Effects of hygromycin during plant regeneration. Hygromycin was added into the RM in the final concentrations of 0 (A), 2 (B), 4 (C) and 6 mg/L (D), respectively. The plate was divided into two regions. About 20 positively transgenic root segments were put onto the right half and similar numbers of control roots were put onto the left half. The pictures were taken 4 weeks after inoculation. Hairy roots developed by A. rhizogenes harbouring no binary vector were used as negative control.