Cryopreservation of winter-dormant apple: iii - bud water status and survival after cooling to -30°C and during recovery from cryopreservation.

In a continuing study to improve the efficiency of dormant bud cryopreservation for tissues hardened in maritime climates, the water status of dormant buds was monitored between -4 degree C and recovery from liquid nitrogen (LN). Measurement of water content, simple thermal analysis and differential scanning calorimetry were employed. Buds did not lose water during cooling to, or holding at -30 degree C indicating that cryodehydration and/or other adaptive responses contributed during this essential step. A bud exotherm that was an artefact of warming was detected due to necessary handling at -4 degree C before cooling to -30 degree C. There were no significant differences between cultivars with respect to water status at -30 degree C or immediately upon rewarming from LN despite significant differences in post-LN survival. Buds rehydrated in 5 days, but up to 14 days may be needed for recovery for some cultivars. In some instances buds could be grafted without rehydration, taking up water across the early graft union.