Continued studies on regeneration of haploid callus lines
--Y. C. Ting and L. J. Forastieri
It was consistently observed that haploid callus lines grew better on N6 medium with 8-10 percent sucrose than those grown on N6 medium with 1-2 percent of the same. In order to make a further study of this, three haploid callus lines, 88-S5, 87-S4 and SAN1, were employed for testings in the last spring and summer. The media were prepared by following the standard N6 medium formula with 100 g/l sucrose; 0.5 mg/l 2,4-D; 0.5 mg/l kinetin. After the callus lines had been on this medium for six weeks, somatic embryos were formed in most of the cultures. The embryos were creamy white, smooth surfaced and globular in shape. Particularly in the cultures of line 88-S5, about 60 percent of the calli differentiated into embryos while in those of lines 87-S4 and SAN1 only less than 10 percent of them did the same.
When the above somatic embryos were transferred onto N6 medium with 20 g/l sucrose but no hormones, over 50 percent of them from line 88-S5 germinated and grew into plantlets within two weeks. Of lines 87-S4 and SAN1 only less than three percent of the embryos grew into plantlets. By the foregoing procedures, about 100 plantlets were obtained in the last year. However, to our disappointment none of these plants grew vigorously and reached reproductive stage. All of them died at the four to five-leaf stage. Even though some IAA (indole-acetic acid) and GA (gibberellic acid) of an amount of 0.5 mg per liter were added to the media, no improvement in the condition of plant growth and development was found. Therefore, it seems reasonable to conclude that if it is necessary to produce haploid plants which can continue to grow and set seeds from these callus lines, more research is needed.
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