ACCLIMATIZATION STUDIES IN STEVIA (STEVIA REBAUDIANA BERT.)

Abstract

Considerable efforts have been directed to optimize the conditions for in vitro stages of micropropagation, but the process of acclimatization of micropropagated plants remains to be not meticulously studied and continues to be a major bottleneck in the micropropagation of many plants. Plantlets were developed within the culture vessels under low level of light, aseptic conditions, on a medium containing ample sugar and nutrients to allow for heterotrophic growth and in an atmosphere with high level of humidity. These contribute a culture-induced phenotype that cannot survive the environmental conditions when directly placed in a greenhouse or field. The physiological and anatomical characteristics of micropropagated plantlets necessitate that they should be gradually acclimatized to the environment of the greenhouse or field. Acclimatization continues to be a major hurdle in the micropropagation of stevia too with lower success reported. In the present study, different hardening media were used under different environments to improve post acclimatization survival. With sand as the hardening media, mist house had higher survival rates than greenhouse. Sand did not retain much water in greenhouse to ensure proper growth and survival compared with mist house with frequent misting. In all other cases, the survival was found to be better in greenhouse (27.89%) compared with mist house (23.11%). With frequent misting, water logging occurred around the plantlets, and they started to rot which lead to reduction in survival. This was absent in sand due to its high porosity and rate of percolation. Inclusion of cocopeat 75% or above in the hardening media brought a dramatic increase in the survival percentage. The survival of the micropropagated plantlets rose above 50% with the addition of 75% cocopeat to the hardening media. The survival percent recorded with cocopeat under greenhouse was around 75.50% that was almost 60 times higher than the lowest survival recorded with 100% sand under greenhouse (1.50%). On an average, sand as a hardening media, gave only 1.35% survival.