Several Alternaria species of agricultural and ornamental importance have been reported, causing diseases such as leaf spot and blight (Palemón-Alberto et al., 2024). Among the affected species are onion (Reyes-Tena et al., 2023), chrysanthemum (Chrysanthemum morifolium) (Domínguez-Serrano et al., 2016), and papaya (Carica papaya) (Vásquez-López et al., 2012). In cacti, Alternaria is associated with golden spot disease and black spot (Montiel- Salero et al., 2022; Chavarría-Cervera et al., 2024). At least 10 different Alternaria species are officially known in Mexico, affecting 23 economically important hosts distributed across 15 states (Table 1). However, knowledge of the fungus’s broader distribution in crops of interest, as well as in alternate hosts, remains limited.

The importance of this fungus depends on the incidence and severity it can generate in different crops. For example, leaf spot caused by Alternaria in chrysanthemum crops has been reported with incidences of up to 30%, presenting symptoms as circular or oval lesions on the leaf margins, brown to black in color with yellow halos, along with other leaves turning completely yellow (Domínguez-Serrano et al., 2016). In onion (Allium cepa) crops, leaf blight shows an incidence of 20% in summer, with symptoms consisting of brown and purple spots on the leaves, whereas in winter, incidence may reach up to 80%, with purple foliar spots and dry lesions. These symptoms affect bulb growth (Reyes-Tena et al., 2023).

Table 1

Species reported	Host	Geographic area	Reference
A. alternata, A. tenuissima	Chrysanthemum morifolium	Yucatán	Dominguez-Serrano et al., 2016
A. limicola	Citrus paradisi, C. aurantium, C. macrophylla y C. sinensis	Colima	Palm & Civerolo, 1994
A. alternata	Triticum spp.	Sonora	Mata-Santoyo et al., 2018
A. tomato	Helianthus annuus	Yucatán	Poudel et al., 2019
A. alternata	Fragaria×ananassa	Guanajuato	Mariscal-Amaro et al., 2017
A. alternata	Carica papaya	Guerrero	Vásquez-López et al., 2012
A. tenuissima, A. alternata	Brassica oleracea	Guanajuato	Fraire-Cordero et al., 2010
A. alternata	Opuntia matudae	Hidalgo	Montiel-Salero et al., 2022
A. alternata	Avena sativa	Tlaxcala	Leyva-Mir et al., 2014
A. embellisia	Allium sativum	Coahuila	Delgado-Ortiz et al., 2019
A. alternata	Brassica oleracea var. italica	Guanajuato	Arratia-Castro et al., 2022
A. solani	Solanum lycopersicum	Chiapas	Quiroga-Madrigal et al., 2007
A. tenuissima	Salix bonplandiana	Estado de México	González-Díaz et al., 2011
A. chrysanthemi	Chrysanthemum morifolium	Yucatán	Villanueva-Couoh et al., 2004
A. alternata	Jatropha curcas	Sinaloa	Espinoza-Verduzco et al., 2012
A. alternata	Solanum lycopersicum	Sinaloa	Félix-Gastelum & Gálvez-Figueroa, 2002; Troncoso-Rojas et al., 2005
A. tenuissima	Malus x domestica	Chihuahua	Madrid-Molina et al., 2023
A. solani	Capsicum chinense	Yucatán	Cristóbal et al., 2006
A. alternata	Allium cepa	Michoacán	Reyes-Tena et al., 2023
A. alternata	Ficus carica	Morelos	Saavedra et al., 2020
A. alternata	Opuntia ficus-indica	Colima	Chavarría-Cervera et al., 2024
A. arborescens	Capsicum pubescens	Guerrero	Palemón-Alberto et al., 2024
Alternaria sp.	Vaccinium sp.	Michoacán	Mondragón-Flores et al., 2012
A. solani, A. alternata	Capsicum annuum	Chihuahua	Guigón-López et al., 2001
A. alternata	Cyamopsis tetragonoloba	Sinaloa	García-León et al., 2024
Alternaria spp.	Capsicum annuum	Sinaloa	Guerrero-Santana & Vega-Camargo, 2024
A. burnsii, A. destruens	Plumeria obtusa	Sinaloa	Márquez-Licona et al., 2025
A. alternata	Vaccinium corymbosum	Sinaloa	Nuñez-García et al., 2025

Sinaloa is a major agricultural state with high production of crops such as maize, bean, pepper, and tomato, and it has documented problems caused by this fungus. Black mold on mature tomato fruits (Solanum lycopersicum) caused by A. alternata has been reported, with severity varying according to humidity conditions during fruit ripening. When prolonged periods of dew, rainfall, or high relative humidity occur, A. alternata conidia germinate in response to soluble nutrients present on the fruit surface. Disease symptoms range from small, light brown superficial lesions to sunken necrotic lesions, and a black layer of conidia develops on the infected tissue (a sign of the pathogen). This represents an economic loss for producers when disease incidence exceeds 8% (Félix-Gastélum and Gálvez-Figueroa, 2002). Additionally, A. alternata has been reported causing soft rot and sunken lesions in tomato fruits, as well as leaf spot in guar (Cyamopsis tetragonoloba) (Félix-Gastélum and Gálvez- Figueroa, 2002; García-León et al., 2024). Alternaria spp. also cause leaf spot in sesame (García-Espinoza, 2022) and fruit rot in pepper (Guerrero-Santana and Vega-Camargo, 2024). Alternaria not only affects foliage and fruits but can also cause inflorescence blight in Jatropha curcas, induced by A. alternata in Sinaloa, where small dark brown lesions coalesce into larger necrotic areas, leading to flower drop (Espinoza-Verduzco et al., 2012). In chile (Capsicum annuum) nurseries and seeds, it induces early damping-off in Aguascalientes and Zacatecas, Mexico, in association with Alternaria, Fusarium, and Rhizoctonia (Velásquez-

Valle et al., 2007).

On the other hand, weeds are important as hosts of this fungus when they are found associated with or near economically relevant crops. For example, in Sinaloa, leaf blight (caused by Alternaria spp.) has been reported in wild tobacco (Nicotiana glauca), which grows along irrigation canals and drainage ditches. Symptoms on the leaves include irregular light to dark brown lesions. Severity increases when daily periods of leaf wetness range from 15 to 18 h and temperatures fluctuate between 14 and 28 °C. Species of Alternaria in the section Alternata are associated with leaf blight in tabaquillo (Nicotiana trigonophylla) and black nightshade (Solanum nigrum), while Alternaria ricini has been associated with leaf blight in wild castor bean (Ricinus communis) and foliar lesions in tabacón (Nicotiana glauca) and wild tobacco (Figure 2D-E) (Félix-Gastélum et al., 2023).

Generally, this fungus exhibits characteristic symptoms; however, it has also been reported in association with other fungi. For example, black spot in prickly pear (Opuntia ficus-indica) is caused by a complex involving Alternaria alternata, Corynespora cassiicola, and Neocytalidium dimidiatum. Among these, A. alternata has shown incidences of up to 60%, with symptoms including softening of cladodes and circular to irregular black lesions (Figure 2C) (Chavarría-Cervera et al., 2024). The same pathogen is responsible for golden spot disease, described in Mexico in O. matudae (xoconostle), producing lesions on cladodes characterized by yellowing or chlorosis near the areoles, which later develop into a golden spot that progresses to tissue necrosis (Figure 2A) (Montiel-Salero et al., 2022).

Figure 2

Another case of association with other fungi is floret rot in broccoli (Brassica oleracea var. italica), which reduces crop quality and yield. Under conditions of high relative humidity (70%) and temperatures of 30 °C, losses exceed 40% (Arratia-Castro et al., 2022). Alternaria tenuissima, A. alternata, and Fusarium oxysporum were identified as the causal agents of the disease in the commercial varieties Marathon, Patron, and Monaco in Guanajuato (Fraire- Cordero et al., 2010). Arratia-Castro et al. (2022) reported the association of A. alternata, F. verticillioides, and F. oxysporum as causal agents of broccoli floret rot (Figure 2B).

To establish control measures, it is necessary to diagnose the causal agent of the disease in order to implement management strategies appropriate for each crop. For integrated management, at least three approaches are typically applied: chemical, cultural, physical, and biological control. The latter includes the use of biological control agents, plant extracts, and microalgae. Although chemical control is the most effective option, its improper use has led to contamination of agroecosystems, in addition to posing public health risks due to the handling of these products (Zavaleta-Mejía, 1999; Zepeda-Jazo, 2018).

Chemical control. This is one of the methods most widely used by agricultural producers due to its high efficacy and rapid results. The main chemical groups used for the control of Alternaria spp. are triazoles, which include propiconazole. This systemic fungicide inhibits radial mycelial growth and conidial germination, as does the mixture of azoxystrobin + cyproconazole, belonging to the methoxyacrylate and triazole groups (Ramírez-Jiménez et al., 2025). The combination of these two chemical groups has also been evaluated with azoxystrobin + epoxiconazole, which delays senescence in wheat plants, induces an increase in the antioxidant enzyme superoxide dismutase, and reduces O₂ levels (Wu and Tieddmann, 2001).

Among the carboxamides, Captan inhibits mycelial growth by interfering with cellular respiration, thereby hindering mycelial development; it also translocates to various tissues when applied to seeds or soil. Likewise, dithiocarbamates such as mancozeb modify and inactivate proteins involved in DNA translation and transcription (Zarate-Ramos et al., 2022). Chloronitriles (chlorothalonil) reduce mycelial growth by competing with glyceraldehyde-3- phosphate for the active site of glyceraldehyde-3-phosphate dehydrogenase and by reducing fungal glutathione molecules to alternative forms. In addition, the degradation of this compound into byproducts that bind to target sites has been observed (Fairchild et al., 2013).

Although in some cases fungicides with the same mode of action are applied to the same crop or pathogen, studies have shown that Alternaria species exhibit cross-resistance to mancozeb, tebuconazole, iprodione, fludioxonil, and cyprodinil in Greece (Malandrakis et al., 2015), and to mancozeb and difenoconazole in China. This suggests that the use of non-site- specific fungicides may lead to reduced pathogen sensitivity and a greater capacity to cause disease, representing a risk to agricultural production (Yang et al., 2019).

The systemic fungicide Amistar GS® (azoxystrobin) at 500 ppm is also used against A. chrysanthemi, reducing foliar damage intensity by 50% and being associated with lower infection rates compared with other synthetic fungicides (Villanueva-Couoh et al., 2004). In postharvest fruits and in vitro, benzyl isothiocyanate has been used with favorable results at

0.1 mg mL⁻¹ and 0.56 mg mL⁻¹, serving as an efficient controller in fruits without affecting quality (Troncoso-Rojas et al., 2005). However, it is important to consider the timing of agrochemical applications during flowering or fruit development and the persistence of these compounds in fruits to avoid postharvest residues.

Similarly, in vitro evaluations have been conducted with Fosetyl-aluminum (800 ppm), Azoxystrobin (500 ppm), Imazalil (750 ppm), Prochloraz (450 ppm), Benomyl (500 ppm), and Thiabendazole (600 ppm). However, only Imazalil and Prochloraz demonstrated 100% effectiveness against Alternaria sp. (Herrera et al., 2011). This suggests possible resistance of Alternaria species to certain agrochemicals. Therefore, studying the resistance acquired by Alternaria species in the country to commercially available products is necessary.

In Sinaloa, azoxystrobin was evaluated in vitro at doses of 7 and 10 ppm; although it inhibited up to 99.5% of conidial germination in Alternaria alternata, it did not reduce mycelial growth (Félix-Gastélum and Gálvez-Figueroa, 2002). Nevertheless, chemical control is not environmentally friendly, as it causes environmental contamination and poses health risks to consumers due to toxic residues in food, as well as to workers who are in direct contact with the chemicals (Rangel-Ortíz et al., 2023). Therefore, the integration of additional management strategies is necessary.

Chemical control based on crop phenology. Although limited information exists in Mexico regarding prediction systems based on crop phenology, environmental variables, and inoculum density for initiating preventive applications of chemical fungicides against diseases caused by Alternaria species, studies from other countries provide insight into the efficient use of fungicides. In Mexico, stages of highest incidence and severity caused by Alternaria have been identified in onion crops; however, information on the practical application of these findings remains scarce (Reyes-Tena et al., 2023). In Israel, periods of greatest susceptibility to A. alternata in apple cultivation were determined through the development of a phenology-based management strategy. Synchronizing fungicide applications with the stage of maximum fruit susceptibility proved effective for controlling Alternaria rot, allowing optimization of fungicide use, cost reduction, and minimization of resistance issues (Lior et al., 2018).

On the other hand, inoculum load is an important factor to consider in preventive management with chemical fungicides. For example, inoculum load influences the severity of leaf spot caused by A. brassicae in cauliflower; therefore, effective disease management requires controlling the amount of inoculum in the soil, maintaining constant monitoring, and considering inoculum load as a key factor when interpreting the efficacy of chemical control (Sunitha and Jha, 2023).

Biological control. Various microorganisms have been evaluated as biological control agents against phytopathogenic fungi, with Trichoderma being the most extensively studied genus. In Mexico, the main species reported as biocontrol agents against phytopathogenic Alternaria species are T. harzianum, T. asperellum, and T. viride (Allende-Molar et al., 2022). This genus employs several mechanisms to suppress the growth and development of phytopathogens: (1) antibiosis, through the production of secondary metabolites that alter the permeability of phytopathogen lipid membranes; (2) competition for space and nutrients, whereby its rapid growth enables it to colonize areas also contested by other microorganisms, even occupying pathogen attachment sites on the plant; (3) mycoparasitism, in which Trichoderma grows chemotropically toward the pathogen, adheres to and coils around it, and induces the production of extracellular lytic enzymes (chitinases, glucanases, and proteases) that degrade the pathogen’s cell wall; and (4) induction of resistance, through activation of systemic resistance mechanisms that accelerate plant responses to phytopathogens by secreting proteins with enzymatic activity (Companioni et al., 2019).

In vitro evaluation is the primary approach for preliminary testing of a biological control organism. Several antagonism assays have been conducted with different Trichoderma species. For example, T. asperellum was evaluated against Alternaria sp., showing effectiveness rates between 50 and 93% (Matas-Baca et al., 2022), and in vivo evaluation of the same antagonist (100 mL) in apple trees demonstrated antagonistic capacity compared with the control (Madrid- Molina et al., 2023). Its effectiveness is attributed to the enzymatic production of glucanases and chitinases, which play a role in defense responses against Alternaria spp. by degrading the pathogen’s cell wall (Infante et al., 2009; Camacho-Luna et al., 2021). In recent years, numerous studies have focused on the use of biological control agents against a wide variety of phytopathogenic fungi; however, studies specifically targeting the control of Alternaria remain limited (Table 2).

Table 2

Alternaria spp.	Antagonistic species	Effective percentage (%)	Reference
Alternaria solani	Trichoderma harzianum	62.9-73.8	Michel-Aceves et al., 2008
A. solani	Trichoderma longibrachiatum	44.2-67.8	Michel-Aceves et al., 2008
A. solani	Trichoderma koningii	81.3	Michel-Aceves et al., 2008
A. alternata	Trichoderma asperellum	56-62	Rios-Velasco et al., 2016
A. alternata	Bacillus methylotrophicus	63	Rios-Velasco et al., 2016
A. alternata	Bacillus amyloliquefaciens	64	Rios-Velasco et al., 2016
A. alternata	Bacillus subtilis	38.2-71.9	Ruiz-Sánchez et al., 2016
A. alternata	Pseudomonas fluorescens	47	Rodríguez-Romero et al., 2019

Bacillus subtilis is also among the bacterial species most widely used as biocontrol agents of phytopathogens. The commercial product Probacil® (1 × 10⁸ cells per mL) has been tested in combination with salicylic acid against A. solani in tomato plants, resulting in reduced disease severity, increased plant growth, and higher fruit yield (Figure 2) (Espinosa-Vázquez et al., 2019). In vitro, B. atrophaeus showed antagonism against A. alternata, with 33.7% spore germination, an effect attributed to the presence of lipopeptides. This strain was compared with Brevibacterium frigoritolerans, which did not exhibit sufficient inhibition; however, conidial germination was only 12% (Chacón-López et al., 2021).

The effectiveness of biological control agents is attributed to the diversity of action mechanisms employed by these microorganisms, which are illustrated in Figure 3 (Martínez et al., 2013; Álvarez-García et al., 2020; Pedraza et al., 2020). However, the use of microorganisms requires time for them to act effectively due to their growth rate, and rapid- action products are often needed for pathogen control. Additionally, the cost of biological control is higher than that of chemical or other types of control, prompting ongoing efforts to identify new alternatives for managing phytopathogens.

Other control alternatives. In addition to biological control, new alternatives have been explored, such as the use of plant extracts, essential oils, or biopolymers. In the case of biopolymers, this is an area with great potential and research is still expanding; however, chitosan has been shown to possess antifungal activity and to increase the production of peroxidase, catalase, and phenylalanine ammonia-lyase, thereby enhancing plant defense (Rodríguez-Guzmán et al., 2019). When combined with biocontrol agents such as P. fluorescens, it inhibits up to 60.2% of mycelial growth and achieves 100% inhibition of conidial germination (Rodríguez-Romero et al., 2019).

Figure 3

Plant extracts. Plant extracts represent a beneficial alternative as a preventive method. Acetone extract of chilemecate (Salmea scandens) at concentrations of 4 000 and 5 000 ppm has shown promising in vitro results and effectiveness on tomato fruits against A. solani. This activity is attributed to the presence of carboxylic acids, aldehydes, ketones, and aromatic compounds, which may act as antagonists (Salas-Marina et al., 2021). Ethanol extract of mamey (Pouteria sapota) residues also exhibits inhibitory effects of up to 46.4% against Alternaria spp. (Rodríguez-Romero and Martínez-Ramírez, 2023). Essential oil of thyme (Thymus vulgaris) (1,000 ppm) displays in vitro antifungal activity against A. citri, the causal agent of citrus rot; its antagonistic effect is attributed to the presence of borneol, thymol, and carvacrol (Soto et al., 2006).

Developing effective extract-based products against phytopathogens is challenging; however, continued evaluation of diverse extracts has yielded promising results, and these products are safe for consumers and the environment (Villa-Martínez et al., 2015). Although they demonstrate good effectiveness, biopesticides require regulation by agencies such as the Secretaría de Salubridad y Asistencia (SSA), in coordination with the Secretaría de Agricultura y Desarrollo Rural (SADER) and the Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT), as permits must be issued for their production and manufacturing.

Microalgae. The use of microalgae has increased due to their low cost, ease of production, and versatile characteristics. They convert carbon dioxide into biomass, which is used to produce food for humans and animals, cosmetics, biofuels, wastewater treatment products, and plant biostimulants. Among the genera with the greatest commercial importance are Chaetoceros, Chlorella, Dunaliella, and Isochrysis (Ortiz-Moreno et al., 2019). In a study conducted by Schmid and collaborators (2022), several microalgae were evaluated against different phytopathogens, including A. alternata. The microalgae tested were Nannochloropsis sp., Phaeodactylum tricornutum, Scenedesmus obliquus, Chlorella vulgaris, and Spirulina sp. It was determined that only P. tricornutum exhibited antagonistic activity against the fungi tested, with the exception of A. alternata.

Nanoparticles. Nanoparticles possess antimicrobial and antifungal activity, making them more efficient nanobiopesticides than traditional pesticides (Wang et al., 2017). These particles can interact directly with the cell membranes of plant pathogens, causing structural alterations. Due to their small size, they are capable of penetrating the cell walls of bacteria and fungi, leading to membrane depolarization, loss of internal cellular contents, and ultimately cell lysis (Sirelkhatim et al., 2015). This effect is attributed to the gradual release of zinc ions (Zn²⁺) as ZnO NPs dissolve in the environment, which interferes with essential enzymatic processes, protein synthesis, and DNA replication, severely affecting microbial cells (Mishra et al., 2025). The application of zinc nanoparticles (ZnO) has been documented. Mishra et al. (2025) reported that mycogenic zinc oxide nanoparticles (produced using Trichoderma harzianum culture filtrate) inhibited the mycelial growth of Alternaria brassicae by 91.48% at 200 μg mL⁻¹, compared with chemically synthesized zinc nanoparticles at 200 μg mL⁻¹ (79.62%) and Mancozeb at 0.2% (82.96%). Silver nanoparticles (AgNPs) also show potential antifungal activity; Ansari et al. (2023) suggest that silver nanoparticles can enhance the growth and yield

of tomato plants while providing protection against Alternaria solani.

On the other hand, Cerna-Chávez et al. (2024) evaluated in vitro the inhibitory effect of silicon dioxide nanoparticles (SiO₂ NPs) and graphene nanoparticles (NPs-Graf), combined with extracts of Bacillus amyloliquefaciens (EcBa), on the mycelial development and reproductive structure formation of A. alternata. The treatment with silicon nanoparticles showed the strongest inhibitory effect, as it suppressed mycelial growth and reduced spore and sclerotia production by 84 to 100%.

In Mexico, studies on the use of nanoparticles against Alternaria species are limited. Hernández-López et al. (2018) developed α-pinene-loaded chitosan nanoparticles (P-CSNP) and a nano-structured edible coating (EC-PCSNP), and evaluated these nanoparticles on bell pepper (Capsicum annuum) inoculated with A. alternata under refrigeration to assess postharvest quality. They observed that the application of chitosan nanoparticles prevented the incidence and severity of the phytopathogen during 21 days of storage.