PLANT CELL BIOTECHNOLOGY AND MOLECULAR BIOLOGY

Development of an effective In vitro plant regeneration system is very important for successful propagation of Citrus grandis. This work aimed to optimize some factors affecting shoot regeneration such as epicotyl-seedling age and plant growth regulators for five pummelo (Citrus grandis L. Osbeck) cultivars that are widely planted in Vietnam- Dien, Phuc Trach, Nam Roi, Da Xanh, and Do. The highest rate of In vitro shoot regeneration was induced from the cut-end of explant segments excised from 20- to 25- day- old seedlings. Of which Dien, Phuc Trach and Do cultivars had better response for shoot regeneration at 20 ds explants, resulting from 26.67, 38.89 and 34.44% respectively. Nam Roi and Da Xanh showed the highest shoot formation rate at 25 ds explants with 26.67 and 34.44% respectively. Regeneration rate was significantly high in the medium containing BAP supplement. The medium containing 2.0 mg l^-1 BAP gave the highest mean shoot regeneration rate (45.83%) and shoot number per explant (5.72). The results of cut mode showed that oblique cut was the best mode for bud induction and shoot regeneration with 96.22% of explants responding. In order to make plantlets, shoots were cultured on medium supplemented with GA3 (1.0 mg l^-1) for their proper elongation. After 4 weeks, the elongated shoots (2.5-3 cm) were transferred into the root induction medium containing 1.0 mg l^-1 NAA that gave 40% rooting explants. These findings could be used for C. grandis improvement through micropropagation, in vitro grafting and genetic modification.