Fungal endophytes of cactus (Stenocereus spp.) as a potential alternative to alleviate drought stress in juveniles of Theobroma cacao L. ICS95

Theobroma cacao, one of Colombias most economically and socially significant crops, faces productivity challenges due to drought. This stress can reduce growth, leaf area, and stomatal conductance (Ks), and generate reactive oxygen species (ROS). Therefore, exploring solutions to enhance drought tolerance is crucial. This study aimed to evaluate the use of fungal root endophytes from Stenocereus spp. to induce drought tolerance in T. cacao genotype ICS95. In vitro drought tolerance screening identified five fungal isolates that exhibited the highest biomass production and less than 20% biomass loss under drought compared to non-drought conditions. The soil of juvenile T. cacao plants was inoculated with these isolates, and physiological and morphological parameters were assessed, including leaf water potential ({Psi}L), stomatal conductance (Ks), proline content, and growth. The results showed a significant decrease in {Psi}L and Ks in juveniles under drought stress, which was observed across all five fungal isolates tested. However, juveniles inoculated with Phoma sp. exhibited less negative {Psi}L and lower Ks than non-inoculated controls, suggesting that this fungus may be a potential inducer of drought tolerance in T. cacao ICS95. One intriguing result was that plants inoculated with this fungus accumulated less proline during the drought treatment. Under non-drought conditions, juveniles inoculated with Acrophialophora sp., Ectophoma sp., Fusarium sp., and Phoma sp. exhibited an increase in mean leaf area. These findings suggest that fungal endophytes associated with Stenocereus spp. could provide a potential alternative for alleviating drought stress and may also mediate growth promotion under non-drought conditions in cacao. ImportanceTheobroma cacao is among the worlds most valuable crops, yet its productivity is increasingly threatened by fluctuating rainfall and prolonged drought. Identifying sustainable strategies to mitigate these impacts is therefore critical. Xerophilic plants, such as Stenocereus spp., harbor diverse fungal endophytes adapted to arid environments, representing a promising source of microorganisms capable of enhancing stress tolerance in commercial crops. Our study demonstrates that cactus-derived endophytes could improve drought resilience in juvenile cacao by modulating physiological responses such as stomatal conductance and leaf water potential. Furthermore, under favorable conditions, some endophytes could promote growth by increasing leaf area compared to non-inoculated plants. These findings underscore the potential of fungal endophytes from arid ecosystems as biotechnological tools for sustainable cacao production, offering an environmentally friendly alternative to mitigate drought stress while enhancing plant performance.