Effect of different concentrations of plant growth hormones on callus induction and regeneration of Shea tree (Vitellaria paradoxa)

Abstract

The slow natural regeneration pattern of the Shea tree due to the long gestation period and intense harvest has limited the domestication and genetic improvement of this tree. These limitations have necessitated the need for an alternative method of conserving the Shea tree outside the natural habitat. The propagation of the Shea tree by the in-vitro clonal technique presents such an alternative method. The purpose of this study was to determine the optimal concentration of 2, 4-dichlorophenoxyacetic acid (2, 4-D) and Picloram in Murashige and Skoog medium for callus formation and regeneration. The first experiment was done to achieve the best surface sterilization method and the effect of different concentrations of 2, 4-D or Picloram on callus formation. Callus induction percentage (CI%) of the explants in Murashige and Skoog medium were evaluated. The basal media were supplemented with 30 g/L of sucrose, 2.8 g/L phytagel and combinations of 2, 4-D or Picloram in various concentrations (1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 mg/L) replicated four times with five explants in each bottle. From the result, the leaf explants soaked in 70% ethanol for 1 min and 1% sodium hypochlorite for 15 min with 1 µl of tween 20 had the highest percentage (100%) of sterile leaf explants and showed no contaminations both in the leaf and media. Callus was induced at 2 weeks of culturing in all the treatments except for MS basal without growth hormone which induced no callus. A concentration of 1.5 mg/ L 2, 4-D gave the best callus. The highest CI% (100%) was shown at 4 weeks in MS + 3.5 mg/L picloram media. The callus was light in colour and friable in texture. The result indicated that Picloram gave better callus compared to other treatments and will give a better response for regeneration of Shea tree.