What is Seed Dormancy? – Definition
Dormancy is the failure of fully developed, mature, viable seed to germinate even under favorable physical conditions (like moisture and temperature).
The seed with dormancy is termed as dormant seed.
Types of Seed Dormancy
| Primary Dormancy | Examples | |||
|---|---|---|---|---|
| Exogenous dormancy | Physical | It is due to impermeability of seed coat to water. This impermeability is the result of macrosclereid cells, a mucilaginous outer cell layer, or a hardened endocarp. Such seed coats develop during the last stages of seed development. | legumes | |
| Chemical | It is due to the presence of chemical inhibitors in the outer coverings of many fruits and seeds. | grapes, apples, citrus | ||
| Mechanical | It is due to the hard seed coat. Such hard seed coat do not allow embryo to expand during germination. | olive | ||
| Endogenous | Morphological | Rudimentary | Embryo is not fully developed at time of ripening. Additional embryo growth is required after the seed is separated from the plant. | Ranunculaceae, Papaveraceae |
| Linear | Umbelliferaea, Ericaceae | |||
| Undifferentiated | orchids | |||
| Physiological | Non-deep | Often lasts for short period and disappears with storage (usually 1 to 6 months). | herbaceous plants such as annuals and veggies | |
| Intermediate | The embryo itself is quiescent, not dormant and can germinate if excised. | conifers | ||
| Deep | Controls are within the embryo itself. | Temperate trees like apple. | ||
| Combinational | Morphological | Epicotyl | There are separate after-ripening requirements for epicotyl, hypocotyl and radicle. | Lilium |
| Epicotyl and radicle | Trillium | |||
| Exo-endodormancy | Combination of exo and endogenous dormancy | |||
| Secondary dormancy | Example | |||
| Thermodormancy | In this type new dormancy mechanism is imposed during unfavorable conditions. | Celery, lettuce | ||
| Conditional dormancy | ||||
Causes, advantages and breaking methods for dormancy i.e. ways to overcome dormancy are on the page Dormancy – causes, benefits and breaking