Discussion
In General, modern rice cultivars carrying the sd1 semi-dwarf gene are sensitive to GA3, while lines carrying dwarf gene d1 are insensitive to GA3 at least at a low GA concentration (Kumar, 1984; Ueguchi-Tanaka et al., 2000; Li et al., 2005). No matter whether
other semidwarf genes or the recessive tall gene eui were present (Tables 1 and 2), all lines carrying sd1 were highly sensitive to GA 3 in the present study. Nevertheless, four lines carrying either sdq (t) or sdg were also sensitive to GA3, which was different from the results of Li et al. (2005). This may have resulted from different GA treatment methods: we treated the seeds at germination stage by soaking them in 50 mg l-1 GA3, whereas Li et al. (2005) treated the seedling at 2-3 leaf stage or adult stage by spraying 50 to 400 mg l-1 of GA3. The inconsistency suggested that the response of rice plants to GA3 treatment might be varied depending on the growth stage of rice, the concentration of GA3 and the method of GA3 treatment.