STUDIES ON PRE ACCLIMATIZATION TREATMENTS TO IMPROVE POST ACCLIMATIZATION SURVIVAL IN STEVIA (STEVIA REBAUDIANA BERT.)

Abstract

The special conditions during in vitro culture result in the formation of plantlets of abnormal morphology, anatomy and physiology. After ex vitro transfer, these plantlets might easily be impaired by sudden changes in environmental conditions, and so need a period of acclimatization to correct the abnormalities. The large number of plants lost or damaged during acclimatization often restricts application of micropropagation for rapid multiplication of plants. Acclimatization continues to be a major bottleneck in the micropropagation of stevia too with lower success reported. In the present investigation, pre acclimatization treatments such as dipping the explants in high concentration cytokinin (benzyl adenine, BA) before culture and use of growth retardants that inhibit gibberellin biosynthesis (ancymidol) in culture were used to study their effect on post acclimatization survival of micropropagated plantlets. Dipping of explants in high concentration BA resulted in an increase of number of multiple shoots and number of leaves per shoot and survival percentage after acclimatization. But a significant reduction was noted in internode length and shoot height. Dipping the explants with 100 mg/L BA before culture resulted in highest survival after acclimatization. Ancymidol reduced the length of the shoot, number of leaves, and internodal length considerably. Survival percentage increased with concentration until 3 mg/L ancymidol and reduced with further increases in ancymidol concentration. This reduction might be because the excessive reduction in growth characteristics, which made the plants too fragile to withstand the pressure of acclimatization. The use of 3 mg/L resulted in a higher number of multiple shoots and average growth parameters and a better survival percentage (75.80% - increase of 25.29% over the control - 60.50%).