For exceptional (or non-orthodox) plants that cannot be conserved long-term using conventional seed banking methods, three alternatives traditionally used by botanical gardens are tissue culture, cryogenic storage, and field genebanks. (See Overview.) Each requires different institutional commitment to space, resources, staff time, and expertise.
Considering the broad diversity of plant groups, like orchids, that require cryogenic storage, many of the world’s plant species may require alternatives to conventional storage (e.g., Seaton et al. 2018). Because most tissue culture and cryopreservation standards have been developed with commercially important species, we have relatively little information about the intricate needs of wild rare species’ storage needs.
Tissue culture and cryogenic storage are integral processes to long-term secured conservation collections. Growing seeds or plant shoots on in vitro medium is the most delicate horticultural treatment available. Though standard protocols exist, as is true for conventional seed banking, most protocols have been developed for commercially important species. Wild rare plants have unique needs. This means that carefully documented research by CPC practitioners can contribute importantly to the growing science. Collaborative work across CPC Network partners may help spread costs for efficient ex situ (off-site) conservation and may certainly aid our collective understanding of best practices for rare plant species’ conservation. For example, some species have seeds that are short-lived even in cryogenic storage, while other species have embryos that can withstand cryogenic freezing, but they are difficult to regenerate back to rooted whole plants (Xia et al. 2014). Because the longevity of wild rare species’ seeds stored cryogenically is largely unknown, cryogenic storage provides a ripe opportunity for experimentation and scientific advancement.
Field genebanks and inter situ collections are increasingly recognized as important stopgaps to plant extinction. New genetic research is enabling practitioners to evaluate the size of collection needed to capture a good representation of the genetic diversity of the species. Due to space constraints, collaborations across institutions are necessary. Planned fertilizations across sister institutions or from wild populations can help maintain the genetic health of the collection and foster valuable next generation reproduction.
Seaton P.T., S.T Hosomi., C.C., Custódio, T.R. Marks, N.B. Machado-Neto, and H.W. Pritchard. 2018. Orchid Seed and Pollen: A Toolkit for Long-Term Storage, Viability Assessment and Conservation. In: Y.I. Lee and E.T. Yeung (eds) Orchid Propagation: From Laboratories to Greenhouses—Methods and Protocols. Springer Protocols Handbooks. Humana Press, New York, NY
Xia K., L. M. Hill, D-Z. Li, and C. Walters. 2014. Factors affecting stress tolerance in recalcitrant embryonic axes from seeds of four Quercus (Fagaceae) species native to the USA or China. Annals of Botany 114:1747–1759.