Micropropagation of Primulina dryas (Dunn) Mich. Möller & A. Webber: High frequency regeneration from leaf explants

• An efficient in vitro regeneration system for the rapid multiplication of the horticultural plant Primulina dryas was developed using thidiazuron.
• Shoot and somatic embryo-like structures were regenerated from different explants including leaf and petiole using this system.
• Explants also regenerated on a medium devoid of phytohormones.
• Growth and development of the regenerants could also be achieved in temporary immersion bioreactors.

Primulina dryas (P. dryas), a popular ornamental plant species has recently gained interest among hobbyists and collectors due to its attractive foliage and flowers. An efficient protocol for in vitro regeneration of P. dryas from leaf and petiole explants was developed using thidiazuron (TDZ) as the sole inductive stimulus. The objective of this study was to evaluate the potential of P. dryas for mass propagation in vitro. Orientation of the explants on the culture medium also affected regeneration with significant enhancement in the number of shoots and somatic embryos when the abaxial surface of the leaf was in contact with the culture medium. Explants also showed a capacity to regenerate on a medium devoid of growth regulators indicating active endogenous hormone metabolism sufficient to stimulate de novo differentiation. The inhibitors of auxin biosynthesis and transport, p-chlorophenoxyisobutyric acid (PCIB) and 2,3,5-triiodobenzoic acid (TIBA) significantly reduced regeneration in an optimal growth environment suggesting the involvement of endogenous auxin in regeneration of P. dryas. Growth and development of regenerants was further improved in temporary immersion bioreactors and the resulting plants were successfully transplanted in the greenhouse. High efficiency and reproducibility of Primulina regeneration system reported here may facilitate large scale production of this ornamental species.