Daniel Ballesteros, Millennium Seed Bank Partnership at Royal Botanic Gardens Kew
Wild plant species are highly biodiverse. Biodiversity is typically measured as variation at the genetic, species, and ecosystem levels. But, as a consequence, wild plant species are also highly diverse in their responses to preservation, and ex situ conservation of a wide range of wild plant species can become challenging. For example, ex situ conservation of wild plants, as with most crops, is broadly achieved by conventional dry seed storage at -18°C. Seeds that tolerate desiccation can be stored dry at sub-zero temperatures for extended periods of time. However, dry seeds and other plant propagules still deteriorate and eventually die during sub-zero storage, including at liquid nitrogen temperatures (i.e., < -150°C). The rates of deterioration are diverse depending on species and genotypes, and are influenced by the “dry architecture” of the propagule’s cells. Understanding this variation is essential to design strategies to increase longevity of seeds and other propagules in species with short life spans.
In addition, not all plants produce seeds that tolerate drying and some succumb when stored ‘wet’ at -18°C. For example, about a half of tropical trees and some of the tree species that dominate temperate forests (such as, oaks) produce recalcitrant (i.e., desiccation sensitive) seeds. For these species, cryobiotechnology is the only approach for their long-term ex situ conservation. But cryobiotechnologies are not straight forward. Several challenges related to the manipulation of the plant samples, their drying, cooling, warming and in vitro propagation remain to be resolved. The C-Flora, or Cryo-Flora, defines a range of species and tissues that will enable a wide range of material to be preserved beyond conventional seed storage. Although immediate implementation is possible for diverse materials of the C-Flora, diverse research is needed. To overcome these research challenges, Royal Botanic Gardens, Kew, in its new Science Collection Strategy, highlights the need of a new space within Kew (the Kew Cryosphere), where innovative research, advanced training, and specialized infrastructure are framed to secure the conservation of non-orthodox germplasm of wild plant species using cryobiotechnological approaches.