In vitro conservation of redwood (Sequoia sempervirens) by slow growth storage and cryopreservation

Redwood (Sequoia sempervirens (D. Don.) Endl.) is an evergreen conifer tree of the Sequoia genus. The reddish-brown lumber of the tree is highly valued, not only for its beauty, but also for its light weight, resistance and wood quality, making the tree the most attractive species for timber and plywood production. Present study aimed to develop medium- and long-term conservation approaches for redwood germplasm. For medium-term conservation, in vitro shoot cultures were maintained at 4°C, in darkness, up to 15 months ('slow growth storage'). Study evaluated the effects of different medium compositions on survival and regrowth of the material following the storage at low temperature. Outcomings of the study demonstrated that cold storage could be prolonged to 12 months on QL-based media without any significant decrease in the survival and regrowth potential of the cultures. Elongated and etiolated shoots, obtained after storage, were highly vigorous and multiplication could be re-initiated easily. MS-based media, however, were less effective, permitting 9 months of storage when the medium was hormonefree. As for long-term conservation, following cold hardening of in vitro shoot cultures and sucrose preculturing of excised buds, cryopreservation was performed by using droplet vitrification method. Post-thaw recovery was possible for a large range of PVS2 exposure, 135 min treatment providing 18 and 22% recovery of apical and basal buds, respectively.