In fact, mycorrhizal fungi apparently fail to unleash a complete unspecific defense cascade by host root. According to Dumas-Gaudot et al., this behavior could be explained not only because the fungus shows low elicitation ability, but also because it possesses fungal inhibitors or because compatibility fungal factors exist which could interact with elicitor’s activity, stopping or reducing it. As can be seen in short-time experiments, the initial defense reaction, characterized by an early oxidative burst, was really attenuated in roots in contact with AMF, never reaching MeJA elicited roots levels neither PF treated roots one to several days or weeks after the interaction with AMF, as one to three months is the normally agreed time to develop a complete mycorrhization process from the first contacts for colonization. Therefore, this study’s interesting and Axitinib revealing experimental setting is able to reflect what happens from the very first step of recognition on. So, it was during these early stages when the first defense reactions against pathogens attack by ROS production were recorded, and thus was possible to check how roots attenuated these defenses when they were in contact with an AMF, not with a PF. Taken together, our results regarding redox activities indicate that, contrastingly to what happened with PF, roots attenuated their redox defense reactions against AMF from the very early stages of fungal contact. These results are in agreement with Hause and Fester’s revision on plant-micorrhyzal fungus interactions, where they concluded that defense processes occur in a moderate way after these contacts. Our phenolic content results also indicate that roots clearly discriminated between AMF and PF contact regarding the biosynthesis of the measured secondary phenolic methabolites, these being higher when in contact with PF but not AMF, at least from 8 to 24 h. Induction of phenolic compounds biosynthesis is a classic defense reaction to pathogens attack. Some of these compounds are excreted and linked to cell walls where oxidyzed by ECPOXs with H2O2 from the oxidative burst, forming lignin and suberin which harden cell walls and avoid or at least difficult pathogen penetration. Others, as flavonoids and some phenylpropanoids, are phytoalexins that plants synthesize as toxins against microorganisms. Therefore, root response to contact with PF could be a typical defense reaction, as all the secondary phenolic methabolites increased with fungal contact time. However, this response was strongly attenuated when roots contacted AMF, and no significant increases in phenolics biosynthesis was observed. Meanwhile, it is known that some flavonoids present in roots exudates stimulate micorrhyzation by inducing germination of AMF spores and positively affecting hyphal growth during symbiosis. Also, Vierheiling and Piche observed a slight increase in flavonoids content after 2 h AMF contact with roots with respect to controls. More recently, Abdel-Lateif et al. have reviewed the role of flavonoids in the establishment of plant roots endosymbioses, concluding that changes in flavonoid pattern of AMF treated roots suggest they play a regulatory role in first stages of colonization and in later stages of AM association.