Plant cryopreservation is a genetic resource conservation strategy that allows plant material, such as seeds, pollen, shoot tips or dormant buds to be stored indefinitely in liquid nitrogen.[1] After thawing, these genetic resources can be regenerated into plants and used on the field. While this cryopreservation conservation strategy can be used on all plants, it is often only used under certain circumstances: 1) crops with recalcitrant seeds e.g. avocado,[2] coconut[3] 2) seedless crops such as cultivated banana and plantains[4] or 3) crops that are clonally propagated such as cassava, sweet potato.[5]
The history of plant cryopreservation started in 1965 when Hirai was studying the biology activities that happened when biological samples were frozen.[1] Three years later, there was the first successful attempt cryopreserving callus cells.[1] The following years, new methods to cryopreserve were developed, such as direct immersion, slow freezing and vitrification, as well as applied to more and more plants species and plant tissues.
Aside from the challenges involved with cryopreservation in general, an important hurdle, when developing cryopreservation protocols for storage of plant germplasm, is that plants within a species can have a different tolerance to cryopreservation.[8][5] This difference seems to be linked with the drought resistance of the different cultivars within the species.[8][9] Even within the plant itself there can be noticeable differences depending on the tissue that is used, as both structure and composition play an important role during cryopreservation.[5][10]