Cryopreservation ofin vitro-grown shoot tips of strawberry by the vitrification method using aluminium cryo-plates

Abstract

Cryopreservation using an aluminium cryo-plate was successfully applied toin vitro-grown strawberry (Fragaria × ananassaDuch.) shoot tips. The shoots were cold-hardened at 5°C for 3 weeks with an 8-h photoperiod. The shoot tips (1.5–2.0 mm × 0.5–1.0 mm) were dissected from the shoot and pre-cultured at 5°C for 2 d on Murashige and Skoog medium containing 2 M glycerol and 0.3 M sucrose. The pre-cultured shoot tips were placed on the aluminium cryo-plate containing ten wells embedded in alginate gel. Osmoprotection was performed by immersing the cryo-plates in a loading solution (2 M glycerol and 0.8 M sucrose) for 30 min at 25°C. Dehydration was performed by immersing the cryo-plates in plant vitrification solution 2 for 50 min at 25°C. Then, the cryo-plate with shoot tips was transferred into an uncapped cryotube that was held on a cryo-cane and directly immersed into liquid nitrogen (LN). After storage in LN, shoot tips attached to the cryo-plate were directly immersed into 2 ml of a 1 M sucrose solution for regeneration. Using this procedure, the average regrowth level of vitrified shoot tips of 15 strawberry cultivars reached 81%. This new method has many advantages and will facilitate the cryostorage of strawberry germplasm.