Abstract: High regeneration system for diploid potato was developed using segments as explants of in vitro plantlets of three genotypes, ED13 (bacterial wilt resistant), CE171 (bacterial wilt resistant), and ED25 (bacterial wilt susceptible). The role of plant hormones and their combinations was studied for callus formation and shoot differentiation. The result showed that different genotype needed different hormone combination for its callus formation and shoot differentiation. Solid-liquid nurse medium was helpful for callus induction of diploid potato and the best hormone combination in solid medium was NAA (2.0 mg · L^-1): 6-BA (2.0 mg · L^-1). For ED13, the best hormone combination in liquid medium was 2,4-D (2.5 mg · L^-1) : KT (0.5 mg · L^-1); whereas, for CE171, combination of 2,4-D (1.5 mg · L^-1) : KT (1.0 mg · L^-1) was the best. Both of these medium combinations gave high callus induction up to100%. But for genotype ED25, only the combinations of NAA (2.0 mg · L^-1) : 6-BA (1.0 mg · L^-1) and 2,4-D (1.5 mg · L-1) : KT (1.0 mg · L^-1) could give good callus induction result. ZT played an important role in the induction of shoot differentiation. More than 95% explants of genotype ED13 and CE171 were differentiated using only ZT (1.0 mg · L^-1). However, the combination of ZT (0.5 mg · L^-1): 6-BA (2.5 mg · L^-1) was needed for high shoot differentiation of ED25.

Key words: diploid, potato, segment, callus, differentiation, plant regeneration