One-half-strength modified Murashige and Skoog medium (pH 5.7) with 0.7% Phyto agar (Duchefa Biochemie B.V.) was autoclaved. The sterilized medium was cooled to 50°C to 60°C and then aliquoted into petri dishes (100- × 20-mm depth), 20 mL each, for solidification. PEG-infused plates were made by dissolving PEG-8000 (Sigma) powder into one-half-strength Murashige and Skoog solution (pH 5.7) with the above-mentioned components, except phyto agar, and then filter sterilized; this PEG solution was then overlaid on agar-solidified medium at a ratio of 3:2 (v/v) and equilibrated overnight (≥12 h). The excess PEG solution was then removed. The procedure essentially followed the protocol of Verslues and Bray (2004).