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 Colombia's most 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. Therefore, exploring solutions to enhance drought tolerance is crucial. This study aimed to (i) design a strategy to select fungal root endophytes with the potential to alleviate drought stress in plants; (ii) isolate fungi 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 conditions compared with 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 (ΨL), Ks, proline content, and growth. The results showed a significant decrease in ΨL and Ks in juveniles under drought stress, which was observed across all five fungal isolates tested. However, juveniles inoculated with Phoma sp. exhibited significantly less negative ΨL 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 Fusarium sp. exhibited a significant increase in specific leaf area under non-drought conditions compared to non-inoculated control. These findings suggest that fungal endophytes associated with Stenocereus spp. affect the physiological response of cacao juveniles under drought conditions.IMPORTANCETheobroma cacao is among the world's 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 juveniles of cacao, in particular, the fungal endophyte Phoma sp. maintained less negative leaf water potential values under drought stress conditions and exhibited significantly lower proline accumulation compared to non-inoculated controls. 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. Further studies should explore the role of fungi when affecting plant proline metabolism.