• Definition:
  1. The ability of seeds to delay germination until the time and place are right
  2. Differs from quiescence

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• Major Types
  • Primary
    • Exogenous Dormancy
      • Essential germination components are not available
      • Generally related to the seed coat or other physical factors

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    • Factors responsible for Exogenous Dormancy
      1. Water
      2. Gases
      3. Mechanical Restriction

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    • Methods of Breaking Exogenous Dormancy
      1. Mechanical Scarification
      2. Chemical Scarification

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    • Endogenous Dormancy
      • The most prevalent form of dormancy
      • Due to internal properties of the seed

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    • Causes of Endogenous Dormancy
      1. Environmental conditions during development & maturity
      2. Day-length during seed development
      3. Moisture status of mother plant
      4. Position of the seed on the inflorescence
      5. Age of the mother plant
      6. Environmental conditions during seed development

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    • Rudimentary Embryo Dormancy
      • Seeds shed before they are morphologically mature
      • Occurs in several tree and fruit species

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    • Physiological Dormancy
      • Generally results from an imbalance of inhibitors & promoters
      • Light & temperature are frequently involved

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    • Examples of Physiological Dormancy
      1. Metabolic Inhibition
         • Cyanide
         • Phenolic compounds
         • Abscisic acid
      2. Osmotic Inhibition
         • Sugars & salts
         • Other electrolytes

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    • Methods of breaking Physiological Dormancy
      1. Leaching
      2. Scarification
      3. Stratification
      4. After-Ripening
      5. Light

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  • Other types of dormancy
    • Circadian Rhythms
      • Involves an internal time measuring mechanism

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    • Examples of Circadian Rhythms
      1. Pigweed
      2. Bluegrass

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    • Secondary Dormancy
      • Occurs in nondormant seeds after maturity

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    • Possible causes of Secondary Dormancy
      1. Temperature
      2. Moisture
      3. Chemicals
      4. Gases

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    • Suggested modes of action:
      1. Blockage of a metabolic sequence
      2. Unfavorable balance of growth- promoters & -inhibitors

References:

Principles of Seed Science and Technology. 3rd Ed. L.O. Copeland and M.B. McDonald. Chapman and Hill, New York, 1995