Thai rice cultivar RD6 was induced for drought tolerance through somaclonal variation. Nitsch and Nitsch (NN) medium supplemented with 1 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 700 mg/l casein hydrolysate were employed for callus induction and proliferation, whilst the same medium containing 0.5 mg/l naphthaleneacetic acid (NAA) combined with 4 mg/l 6-benzylaminopurine (6-BA) was suitable for plant regeneration. Drought stress was stimulated by treatment with polyethylene glycol (PEG, 0, 0.5, 1, 1.5 and 2% in v/v, MW6000) and/or mannitol (0,150, 300, 450 and 600 mM, MW182.17). The results showed the decreased survival percentage of calli exposed to the increasing PEG or mannitol concentration. Following drought treatment, surviving calli could develop into whole plants when grown on regeneration mediums. RAPD analysis employed to determine the genetic relationship between the control plants and the drought-tolerant plants showed that the control plants and the drought-tolerant plants were genetically different.
