Crop Genebank Knowledge Base

Seed bank

Seed bank of forage grass genetic resources

Contributors to this page: ILRI, Addis Ababa, Ethiopia (Jean Hanson); Bioversity International/ILRI, Addis Ababa, Ethiopia (Alexandra Jorge).

When seed banks should be used

Forage grasses are usually stored as seeds.

Seed storage provides a long-term and economical means of storage for those species whose seeds can be dried (5-8%) and behave as orthodox seeds, i.e. can be stored at -18^oC or -20^oC, maintaining their viability for several years.

There has been little research on seed storage of many forage grasses and there is limited information about the storage behaviour of seeds of many of the species being conserved. The longevity of the forage seeds depends on the species, their initial seed viability and seed moisture content and storage temperature. Seeds from different species can have varied storage and dormancy characteristics and have been classified according to their longevity as being short-lived, moderately long-lived or long-lived.

Many of the forage grasses have short-lived seeds (seeds that only remain viable for a very few years) or are shy seeders (only a small percentage of the seeds have a caryopsis and will germinate). Species like Panicum maximum (short-lived seeds), Pennisetum purpureum (shy seeder) and Digitaria arianthum shy seeder) are generally maintained in field genebanks.

Seeds of forage grass species that have been found to survive for more than five years of cold storage (at 5 % moisture content and 8^oC) without substantial loss of viability (Chin and Hanson, 1999) can be stored in seed genebanks:

Andropogon gayanus
Brachiaria brizantha
Brachiaria decumbens
Cenchrus ciliaris
Chloris gayana
Cynodon dactylon
Pennisetum clandestinum

Seeds stored for long periods in genebanks are better protected from external climatic or environmental factors that cause seed deterioration. However, during regeneration these seeds may be exposed to the risk of loss of genetic integrity from external pollen contamination, selection or genetic drift. Reducing the regeneration interval by providing the best possible storage conditions to extend longevity helps to reduce genetic change during seed storage.
Grass seeds are usually small and light and grass seedlings are often small and delicate making field establishment difficult. Seeds are the best and easiest way to disseminate and distribute plant genetic resources across regions and countries because of plant quarantine restrictions on vegetative material.
Therefore, depending on the ease of seed production, seed longevity, local conditions and demand, informed decisions can be taken on whether to conserve grasses as seed or incur the additional cost of establishing a field genebank.
When species are difficult to establish or have short-lived seeds (1-2 years), the efforts and cost of constant regeneration of seeds in the field is high and it usually becomes more economical, efficient and practical to maintain perennial plants permanently in a field genebank, rather than store them as seeds. Small quantities of seeds are often stored for short periods to meet demand from users because seeds are usually more readily accepted by plant quarantine for distribution.

How seed storage should be done

Seeds should be stored in controlled and safe environments. After reducing the moisture content of the seeds, store them under cold and dry conditions.
Very little is known about the species' behaviour (breeding system, isolation distance, adaptation, seed production requirements) of many grasses and long-term studies should be done to obtain reliable results to make recommendations for best practices for seed storage of grasses in genebanks.
It is crucial to know for how long seeds of different species will remain viable in cold storage until they need to be regenerated, in order to make informed decisions about storage method and conditions.

References and further reading

Chin HF, Hanson J. 1999. Seed storage. In: Loch DS, Ferguson J, editors. Forage Seed Production Vol. II Tropical and Subtropical Species. CABI, Wallingford, UK. pp. 303-315.