Abstract: The rhizosphere is known to be a highly dynamic environment, where plant – microbe,plant – plant and microbe – microbe interactions take place. Components of root exudates can actas trigger for such interactions. For this work a model system was created consisting of tomato(Solanum lycopersicum L.), the intercropping partner cucumber (Cucumis sativus L.), thesoilborne tomato pathogen Fusarium oxysporum f.sp. lycopersici (FOL) and the arbuscularmycorrhizal fungus Glomus mosseae (GM).Tomato/tomato and tomato/cucumber combinations were grown together in pots andreceived the following treatments: FOL, AMF, FOL and AMF in combination, to assess changesin root exudation, the AMF colonization rate and the FOL infection rate. Furthermore, theexudates were used for in vitro tests of the initial behaviour and development of FOL and foranalysing the components (e.g. sugars, secondary metabolites) of the exudates. FOL significantlyincreased the AMF colonization rate in the FOL and AMF combination compared to the AMFtreatment in tomato/cucumber, whereas for the tomato/tomato combination no such effect couldbe detected.