Mycorrhization is initiated by SL exudation which induces AMF hyphal branching towards the plant root (Akiyama et al., 2005). We therefore assessed whether PDR1 OE plants have higher mycorrhization levels than the wild‐type. As mycorrhization levels are influenced by soil Pi conditions (Breuillin et al., 2010), we quantified mycorrhization in different soils, from the Pi‐richer ‘natural soil mix’ to the Pi‐poorer ‘mineral soil’, going through ‘clay’ and mixed substrates with intermediate Pi amounts (see Fig. 1a, Table 1 and Supporting Information Methods S1; Table S1 for statistical analysis).