Testing alternative methods for drying seeds
The secret to successful long-term storage of orthodox seeds is to lower seed moisture content by drying. Dried orthodox seeds:
- live longer (a 1% reduction in seed moisture content approximately doubles seed storage life);
- tolerate sub-zero temperatures (prolonging longevity still further);
- are prevented from germinating, and
- are less likely to be attacked by insects, mites and fungi.
Cooled incubator with bags of seeds arranged on the shelves to dry.
Many of the world's larger seed banks (including the Millennium Seed Bank) use temperature and humidity controlled dry rooms to reduce seed moisture content to safe levels for long term storage. MSB scientists have recently developed an innovative method of seed drying, using cooled incubators, that meets the needs of smaller seed banks that cannot afford, and do not need, large scale dry rooms.
Cooled incubators are widely used for germination testing and can
be set at various temperatures. Temperature is controlled using a
combination of heating and refrigeration coils. The refrigeration
coils remove water vapour from the air, making it drier. A temperature
setting of 18°C produces an average chamber humidity of 15%RH.
These conditions can be used to dry seeds - 10kg of fresh seeds will
dry down to around 7% moisture content in approximately 3 weeks. Seeds
dry best spread loosely in cotton bags. Smaller quantities can be
added continuously without affecting the overall performance.
Cooled incubators used in this way
will operate satisfactorily under external conditions of 16 - 45°C
and 5 - 75%RH.
Key findings:
- Cooled incubators operate successfully under wide external temperature and humidity ranges (16°C to 45°C and 5%RH to 75%RH).
- Up to 10kg of fresh seed can be dried at a time.
- Small seed collections can be added continuously without any loss in drying performance.
Further information:
Probert, R.J. and Hay, F.R. (2000). Keeping seeds alive, pp. 375-410. In: M. Black and J.D. Bewley (eds). Seed technology and its biological basis. Sheffield Academic Press, Sheffield, UK.
Probert, R.J. (2003). Seed viability under ambient conditions and the importance of drying, pp. 337-365. In: RD Smith, JD Dickie. SH. Linington, HW Pritchard &. R.J Probert (eds) Seed conservation: turning science into practice. Royal Botanic Gardens, Kew, UK.