Direct organogenesis from leaf explants of Stevia rebaudiana and cultivation in bioreactor

Shoot buds were induced directly on either side of midrib from adaxial surface of immature leaf explants in Stevia rebaudiana Bertoni five weeks after culturing in Murashige and Skoog's nutrient medium supplemented with 8.88 mu M of N (6)-benzylaminopurine and kinetin ranging from 4.65 to 6.98 mu M. Immature leaves of 0.6 to 1 cm were found to produce best response (93 %) with a highest number of 4.93 shoot buds per explant. For elongation of regenerated shoot buds, MS medium supplemented with 30 g dm(-3) sucrose and indole-3-butyric acid (IBA) ranging from 4.92 to 7.38 mu M were found most suitable. The medium was further modified to suit bioreactor cultivation of regenerated shoots wherein the use of two-fold MS salts and 60 g dm(-3) sucrose resulted in a high biomass yield of 50.68 g dm(-3) (m/v) accounting for about 590 micro-cuttings in three weeks. Best rooting of micro-cuttings occurred in half strength MS medium supplemented with IBA ranging from 4.92 to 7.38 mu M, 15 g dm(-3) sucrose and gelled with 0.8 % agar. Rooted plants were successfully established in substrate containing sand, Vermicompost and garden soil in equal proportions and grown in greenhouse. This is the first report on direct shoot regeneration from Stevia leaves.