- Some species produce so few seeds in the wild that collections of 100 seeds or less are expected. These require additional care.
- For best conservation value, increase seeds before storage by taking steps to grow to maturity, collect next generation seeds, and store.
- Alternatively, plan to collect seeds across multiple years to build the total number held in storage.
- Preferentially use stored material for research or reintroduction rather than wild collected seed.
CPC encourages practitioners to collect from the rarest plant populations as these have high extinction risk. Some of the rarest species may not have populations large enough to support a collection of 3000 seeds, the number of seeds for a collection suggested by National Laboratory for Genetic Resources Preservation (NLGRP). Note that 3000 seeds is a target, not a dictum. If you are lucky enough to make a collection of more than 3000 seeds, it will mean more seeds will be available for future uses. For collections of 100 to 3000+ seeds, follow the practices outlined in Part 1D, “Cleaning, Processing, Drying, and Packaging Seeds for Conventional Storage.” This section pertains to or those collections that have fewer than 100 seeds.
Small seed collections present a challenge for seed banking and may require additional actions.
- If a collection has fewer than 100 seeds, the following steps should be taken:
- Collect species information on breeding system, ecology, and biology.
- Plan to make additional collections from the population in different years to increase the total number of seeds in storage.
- Collecting from extremely small populations with sporadically reproducing individuals may require that you tag individuals so that you can be assured of the genetic representation in your collection across years.
- Try growing seed. Particularly small seed accessions may require advice from experts.
- Consider making plans to collect tissues for tissue culture. Develop a plan with an expert prior to collection. See Part 2B, “Collecting and Maintaining Exceptional Species in Tissue Culture and Cryopreservation.”
Plan to increase the number of seeds for storage or reintroduction use.
- Because genetic drift and artificial selection are possible with every generation, use the most original sample to regenerate accessions (prioritize wild first, then the first generation (F1), then second generation (F2) to grow for increasing the total number of seeds.
- When you regenerate a seed collection, it is advisable to immigrate genes (via pollen or new seeds) from the wild to help add diversity if the wild population still exists.
- For very small seed collections, keep in mind that it may not be possible to produce 30 seed-bearing plants. Research the best germination/propagation protocols to ensure that enough source plants can be propagated (Deno 1993; Cullina 2000, 2002; Baskin and Baskin 2003, 2014; U.S. Department of Agriculture, Forest Service 2008; Native Plant Network.
- Store wild and next generation material (if the species conservation status allows). Be sure to document whether seed is wild collected or next generation (for example, F1, F2, Backcross, or other) in the database. Note the growing conditions of the F1 generation as well.
- Take care to prevent cross-pollination from non-target pollen sources (with congeners or from other populations). FAQ - How can I prevent cross pollination in my nursery?
- Facilitate outcrossing by hand pollination. If feasible, do experimental hand-pollinations to maximize opportunities for setting fruit and understanding mating system. Label flowers to track open pollinated versus hand pollinated from known pollen and maternal sources.
- For reintroductions, it is important to equalize the number of plants across the maternal lines represented in the outplanting. Therefore, track maternal lines as you conduct seed increases.
Gather baseline data on seed viability.
- Gather baseline data on seed viability of every accession prior to placing into cold storage and periodically test stored material for viability.
- Remember that the lifespan of seed in storage is not infinite.
- The periodicity of monitoring should vary with any known ecological and storage characteristics. Seeds with tropical oils, from aquatic habitats, or from spring fruiting parents may be short-lived, therefore they should be tested accordingly.
- Periodic viability testing eventually will reveal a decline in sample quality prompting a management decision about the value of the sample and the need for replenishment. When possible, use ways to sample very few seeds or non-destructive viability testing such as differential scanning calorimetry (DSC) or RNA (Walters, personal communication).
- If you can detect a change in the viability of a stored accession, it is time to regenerate it.
- Any resulting rare seedlings should be raised to maturity, and any germination/ propagation protocols should be recorded to inform future reintroduction efforts.
- When refreshing stock, follow guidelines Part 3C, “Genetic Guidelines for Maintaining a Conservation Collection.”
- Realize that seed that is no longer capable of germinating may still be valuable for genetic research.
Use stored material for reintroductions.Because genetic drift and artificial selection are possible in a cultivated setting, strive to have at least 30 randomly chosen individuals of a fully outbreeding sexual species (outcrossing) or 59 randomly chosen individuals of a self-fertilizing species as the seed-bearing plants as source material (Brown and Marshall 1995).
- When practitioner is ready to do reintroductions, preferentially use stored material rather than wild collected seed.
- If populations are adequate in the wild, add wild genes (via seed or pollen) to the reintroduction.
Reference for CPC Guidelines
FAO Genebank Standards for Plant Genetic Diversity (FAO 2014)
Standards for Regeneration
4.4.1 Regeneration should be conducted when the viability drops below 85 percent of the initial viability or when the remaining seed quantity is less than what is required for three sowings of a representative population of the accession. The most original sample should be used to regenerate those accessions.
4.4.2 The regeneration should be carried out in such a manner that the genetic integrity of a given accession is maintained. Species-speciﬁc regeneration measures should be taken to prevent admixtures or genetic contamination arising from pollen geneﬂow that originated from other accessions of the same species or from other species around the regeneration ﬁelds.
4.4.3 If possible at least 50 seeds of the original and the subsequent most-original samples should be archived in long-term storage for reference purposes.
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Baskin, C. C., and J. M. Baskin. 2003. When breaking seed dormancy is a problem: try a move-along experiment. Native Plants Journal 4:17–21.
Bless, A. 1938. Brief papers: effects of x-rays on seeds. Plant Physiology 13(1): 209–211.
Cullina, W. 2000. The New England Wild Flower Society guide to growing and propagating wildflowers of the United States and Canada. The New England Wild Flower Society, Framingham, Massachusetts.
Cullina, W. 2002. Native trees, shrubs, and vines: a guide to using, growing, and propagating North American woody plants. The New England Wild Flower Society, Framingham, Massachusetts.
Deno, N. C. 1993. Seed germination theory and practice. 2nd ed. National Agricultural Library, U.S. Department of Agriculture.
Dirr, M. A., and Heuser, C. W., Jr. 2006. The reference manual of woody plant propagation: from seed to tissue culture Varsity Press, Inc., Cary, North Carolina.
Emery, D. 1988. Seed propagation of native California plants. Santa Barbara Botanic Garden, Santa Barbara.
Food and Agriculture Organization of the United Nations (FAO) 2014. Genebank standards for plant genetic resources for food and agriculture. Rome, Italy. .
Falk, D. A., and K. E. Holsinger, 1991. Genetics and conservation of rare plants. Oxford University Press, New York.
Guerrant, E. O., Jr., K. Havens, and M. Maunder, editors. 2004. Ex situ plant conservation: supporting species survival in the wild. Island Press, Washington, DC.
IUCN seed specialist group. Accessed August 4, 2017.
Maunder, M., C. Huges, J. A. Hawkins, and A. Culham. 2004. Hybridization in ex situ plant collections: conservation concerns, liabilities, and opportunities. Pages 325–364 in Guerrant, E. O., Jr., K. Havens, and M. Maunder, editors. 2004. Ex situ plant conservation: supporting species survival in the wild. Island Press, Washington, DC.
Millennium Seed Bank Partnership (MSB). 2015. Seed conservation standards for “MSB Partnership Collections.” Royal Botanic Gardens, Kew, UK.
Native Plant Network, Propagation Protocol Database. Accessed August 4, 2017.
U.S. Department of Agriculture. Forest Service. F. T. Bonner and R. Karrfalt, editors. 2008. The woody plant seed manual (No. 727). Government Printing Office, Washington, DC.
Willis, C. G., Baskin, C. C., Baskin, J. M., Auld, J. R., Venable, D. L., Cavender-Bares, J., Donohue, K., and Rubio de Casas, R. 2014. The evolution of seed dormancy: environmental cues, evolutionary hubs, and diversification of the seed plants. New Phytologist 203:300–309.