Experiments were conducted to rapidly produce microtubers of high quality from ´Daiji´, ´Sumi´, and ´Namjak´ potatoes tissue culture. Continuous dark at 20℃ was most favorable for microtuber formation: no tubers were formed under continuous light or in the dark at 25℃. The TI-5 medium which contains 100 times strength of vitamines of MS basic medium was efficient for tuberization of ´Daiji´. Besides TI-5, TI-4 containing 50 times vitamines increased number and size of microtubers of ´Namjak´ The optimum concentration of sucrose in tuber-inducing media was 9% for ´Daiji´ and nine and/or 12% for ´Sumi´. Microtuber size increased at lower concentration of sucrose. With ´Daiji´, the addition of KMnO₄ to tuber-inducing medium increased microtuber number and mean tuber fresh weight when the plantlets were grown at 25℃ under 16 hourdaylength, and microtuber number was increased with reducing size when they were grown at 20℃ under 10 hour-daylength. With ´Sumi´ , the results were similiar to those of ´Daiji´ when plantlets were grown at 20℃ under 10 hour-daylength. But when they were grown at 25℃ under 16 hour-daylength, only mean tuber fresh weight was increased compared with the control. The T_(50) (days needed for 50% plantlets to tuberize) was shortened by adding KMnO₄ in tuber-inducing medium, regardless of plantlet culture conditions.
The addition of 20 to 35 M KMnO₄ to TI-5 medium enhanced tuberization of ´Daiji´, but not of ´Namjak´. Treatments with BAP up to 40 mM did not affect the formation of microtubers from ´Daiji´. Most microtubers from ´Namjak´ were formed by adding BAP at 40 mM, however, average weight of microtubers decreased. Prechilling treatment of the plantlets at 0 and 5℃ for 10 and 15 minute was favorable for tuberization of ´Daiji´ . Prechilled ´Namjak´ plantlets decreased tuber number, but significantly increased mean tuber weights compared with control. CO₂ enrichment to microplantlet before tuber induction significantly increased tuber number per microplantlet and tuber size. Patatin accumulated within seven and ten days in ´Sumi´ and ´Daiji´, respectively, after leaf-node cutting, and this coincided with visible formation of tubers.
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