THIDIAZURON IMPROVES ADVENTITIOUS BUD AND SHOOT REGENERATION IN RECALCITRANT SWEETPOTATO

Induction of adventitious buds and shoots from intact leaves and stem internode segments of two recalcitrant Ugandan sweetpotato (Ipomoea batatas L.) cultivars was investigated in vitro on Murashige and Skoog (MS) medium, supplemented with 3 different levels (0.5, 2.0 and 4.0 µM) of Thidiazuron (TDZ). Shoots were regenerated in all TDZ concentrations in cvs. Kyebandula and Bwanjule. The inclusion of 0.25 µM α-Naphthalene acetic acid (NAA) in MS medium, containing TDZ (0.5 µM), improved shoot regeneration frequency from 12.1 to 22.6 % for cv. Kyebandula stems and from 21.61 to 42.9 % for cv. Bwanjule stems. However, there was about 10 % reduction in adventitious bud induction frequency for both cultivars, when NAA was included in the medium. The highest frequency (66.7%) of adventitious bud induction was achieved from stem explants of cv. Kyebandula. The conversion of adventitious buds into shoots was improved when TDZ was reduced or completely removed in subsequent stages of culture. The number of explants forming shoots was significantly (P<0.001) higher when stem explants were cultured for 7 days on TDZ-supplemented MS medium before transfer to TDZ-free MS medium supplemented with NAA. Stem internode pieces from position 3 were the best (70.0%) in adventitious bud formation. However, most buds (76.2%) were not converted to shoots. The most important application of the de novo regeneration protocol developed in this study is in genetic transformation fo