Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: July 1, 2010
Publication Date: January 1, 2011
Citation: Ballesteros, D. 2011. Conservation of fern spores. pp. 165-172. In H. Fernandez et al. (eds.) Working with ferns: issues and applications. Springer, New York, NY. Book Chapter. Interpretive Summary: Problem: Spore banks for ferns (analogous to seed banks for angiosperms) are a promising ex situ conservation tool, because large quantities of germplasm with high genetic variation can be conserved in a small space with low economic and technical costs. However, fern spore storage has received little research attention, and so methods to maximize survival time of spores in storage are largely unknown. Accomplishment: This book chapter reviews research on fern spore storage conducted over the last 40 years and discusses some recent discoveries. The chapter highlights the importance of optimizing spore water content by precisely controlling relative humidity. The chapter also describes how crystallization of triacylglycerols (TAG also known as storage lipids) appears to be associated with fern spore response to low temperature and is analogous to responses reported for seeds of tropical origin. Impact: Based on this literature review, we suggest that fern spores exhibit a storage physiology that has been described as intermediate between recalcitrant and orthodox storage behaviour or that they exhibit a storage physiology that remains uncharacterized. For germplasm management purposes, fern spore storage in conventional freezers appears to have problems and cryopreservation is not only feasible, but is necessary to maximize spore longevity for long term preservation. More research on fern spore storage physiology is needed understand the response of spores from diverse species to different storage conditions.
Technical Abstract: Ferns are a diverse and important group of plants, but diversity of species and populations are at risk from increasing social pressures, loss of habitat and climate change. Ex situ conservation is a useful strategy to limit decline in genetic diversity and requires technologies to preserve fern germplasm. Fern spore storage has received little research attention but, by analogy to seeds, may benefit from the extensive knowledge of seed storage gained during the last 50 years. Fern species produce either non green or green spores, which have been considered to exhibit storage physiologies similar to orthodox and recalcitrant seeds, respectively. Consequently, dry storage conditions are conventionally recommended for non green spores and humid storage in the refrigerator over media is recommended for medium term storage of green spores and some non green spores not tolerant to desiccation. Recently, we have shown that water content of stored ferns can be precisely controlled by adjustments in relative humidity, and that this control can be used to maximize longevity at a range of storage temperatures. Spore longevity is unexpectedly poor when they are stored at temperatures between 0 and -25°C and this has necessitated the use of cryogenic technologies developed over the last 15 years for fern spore storage. Crystallization of triacylglycerols (TAG also known as storage lipids) appears to be associated with fern spore response to low temperature and is analogous to responses reported for seeds of tropical origin. These recent discoveries and perspectives suggest that fern spores exhibit a storage physiology that has been described as intermediate between recalcitrant and orthodox storage behaviour or that they exhibit a storage physiology that remains uncharacterized. More research on fern spore storage physiology is needed to contrast and compare various responses of diverse plant germplasm to different storage conditions. The unicellular structure of the fern spore may provide a useful model system to obtain a greater understanding of multicellular germplasm to improve storage techniques lead to more effective conservation.