Comparison of Thidiazuron and Two Nitroguanidines to Kinetin on Potato Microtuberization in vitro under Short and Long Days

Abstract

Thidiazuron and many nitroguanidines (for example, AC239,604 and AC243,654) act as cytokinins similar to kinetin in many bioassays. Potato tuber initiation effects by thidiazuron, and AC239,604 and AC243,654 have not been investigated. These compounds were compared with kinetin for tuber initiation on nodal segments in vitro under short and long photoperiods. Potato plantlets 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 removed and cultured on MS medium containing 6% sucrose and a test compound. Half the nodal segments remained under 16-h days (long photoperiod) and half 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, Stolon number and length, root length, stem length, time to microtuber initiation, and microtuber size and number were recorded at 5-day intervals up to 80 days after culture. Thidiazuron behaved much like kinetin in promoting the percent of nodal segments producing stolons and inhibiting the growth of stems and roots under both long and short photoperiods. Thidiazuron and kinetin delayed the onset of tuber initiation and lessened tuber production compared with untreated nodal segments under long days. Under short days, thidiazuron and kinetin increased the rate of stolon elongation, hastened tuber initiation, and increased tuber production. The two nitroguanidines were not as active on stolons, roots, and stems as kinetin. But, under long days, AC243,654 and, to a lesser extent, AC239,604 increased microtuber production without changing the time to tuber initiation. Under short days, the nitroguanidines, as with kinetin, also hastened the onset of tuber initiation but did not increase the number of microtubers produced. Thidiazuron acted like kinetin, promoting tubers under short days, but the nitroguanidines acted differently, promoting tuber production primarily under long days.