Micropropagation of Sapindus trifoliatus L. and assessment of genetic fidelity of micropropagated plants using RAPD analysis

An efficient in vitro propagation system has been developed for rapid micropropagation of Soapnut (Sapindus trifoliatus Linn.), a medicinally and economically important tree from nodal (axillary bud) segments of seedlings. The frequency of shoot regeneration from seedling node explant was influenced by the age of the seedlings, growth regulators and successive transfer of the mother explant. Explants from 4-week-old seedlings yielded the maximum shoot regeneration frequency (97.22%) on full-strength MS medium supplemented with 1.0 mg l⁻¹ of 6-benzylaminopurine (BAP). After harvesting the newly formed shoots, the mother explants transferred to same medium subsequently produced a maximum of 5.16 shoots per explant after third passage. Further improvement in the morphogenic response occurred when the nodal explants excised from in vitro regenerated shoots were employed, and 6.89 shoots per explant were obtained on the same medium after the third subculture. Optimal rooting (91.67%) was obtained by placing the micro-shoots in liquid MS medium with 1.0 mg l⁻¹ IBA for 24 h and then transferring to the agar solidified MS medium devoid of IBA. The micropropagated shoots with well-developed roots were acclimatized and successfully transplanted to soil with 90% survival rate. Genetic stability of the regenerated plants was assessed using random amplified polymorphic DNA (RAPD). The amplification products were monomorphic in micropropagated plants and similar to those of mother plant. No polymorphism was detected revealing the genetic integrity of micropropagated plants. This is the first report of an efficient protocol for regeneration of S. trifoliatus through organogenesis, which can be applied for further genetic transformation assays and pharmaceutical purposes.