Development of a PVS2 droplet-vitrification cryopreservation technique for Aranda Broga Blue orchid protocorm-like bodies (PLBs)

　　BACKGROUND: Conservation of commercially important ornamental plants is important to maintain its unique beauty to cater the market demands.

OBJECTIVE: The main objective is to develop an efficient cryopreservation technique for Aranda Broga Blue orchid PLBs using droplet-vitrification method.

MATERIALS AND METHODS: Several critical factors in cryopreservation were accessed such as preculture concentrations and durations, choice of vitrification solutions, two-step or three-step vitrification, growth recovery medium and PVS2 exposure duration.

RESULTS: The best growth regeneration percentage (5%) was obtained when 3-4mm PLBs were precultured in 0.2M sucrose for 3 days, followed by osmoprotection for 20 minutes, dehydration in PVS2 for 20 minutes at 0 degree C, LN storage, thawed and unloading for 20 minutes, and growth regeneration in VW10 medium. PLBs were found to be very sensitive to osmotic stress imposed by high molecular weight cryoprotectant such as sucrose and glycerol. Osmotic potential of growth recovery medium is one of the main factors that affect growth recovery in cryopreserved PLBs.

CONCLUSION: Current report showed possibilities in cryopreserving Aranda Broga Blue PLBs using droplet-vitrification technique. However, further improvement of growth recovery can be done by focussing on approaches that facilitate sufficient water removal from PLBs without causing severe osmotic injuries to the plant cells.