Optimizing In vitro Cryopreservation of Date Palm (Phoenix dactylifera L.)

Cryopreservation, the storage of materials at ultra-cold temperature, is a useful method for long-term storage of a wide variety of plant germplasm including buds, seeds, seed parts, twigs and cell and tissue cultures. The objective of this study was to define the optimal concentrations of key components of the cryoprotectant solution based on sucrose combinations with either dimethyl sulfoxide (DMSO) or glycerol for date palm (Phoenix dactylifera L.) cell suspension. Callus induced from shoot tip explants isolated from young offshoots of cv. Khalas, the most important commercial cultivars in Saudi Arabia, was used to establish cell suspension cultures. The cells were pretreated in sucrose solution and kept in a cryoprotectant solution containing sucrose at a concentration corresponding to that used in the pre-treatments (0.1, 0.25, 0.5, 0.75 and 1 M) and supplemented with either DMSO at 0, 5 and 10% or glycerol at 0, 1 and 2 M. After freezing in liquid nitrogen for 14 day, cell samples were revived and tested for survivability and competency in terms of colony formation, callus re-growth and subsequent somatic embryogenesis. The highest colony formation (21 colonies), greatest callus growth (0.12 g) and highest embryos number (11 embryos) was recovered from cell cryoprotected in 10% DMSO supplemented with 0.75 M sucrose. This study has resulted in cryoprotectant solutions suitable for date palm cells suspension; thus provided the necessary fundamental knowledge for establishing a germplasm bank based on cryopreservation approach for date palm conservation.