Endophytic fungi live inside plant tissues asymptomatically forming a symbiotic relationship. Entomopathogenic fungi (EPF) can be experimentally established in several plant species as endophytes, causing growth promotion and affect plant-herbivore interactions, likely by altering plant physiological responses. However, the role of plant physiological responses in plant-fungus-herbivore tripartite interactions has not been examined. Steroidal glycoalkaloids (SGAs) are plant secondary metabolites harboring bioactive properties against arthropod pests. In the present study, the effects of seed treatments by three entomopathogenic fungal isolates, Beauveria bassiana, Metarhizium brunneum and Metarhizium robertsii on tomato (Solanum lycopersicum) plant growth and reproduction of the two-spotted spider mite (Tetranychus urticae Koch) were evaluated through in planta feeding trials. The variability in selected SGAs were determined in the tomato plants by LC-MS after fungal inoculations and T. urticae infestations. The results revealed that B. bassiana colonized all plant parts whereas Metarhizium isolates were only able to colonize the stem and roots. All the isolates significantly increased plant height and biomass compared to the un-inoculated control. T. urticae reproduction was highest in plants inoculated with M. brunneum, which also produced low concentrations of SGAs. In contrast, tomato plants inoculated with B. bassiana and M. robertsii produced significantly higher amounts of secondary metabolites and exhibited lower rates of T. urticae reproduction. We conclude that EPF endophytes alters profiles of specific plant secondary metabolites to influence the biotic interaction of tomato with T. urticae. The study provides a link between the ecological effects and the physiological responses of tomato plants caused by EPF inoculations, with their implications in plant protection strategies.
Coauthors: Pablo Cárdenas – University of Copenhagen;Birgit Jensen – University of Copenhagen;Nicolai Meyling – University of Copenhagen