Seed dormancy and viability

Seed dormancy

Seed dormancy is a state where seeds fail to germinate even under favorable conditions. It ensures seeds germinate when conditions are optimal for growth and survival.

Types of dormancy

1. Primary dormancy:

   • Present at seed dispersal.
   • Internal changes (after-ripening) are needed before germination can occur.

   Causes:

   • Immature embryo: Seeds wait for the embryo to mature while remaining viable.
   • Hard testa (seed coat): Prevents water and oxygen from reaching the embryo.
   • Growth inhibitors (e.g., abscisic acid): Prevents premature germination.

2. Secondary dormancy:

   • Induced when external conditions (e.g., water, oxygen, temperature) are lacking.
   • Dormancy persists until the external environment becomes favorable.

Causes of dormancy

1. Primary causes:

   • Internal factors like seed coat hardness and inhibitors.
   • Immature embryos.

2. Secondary causes: External environmental factors like insufficient moisture, oxygen, light, or temperature.

Breaking dormancy

Natural methods: Occur when the environment becomes favorable, providing adequate moisture, temperature, and oxygen.

Artificial methods:

1. Scarification:

   • Mechanical scarification: Weakening the seed coat by cutting, striking, or abrasion.
   • Chemical scarification: Using acids (e.g., HCl, H₂SO₄) or alcohol (e.g., ethanol) to soften the seed coat and remove inhibitors.

2. Partial digestion: Seeds pass through animal digestive systems, softening the seed coat and removing inhibitors.

3. Stratification:

   • Cold stratification: Mimicking winter conditions using moist sand and cold storage.
   • Fire stratification: Exposing seeds to heat under a thin film of sand to mimic conditions in fire-prone areas.

4. Hormonal treatments: Applying growth hormones to stimulate germination.

5. Dry storage: Allowing time for embryo maturity to eliminate primary dormancy.

Significance of dormancy

1. Protects seeds during unfavorable conditions.
2. Prevents premature germination.
3. Synchronizes germination with favorable seasons.
4. Assists in seed dispersal and long-term storage.

Seed viability

Definition: Viability refers to a seed's ability to germinate under suitable conditions.

Factors affecting viability

1. Embryo maturity: Immature seeds cannot germinate.
2. Enzyme activity: Enzymes are vital for metabolic processes during germination.
3. Storage duration: Seeds lose viability over time, with some seeds viable for years, while others lose viability within one year.
4. Seed health: Diseased or damaged seeds are often non-viable.

Importance of viability

1. Determines the potential for successful germination.
2. Vital for agriculture and species propagation.

Practical applications

The content discusses strategies for overcoming dormancy and maintaining seed viability, which are critical for:

1. Enhancing crop production.
2. Conservation of plant species.
3. Managing seed storage for agricultural and ecological purposes.