- While the conservation collection grows in the nursery, take care to maintain genetic diversity.
- Keeping records and labels on maternal lines will help track the potential genetic diversity represented in the collection and can be used to equalize family lines for reintroductions or other conservation translocations.
- If maintaining more than one population or related species, take care to avoid unintended cross-pollination.
Minimize artificial selection and genetic drift.
- While maintaining seed or growing the accession in the nursery or garden, minimize artificial selection and genetic drift.
- Maintain ex situ collections as dormant seed if seeds are orthodox. This is a cost-effective method.
- During seed processing, take care to use cleaning equipment that allows for the greatest proportion of viable seeds to be processed (Basey et al. 2015).
- Seeds produced within a single population may vary in size. Take care to conserve seeds of varying size, rather than just large seeds (Basey et al. 2015).
- Seeds within the same capsule or pod may vary in maturity and require different storage protocols. (See Part 1B, “Collecting Seeds from Wild Rare Plant Populations.”) Mature seeds may be able to be stored by conventional methods, whereas immature seeds may be able to be cryopreserved or grown as a display or nursery plant but would not survive freezing. (See Part 2B, “Collecting and Maintaining Exceptional Species in Tissue Culture and Cryopreservation” and Part 2C, “Guidelines for Field Genebanks and Inter Situ Collections.”) For particularly rare species, there may be value to conserving seeds of varying maturity to capture full genetic diversity.
- Many seeds can be dried and maintained at cold temperatures for long periods. While in storage, they will be under reduced selection pressures, theoretically, although some genotypes may have lower survival when frozen (Crossa and Vencovsky 2011). Some species survive 5 to 10 years, but not longer, in cold, dry conditions. For these taxa, regenerating the seed collection may be necessary. (See Part 1E, “Curating Small Samples: Increasing the Number of Seeds for Storage and Restoration.”)
- For species that cannot be stored long-term as seeds, maintain multiple genetically unrelated plants in one or more living collections (Fant et al. 2016). The minimum number of plants needed to represent the genetic diversity of a species in a conservation collection can be determined with genetic studies (Griffith et al. 2015).
- Be conscious of artificial selection while growing plants in the conservation collection. Attempt to mimic the water and nutrient regimes the species faces in the wild, especially for individuals that will be returned to the wild.
- For advice for plants held in tissue culture, see Part 2B, “Collecting and Maintaining Exceptional Species in Tissue Culture and Cryopreservation.”
Maximizing germination of a seed accession may require using varying conditions and allowing enough time.
- Within a single accession, seeds may have variable germination rates or some seeds may have dormancy, while others do not. Planning to encompass this variation when doing germination trials will help ensure genetic diversity of seedlings.
- Labeling germination trials by maternal lines allows practitioner to track diversity and ensure equal representation in subsequent research or reintroduction trials.
Maintain material across maternal lines.
- Consciously maintain material across maternal lines to capture diverse growth rates, flower production, and presumably genetic diversity.
- Monitor the survivorship and health of the clearly labeled maternal lines represented in the accession.
- Maintain accurate records of the number of surviving individuals and total maternal lines to approximate the genetic representation of the collection. Note that genetic studies would be required to know the true genetic diversity in the collection.
- Avoid artificial selection. When trying to increase numbers of an accession, it is easy to choose the best and most fecund to replicate. It is important to have and maintain all maternal lines in the living collection whether they be on display in the garden, in a tissue culture lab, or in the nursery.
- If mortality occurs excessively for one maternal line, consider replanting to refresh the diversity represented.
Maintaining accessions offsite for generations requires periodic immigration from wild sources.
- If an accession must be maintained offsite as whole plants for a number of generations, maintain as large a population as possible and provide periodic immigration from a wild source population of approximately five migrants per generation and increase (triple, if possible) the sample size each generation (Havens et al. 2004).
Minimize unintended hybridization.
- Use knowledge of breeding system and wild population dynamics to inform these actions.
- Grow seeds from different populations at different times.
- If growing seeds from more than one population simultaneously, physically separate them or place them under netted cages to avoid pollen transfer.
- Note that there may be compelling reasons to cross-pollinate populations, such as one population consists of a single self-incompatible clone (Menges et al. 2016).
- Because genetic loss and change can occur during a single generation, best practice is to grow plants from wild-collected seeds (Basey et al. 2015) and preferably use F1 or F2 seeds for conservation introductions whenever possible. Seeds produced in a cultivated condition may have attributes that are disadvantageous in the wild, yet many conservation introductions must rely on seeds generated in a nursery in order to have adequate numbers to reintroduce to the wild. (See Part 1E, “Curating Small Samples: Increasing the Number of Seeds for Storage and Restoration.”)