Cryopreservation of winter-dormant apple buds: II - tissue water status after desiccation at -4C and before further cooling.

The established protocol for the cryopreservation of winter-dormant Malus buds requires that stem explants, containing a single, dormant bud are desiccated at -4 degree C, for up to 14 days, to reduce their water content to 25-30 percent of fresh weight. Using three apple cultivars, with known differences in response to cryopreservation, the pattern of evaporative water loss has been characterised, including early freezing events in the bud and cortical tissues that allow further desiccation by water migration to extracellular ice. There were no significant differences between cultivars in this respect or in the proportions of tissue water lost during the desiccation process. Differential Scanning Calorimetry (to -90 degree C) of intact buds indicated that bud tissues of the cultivar with the poorest response to cryopreservation had the highest residual water content at the end of the desiccation process and froze at the highest temperature.