| Summary: | A greenhouse experiment was established with loquat plants to investigate the role of arbuscular mycorrhizal fungi (AMF) in the control of the white root rot fungus <i>Armillaria mellea </i>and to determine the changes produced in the plant metabolome. Plants inoculated with two AMF, <i>Rhizoglomus irregulare</i> and a native AMF isolate from loquat soils, were infected with <i>Armillaria</i>. Although mycorrhization failed to control the <i>Armillaria</i> root infection, the increased growth of infected plants following inoculation with the native mycorrhizal isolate suggests an initial tolerance towards <i>Armillaria. </i>Overall, metabolomics allowed highlighting the molecular basis of the improved plant growth in the presence of <i>Armillaria</i> following AMF colonization. In this regard, a wide and diverse metabolic response was involved in the initial tolerance to the pathogen. The AMF-mediated elicitation altered the hormone balance and modulated the production of reactive oxygen species (mainly via the reduction of chlorophyll intermediates), possibly interfering with the reactive oxygen species (ROS) signaling cascade. A complex modulation of fucose, ADP-glucose and UDP-glucose, as well as the down-accumulation of lipids and fatty acids, were observed in <i>Armillaria</i>-infected plants following AMF colonization. Nonetheless, secondary metabolites directly involved in plant defense, such as DIMBOA and conjugated isoflavone phytoalexins, were also involved in the AMF-mediated plant response to infection.
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