Abstract
A possibility of the application of the cultural technique in vitro for the isolation, fixation and propagation of the mutant plant from sectorial mutation induced by gamma irradiation on Begonia rex has been investigated.
The variety‘Winter Queen’was employed throughout all the experiments. The mature leaves from stock plants were removed and cut into small leaf fragments approximately 3mm×3mm in size. The fragments were sterilized by 3% antiformin and washed with sterilized water. The sterilized leaf fragments were planted horizontally onto the White′s agar medium aseptically and cultured in the plant growth cabinet at 25±2°C, 40-50% relative humidity and 3000lux illumination for 11 hours a day.
After a month of culture in vitro, adventitious buds arose from the leaf fragments (Fig. 1). The adventitious buds in tubes grown to 0.5mm in length were irradiated with 10krad of γ-ray at dose rate of 0.2krad/hr. After the irradiation, the tubes were placed again in the same cabinet and the leaf fragments cultivated for another 3-4 months. Then, the buds were grown until the young plants produced several leaves. Two of the thirty young plants produced the chimeric variegations on their leaves (Table 1). Then, these two plants were transplanted to water culture bed in green house and cultivated for 6 months. The apperance of the plant cultivated for 6 months is shown in Fig. 3 for comparison with the normal plant. As shown in the figure, the leaf of chimeric plant has the sectors of green leaf color with silver white spots. Whereas, the original leaf color of‘Winter Queen’is covered with silver white.
For the isolation and fixation of this somatic mutation, the sector of the leaf was cut into leaf fragments approximately 3mm×3mm to 5mm×5mm in size, and these fragments were planted onto White′s agar medium. The fragments were cultured under aseptic conditions for 4-5 months in vitro. After a month, the adventitious buds arose from the leaf fragments cultured and grew to young mutant plant after another 4-5 months of the culture. Among these plantlets, three sound plants were transplanted to flower pots in the water culture bed in green house.
These new plants propagated from the mutant sector were changed wholly in leaf color as that of the sector. The appearance of the changed plant and that of the leaf are shown in Figs. 4 and 5, respectively.
Some histological explanations on the development of wholly changed plant from leaf fragment were presented.
The procedures of these experiments are illustrated in Fig. 6.
From this investigation, it is suggested that the adequate combination of irradiation and of in vitro culture will be useful in the breeding of the horticultural crops.
