Shoot morphology and strigolactone (SL) quantification in wild‐type (W115 (WT)) and PDR1 OE Petunia hybrida plants grown on full soil. (a) Leaf series (from cotyledon to leaf number 15) in 2‐month‐old WT (W115) and PDR1 OE plants. (b) Leaf areas in W115 and PDR1 OE from leaf 5 (l5) to leaf 12 (l12). (c) Representative stem sections (node 9). (d) Significant differences in stem section areas in W115 to PDR1 OE from internode 7 (in7) to internode 9 (in9). (e) Ratio of leaf length : width in WT and PDR1 OE plants. (f) Representative light microscopy pictures of adaxial (ad) and abaxial (ab) epidermal cells in WT and PDR1 OE middle blades. (g) Ratio of PDR1 OE : WT epidermal cell areas. (h) Germination rates of Phelipanche ramosa induced by shoot extracts of WT and PDR1 OE plants. 1 nM GR24 as positive control. (i) PDR1 OE : WT ratio for internode (in) elongation ± mycorrhization. (j) Germination rates of P. ramosa induced by root extracts of WT and PDR1 OE plants. 1 μM GR24 as positive control. Root extracts diluted 10−3 (high) and 10−5 (low). Bars: (a) leaves, 1 cm; (c) stems, 3 mm; (f) epidermal cells, 20 μm. Values are means ± SE. *, P < 0.05; **, P < 0.005; ***, P < 0.0005.