Organogenesis and high-frequency plant regeneration in Caryopteris terniflora Maxim. using thidiazuron

In vitro culture is employed as a means of producing plant materials from medicinal plants to meet the increasing demands of the market. Herein, we focused on an efficient protocol for organogenesis through two pathways in six explant types from Caryopteris terniflora Maxim (C. terniflora), a medicinal and ornamental plant. For direct organogenesis, the maximum number of shoots per internode explant (62.5) was achieved on Murashige and Skoog (MS) medium containing 3.0 mg L−1 thidiazuron (TDZ) and the maximum number of shoot tips per explant (45.5) was obtained by 1.5 mg L−1 TDZ, with 100% response. A protocol was also developed for indirect organogenesis from leaf, leaf-petiole, petiole, and root explants on MS basal medium containing a range of TDZ concentrations. Leaf-petiole explants induced more adventitious shoots (57.6 per explant) and leaves (31.4 per explant) than petioles (37.5 per explant) or roots (25.0 per explant), and the differentiation rate ranged from 87.2 to 100%. The regenerated shoots were elongated on MS medium containing 0.3 mg L−1α-naphthaleneacetic acid (NAA) and 1.0 mg L−1 gibberellic acid (GA3). The elongated shoots developed roots on ½ MS medium containing 0.3 mg L−1 NAA. Successful acclimatization of rooted plantlets in a greenhouse was achieved with 100% survival. Furthermore, the embryogenic-like structure was observed and the morphological characteristics of C. terniflora assessed at different stages of in vitro development. Our protocol offers, for the first time, an efficient, scalable propagation procedure for C. terniflora useful for large-scale cultivation for the purposes of conservation and genetic manipulation.