In vitro propagation and cryopreservation of the medicinal species Hovenia dulcis Thunb. (Rhamnaceae)

This study describes in vitro propagation and cryopreservation of Hovenia dulcis, a woody species used in traditional medicine. Stem and leaf explants from axenic seedlings were cultivated on Murashige and Skoog (MS) medium containing 6-benzyladenine (BA) and kinetin (KIN) alone or in combination (0.1, 0.2, 0.5 mg L-1). For in vitro propagation, rates of regeneration (percentage of responsive explants) and proliferation (multiplication capacity of explant-derived shoots) were evaluated after 30 days and five subcultures, respectively. For cryopreservation by V Cryo-plate technique, shoot tips were excised from microcuttings cultured from in vitro-grown stock plants, or excised directly from axillary shoots of stock plants. The shoot tips were precultured in 0.3 M sucrose (24 h), exposed to loading (20 min) and to PVS2 (0-150 min) before storage in liquid nitrogen. The regrowth was assessed by plating of shoot tips on recovery medium (MS with BA + KIN), with or without a sterile filter paper over the culture medium. Cryopreservation was evaluated by survival (4-weeks) and recovery (8-weeks). The highest regeneration by direct organogenesis (100%) were reached on medium with BA + KIN (0.5 mg L-1 each). Shoots maintained multiplication capacity, showing the highest proliferation (87%) in the presence of BA. Shoot elongation and rooting were achieved on growth regulator-free MS. The most efficient cryopreservation protocol (68% survival and 62% recovery) applied exposure to PVS2 (120 min), and recovery on medium containing BA + KIN (0.5 mg L-1 each) with filter paper. The propagation and cryopreservation of H. dulcis may contribute to its conservation and that of other woody species.