Seed dormancy and types of seeds

Seed dormancy

Seed dormancy is a state in which a viable seed does not germinate even when water, oxygen and temperature are favourable. It prevents germination of seeds while still on the plant (pre-harvest sprouting) and spreads germination over time, helping survival.

Causes and remedies:

• Hard or impermeable seed coat (common in legumes) → scarification: rubbing with sand paper, nicking, or treatment with concentrated sulphuric acid; hot water soaking.
• Mechanically resistant seed coat → cracking or removing the coat.
• Immature (rudimentary) embryo → after-ripening in storage.
• Chemical inhibitors such as abscisic acid (ABA) → leaching (soaking in running water) or treatment with gibberellic acid (GA₃) or potassium nitrate.
• Need for chilling → stratification: keeping moist seeds at low temperature for weeks (common in temperate fruits).
• Light requirement → exposure to light (some small seeds, e.g. lettuce).

Classes of seed

In India, quality seed is multiplied in a fixed chain:

• Nucleus seed: produced by the plant breeder who developed the variety; highest genetic purity.
• Breeder seed: produced from nucleus seed under the breeder's direct control; golden yellow tag.
• Foundation seed: produced from breeder seed by seed agencies; white tag; certified by a seed certification agency.
• Certified seed: produced from foundation seed and sold to farmers; blue (azure blue) tag.

Seed quality is regulated under the Seeds Act, 1966. Good seed has high genetic and physical purity, high germination and vigour, safe moisture content, and is free from weeds, diseases and insects.

Key points

• Dormancy: viable seed that will not germinate in favourable conditions.
• Hard seed coat → scarification; chilling need → stratification; inhibitors → leaching/GA₃.
• Nucleus → breeder → foundation → certified.
• Tags: breeder golden yellow; foundation white; certified blue.

Exam tips

Match each cause to its treatment and each seed class to its tag colour and producer.

Common mistakes

• Confusing scarification (seed coat) with stratification (cold, moist treatment).
• Thinking a dead seed is dormant; dormant seeds are alive.