Abstract: Arbuscular mycorrhizal fungi (AMF) are soil fungi that form mutualistic symbioseswith the roots of about 80% of all terrestrial plants. The association improves plant fitness interms of nutrition and resistance to biotic and abiotic stresses. We analyzed the susceptibility ofmycorrhizal and non-mycorrhizal tomato plants to the necrotrophic fungus Botrytis cinerea,causal agent of gray mold in tomato leaves. Disease severity was lower in mycorrhizal plants.Moreover, the amount of pathogen in the tissues was significantly reduced in those plants.Similar results were obtained in whole plant and detached-leaf assays, confirming MycorrhizaInduced Resistance (MIR) to B. cinerea. We have analyzed the possible role of jasmonateregulated defense responses in the enhanced resistance. The induction of jasmonic acid (JA)-dependent marker genes in response to Botrytis inoculation was higher in mycorrhizal plants.Furthermore, mycorrhizal plants displayed a potentiated response to exogenous application of JA.Altogether, our results suggest that systemic resistance to B. cinerea in mycorrhizal plants isassociated to priming of JA-dependent responses.