Seed Dormancy

• Dormancy is the arrested development and reversible rest period of plant organs either of a seed or of any vegetative part.

Causes of Dormancy

Innate Dormancy (Primary / Endogenous Dormancy)

• This type of dormancy is imposed by factors inside the embryo.
• It is different from quiescence stage. A seed which is just waiting for favourable environmental condition to germinate is called Quiescent seed.

Enforced Dormancy (Secondary / Exogenous Dormancy)

• This type of dormancy is imposed by factors outside the embryo.

Physiology of Dormancy

• The formation of dormant structures is commonly associated with the suspension of metabolic, synthetic and morphogenetic activities that are associated with the minimum physiological and a minimum moisture content.
• During this period, there is very poor or total suspension of respiration or rather anaerobic respiration with higher respiration quotient (infinite).
• Dormancy is due to lack or inactivity of hydrolytic enzymes.
• Gibberellins are the predominant germination agents found in the germination phase during the food reserve degradation stage.
• Cytokinis exert their influence later on the initiation of cell proliferation and expansion.
• Red light (660 μm) promotes and blue especially far-red light (735 μm) inhibits germination.

Causes of Dormancy

• Hard Seed coat
• Seed coats being impermeable to water
• Seed Coat being impermeable to oxygen
• Rudimentary embryo of seeds
• Dormant embryo
• Synthesis and accumulation of germination inhibitors in the seeds.

Methods of Breaking Seed Dormancy

Physical Treatment

• Scarification: Dehusking or removal of seed coats by rubbing to make it permeable to water.

  

• Stratification: ^{NABARD 2021} Low temperature treatment at 2-8 °C for 12-24 hours but Seeds should be presoaked for 36 hours before they are given the low temperature treatment.

  

• Heat treatment at 40-45° C for different duration.
• Alternate heating and cooling for several times.
• Alternate drying and wetting for several times.
• Exposure for 24 hours of water-soaked seeds to red light for 1-2 hrs. at 15-25°C temperature.

Chemicals

• Inorganic Chemicals:
  • By acid treatment: Dilute solutions of HNO₃, HCl or H₂SO₄ (0.10 - 0.5%) for different durations in minutes.
  • Potassium Nitrate (KNO₃) @1-3%: Strongest and used for immediate dormancy break after harvesting; NH₄NO₃ (1-3%), H₂O₂, H₃BO₄ etc. Ex. Rice, Tomato, Chilies etc.
  • By gases: by increasing O₂ concentration.
• Organic Chemicals:
  • Non-hormonal: Thiourea, Ascorbic acid.
  • Hormonal: GA3 (1-1000 ppm) — Commonly used hormone to break dormancy; Others are Kinetin (1-100pm), Ethylene (Ethrel solution of 100-300 ppm).

Seed Storage

• Cryopreservation: Non-orthodox seeds are stored at -196°C the temperature of liquid nitrogen.

• Dehumidification: Removal of water - vapour from the air in storage. Silica gel is the most common desiccant used as chemical dehumidifier.
• Tempering: Process of bringing grains or other products to a desired moisture or temperature for processing.
• Matrical is the heterogeneity in the quality due to location of the seeds in the inflorescence e.g. difference in flowering pattern.
• Acclimatization: The process that leads to adaptation of a variety, line or population to a new environment is known as Acclimatization.

Seed Dormancy

• Dormancy is the arrested development and reversible rest period of plant organs either of a seed or of any vegetative part.

Causes of Dormancy

Innate Dormancy (Primary / Endogenous Dormancy)

• This type of dormancy is imposed by factors inside the embryo.
• It is different from quiescence stage. A seed which is just waiting for favourable environmental condition to germinate is called Quiescent seed.

Enforced Dormancy (Secondary / Exogenous Dormancy)

• This type of dormancy is imposed by factors outside the embryo.

Physiology of Dormancy

• The formation of dormant structures is commonly associated with the suspension of metabolic, synthetic and morphogenetic activities that are associated with the minimum physiological and a minimum moisture content.
• During this period, there …

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