Comparison of thidiazuron and two nitroguanidines to kinetin on potato microtuberization in vitro under short and long days

Thidiazuron and many nitroguanidines (for example, AC239,604 and AC243,654) act as cytokinins similar to kinetin in many bioassays. Potato tuber initi ation effects by thidiazuron, and AC239,604 and AC243,654 have not been inv estigated. These compounds were compared with kinetin for tuber initiation on nodal segments in vitro under short and long photoperiods. Potato plantl ets from "Atlantic" tubers were grown in vitro under 16-h days on Murashige -Skoog (MS) medium with 2.5% sucrose. After 2 months, nodal segments were r emoved and cultured on MS medium containing 6% sucrose and a test compound. Half the nodal segments remained under 16-h days (lon,a photoperiod) and h alf under 8-h days (short photoperiod). Kinetin was added to the MS medium at 2 mg/L. The test treatments were 0.1 mg thidiazuron/L 0.01 mg AC239,604/ L, and 1.0 mg AC243,654/L, Stolen number and length, root length, stem leng th, time to microtuber initiation, and microtuber size and number were reco rded at 5-day intervals up to 80 days after culture. Thidiazuron behaved mu ch like kinetin in promoting the percent of nodal segments producing stolon s and inhibiting the growth of stems and roots under both long and short ph otoperiods. Thidiazuron and kinetin delayed the onset of tuber initiation a nd lessened tuber production compared with untreated nodal segments under l ong days. Under short days, thidiazuron and kinetin increased the rate of s tolen elongation, hastened tuber initiation, and increased tuber production . The two nitroguanidines were not as active on stolons, roots, and stems a s kinetin. But, under long days, AC243,654 and, to a lesser extent, AC239,6 04 increased microtuber production without changing the time to tuber initi ation. Under short days, the nitroguanidines, as with kinetin, also hastene d the onset of tuber initiation but did not increase the number of microtub ers produced. Thidiazuron acted like kinetin, promoting tubers under short days, but the nitroguanidines acted differently, promoting tuber production primarily under long days.