Abstract
Background: Explant recalcitrance is one of the major challenges during the tissue culture of a tree species, especially when explants are derived from mature plants. It is mainly associated with the genotypes/species, source and physiological status of explants, seasonal variations, and competency/incompetency of explants towards PGRs for in vitro manipulations. Therefore, to optimize the appropriate conditions and minimize explant recalcitrance, it is necessary to elucidate the different factors influencing the tissue culture of a tree species.
Objective: Several factors influencing in vitro shoot induction from nodal explants derived from mature plants of Sapindus trifoliatus were investigated.
Methods: Nodal segment obtained from mature plants was used as an explant for shoot regeneration. The factors assessed in this study included the types and concentrations of plant growth regulators, nutrient composition of MS (Murashige and Skoog) medium, sucrose concentrations, the position of nodes on their respective branches, seasonal variations, and successive transfers of mother explant.
Results: The performance of nodal explants was better on modified MS medium, i.e., M4 medium (half-strength of MS major salts and full-strengths of MS minor salts, Fe-EDTA and MS organic nutrients each) than the full-strength MS medium. The addition of BAP in the medium resulted in a higher shoot induction rate than other cytokinins i.e., Kin, Zeatin, TDZ. M4 medium supplemented with 3.0 mg l-1 BAP and 2% sucrose was optimum for shoot proliferation. However, elongation of shoots was observed only when induced shoots, along with the mother explant, were subcultured on a medium containing 1.0 mg l-1 BAP. The shoot multiplication was positively affected by the repeated transfer of the mother explant for different passages on the multiplication medium. Mother explant transferred to multiplication medium (0.8% agar-solidified M4 medium + 2% sucrose + 1.0 mg l-1 BAP) proliferated maximum shoots after fourth passages. Regenerated shoots were rooted in vitro and further successfully acclimatized in field conditions.
Conclusion: The in vitro regeneration system developed from an explant obtained from mature trees can be successfully exploited for mass multiplication of Sapindus trifoliatus, a medicinally and commercially important tree.
Keywords: Explant recalcitrance, plant growth regulators, Sapindus trifoliatus, shoot proliferation, tree micropropagation, soapnut tree.
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