Plant Regeneration from Leaf Disks and Stem Segments of Sweet Potato Using Only NAA as Supplementary Growth Regulator.

To determine the most suitable culture medium for regeneration from explants of sweet potato, various culture media were tested on leaf disks, stem and petiole segments of line KT, a clone previously regenerated from stem callus of Kokei 14, and cultivar Jewel. Two media, R6 and R7, both of which contain only NAA as supplementary growth regulator, gave high root and shoot regeneration rates particularly in leaf disks and stem segments. Other media exhibited either no or a very low frequency of shoot formation except for moderate rooting in some media. Among the explants tested, petioles had the lowest regeneration rate. In experiments conducted to determine appropriate levels of NAA, leaf disks and stem segments responded to a narrow range of NAA concentrations (0.1-0.6mg/l) for shoot regeneration. Addition of either trans-zeatin or BAP to the regeneration medium, even at a concentration as low as 0.01mg/l reduced the shoot regeneration rate, particularly from leaf disk. The decline in shoot regeneration rate with increase in cytokinin level was more gradual in stem segments than in leaf disks. In treatments where roots and shoot were observed, shoot regeneration was preceded by root regeneration, and most of the shoots arose directly from explants close to the cut ends and only few arose from regenerated roots.