🕸 Seed Dormancy

Types, Causes, Seed Storage

Seed Dormancy

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

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.

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.

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.

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).

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.