Establishment of Salt Stress Tolerant Rice Plants Through Step Up NaCl Treatment In Vitro

Establishment of salt tolerant rice plants was examined by single step or step up NaCl treatments of shoot bud clumps in vitro, and variation among in vitro salt tolerant plants were examined by rapid amplified polymorphic DNA (RAPD). Shoot bud clumps were necrotic, stubbed or dead when subjected to single step treatment with 1.5 or 2.0 % NaCl. Conversely all the clumps could grow vigorously when subjected to step up salt treatment with 0.5, 1.0, 1.5 and 2.0 % NaCl at 3 week intervals and 2 % NaCl tolerant plants were established. RAPD revealed shoot bud clumps with and without different NaCl treatments, seedlings from field and grown in vitro, and regenerants from callus were genetically close to one another. Conversely, callus cultures were genetically isolated. Growth under different salt stress conditions was not correlated with the genetic variation, suggesting that 2.0 % NaCl tolerant plants might not result from genetic mutation but were due to adaptation of plants by step up NaCl treatment in vitro.