Entomopathogenic fungal endophytes in plant-fungus herbivore interactions: exploring the importance of selected physiological responses in regulation of arthropod populations

Abstract

Entomopathogenic fungi (EPF) are well-studied natural enemies of insect and mite pests and several isolates with relatively broad host ranges have been developed as biological control agents. Besides their direct interaction with insect and mite hosts as pathogens, these fungi are also able to associate symbiotically with plants as endophytes, hence living inside plant tissues asymptomatically. Several species of EPF can be experimentally established as endophytes in a range of plant species, including important crops, causing growth promotion and affecting plant-herbivore interactions. The effects of these endophytes on insect herbivores have been widely studied, but the mechanisms behind the reported effects are not documented. The general absence of fungal propagule production in colonized plant tissues and lack of infection in insects feeding on endophytically colonized plants support the notion of antibiosis and feeding deterrence over direct infection by EPF endophytes. Moreover, plants colonized by EPF below-ground can lead to effects on herbivores above-ground, suggesting complex interactions between the two organisms, potentially mediated by changes in the physiological response of the plant. This thesis addresses the question of how EPF seed inoculations can alter plant physiology with a focus on modifications of the activities of key carbohydrate and antioxidant enzymes and profiles of specific plant secondary metabolites (PSMs) and evaluate the potential role of these compounds in plant-fungal-herbivore tripartite interactions. […]