Seeds require specific temperature, moisture and light cues to germinate, to ensure that they begin to grow when temperatures are not too harsh and rainfall is sufficient to keep the tiny seedlings alive. If moisture, appropriate temperature and light conditions are provided, but seed still does not germinate, then two things may have happened - the seed is dead or the seed is dormant.
What is dormancy?
Dormancy is a characteristic of the seed that defines the environmental conditions required for germination. It is influenced by genetics and by the environment, both during seed maturation and following seed dispersal. Dormancy ensures that seeds germinate under favourable conditions and often, over an extended period of time rather than all in one flush. This minimises the risk that all seedlings will be destroyed soon after germination and ensures species survival into the future.
Cues to break dormancy include seasonal temperature cycles, heat from fires or hot days, smoke, stratification (exposing moistened seed to a period of warm or cold), after-ripening (maturation in dry conditions following dispersal) and scarification (to break the seed coat). Understanding which cues break dormancy in the natural habitat helps researchers choose which conditions will help seeds to germinate in the laboratory. In the laboratory, germination may also be stimulated by chemicals such as gibberellic acid. Seeds may be scarified by chipping the coat with a scalpel or abrading with sandpaper. Storage in the seedbank may also change the germination response to particular cues.
Germination and dormancy in Australian species
Some Australian species have unknown dormancy and germination mechanisms, which hampers efforts to germinate seeds from conservation seed banks. It also means that many popular ornamental Australian species are propagated by cuttings rather than from seed. Australian plant families with known dormancy include Cyperaceae, Dilleniaceae, Ericaceae (Epacridaceae), Goodeniaceae, Lamiaceae, Restionaceae, Rutaceae and Violaceae.
Further reading on seed dormancy and germination:
- Baskin, C.C. & Baskin, J.M. (1998) Seeds. Ecology, Biogeography and Evolution of Dormancy and Germination. Academic Press, San Diego, USA.
- Baskin JM and Baskin CC (2004) A classification system for seed dormancy. Seed Science Research 14: 1-16.
- Bell DT (1999) The process of germination in Australian species. Australian Journal of Botany 47:475-517.
- Turner SR and Merritt DJ (2009) Seed germination and dormancy. In Offord CA and Meagher PF. Plant Germplasm in Australia: strategies and guidelines for developing, managing and utilising ex situ collections. Australian Network for Plant Conservation Inc., Canberra. Available from the Australian Network for Plant Conservation.
- Offord CA, Guja LK, Turner SR and Merritt DJ (2017) Seeds at the forefront: synthesis of the inaugural National Seed Science Forum and future directions in Australian seed science. Australian Journal of Botany 65 (8): 601-608.