1. Introduction
Banana (
Musa paradisiaca), a food of great importance in tropical regions and in many developing countries, plays an essential role in serving as a pillar for economic growth and social development of local communities, for its ability to maintain consistent production throughout the year [
1]. Over the past decade, countries such as Ecuador, the Philippines and Costa Rica have excelled in their significant banana export activity, while the European Union, the United States and Russia position as the main importers, followed by markets such as the Middle East, Eastern Europe, Africa and Asia.[
2].
Ecuador’s banana production is essential to its economy and food security [
3]. It contributes significantly to employment and represents approximately 2% of total PIB and 35% of agricultural PIB. The main producing provinces are Guayas, El Oro and Los Ríos, highlighting El Oro for its quality, while Guayas and Los Ríos for the major producers [
2,
4]. In production, various factors, both external and internal, affect the quality of the fruit during the post-harvest phase. External factors include environmental conditions such as relative humidity and temperature and among internal factors, metabolic changes and the presence of fungal pathogens are highlighted [
3].
It is important to emphasize that fungal pathogens, in particular diseases associated with
Fusarium spp., Penicillium spp., Trichoderma spp., y Aspergillus spp., represent the main causes of banana wilt [
5]. These diseases manifest as a reduction in the firmness of the superficial tissues in the areas of the rachis and the banana crown, accompanied by changes in leaf coloration and cracks at the base of the pseudo stem [
6]. This causes internal rot in the fingers of the banana, eventually resulting in the crown rot and, in more severe cases, the death of the fruit.
Today, there is a growing preference for organically produced fruits, free of toxic residues. Therefore, the search for new alternatives to combat fungal pathogen rot is of vital importance [
7]. One of the most promising and natural solutions are essential oils that have demonstrated their ability to prolong the life of the fruit, provide fungitoxic effects and increase resistance to post-harvest diseases.
Essential oils of oregano and thyme share similar volatile compounds [
8], such as the carvacrol, thymol and p-cymene, the rosemary contains alpha-pinene, 1.8 cineol, camphor and verbenone [
9,
10]. Clove oil, is characterized by its content of eugenol, acetyl eugenol and α and β caryophyllenes and the basil contains estragole, linalool, eugenol and methyl cinnamate [
9], while cinnamon has cinnamic aldehyde and eugenol and is used as a bioactive compound in coatings [
11].
The main objective of this study was to investigate the potential of essential oils oregano, thyme, clove, basil, rosemary and cinnamon as antifungal agents [
12], for the control of
Fusarium spp., Penicillium spp., Trichoderma spp., y Aspergillus spp. Effectiveness in antifungal activity with low environmental impact, their use can be a notable alternative to replace synthetic fungicides in the postharvest disease control [
13], keeping intact the physico-chemical and organoleptic properties of the treated products.
Fusarium is a genus known as sabrophite, filamentous fungus, has a variety of species and ability to adapt to different environmental conditions, affects the banana causing vascular wilt, infecting the conducting vessels of the bananas by blocking the transport of water and nutrients in the plant as a result decreases the quality and quantity of fruits produced [
14]. In Ecuador is generally found the species
oxysporum, verticillioides and
solani that are studied to innovate management and control strategies to avoid damage to the banana [
15].
This genus grows at a temperature of approximately 37°C and is known as opportunistic because it can cause diseases [
16].
Fusarium have mycelium that are networks of filaments (hyphae), conidia (asexual and sexual spores or ascospores), because of their variety of species, the morphological characterization can have multiple differences. In the microscope, the phialide is generally thin, with a bottle – shaped that can be simple or branched; short or long, they can have different characteristics depending on their species. Therefore, DNA sequencing is required to identify the species [
17].
Penicillium is a common fungus that can survive in different habitats and some species have antagonistic activity against pathogens that can cause deterioration of the fruit in post-harvest [
18]. On the surface of the banana are commonly species such as
citrinum, expansum and
digitatum, mandarin essential oil was used to prevent the growth of
Penicillium by the presence of Carvacrol on the
P. digitatum [
19].
The presence of citrinum can cause stains and discoloration on the peel of the banana, affecting its appearance and quality,
expansum can affect the bananas during storage, causing rotting and loss of firmness, while
digitatum is more common in citrus fruits but can affect bananas if are stored in wet and warm storage conditions, causing rotting and stains on the peel [
20]. To prevent the presence of this fungus should be handled properly during the storage and transport of the fruit.
Trichoderma is a genus of filamentous, cosmopolitan fungi commonly found in soil, in decomposing organic matter and in other environments [
21,
22]. It has the capacity of adaptation and production of metabolites, enzymes and compounds that by its mechanism of action of antibiotics, microparasitism, production of secondary metabolites, competition for space and nutrients, it is classified as a biocontrol agent against phytopathogenic fungi [
23]. India distributes certified species of
T. asperellum, T. atroviride, T. gamsii, T. hamatum, T. harzianum, T. polysporum, T. virens, and
T. viride and with genetic engineering made significant improvements to apply in industrial processes [
21].
Some macroscopic characteristics are that their colony grows rapidly and can be white, green, yellow or even orange, the texture can vary from cottony to velvety or granular, depending on the medium, the species, the age of the colony and the growth conditions. They can produce branched conidiophores with verticils, the conidia are small and can form in chains or clusters, being oval or cylindrical shape and may be unicellular or multicellular, usually have a characteristic odor, which is not considered a easily distinguishable macroscopic feature [
24].
Aspergillus is another genus that affects bananas during storage and transportation, they are found in diverse environments and among the morphological characteristics, the conidiophores, are long and slender structures that emerge from the substrate surface of the substrate to produce asexual spores called conidia, which are asexual spores that are produced at the tip of the conidiophores and are generally spherical or oval and are grouped in a structure called sporangiophores [
25].
Colonies of
Aspergillus are usually green, gray, white or black, depending on the species and the medium of growth, have a cottony or velvety appearance, the hyphae are septate (divided by cross-walls) and branched, these structures form the network of the mycelium that grows on the substrate. In some species, conidiophores may be branched and have a brush-like or pencil – like appearance, in some cases, conidiophores may end up in a spherical or vesicle – shaped structure that produces conidia on its surface [
25].
Species such as
A. niger are known for their ability to produce enzymes that decompose cellulose and other plant components that can contribute to the decomposition of fruit tissues,
A. flavus can produce toxins called aflatoxins, which are dangerous to human health and can contaminate agricultural products if storage conditions are not adequate, while
A. parasiticus is similar to
A. fravus, this species can also produce aflatoxin and affect the quality and safety of bananas [
26].
5. Conclusions
The characterization of the strains by order of severity identified Penicillium spp., Trichoderma spp., Fusarium spp., and Aspergillus spp. In the in vitro analysis of essential oil effectiveness, oregano and thyme were effective at 400 ppm, cinnamon at 600 ppm, and clove at 1000 ppm. Basil and rosemary did not inhibit the growth of the analyzed pathogens. Specifically, Penicillium spp. was controlled with 400 ppm of cinnamon, oregano, thyme, and 1000 ppm of clove.
Trichoderma spp. was inhibited by 200 ppm of oregano, 400 ppm of clove and thyme, and 600 ppm of cinnamon. Fusarium spp. was effectively managed with 200 ppm of cinnamon and thyme, and 400 ppm of oregano. Aspergillus spp. was controlled by 200 ppm of oregano, and 400 ppm of cinnamon, clove, and thyme.
At 400 ppm of oregano and thyme essential oils, 600 ppm of cinnamon, and 1000 ppm of clove, the growth of all four analyzed fungi was inhibited.
Figure 1.
Fungal growth (cm) for 6 weeks in 20 banana samples inoculated with Trichoderma spp., Penicillium spp., Aspergillus spp., and Fusarium spp., stored at 13°C and 95% relative humidity.
Figure 1.
Fungal growth (cm) for 6 weeks in 20 banana samples inoculated with Trichoderma spp., Penicillium spp., Aspergillus spp., and Fusarium spp., stored at 13°C and 95% relative humidity.
Figure 2.
In vitro growth analysis of Trichoderma spp. on PDA medium with basil, cinnamon, clove, oregano, rosemary, and thyme essential oils at 200, 400, 600, 800, and 1000 ppm, stored at 25°C (n=4).
Figure 2.
In vitro growth analysis of Trichoderma spp. on PDA medium with basil, cinnamon, clove, oregano, rosemary, and thyme essential oils at 200, 400, 600, 800, and 1000 ppm, stored at 25°C (n=4).
Figure 3.
In vitro growth analysis of Penicillium spp. on PDA medium with basil, cinnamon, clove, oregano, rosemary, and thyme essential oils at 200, 400, 600, 800, and 1000 ppm, stored at 25°C (n=4).
Figure 3.
In vitro growth analysis of Penicillium spp. on PDA medium with basil, cinnamon, clove, oregano, rosemary, and thyme essential oils at 200, 400, 600, 800, and 1000 ppm, stored at 25°C (n=4).
Figure 4.
In vitro growth analysis of Aspergillus spp. on PDA medium with basil, cinnamon, clove, oregano, rosemary, and thyme essential oils at 200, 400, 600, 800, and 1000 ppm, stored at 25°C (n=4).
Figure 4.
In vitro growth analysis of Aspergillus spp. on PDA medium with basil, cinnamon, clove, oregano, rosemary, and thyme essential oils at 200, 400, 600, 800, and 1000 ppm, stored at 25°C (n=4).
Figure 5.
In vitro growth analysis of Fusarium spp. on PDA medium with basil, cinnamon, clove, oregano, rosemary, and thyme essential oils at 200, 400, 600, 800, and 1000 ppm, stored at 25°C (n=4).
Figure 5.
In vitro growth analysis of Fusarium spp. on PDA medium with basil, cinnamon, clove, oregano, rosemary, and thyme essential oils at 200, 400, 600, 800, and 1000 ppm, stored at 25°C (n=4).
Figure 6.
Fungi isolated and purified from banana peel rot, inoculated on selective medium (PDA with chloramphenicol), and stored on PDA at a temperature of 25°C approx. in the incubator, (a) strain of Trichoderma spp., (b) Penicillium spp., (c) Aspergillus spp. and (d) Fusarium spp.
Figure 6.
Fungi isolated and purified from banana peel rot, inoculated on selective medium (PDA with chloramphenicol), and stored on PDA at a temperature of 25°C approx. in the incubator, (a) strain of Trichoderma spp., (b) Penicillium spp., (c) Aspergillus spp. and (d) Fusarium spp.
Figure 7.
Mean diameter (cm) of fungal decay circles in banana samples inoculated with Trichoderma spp., Penicillium spp., Aspergillus spp., and Fusarium spp. for 6 weeks, stored at 13°C and 95% HR (n=20).
Figure 7.
Mean diameter (cm) of fungal decay circles in banana samples inoculated with Trichoderma spp., Penicillium spp., Aspergillus spp., and Fusarium spp. for 6 weeks, stored at 13°C and 95% HR (n=20).
Table 1.
Macroscopic characterization of (a) Trichoderma spp, (b) Penicillium spp. (c) Aspergillus spp. and (d) Fusarium spp. considering appearance of upper side and lower side.
Table 1.
Macroscopic characterization of (a) Trichoderma spp, (b) Penicillium spp. (c) Aspergillus spp. and (d) Fusarium spp. considering appearance of upper side and lower side.
Fungus |
Macroscopic characteristics |
Upper side |
Lower side |
Shape |
Appearance |
Elevation |
Shore |
Surface |
Color |
Top |
Bottom |
a
|
|
Circulate too spherical |
Cottony |
Flat, slightly elevated, convex |
Entire, slightly undulating |
Smooth, rough and granular |
White, green or yellow |
Color of the fungal colony, yellow |
b
|
|
Variable |
Cottony, dusty |
Convex and crateriform |
Irregular and wavy |
Smooth and rough |
Green and white |
Beige and yellow |
c
|
|
Variable |
Velvety, Cottony and dusty |
Flat, elevate and umbonate |
Irregular and wavy |
Smooth and rough |
Green, yellow and brown |
Pale yellow |
d
|
|
Cerebriform |
Cottony |
Flat |
Irregular |
Smooth |
Orange |
Orange |
Table 2.
Microscopic characterization of (a) Trichoderma spp., (b) Penicillium spp., (c) Aspergillus spp. and (d) Fusarium spp. observed under the microscope.
Table 3.
Evaluation of antifungal activity in vitro of Trichoderma spp, Penicillium spp. Aspergillus spp. and Fusarium spp. use essential oil of oregano, rosemary, clove, thyme, cinnamon and basil.
Table 3.
Evaluation of antifungal activity in vitro of Trichoderma spp, Penicillium spp. Aspergillus spp. and Fusarium spp. use essential oil of oregano, rosemary, clove, thyme, cinnamon and basil.