3. Results
3.1. Selection of culture medium
The initial screening of six culture media consisting of 18 treatments showed that the cut end of the shoot explants became brown, causing the medium surrounding the cut end to exhibit a brown color as well (Fig. 2a and b). Shoot explants cultured on DKW medium showed less degree of browning than the other media. Axillary shoots appeared from explants three weeks after culturing on DKW medium, and the shoots induced by the treatment of 0.5 mg L−1 ZT with 0.1 mg L−1 IBA were longer than the treatments of ZT with either IAA or NAA (data not shown). The other five media did not enhance axillary shoot production due to the browning and death of explants. Based on the degree of explant browning and shoot multiplication, DKW supplemented with ZT at 0.5 mg L−1 and IBA at 0.1 mg L−1 was found to be the most successful medium for inducing axillary shoots of C. wilsoniana.
3.2. Control of explant browning
The percentage of browning of explants cultured on DKW medium without anti-browning agents was 100% (Table 1). Addition of activated carbon reduced the browning. With the increased concentration of activated carbon from 100 to 300 mg L−1, the browning percentage decreased from 75% to 61.7%. The supplementation with PVP had a significant effect on suppression of browning. As the concentration increased from 100 to 300 mg L−1, the percentage of browning decreased from 31.7% to 18.3%.