2.4. Plant regeneration from callus cultures
The calli subcultured on MS medium for 8–12 weeks was used for inducing adventitious shoots. Callus pieces (4–6 mm) were first transferred to SH medium supplemented with different concentrations of 6-benzyladenine (BA; 1.0–5.0 mg l−1) in combination with alpha-naphthalene acetic acid (NAA; 0.1–1.0 mg l−1) and indole-3-butyric acid (IBA; 0.1–1.0 mg l−1). Based on the first results, three BA concentrations (2 mg l−1, 3 mg l−1 and 5 mg l−1) in combination with 0.1 mg l−1 NAA and 0.1 mg l−1 IBA were tested. Shoot induction was evaluated and expressed as the shooting frequency and number of shoots per callus after 8 weeks. Four calli were cultured per jar (containing 30 ml medium), and each treatment contained 20 calli. Every experiment was repeated three times.