An encapsulation-dehydration protocol for cryopreservation of the azalea cultivar 'Nordlicht' (Rhododendron simsii Planch.)

Azalea is important for Flanders (Belgium). An in vivo breeding collection, with more than 600 accessions, is available at the Department of Plant Genetics and Breeding (CLO, Melle, Belgium). The aim of our research is to develop a cryopreservation protocol for this collection, one of the most important in the world. With 'Nordlicht' as test cultivar, we developed an encapsulation-dehydration protocol. Optimal survival was observed after preculturing shoot tips in liquid culture medium supplemented with 0.3 + 0.45 + 0.6 M sucrose (24 h in each solution). After preculture, shoot tips were encapsulated in alginate beads (1.62 M glycerol + 0.32 M sucrose) and dehydrated to a low WC (38.6%) prior to freezing (direct immersion in LN). Detoxification in 1 M sucrose (2 h) appeared to be essential to achieve acceptable regrowth after cryopreservation. After thawing approximately 40% of the cryopreserved shoot tips survived.