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seed storage temperature

Seed storage temperature

What is meant by seed storage?

In a genebank, seed storage is the preservation of seeds under controlled environmental conditions which will prolong the viability of the seeds for long periods. Two types of seed stores are used for collections of genetic resources, those holding base collections and those holding active collections. The temperature, relative humidities, seed moisture contents, containers and distribution arrangements vary between these stores.

Why are seeds stored?

Seeds must be stored in a way which maintains their viability for long periods. Seeds left at ambient temperatures and relative humidities will lose their viability quickly whilst seeds stored in conditions of low moisture content and temperature will retain their viability for longer periods. Accessions held in a genebank are valuable and represent plants which are no longer available or which are endangered in their natural environment. These seeds must be conserved in the genebank for use in plant breeding in the future.

When should seeds be placed into store?

As soon as the seed has matured on the plant the slow process of deterioration begins. Therefore the sooner that seeds are placed into store the better. In practical terms this means that seeds collected in the field should be quickly returned to genebanks, processed and placed into store as soon as the cleaning, drying and packaging processes are complete.

How many seeds of each accession should be stored?

The IBPGR Advisory Committee on Seed Storage has recommended that for materials showing little morphological variation (genetically homogeneous) 3000 seeds are acceptable, but 4000 seeds are preferred, to represent each accession. For materials showing a large amount of morphological variation (heterogeneous) an accession should consist of at least 4000 seeds, but 12000 seeds are preferred. These sample sizes are recommended as number of seed but many genebanks would prefer to work with weight. An inter-conversion of numbers and weights is possible from the thousand seed weight of any accession. A list of approximate thousand seed weights of some common species is given in Appendix 2 of Cromarty, Ellis and Roberts (1982).

How should seeds be stored?

The conditions which prolong viability during storage have been well defined for seeds which are tolerant of desiccation. Storage conditions have been recommended by the IBPGR Advisory Committee on Seed Storage. For base collections, seeds of between 3-7 % moisture content should be stored in sealed containers. Sub-zero temperatures are acceptable, but -18 °C or less is preferred. For active collections sealed storage of seeds dried to 7% moisture content or less is recommended at temperatures of less than 15 °C. Unsealed storage is not encouraged. In particular, it is not recommended in tropical areas.

Table of thousand seed weights of species in your genebank

Fill in this table to use for future reference:

Seed storage temperature What is meant by seed storage? In a genebank, seed storage is the preservation of seeds under controlled environmental conditions which will prolong the viability of

Seed Storage

Quality Seed from the Start
At the time of physiological seed maturity the germination and vigor of the seed is optimal and at its maximum. This is the time where our farmers are harvesting the seed. The seed is dried immediately after harvest to reach a moisture content of 12 to 13%. This puts the seed in the best position to be stored. Careful and soft handling during seed processing is also your guarantee for a high quality product with a long shelf life. Nevertheless, seed is a living organism and aging of seeds starts right after harvest. The goal for storage should be to create conditions to slow the aging process.

Water Content and Temperature
Low moisture is more important than low temperature. You might experience problems if the seed is exposed to large differences in temperature. In that case air circulation can be initiated which not only transports heat, but also moisture from seed to seed. This is possible because the difference in the temperature of warm seed and cold air condense water on the seed in the bag. The high moisture content accelerates the respiration of the seed and thereby the loss of energy.

Storage Condition Impact on Shelf Life.
The temperature and humidity decides how long you can store the seed. Each seed has a built-in “shelf life meter” which is the potential time the seed can be stored.

Figure 1 – Deterioration of Seed Over Time

In Figure 1, Line A is the maximum period of seed shelf life, whereas Line B shows the effect of poor seed storage conditions in the warehouse. When conditions deteriorate, the seed germination will deteriorate accordingly. In the majority of cases, the germination will stay stable for a length of time before starting to decline.

Optimal Seed Storage Conditions
Generally, the colder and drier the surrounding environment, the better. The conditions to aim for are 30% relative humidity, or as low as possible and with temperatures below 59°F (15°C). The aim is a temperature that is as consistent as possible. It is more important to maintain consistency, rather than maintaining a low temperature level; a range from 59 to 63°F (15 to 17°C) is far better than a range from 46 to 86°F (8 to 30°C). Darkness is a third rule of optimal seed storage. Light stimulates and supports the germination process in the seeds; storage in darkness helps keep the pre-germination processes in the seed at a low level.

Seed Storage Quality Seed from the Start At the time of physiological seed maturity the germination and vigor of the seed is optimal and at its maximum. This is the time where our farmers are