Dormant bud cryopreservation of Rubus idaeus L

Cryopreservation of dormant buds offers a reliable and cost-effective method for the long-term preservation of plant genetic resources, particularly for woody plants like raspberry (Rubus idaeus L.). This study aimed to develop an optimized protocol for the cryopreservation of dormant raspberry buds by investigating the role of dehydration and freezing conditions in maintaining bud viability. Dormant canes of two raspberry varieties, 'Sanibelle' and 'Willamette', were collected and prepared by dehydrating single-node cane segments at -4 °C until the desired water content was achieved. The study focused on assessing the impact of dehydration on bud viability and the physical state of water within the buds, using differential scanning calorimetry to analyse thermal transitions during cooling and heating. The cryopreservation process followed a two-step freezing protocol, with the first step involving slow cooling to -30 °C, followed by rapid immersion in liquid nitrogen (-196 °C). After cryopreservation, buds were thawed either slowly at +4 °C or rapidly at +38 °C, with rehydration taking place over 14 days. The study found that the most effective preservation (74-86 % of buds) occurred when the buds were dehydrated to 22-23 % humidity and had a water activity of 0.83-0.85. Rapid thawing significantly improved bud survival, especially for moderately dehydrated buds (with water content 25-35 %), while recrystallization during slow thawing was associated with lower viability. The results highlight the complexity of cryopreservation protocols, where factors such as dehydration levels, cooling and thawing rates, and bud dormancy status play crucial roles in ensuring successful long-term storage.