Seed Processing

Some precautions • Do not mix seeds harvested in different seasons as the quality and longevity of the samples can be different. Assign batch numbers (indicating season of harvest, site or field number and generation number) to differentiate the seed lots. • Keep seeds from different seasons in separate containers or within the same container using separate cloth or re-sealable plastic bags if the container can accommodate them. • Remember that containers removed from cold storage or freezers should be allowed to warm to room temperature before opening to avoid condensation of water on the seed surface. This may take several hours, especially for large seeds and those removed from sub-zero temperatures. • The self-adhesive labels and ink used for labelling must be water resistant and very durable. To ensure long-term conservation and continued availability of high-quality seeds for utilization, seeds packed in moisture-proof containers should be stored under controlled environmental conditions as described in the following section. Table 6.1. Model table for recording information on seed packaging. Date of packaging: Name of staff: Accession number Type of container Container number ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

Weight of container empty Weight of container and seeds Weight of seeds 1 2 3 91 Manual of Seed Handling Further reading FAO/IPGRI, 1994. Genebank standards. FAO and IPGRI, Rome. 6.2 Seed storage What is seed storage? Seed storage is the preservation of seeds under controlled environmental conditions that maintain seed viability for long periods. The longevity of seeds ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

depends on initial seed quality, moisture content and temperature during storage. In general, low moisture content and low temperature reduce the loss of seed viability. Different combinations of moisture content and temperature can be used to prolong seed viability during storage. Types of storage Two types of seed stores are used for conservation of genetic resources: those holding seed samples for long-term security—referred to as base collections—and those holding seed samples for vimmediate use— referred to as active collections. The temperature, RH, seed moisture content, containers and distribution arrangements of these stores vary. Base collections A base collection is a set of accessions in which each is distinct and as close as possible to the original sample in terms of genetic integrity. Normally, seeds are not distributed from base collections directly to users but are only used to regenerate active collections (FAO/IPGRI, 1994). Base collections are stored for long periods at below 0°C—usually at -18° to -20°C—to maintain seed viability. Engels and Visser (2002) introduced the term ‘most-original sample’ (MOS) to qualify the samples in base collections. A MOS consists of seeds that have undergone the lowest number of regenerations since the material was acquired by the genebank; it may be a sub-sample of the original seed lot or a seed sample from the first regeneration cycle if the original seed lot required regeneration before storage. Active collections Active collections consist of accessions that are immediately available for distribution. ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

These accessions are accessed frequently and maintained in conditions that ensure at least 65% viability for 10–20 years (FAO/IPGRI, 1994). Combinations of temperatures and moisture contents for storage of active collections that can assure viability above 65% for 10–20 years are given in Table 6.2. It is more practical to use a lower moisture content and store at a higher temperature to save on refrigeration costs. However, when drying 92 Handbooks for Genebanks No. 8 to the low moisture contents is not possible, storage with higher moisture but at a lower temperature can be considered. Table 6.2. Suggested storage temperature and moisture content for active collections (source: ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

Bioversity, unpublished). Temperature (°C) Storage characteristics Poor (e.g. onion) Good (e.g. barley) Moisture content (% wet basis) 25 3 7 20 3.5 7.5 15 5.0 8.0 10 6.0 9.0 5 7.0 10.0 0 8.0 11.0 Organization of collections The underlying principle of maintaining a base collection or MOS is that at least some seed of the original sample should be kept aside under the best possible conditions to ensure safe long-term survival. This may be achieved by keeping seeds for distribution physically separate (as active collections) from the original sample but there is no absolute requirement to do so.