Evaluation of regeneration response in tissue culture of selected groundnut (Arachis Hypogaea L.) varieties adapted to Eastern and southern Africa

Abstract

Cotyledon explants from mature groundnut seeds (Arachis hypogaea L.) adapted to eastern and southern Africa, were optimized to obtain adventitious shoot buds with high frequencies. This was done using commercial bleach {jik, active ingredient sodium hypochlorite (3.5% v/v NaOCI) at different concentrations and exposure time as compared to 0.1% mercuric chloride. Results showed that 0.525% NaOCI and 1.050% NaOCI concentrations within an exposure time of 10-20 minutes were the optimum active range in all the varieties provided. There was constant contamination of CG-2 even after repeated sterilization indicating endogenous contamination. This showed that surface sterilization was not sufficient to sterilize it. While using mercuric chloride treatment, Chalimbana variety recorded the highest percentage of surviving explants (100%) and CG-2 had the lowest (82%). Regeneration experiments performed using already established optinum NaOCI sterilant concentration in each variety as compared with 0.1% mercuric chloride for 10 minutes (sterilant). Cotyledon explants were cultured in shoot induction medium (with BAP and 2, 4-D), shoot buds started to form along the proximal cut end of the cotyledon since this was the area of high regeneration potential due to presence of high number of meristematic cells. Well-formed shoots transferred to shoot elongation medium (SEM) elongated well in the presence of BAP growth regulator and later developed multiple shoots of about 4-8 shoots per explant. In SEM tubes, growth of all the varieties was rapid and prolific. Results showed that explants regenerated rapidly and with vigour. There was interaction (p>0.05) between variety and treatments in percentage regenerated plants. For example, JL-24 variety regenerated better using NaOCI than mercuric chloride. In terms of rapid growth and number of plants produced using NaOCI treatment, JL-24 variety was the best followed by CG-2, the least was ICGV-12991. Using mercuric chloride JL-24 regenerated the most plants followed by ICGV-90704 while the least was CG-2. All the groundnut varieties introduced into tissue culture in this study responded well, acclimatized, produced normal flowers and seedpods within 4 months. The cotyledon regeneration protocol proved to be a good regeneration system using both NaOCI and mercuric chloride sterilants. Of the selected African adapted varieties evaluated in this study ICGV-90704 performed best using mercuric chloride while CG-2 using NaOCI was the best. These are the varieties recommended for transformation, which could be one of the possible methods to offer resistance to viruses and this should have impact on crop improvement on productivity and food security, especially in the semi-arid tropics