Ex Vitro Growth Of Coconut (Cocos Nucifera L.) Seedlings Under Different Pre-Nursery Hardening Conditions

Abstract

One of the most challenging milestones in tissue culture of coconut (Cocos nucifera L.) is soil acclimatization due to the variable conditions between in vitro and ex vitro stages. The present study aims to investigate efficient conditions for rooting and soil acclimatization. Prior to the ex vitro stage, the root system was induced and hardened, using various concentrations of 1-naphthaleneacetic acid (NAA), i.e. 0, 30, and 60 µM. Well-developed seedlings were transfered to a mini growth chamber (MGC) for ex vitro acclimatization. Three concentrations of Y3 basal salts were investigated: nill, half-strength and full-strength. Furthermore, a comparison was made between 1-naphthaleneacetic acid (NAA) and indole-3-butyric acid (IBA) to elucidate their effect on ex vitro growth of the seedlings in the MGC. Results showed 30 µM NAA was likely to promote leaf and root formation, while 60-µM NAA enhanced shoot and root elongation. In terms of seedling survival, half-strength Y3 basal medium was demonstrated to be more suitable. This study confirmed that the presence of Y3 in MGC was necessary for the survival of seedlings during the first two weeks of the ex vitro stage. It was also found that IBA can help boost up the survival rate of seedlings (up to 73%). This study provided important insight into soil acclimatization of in vitro coconut seedlings and will open up new opportunity for efficient transfer of tissue-cultured plantlets into soil for palm species.