Types of germination, factors affecting germination

1. Introduction

1. Seed germination is the process by which a dormant seed develops into a seedling.
2. It is essential for the propagation and survival of plant species.
3. Dormancy is a condition where a viable seed fails to germinate even under favorable conditions.

2. Process of Seed Germination

1. Germination begins when the seed absorbs water (imbibition).
2. Enzymes activate, breaking down stored food in the cotyledons or endosperm.
3. The radicle emerges first, forming the root system.
4. The plumule emerges later, forming the shoot system.
5. The seedling undergoes growth and development into a mature plant.

3. Types of Germination

1. Epigeal Germination

1. The cotyledons are pushed above the soil surface.
2. Occurs due to the elongation of the hypocotyl.
3. Examples: Bean, Castor, Cotton.

2. Hypogeal Germination

1. The cotyledons remain below the soil surface.
2. Occurs due to the elongation of the epicotyl.
3. Examples: Pea, Maize, Coconut.

3. Viviparous Germination

1. Occurs in mangrove plants where seeds germinate while still attached to the parent plant.
2. Helps in survival in waterlogged conditions.
3. Examples: Rhizophora, Sonneratia.

4. Factors Affecting Seed Germination

External Factors

1. Water: Essential for imbibition, enzyme activation, and metabolic activities.
2. Oxygen: Required for cellular respiration to produce energy.
3. Temperature: Optimum temperature (25-30°C) is needed for enzyme activity.
4. Light: Some seeds require light (photoblastic seeds) to germinate.

Internal Factors

1. Seed Maturity: Only fully developed seeds can germinate.
2. Seed Viability: A seed must be alive and capable of germination.
3. Hormones: Gibberellins promote germination, while abscisic acid inhibits it.

5. Seed Dormancy

1. Seed dormancy is a condition where seeds fail to germinate even under favorable conditions.
2. It prevents premature germination and ensures survival during unfavorable conditions.

Causes of Dormancy

1. Hard Seed Coat: Prevents water and oxygen entry (e.g., Pea, Lotus).
2. Immature Embryo: Seeds require further development before germination.
3. Chemical Inhibitors: Abscisic acid prevents germination.
4. Light Requirement: Some seeds need light or darkness to germinate.

Breaking Seed Dormancy

1. Scarification: Breaking or softening the seed coat (mechanically or chemically).
2. Stratification: Providing cold or warm treatments to stimulate germination.
3. Leaching: Washing out chemical inhibitors from the seed.
4. Hormonal Treatment: Using gibberellins to stimulate germination.

6. Importance of Germination and Dormancy

1. Ensures plant growth and survival.
2. Dormancy helps seeds survive harsh conditions.
3. Germination knowledge is useful in agriculture and forestry.
4. Helps in seed storage and conservation programs.

7. Conclusion

1. Germination is the activation of a seed to develop into a plant.
2. It is influenced by water, oxygen, temperature, and hormones.
3. Dormancy helps in seed survival and can be broken using various treatments.