3. Results and discussion
3.1. Optimization of callus induction medium
Vigorous callus growth was observed throughout the entire culture period. Embryogenic calli quickly developed in all eight induction media within the first week of incubation. Callus induction rate was the highest on medium M11AP (84.0%) followed by M11APC1 (78.7%). However, callus fresh weight was significantly lower on M11AP than on M11APC1 (Table 2). Overall, M11APC1 was found to be the most efficient callus induction medium for SA281 among the eight media tested. Similar experiments were preformed to optimize callus induction media for Tx430 (Fig. 1c) and 91419R (data not shown). Results indicated that M11APC1 was the optimal medium for those two lines as well.
The callus fresh weight was significantly higher on M11AP (0.058 g/IE) than on M11 (0.030 g/IE) (Table 2), indicating the beneficial effects of L-asparagine and L-proline on callus growth which is in agreement with a previous report (Elkonin et al., 1995). We further observed that callus fresh weight was significantly higher on M11APC1 (0.068 g/IE) than on M11AP (0.058 g/IE), suggesting that CuSO4·5H2O at 1.0 μM has a positive effect on callus proliferation. These results highlighted the importance of an appropriate concentration of additional ingredient for optimizing callus induction medium in sorghum.