Getting difficult seeds to germinate
There is little point in conserving seeds unless those seeds can one day be converted back into plants for use (e.g. in habitat restoration, re-introduction, or research). Tackling seed collections that don’t germinate during routine germination monitoring is a major challenge for the Millennium Seed Bank.
Mature, healthy seeds that fail to germinate under favourable environmental conditions are described as dormant.
The MSB’s experimental approach to dormant collections is to first consider the natural conditions likely to trigger germination of a particular species. Based on information from sources such as the Seed Information Database (SID), experimental factors are then chosen that aim to mimic natural light and temperature conditions and external stimuli such as bush fires.
Bush fire in Northern Territories, Australia. (Photo: © Jason Poynting)
Natural fires stimulate seed germination in many species native to fire-prone tropical and sub-tropical dryland habitats. MSB scientists have been trying to use plant-derived smoke solutions, dry heat, and gases such as nitrogen dioxide to stimulate seed germination in the laboratory. Seeds of the tropical grass Eragrostis pilosa (Tef) may remain dormant for months or even years in the wild. Laboratory treatments that mimic natural fires can overcome this dormancy. An aqueous smoke extract, made by burning plant material and sending the smoke produced through water, can be applied to the seeds. Seeds are also exposed to extremely high temperatures such as 90 – 120ºC. These methods have been adopted for routine germination tests.
Other tropical species possess seeds that normally remain dormant in the soil over the hot, dry season and only germinate when the rains come. The MSB uses a “dry after ripening” treatment, in which seeds are exposed to warm-hot temperatures and moderate humidity levels, to over come this type of dormancy.
Seeds of Nigella damascena (Love in a Mist) germinating with and without Gibberellic acid
Some seeds respond to chemicals in their natural environment. A change in soil pH or soil nitrate levels may trigger germination. Gibberellic acid, a naturally occurring plant hormone, is known to stimulate germination in many species. Studies at the MSB have looked at gibberellic acid, potassium nitrate and ethylene, with a particular focus on the optimal concentration and length of treatment needed to yield maximum germination in problem collections. The effect of the germination medium pH has also been investigated.
Seeds with physiological dormancy often germinate when a small section of the seed coat close to the underlying embryo is surgically removed. For very small seeds these surgical treatments are carried out under a binocular microscope using forceps and a scalpel. This method can be particularly effective in tropical grasses but has also been applied successfully to seeds from other families including Apiaceae, Iridaceae, and Liliaceae. Insert seed germination 3 image in appropriate place.
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| Surgical excision of the pericarp directly above the embryo in seeds of Eragrostis pilosa (Tef) |
Key findings:
- Fire related cues can stimulate germination of a range of species including some grass species under laboratory conditions.
- Physiological dormancy is the prevalent type of dormancy in the Millennium Seed Bank collections.
- Specific surgical treatments can sometimes alleviate dormancy very effectively.
Further information:
Baskin, C. C. and Baskin, J. M. (1998) Seeds: Ecology, Biogeography and Evolution of Dormancy and Germination. Academic Press.