Contributors to this page: ILRI, Addis Ababa, Ethiopia (Jean Hanson); Bioversity International/ILRI, Addis Ababa, Ethiopia (Alexandra Jorge).
When field banks should be used
Many forage grasses have short-lived seeds (seeds that only remain viable for 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 in addition to seed storage, where feasible.
Grasses stored in field genebanks have a lower risk of losing genetic integrity (due to pollen contamination or genetic drift) if the mother plants are maintained for many years and are readily available for study and use. However, grasses maintained in field genebanks are more exposed to physical risks (climate, diseases, pests) and costs are higher for storage (labour, inputs and space) than in seed genebanks. This balance must be considered when taking the decision to establish a field genebank for forage grasses, if they produce seeds with good longevity during storage.
Very little is known about the species behaviour (breeding systems, adaptation, seed production requirements) of many grasses and long-term studies should be carried out to obtain reliable results to make recommendations for best practices for field genebanks. It is crucial to know if species can produce seeds and for how long these seeds will remain viable in cold dry storage until they need to be regenerated to make informed decisions about whether to mantain accessions in a field genebank.
Grass seeds are usually small and light, and grass seedlings are often small and delicate making field establishment difficult. 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 are high and it usually becomes more economical, efficient and practical to maintain them permanently in a field genebank.
Seeds of forage grass species that have been found to survive for more than five years of cold storage (at 5% moisture content and 8oC) without substantial loss of viability (Chin and Hanson, 1999) can be stored in seed genebanks:
References and further reading
Maass BL, Escobar AO. 1996. Managing tropical forages field genebanks at CIAT. Paper presented at the IPGRI/SGRP/CIAT/FAO Consultation meeting on Management of Field and In Vitro Genebanks at CIAT, 15-20 January 1996. Cali, Colombia.