Arbuscular mycorrhizal fungi (AMF) form a symbiosis with a wide range of vascular plants including many important crop species. Apart from improved plant nutrition, AMF are reputed to control a number of plant diseases, especially soil-borne diseases. In this work the focus was laid on the role of AMF in the control of the soil-borne fungus Fusarium oxysporum f. sp. lycopersici (Fol) in tomato. Thereby, different tomato varieties and different intercropping partners were assessed. Additionally, root exudation and its role in disease development was selected as one specific area of interaction and investigated in greater detail. For the intercropping studies AMF were tested against Fol with tomato intercropped with either leek, cucumber, basil, fennel or tomato itself. Arbuscular mycorrhizal root colonization of tomato was clearly affected by its intercropping partner. Furthermore, bioprotective effects of AMF resulting in the decrease of Fol disease severity and/or compensation of plant biomass were evident. However, these effects depended on the intercropping partner. Leek and basil proved to be beneficial intercropping partners. Furthermore, wild-type, old and modern tomato cultivars alone were compared in their interactions with AMF and Fol. The cultivars differed in their susceptibility to AMF and Fol. Furthermore, bioprotective effects of AMF were also cultivar dependent. Additionally, alterations in root exudation of tomato mediated by AMF and Fol were investigated. AMF inoculation increased the germination rate of Fol in total exudates, whereas, the simultaneous inoculation of AMF and Fol decreased the germination rate of Fol in total exudates. The GC-MS analyses revealed an AMF-dependent increase of sugars and decrease of organic acids, mainly glucose and malate. Furthermore, an increase of chlorogenic acid in root exudates of tomato plants inoculated with AMF and Fol was found with HPLC analyses, an effect, which could be shown for the first time.