Factors Affecting the Micropropagation of Sapindus trifoliatus from Nodal Explants of Mature Tree

Abstract

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 as-sociated with the genotypes/species, source and physiological status of explants, seasonal varia-tions, and competency/incompetency of explants towards PGRs for in vitro manipulations. There-fore, 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. Several factors influencing in vitro shoot induction from nodal explants derived from mature plants of Sapindus trifoliatus were investigated. Nodal segment obtained from mature plants was used as an explant for shoot regenera-tion. The factors assessed in this study included the types and concentrations of plant growth reg-ulators, 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. The performance of nodal explants was better on modified MS medium, i.e., M4 medi-um (half-strength of MS major salts and full-strengths of MS minor salts, Fe-EDTA and MS or-ganic nutrients each) than the full-strength MS medium. The addition of BAP in the medium re-sulted 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. Howev-er, 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 positive-ly affected by the repeated transfer of the mother explant for different passages on the multiplica-tion medium. Mother explant transferred to multiplication medium (0.8% agar-solidified M4 me-dium + 2% sucrose + 1.0 mg l-1 BAP) proliferated maximum shoots after fourth passages. Regen-erated shoots were rooted in vitro and further successfully acclimatized in field conditions. 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.