We found that a long period of in vitro culture is a critical factor on the low transformation rate for a specific potato genotype, Solanum tuberosum L. var. Atlantic when phosphinothricin (PPT) was added to select putative transformants in a solid media. The fresh explants of the newly produced plants from a micro-tuber was able to increase the transformation rate significantly while the old explants prepared from a plant maintained for longer than 6 months in vitro by sub-culturing every 3 ~ 4 weeks resulted in a very low transformation frequency. However, Jowon cultivar was not so much influenced by the period of in vitro culture with high transformation rate (higher than 10.0%). Further research need to be explored for the reason why a particular potato genotype, Atlantic is more vulnerable than the Jowon cultivar during the regeneration stage resulting in the low transformation frequency.

Keywords: Transformation, Solanum tuberosum L. var Atlantic, in vitro culture period, Carbon source, Regeneration, Bar