Advances in cryopreservation of in vitro-derived propagules: technologies and explant sources

Genetic improvements in plant breeding are dependent upon having access to novel plant genetic resources that are available in plant genebanks. Many crops that are vegetatively-propagated are maintained as plants in the field or greenhouse, making them vulnerable to biotic and abiotic threats. Increasingly, plant genebanks are using cryopreservation technologies to secure vegetatively propagated collections at secondary locations. Droplet vitrification and cryo-plate cryopreservation methods have been used to successfully cryopreserve the shoot tips of many plant species. New propagule types, including small leaf square-bearing adventitious buds, stem disc-bearing adventitious buds, microtubers and rhizome buds are alternative explants for use in cryopreservation. This review describes new technologies for in-vitro based cryopreservation systems that have advanced the field of plant cryopreservation. Future advances will allow even more diverse germplasm to be successfully preserved in cryobanks.