A novel preculture method for the induction of desiccation tolerance in gentian axillary buds for cryopreservation

Axillary buds of in vitro-grown gentian ( Gentiana scabra Bunge var. buergeri Maxim.) were successfully desiccated and cryopreserved using a novel two-step preculture method: preculturing axillary buds excised from in vitro-grown gentian plants on Murashige and Skoog (MS) semi-solid medium containing 0.1 M sucrose for 8–13 days at 25°C under a 16 h-photoperiod (first step) and the subsequent short period incubations on 0.4 M sucrose (MS agar medium) for 1 day followed by 0.7 M sucrose (MS agar medium) for 1 day (second step). After preculturing, the buds were air-dried down to about 10% water content (fresh weight basis) without encapsulation, and then immersed in liquid nitrogen (LN). With this cryogenic protocol, we could obtain 78–90% of survival of axillary buds following desiccation and LN exposure. Most of the buds that survived showed normal shoot and root development. The most important part of this protocol was the preculture which circumvents the conventionally used lengthy cold-hardening treatment. The results show that induction of desiccation tolerance by preculturing was specific to a few species of sugars used in the medium and not merely caused by osmotic effects. The efficient desiccation–cryopreservation protocol shown here using the new preculture method appears promising for routinely cryopreserving gentian germplasm.