanlı [98] studied the EO efficiency of *Cuminum cyminum, Anethum graveolens, Salvia officinalis, Origanum onites, Rosmarinus officinalis*, and *Lavandula intermedia* against *R. solani* and *Streptomycetes scabies* on potato and found that EO of *S. officinalis* reduced *R. solani* infection in 4.2%, and oregano's EO reduced the disease severity caused by *S. scabies* to 1.8%. Fusarium species are also important phytopathogens. The EO of *Artemisia absinthium* showed effectiveness against *Fusarium moniliforme, F. oxysporum, F. solani* [99]. Other positive results have also been reported in field experiments. Citral, methyl anthranilate, and nerol tested at the concentration of 5.0 ml/L reduced 78.1 and 80% of Cercospora (*Cercospora beticola*) and Alternaria (*Alternaria tenuis)* in sugar beet, respectively [100]. El-Mohamedy and Abd-El-latif [101] tested the EO of *T. vulgaris* applied alone or in combination with humic acid and observed a 92.2% reduction in tomato blight caused by *P. infestans* when tested at the concentration of 6.0 ml/L. In postharvest, treatment with EOs of basil (*Ocimum basilicum* L.), fennel (*Foeniculum sativum* Mill.), lavender (*Lavandula officinalis* Chaix), marjoram (*O. majorana* L.), oregano (*O. vulgare* L.), mint (*Mentha piperita* L.), rosemary (*Rosmarinus officinalis* L.), sage (*Salvia officinalis* L.), savory (*Satureja montana* L.), thyme (*T. vulgaris* L.), and wild mint (*Mentha arvensis* L.) was effective against *B. cinerea* and *Penicillium expansum* [102]. Al-Reza et al. [103] tested the EO of *Cestrum nocturnum* L. at 1000 ppm concentration and showed that EO inhibited up to 80.6% growth of *B. cinerea, Colletotrichum capsici, F. oxysporum, F. solani, P. capsici, R. solani*, and *S. sclerotiorum*. The EO of *C. nocturnum* also inhibited the spore germination and reduced the disease by 82–100% in pepper seedlings. Muchembled et al. [104] studied some OEs against *Venturia inaequalis* strains of apples with different sensitivities to Tebuconazole compared to the application of copper sulfate and highlighted the effectiveness of clove EOs (*Syzygium aromaticum*), eucalyptus (*Eucalyptus citriodora*), mint (*Mentha spicata*), and savory (*Satureja montana*) with priority components such as eugenol and carvacrol. They also found that each strain of the fungus reacted differently to each treatment, indicating that each strain of the pathogen had different survival mechanisms.

for long time. *Laurus nobilis* EO has been proven to be effective in cherry tomatoes applied in this way [107]. **Nanoemulsions** of thymol without carrier oil have also been studied to avoid the deployment of wheat due to *Fusarium gramineum* [108]. **Double w/o/w emulsion** type prepared lipophilic and hydrophilic emulsifiers with xanthan gum as thickener showed stability and water-dilution tolerance and retained most of the electrolytes included in the internal aqueous phase. Antifungal activity of the EOs increased, and the absence of organic solvents makes these formulations environmentally safe. Also, the property of controlled electrolyte

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The **microencapsulation** in porous materials allows direct contact between the fungus and the microparticle in the soil, which acts more efficiently against the fungus. That is, these could be put directly into the crop acting as biopesticides throughout the growth of the vegetables. Microencapsulation can be done by simple coacervation [110–111] and it has been tried already in fruits such as mango with thyme and rosemary EOs [110] and to preserve peanut seeds with *Lippia turbinata* EO [111]. Carvacrol and thymol from oregano and thyme have also been studied in microcapsules of mesoporous silica and B-cyclodextrin, together with cinnamaldehyde and eugenol from cinnamon and clove, respectively. **Nanoencapsulation** is also used to enhance antifungal activity and stability of the oils against fungi. Nanoencapsulation in chitosan nanoparticles (CSNPs) is done by an ionic gelation technique. This technique has shown a controlled and sustained release of EOs for 40 days in comparison with unmodified EOs [101]. Nanoparticle carriers of EOs, as compared to microsize carriers, show a better surface area rate, solubility, bioavailability, controlled release, and targeting of the ingredients [101]. Nanoencapsulation of EOs has been studied also for their incorporation into fruit juices to prevent fungal activity while not

**Simple vapor application** of EOs can change the sensory profile of fruits and vegetable [113–114]. EOs from cinnamon (*Cinnamomum zeylanicum* Nees.), thyme (*Thymus vulgaris* L.), oregano (*Origanum vulgare* L.), clove (*Syzygium aromaticum* L.), lemongrass (*Cymbopogon citratus* [DC] Stapf.), and ginger (*Zingiber officinale* Rosc.) have shown to inhibit the growth of Aspergillus spp. in oats [114]. But furthermore, there are new technologies of application of the EOs, such as the combination with **warm air flow (WAF)**, that can be used in the control of postharvest fungal pathogens of grains [115], being more effective compared to standard

EOs are a very good source of natural additives for **active packaging (films & coatings)**, which refers to the incorporation of additives into the packaging material, maintaining its properties without adding active agents in the food product, thus reducing the use of aggressive techniques and synthetic chemicals in food. Oregano is one of the EOs that has been positively tested in this way [116]. In that sense, chitosan **composite films** enriched with essential oils of cinnamon, thyme, clove, and lime alone or in combination have been tried against *Colletotrichum gloeosporioides* in papaya fruit. This coating can be an alternative to potentially reduce the need for cold storage during postharvest handling [117]. Edible coatings with oregano EO have been proved for the preservation of tomatoes against *Alternaria alternata*

vapors in disc volatilization [113] with very low effect on their sensory profile.

growth maintaining the sensorial acceptability of tomatoes [118].

release makes these formulations attractive [109].

affecting on the quality attributes of the product [112].
