Freezing of Water in Dormant Vegetative Apple Buds in Relation to Cryopreservation

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Abstract
Various empirical prefreezing protocols have been used to facilitate cryopreservation of dormant buds from woody plants. The objective of this research was to determine the quantity of water remaining in liquid phase, under different prefreezing conditions using pulsed nuclear magnetic resonance spectroscopy of dormant apple (Malus domestica Mill.) buds from three cultivars. During prefreezing, the quantity of water remaining in the liquid phase was less at −40°C<−30°C<−20°C for all cultivars tested. The prefreezing temperature had a greater influence on reducing the quantity of liquid water than the duration of prefreezing. Prefreezing to −40°C for 24 hours was optimal for `Patterson' and `McIntosh,' the hardiest cultivars, compared to −30°C for 24 hours with `Red Delicious.' Cryopreservation of dormant apple buds depends upon the quantity of liquid water during prefreezing, prior to immersion in liquid nitrogen, and upon the cultivar.