Model Answer
0 min readIntroduction
Seed dormancy, a crucial evolutionary adaptation, prevents premature germination under unfavorable conditions. It’s a state where seeds fail to germinate even under conditions seemingly suitable for growth. “Hard seeds” represent a specific type of dormancy characterized by a hard seed coat that prevents water imbibition. The National Seed Policy (2002) emphasizes the importance of quality seed production and distribution, highlighting the need to understand and overcome dormancy issues to ensure agricultural productivity. This response will define these terms, explore the physiological basis of dormancy, and detail methods to break it.
Defining Dormant and Hard Seeds
Dormant seeds are viable seeds that are prevented from germinating due to internal factors, even when external conditions (moisture, temperature, oxygen) are optimal. This is a survival mechanism. Hard seeds, often found in legumes (e.g., *Cajanus cajan* - Pigeon Pea), possess a very hard seed coat (testa) that is impermeable to water and gases, thus preventing imbibition and germination. They are a subset of dormant seeds but with a specific physical barrier.
Physiological Basis of Seed Dormancy
The physiological basis of dormancy is complex, involving hormonal interactions and physical barriers:
- Abscisic Acid (ABA): High ABA levels inhibit germination by suppressing cell elongation and radicle emergence. ABA is often synthesized during seed maturation.
- Gibberellic Acid (GA): GA promotes germination by overcoming ABA’s inhibitory effects and stimulating cell division and elongation. The GA/ABA ratio is a key determinant of dormancy.
- Ethylene: In some species, ethylene accumulation contributes to dormancy.
- Physical Barriers: As seen in hard seeds, the seed coat's impermeability restricts water and oxygen uptake.
- Embryo Maturity: Immature embryos may exhibit physiological dormancy, requiring a period of after-ripening for full germination potential.
Methods to Overcome Seed Dormancy
Overcoming dormancy requires addressing the underlying physiological or physical barriers. Methods can be broadly categorized:
Physical Methods
- Scarification: Weakening or breaking the seed coat. This can be achieved through:
- Mechanical scarification: Abrasion with sand, grit, or nicking the seed coat.
- Hot water treatment: Immersing seeds in hot water (e.g., 80-90°C for a specific duration) to soften the seed coat.
- Acid scarification: Soaking seeds in diluted sulfuric acid (e.g., concentrated H2SO4 diluted to 10%) – used with caution.
- Stratification: Exposing seeds to a period of cold, moist conditions, mimicking natural winter conditions. This breaks dormancy in many temperate species.
Chemical Methods
- GA3 Treatment: Soaking seeds in GA3 solutions promotes germination by overcoming ABA's effects.
- KNO3 Treatment: Potassium nitrate can improve water uptake and stimulate germination.
Physiological Methods
- After-ripening: Allowing seeds to age under ambient conditions, which gradually reduces dormancy.
- Alternating Temperature: Exposing seeds to fluctuating temperatures can break dormancy in some species.
The effectiveness of these methods depends on the specific species and the type of dormancy involved. For example, pigeon pea seeds (hard seeds) often require hot water treatment to overcome their dormancy.
| Method | Mechanism | Suitable For |
|---|---|---|
| Scarification | Weakens/breaks seed coat | Hard seeds, seeds with thick pericarp |
| Stratification | Mimics winter conditions, alters hormone balance | Temperate species with physiological dormancy |
| GA3 Treatment | Overcomes ABA inhibition | Seeds with ABA-mediated dormancy |
Conclusion
In conclusion, seed dormancy, whether physiological or manifested as hard seeds, is a complex phenomenon crucial for species survival. Understanding the physiological basis of dormancy allows for targeted interventions using physical, chemical, and physiological methods. Continued research and the promotion of sustainable seed treatment practices are vital to enhance germination rates, improve agricultural productivity, and ensure food security, particularly in regions reliant on pulse crops. The National Seed Policy’s emphasis on quality seed remains paramount for achieving these goals.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.