The Canary Island archipelago comprises eight islands located in the subtropical region of the Atlantic Ocean near the Tropic of Cancer, off the African coast of Western Sahara (between 27°37′-29°25′N and 13°20′-18°10′W). Its climate is characterized by low annual thermal variations, mainly due to the influence of cold ocean currents and trade winds from the NE (cold and humid) that blow for most of the year (Carracedo et al., 2002). The Canary Islands are one of the most biodiverse areas in the European Union and one of the most outstanding in the world for its endemism. This region contains half of Spain’s endemic flora and provides the right conditions for the cultivation of a wide variety of subtropical and tropical species (Madruga et al., 2016). Banana (Musa acuminata) is the most important crop in the Canary Islands. It covers a total area of 8,891 ha (38.9% of the cultivated area of the whole archipelago) and provides 63% of the total banana production in Europe (Food and Agriculture Organization of the United Nations, 2022; Instituto Canario de Estadística [ISTAC], 2022). Due to the commercial importance of the crop, since 2013, it has been included in the Register of Protected Designations of Origin (PDO) and Protected Geographical Indications (PGI) (EUR-Lex, 2013).

Various pests and diseases affect banana crops in subtropical areas. Among these, Fusarium wilt of musaceae, also known as Panama disease is worth highlighting. This disease is caused by the soil fungus Fusarium oxysporum f. sp. cubense (Foc) and is one of the most destructive diseases for the musaceae (Ploetz, 2015a). Tropical race 4 (Foc-TR4) is the most pathogenic among the major commercial cultivars of the Cavendish subgroup (AAA) (Ploetz, 2006). In the Canary Islands, studies carried out at the Department of Plant Protection of the Canary Institute of Agricultural Research (ICIA)¹ from the 1980s to the present have shown that the causal agent of Panama disease is the subtropical race 4 of Foc (Foc-STR4) and that Foc-TR4 has not been detected. Perera-González et al. (2023) showed that 23% of banana farms on Tenerife had plants with Foc symptoms (yellowing of leaves, drying of leaves, and xylem necrosis on corm and pseudostem). Nevertheless, the incidence of the disease is generally low (3.4% of plants on affected farms present symptoms of the disease), and these plants are usually found in places with poor drainage, acid pH, soil compaction, excessive humidity, and/or shady areas. In other (minority) cases, the incidence of the disease is higher (49.1% of plants with symptoms) and leads to abandonment or change in crops.

A large number of publications describe different alternatives to control the pathogen, however, several reasons make control difficult (Ploetz, 2015b; Dita et al., 2018; Siamak and Zheng, 2018). Among them are: (a) the ability of the pathogen to survive in the soil for long periods of time (more than 40 years) (Buddenhagen, 2009); (b) the spread of the pathogen through contaminated materials (plants, tools, farm equipment, irrigation water, etc.); (c) the endophytic properties of the fungus, which protect it from the action of contact fungicides or non-endophyte biological control agents (Bubici et al., 2019); (d) the lack of rotation in most commercial crops of intensive production (monoculture) cause the pathogen to multiply in a continuous cycle, increasing the inoculum in the soil over time (Dita et al., 2018). Considering these factors, probably, the most effective alternative for its control could be the use of resistant cultivars, although the appearance of new pathogenic variants of the fungus can overcome this resistance (Ploetz, 2015b; Dita et al., 2018). Nevertheless, the key measures to control the disease and prevent the spread of the pathogen in those regions free of the fungus or with low infestation levels are pathogen exclusion, contingency plans and destroying infected materials (Ploetz, 2015b; Dita et al., 2018).

Other management alternatives aimed at improving soil health are mainly based on the application of appropriate agronomic practices, the use of cover crops or the application of organic amendments and biological control agents (BCA) (Dita et al., 2018). In this sense, soil microorganisms have a fundamental role in plant health and protection, especially those that colonize the rhizosphere zone, by enhancing nutrient uptake, disease resistance, plant defense response, and tolerance to various biotic and abiotic stresses (Raaijmakers et al., 2009; Liu et al., 2021). A well-researched example is the genus Trichoderma (syn. Hypocrea, Hypocreales), which consist of more than 400 species (Cai and Druzhinina, 2021) divided into three representative groups, Harzianum, Trichoderma, and Longibrachiatum (Kubicek et al., 2019), known as linages (Gutiérrez et al., 2021). Trichoderma is a cosmopolitan and opportunistic filamentous fungus and a ubiquitous colonizer in almost all environments, commonly found in agriculture soils (Woo et al., 2023). Of particular interest in this genus are the processes involved in the biological control of plant diseases, with direct action on plant pathogens and indirect mechanisms through the induction of local and systemic plant defenses (Harman et al., 2004). Due to these characteristics, Trichoderma has remained a notable BCA and has become a popular protagonist as the key component of plant biostimulants, bioprotectants, biofertilizers, and soil amendments (Woo et al., 2023).

In relation to the biological control of Foc, a wide variety of scientific articles describe the biocontrol potential of Trichoderma against this pathogen (mainly on Foc-TR4) (Bubici et al., 2019; Izzati et al., 2019; Damodaran et al., 2020). However, there are few studies that evaluate Trichoderma isolates obtained from banana soils or plants (Thangavelu et al., 2004; Thangavelu and Mustaffa, 2010; Caballero et al., 2013; Galarza et al., 2015; Thangavelu and Gopi, 2015; Chaves et al., 2016; Taribuka et al., 2017; Damodaran et al., 2020; Olowe et al., 2022). In many cases, the reduced efficacy of BCAs under field conditions could be due to their inability to grow under local biotic and abiotic environmental conditions. For this reason, it is extremely important to know the natural microbial biodiversity in the different ecosystems and to have a wide collection of native strains adapted to the specific agroclimatic conditions of the crop where it is to be applied.

The main purpose of this study was to collect a representative number of rhizosphere soil samples from healthy and Foc-STR4-affected banana plants in different agroecosystems on Tenerife, in order to: (i) describe the diversity and distribution of Trichoderma species in different agroecosystems, (ii) develop and preserve a culture collection of native Trichoderma species, and (iii) evaluate the influence of soil chemical properties on Trichoderma community composition. The practical importance of this study is to provide an initial knowledge base about the diversity and distribution of Trichoderma species in different banana ecosystems of Tenerife, and to preserve a culture collection of native Trichoderma as a reservoir of potential beneficial microorganisms to develop sustainable agro-biotechnological alternatives. Indeed, it is important to highlight the role of the microbial culture collection as an essential source for the selection of potential BCA against Foc-STR4 or plant growth promoting microorganisms (PGPM) naturally adapted to the agroclimatic conditions of banana crops in the Canary Islands.

This is the first work that describes the Trichoderma community in the rhizosphere soil of banana plants with and without symptoms of Panama disease in the different bioclimatic conditions and growing areas of the island of Tenerife. In addition, six species of Trichoderma are reported for the first time in the Canary Islands (T. afroharzianum, T. asperellum, T. atrobrunneum, T. guizhouense, T. hamatum, and T. hirsutum) and six species that have not been previously reported associated with banana rhizosphere (T. afroharzianum, T. atrobrunneum, T. gamsii, T. guizhouense, T. hirsutum, and T. virens). Furthermore, we detected two groups of isolates, which we identified as T. aff. harzianum and T. aff. hortense, corresponding to putative novel endemic species to be described in the near future.

It is widely recognized that soil features, plant characteristics, microorganism diversity, agronomic management, and environmental factors significantly influence the plant/root-microorganism relationship (Lemanceau et al., 1995). Likewise, the amount of phytopathogen in the soil and its relationship with BCA microorganisms is another important aspect to consider. Xue et al. (2015) found significantly lower colony forming unit numbers of F. oxysporum f. sp. cubense in the disease-suppressive rhizospheric soil (no disease plants) (approximately 5 × 10³ cfu/g) compared to the wilted banana rhizosphere (disease plants) (approximately 1 × 10⁵ cfu/g). Likewise, Zhou et al. (2019) quantified a F. oxysporum f. sp. cubense population less than 1.3 × 10³ cfu/g in disease-free soils and more than 1.7 × 10³ cfu/g in diseased soil samples of three banana farms in China. Based on these results, the authors indicate that a Foc population lower than 1.3 × 10³ cfu/g does not cause Fusarium wilt banana in the field. However, these data are not in agreement with our results where 41.6% of diseased soil samples had less than 1.3 × 10³ cfu/g, and no significant differences were detected between the rhizosphere Fusarium population of healthy and diseased plants (Figure 1). On the other hand, soil chemical parameters can play an important role in the amount of the pathogen. In this regard, Senechkin et al. (2014) and Zhou et al. (2019) describe a positive correlation between soil organic matter and Fusarium abundance, and a negative correlation for pH. In this aspect, the results of our work are consistent with these authors: the Foc population in the soils of the northern slope was significantly higher than in the southern soils, where organic matter and pH were higher and lower, respectively (Figure 1 and Table 4).

Trichoderma is a fungus with a worldwide distribution and widely studied in different natural and agricultural ecosystems of the world. However, there are few works related to Trichoderma distribution and biodiversity in banana rhizosphere soils under different environmental conditions or in relation to the health status of the plant. In the specific case of the Canary Islands, Zachow et al. (2009) analyzed the fungal diversity in the rhizosphere of endemic plants of six different climatic and vegetation zones in Tenerife, indicating that it is an interesting place to study biodiversity and species diversification. However, in contrast to other fungi analyzed, the Trichoderma species described were ubiquitous and widely distributed and no significant differences were detected between the biodiversity of the different sampling areas. Moreover, Jaklitsch and Voglmayr (2015) analyzed Trichoderma populations in Tenerife, La Palma, and La Gomera (the western Canary Islands) and identified 17 described species and 3 putatively new Trichoderma species, of which 62% belonged to the Viride clade and 16.7% to Trichoderma harzianum s.l.

Trichoderma harzianum is a cosmopolitan species widely distributed in different parts of the world, such as Tunisia (Sadfi-Zouaoui et al., 2009), Sardinia (Migheli et al., 2009), Egypt (Gherbawy et al., 2004), South America (Barrera et al., 2021), Canary Islands (Tenerife) (Zachow et al., 2009), etc. Moreover, it is the species with the highest number of citations in soil samples from banana crops: China (Yang et al., 2016; Du et al., 2020), India (Thangavelu et al., 2004; Thangavelu and Gopi, 2015), Malaysia (Naher et al., 2019), Mexico (Hernández-Domínguez et al., 2019), and Tenerife (Canary Islands) (Ciancio et al., 2022). In our study, this species was detected in healthy and Foc-STR4 diseased plants on both slopes of the island (Figures 6–8). Likewise, T. aff. harzianum (a putatively new species) was one of the dominant species (27.48% of the isolates) (Figures 2, 8) and was detected on both slopes of the island in healthy and diseased plants (Figure 7). Notably, it was the only species detected in 100% of the southern farms in the rhizosphere of healthy plants (Figure 6). Additionally, a positive correlation (p < 0.05) with the soil pH was detected on the northern slope (Figure 9). These results agree with those described by Mayo-Prieto et al. (2021), who observed an increase in the development of T. harzianum T059 in Esla-Campo’s soils with high pH values.

Trichoderma virens was the most frequently isolated species (35.89% RA) (Figure 2). On the northern slope, it was detected in 62.5% and 75.0% of the farms (from healthy and diseased soils samples, respectively), while on the southern slope it was observed in 66.7% and 83.3% of the farms (healthy and diseased soils, respectively) (Figures 6, 7). According to the Olmstead-Tukey test, T. virens was classified as a dominant species on both slopes of the island (Figure 8) and in the north, its abundance was significantly positively correlated (p < 0.001) with the phosphorus content in the soil (Figure 9). Surprisingly, this species has not been previously described in banana soils elsewhere in the world and, in Tenerife, it was identified by Ciancio et al. (2022) from a “control” sample of rhizospheric soil free of banana roots. Trichoderma virens is a potent bioeffector for plant protection (biofungicide) and plant growth promotion (biofertilizers) (Harman et al., 2004) and is currently marketed as a BCA in organic farming (Woo et al., 2023). Muthukathan et al. (2020) identified T. virens proteins involved in banana/root-Trichoderma interaction that could be relevant for disease management in banana. These proteins are associated with penetration, colonization and induction of the plant defense response. For this reason, finding this dominant species in the banana soils rhizosphere in Tenerife opens a promising avenue of research into the selection of potential Foc-STR4 biocontrol agents adapted to the environmental and crop conditions of the Canary Islands.

Trichoderma atrobrunneum is a widely distributed species and has been described in different parts of the world in soil samples or decaying wood of North America, Europe (Jaklitsch and Voglmayr, 2015), and Africa (Haouhach et al., 2020; Nyang’au et al., 2023). However, none of the previous works performed in the Canary Islands or in banana soils in other parts of the world describe this species. In our work, the highest occurrence frequency in the rhizosphere of healthy plants from the northern slope was observed (Figures 6–8) and a significant positive correlation (p < 0.05) with the soil pH of the northern slope was detected (Figure 9). Therefore, this is the first time it has been described in Tenerife and in banana rhizosphere.

The ability of T. atrobrunneum as BCA has been demonstrated in many studies. The genomic analysis reveals the presence of different genes encoding for carbohydrate-active enzymes, proteins associated with the synthesis of secondary metabolites, peptaboils, epidithiodioxopiperazines, and siderophores potentially involved in parasitism, saprophytic degradation as well as in biocontrol and antagonistic activities (Fanelli et al., 2018). Pavlovskaya et al. (2020) demonstrate the ability to control Fusarium wilt in cucumber through an efficient protective effect and growth stimulation. Natsiopoulos et al. (2022) report the efficacy of an isolate obtained in Serres (Northern Greece) from corn cobs to significantly reduce the in vitro development of F. oxysporum f. sp. lycopersici and to decrease the incidence of the disease in tomato plants grown in pots. This background demonstrates the biocontrol capacity of T. atrobrunneum and its potential use in the control of Foc-STR4 on banana crops in the Canary Islands.

Trichoderma guizhouense was first described in soil samples from two different regions in Guizhou province in China (Li et al., 2013) and has subsequently been detected in different countries in southern Europe (Croatia, Italy, Greece, and Spain) and South America (Argentina) (Jaklitsch and Voglmayr, 2015; Barrera et al., 2021). However, in the Canary Islands, previous works do not describe this species, whereas in our study, we obtained isolates from both slopes of the island in the rhizosphere of healthy and diseased plants (Figures 6–8). Furthermore, a significant positive correlation (p < 0.05) was detected with the phosphorus content of the soil on both slopes (Figure 9). Regarding its agronomic utility, several studies have demonstrated the ability of this species to promote plant growth, produce volatile compounds and antioxidants, and control the development of phytopathogens (Wang and Zhuang, 2019; Liu et al., 2021). In this regard, the NJAU 4,742 strain isolated in China from aromatic plant tissue has been intensively studied for its antifungal capacity against different plant pathogens of different crops, including Foc-TR4 (Zhang et al., 2016, 2019; Pang et al., 2020).

Trichoderma hamatum has been described in banana soils in Mexico with a relative abundance of 5% (referring to the total number of Fusarium and Trichoderma isolates evaluated) (Hernández-Domínguez et al., 2019). In our work, this species constituted 4.6% (RA) of the Trichoderma isolates (Figure 2) and was only detected in samples from the northern slope as a dominant species in healthy plants and rare in diseased plants (Figures 7, 8). Previous works in the Canary Islands have not reported this species, while in other parts of the world it is described as a widely distributed species in different environmental conditions. Danielson and Davey (1973) and Jiang et al. (2016) highlight the ability of T. hamatum to tolerate excessive moisture conditions in forest soils in the United States (North Carolina, Virginia, and Washington) and in farmland soils of East China, respectively. However, Sadfi-Zouaoui et al. (2009) found T. hamatum to be a dominant species in all areas of Tunisia and detected no differences in its distribution with respect to different climatic conditions. By contrast, in Tenerife, the distribution of this species seems to be affected by the climatic and soil conditions of the slope, with the northern area being more favorable for its development (Figures 6–8). Additionally, highlighting the significant negative correlation (p < 0.01) with the soil pH (Figure 9) could explain its non-detection in the soils of the southern slope (significantly more alkaline than those of the north) (Table 4). This result would agree with that described by Danielson and Davey (1973), who define T. hamatum as one of the most widely distributed species in North American acid forest soils. Another aspect to highlight in our study is the significant positive correlation (p < 0.05) with the total nitrogen and the organic matter content (Figure 9), which could also contribute to the non-detection in the southern slope soils (with a significantly lower amount of organic matter) (Table 4). These results concur with those described by Migheli et al. (2009) on Sardinia (Italy), where they describe a positive correlation with the content of organic compounds in the soil.

Trichoderma asperellum is a species widely used as a BCA against different pathogens, including the different “special forms” (f. sp.) of F. oxysporum (Patel and Saraf, 2017; Sehim et al., 2023). Therefore, this species is part of the active ingredient of several microbial fungicides marketed in different countries around the world (Woo et al., 2023). In banana soils, it is cited in different places, such as: India (Thangavelu and Gopi, 2015; Damodaran et al., 2020), Nigeria (Akinyele et al., 2019), and China (Win et al., 2021). Some authors also describe it as an endophytic species of banana (Xia et al., 2011; Thangavelu and Gopi, 2015; Olowe et al., 2022). However, in the Canary Islands, previous works do not describe this species in any of the bioclimatic conditions, while in our study, it was detected as a rare species on the northern slope of healthy and diseased plants (Figures 6–8). The non-detection in the southern soils could be due to the inability to establish in the warmer and drier conditions of this slope of the island. In this sense, similar results were observed by Migheli et al. (2009) on the island of Sardinia (Italy).

Trichoderma afroharzianum is an opportunistic environmental species with an outstanding aptitude for biocontrol, plant growth promotion and enzyme production (Chaverri et al., 2016; Xiao et al., 2023). Previous studies do not report this species in the Canary Islands or in the banana rhizosphere in other parts of the world. In this study, this species was detected with a low occurrence frequency (rare species) on the southern slope of both types of plants (healthy and diseased) (Figures 6–8).

Trichoderma longibrachiatum has been previously described in banana soils in different parts of the world: Mexico (Hernández-Domínguez et al., 2019), Brazil (Sanó et al., 2022), and Tenerife (Spain) (Ciancio et al., 2022). In our work, this species has been detected as rare (Figure 8) in soils from the southern slope (Figures 6, 7), which agrees with what was previously described by Ciancio et al. (2022).

Trichoderma aff. hortense was first described in Argentina from horticultural soil samples. However, isolates of this species previously identified under other names (T. harzianum, T. aureoviride, Hypocrea lixii) have been described in Japan, Italy, and New Zealand, suggesting a cosmopolitan distribution (Barrera et al., 2021). In our study, the tef1-α gene sequences obtained from banana soil isolates from Tenerife were related to the same clade as the T. hortense sequences. However, these sequences were not identical to those deposited in the GenBank database (95.6% similarity), therefore, we use the term affinis (aff.) to indicate that the OTUs are similar but not identical to the assigned species (accession no. MH253895). According to the Olmstead-Tukey test, this species is classified as rare in the banana crops of Tenerife (Figure 8), with a low number of isolates (3) from the rhizosphere of diseased plants from a single farm on the southern slope (Figures 6, 7).

Trichoderma gamsii has been described in Greece, Italy, Spain, Africa, India, and China (Migheli et al., 2009; Ding et al., 2012; Rinu et al., 2014; Jaklitsch and Voglmayr, 2015). Zachow et al. (2009) describes this species in Tenerife in soil/rhizosphere samples from different vegetation zones: Arico (Cardonal/Tabaibal; subtropical, arid) and Buenavista del Norte (Laurisilva/Fayal-Brezal; subtropical, subhumid). In our study, a single isolate was obtained from the rhizosphere of a healthy plant from the southern slope of Tenerife (Guía de Isora) (Figures 6, 7) and to our knowledge, there are no previous records associated with banana crops in other parts of the world. Trichoderma gamsii has already demonstrated it can reduce the growth of Fusarium head blight in wheat and F. oxysporum rot and wilt black gram (Vigna mungo) (Alukumbura et al., 2022; Valan-Arasu et al., 2023). Consequently, the ability of T. gamsii to control F. oxysporum f. sp. cubense STR4 under the environmental conditions of the Canary Islands should be analyzed.

Trichoderma hirsutum was first described in China in the Shennongjia Natural Reserve in soil samples at 1,200 m.a.s.l. (Chen and Zhuang, 2017) and subsequently in northern Algeria (Sub-humid bioclimate) at very low frequency from the tomato rhizosphere (Benttoumi et al., 2020). In Tenerife, a single isolate was obtained from the rhizosphere of a healthy plant from the northern slope (La Orotava) (Figures 6, 7).

This work represents the first investigation of the biodiversity of Trichoderma species in the soil rhizosphere of the Canary Island banana agroecosystem. The results presented here mainly concern the taxonomic analysis of Trichoderma and the distribution of the species in the rhizosphere of healthy and Foc-STR4 diseased plants in different bioclimatic conditions of Tenerife (Canary Islands, Spain). The findings demonstrate the biodiversity of Trichoderma in banana crops. Many of the species identified (6 out of 12 total) had not been previously described in the Canary Islands (T. afroharzianum, T. asperellum, T. atrobrunneum, T. guizhouense, T. hamatum, and T. hirsutum) or associated to banana rhizosphere (T. afroharzianum, T. atrobrunneum, T. gamsi, T. guizhouense, T. hirsutum, and T. virens). Therefore, to the best of our knowledge, this work is the first report of these species in the Canary Islands or in banana ecosystems. In addition, two putative novel species, named T. aff. harzianum and T. aff. hortense, were detected. The analysis of species distribution showed that T. virens and T. aff. harzianum were the most abundant (35.89% and 27.48% RA, respectively) (Figure 2) and dominant species in the rhizosphere of banana soils on both slopes of Tenerife (north and south) (Figures 7, 8). While other species were mainly associated with a particular bioclimatic condition: T. hamatum, T. asperellum, and T. hirsutum were isolated only on the northern slope, and T. afroharzianum, T. longibrachiatum, T. gamsii, and T. aff. hortense on the southern slope (Figures 6, 7). Probably, the species associated with the northern slope are better adapted to lower temperatures and higher humidity, while the species associated with the southern slope are better adapted to higher temperatures and lower humidity. Likewise, the edaphic characteristics could influence species distribution: soils on the southern slope had a significantly higher pH than those on the north, while the relationship of the organic matter was the opposite.

Trichoderma species have long been recognized as agents for the control of plant diseases and for their ability to enhance root growth and development, crop productivity, resistance to abiotic stresses, and nutrient uptake and utilization (Berg et al., 2005). Knowledge and understanding of the biodiversity of the rhizosphere microbiota in relation to plant health and the environment is essential for the prevention and treatment of plant diseases (Xue et al., 2015). For this reason, it is recommended to select potential biocontrol agents from native Trichoderma isolates obtained under similar conditions (soil or plant parts) to those encountered during pathogen control (Howell, 2003). These isolates will be naturally adapted to the specific environmental conditions of biocontrol (temperature, humidity, nutrient availability, microbiota, etc.) and represent a suitable strategy to overcome problems related to the introduction of exogenous microorganisms (Howell, 2003; Anees et al., 2010). In this context, the analysis of the Trichoderma population distribution and the culture collection developed in this study will contribute to the future selection of new isolates or novel native species as BCAs against the most important banana disease in the Canary Islands (Foc-STR4). In this sense, our work demonstrates the existence of a high number of Trichoderma species with biocontrol potential and that are naturally adapted to the environmental and agronomic conditions of banana cultivation in the Canary Islands. This is in line with the ultimate goal of finding a cost-effective and environmentally friendly alternative for disease control.

The datasets generated for this study can be found in the GenBank (https://www.ncbi.nlm.nih.gov/genbank/) accession number (OQ858692 to OQ858800).

RC-D: Data curation, Formal analysis, Investigation, Software, Visualization, Writing – original draft. PB-L: Data curation, Investigation, Writing – original draft. MJV: Funding acquisition, Resources, Supervision, Writing – review & editing. FL: Formal analysis, Funding acquisition, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – review & editing.