Seed Dormancy

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