Optimization of sterilization conditions for in vitro propagation of white yams (Dioscorea Rotundata)

Abstract

White yam is an important food crop that is traditionally propagated by planting tubers. This traditional methods is however not effective for large scale production. The alternative to this traditional propagation is in vitro propagation. However, this in vitro propagation is also faced with the problem of microbial contamination, as it is associated with decrease in quality of white yams. This is because the success of in vitro propagation largely dependent on effective surface sterilization of the explants to prevent contamination. Currently, there is no cost effective protocol of surface sterilization conditions for in vitro propagation of white yam, which is hindering the adoption and success of this alternative method. The aim of this study was to develop an effective sterilization protocol for in vitro initiation and propagation of white yam. Plant materials used were nodal segments from young plants of the Dioscorea rotundata obtained from the screen house at National Crop Resources and Research Institute (NACRRI). The medium used was MS and the pH was set at 5.8 ± 0.02. viii Cultures were maintained under a light intensity of 1,500 lux and 16-hour photoperiod and temperature of 24 to 26 OC. Two protocols for surface sterilization were tested i.e. Fungicides such as Carbendazim was used in surface sterilization and non-readily available Benomyl was incorporated in media, as well as variation in the exposure of explants to Sodium Hypochlorite and Ethanol. The most common microbial contaminants observed in the white yam cultures were fungi. Benomyl fungicide incorporated in media treatment was found to be the most effective in suppressing microbial contaminants at 83% microbial elimination rate. Sterilization with 70% Ethanol and10% Sodium Hypochlorite for 25 minutes was found to be the most effective in suppressing the microbial contamination at 92% microbial elimination rate but was very toxic to the explants. Treating explants for 10 min (control) was found to be ineffective in suppressing the microbial contamination but non-toxic to explants. Subjecting the white yam explants to sterilization with 70% Ethanol and 10% Sodium Hypochlorite for 25 min was found to be the most efficient exposure time in elimination of contamination of white yam explants. These findings will help alleviate much of the burden associated with initiation of white yam cultures thereby reducing cost of plantlets production.