Most terrestrial flowering plants have the ability to establish symbiotic associations with arbuscular mycorrhizal (AM) fungi. The fungus improves the uptake of water and mineral nutrients in the host plant, mainly phosphorus and nitrogen, in exchange of photoassimilates. AM symbiosis not only promotes plant growth through facilitation of nutrient uptake, but it might also protect the plant from abiotic and/or biotic stresses. The benefits received by the AM symbiosis vary depending on the host genotype and the AM fungus species. In nature, as well as in crop fields, different AM fungi can be present in the soil or the plant, and affected by P availability or plant genotype. This has been little documented in field-grown crops however. In this study, we examined AM colonization in roots of a panel of maize genotypes grown in soils with contrasted P levels. We examined the relative level of colonization by 5 different AM fungi. Field experiment was carried out at the long-term P fertilizer trial of INRA-Auzeville (SW France). The field consisted in 4 P levels replicated in 4 blocks, ranging from P-deprived soils (P0, soil that had not been fertilized for 45 years), to soils that have been under excess P fertilization (P4, 4-fold the P offtake by crops). A total of 23 maize genotypes (selected for their contrasting root traits) grown in the two extreme P regimes (P0 and P4) were assessed. The level of root colonization was examined by microscopy observations of trypan-blue stained roots. AM colonization was further quantified by qPCR. Differences in susceptibility to AM colonization among the different maize genotypes grown under different P levels will be presented. Acknowledgement: This research was part of the EURoot project, which received funding from the European Community Seventh Framework Programme FP7-KBBE-2011-5 under grant agreement no.289300.