Plant growth promotion and biocontrol by novel thermotolerant fungal strains isolated from an active volcano crater

Microorganisms present in the rhizosphere of plants from extreme environments have become a subject of great interest as an alternative to chemical fertilizers for sustainable agriculture. This study focused on the isolation, identification and characterization of extremophilic rhizospheric fungi strains present in a habitat with challenging environmental conditions in terms of temperature, pH, and heavy metal concentrations. Studies were conducted with the aim of finding new microorganisms for the development of novel, robust inoculants that meet the agricultural needs of Solanum lycopersicum , a crop consumed worldwide that, at least in Mexico can be exposed to heat shock in certain seasons. All the strains showed at least five plant growth promoting traits. Noticeably two of the isolated strains (R_34 and R_40) produced indole related compounds (probably indoleacetic acid (IAA)); others hydrolytic enzymes (cellulases, xylanases, and chitinases), as well as siderophores and showed the ability to solubilize inorganic phosphate. All strains reduced the progression of infection caused by Botrytis cinerea on S. lycopersicum leaves and fruits compared to the control, and they also inhibited the growth of various phytopathogenic fungi under in vitro conditions, suggesting an important role in biological control. The microorganisms were identified at the species level through phylogenetic analysis. The fungal strains belonged to the genus Trichoderma sp., Penicillium sp., and Aspergillus sp. In addition, these fungi demonstrated the ability to enhance germination rates, and overall plant growth in S. lycopersicum compared to controls. This research demonstrates that extremophilic fungi can serve as effective probiotics for crops, allegedly in regions affected by climate variability and heatwaves.