Biomasses and mycorrhization rates of PDR1 OE and wild‐type Petunia hybrida plants on soils containing different amounts of inorganic phosphate (Pi). (a) Pi abundances in soil, clay and mineral soil. (b) Mycorrhization rates at 4 wk after germination (wag) on natural soil mix in wild‐type (W115, WT), PDR1 OE (OE), the wild‐type background for pdr1 ko (W115 × W138) and pdr1 ko. (c, d) Glomus intraradices (now Rhizophagus irregularis) TUBULIN_1 (GiTUB_1) expression levels in wild‐type and PDR1 OE roots at 6 and 8 wag. (e, f) Glomus intraradices (now Rhizophagus irregularis) TUBULIN_2 (GiTUB_2) expression levels in wild‐type and PDR1 OE roots at 6 and 8 wag. (g) Shoot biomass production on clay+. (h) Shoot biomass production on natural soil mix. Values are means ± SE. *, P < 0.05; **, P < 0.005; ***, P < 0.0005.