Seed Dormancy and Germination: Stages Explained Simply

A mature seed may not sprout immediately even when placed in soil. It may be alive but resting, a state called seed dormancy. When conditions become favourable and dormancy breaks, the embryo resumes growth and emerges as seedling, a process called germination. Dormancy and germination control when a new plant begins life.

Understanding them is vital for farming sowing times, seed storage, weed control and forest regeneration, because seeds must germinate uniformly in fields but stay dormant safely in seed banks.

Key Concepts

Dormancy causes: Hard impermeable seed coat preventing water and oxygen entry, immature embryo needing after-ripening, chemical inhibitors like abscisic acid in coat or fruit, requirement for light or specific temperature. Methods to break dormancy: Scarification scratching coat mechanically or with acid, stratification cold moist treatment, leaching inhibitors by soaking, light exposure and gibberellin hormone application. Germination requirements: Water for imbibition and enzyme activation, oxygen for respiration, suitable temperature for enzyme activity. Types: Epigeal cotyledons come above ground as in bean. Hypogeal cotyledons stay below ground as in pea and maize. Vivipary germination on mother plant in mangroves like Rhizophora.

How It Works

1. Dry seed has low metabolism. On imbibing water seed coat softens, enzymes like amylase become active and stored food is hydrolysed to sugars.
2. Respiration increases, embryo cells divide and elongate, radicle emerges first through micropyle and grows down to absorb water.
3. Plumule grows upward, in epigeal type hypocotyl elongates lifting cotyledons out, in hypogeal epicotyl elongates keeping cotyledons below.
4. Seedling becomes photosynthetic and independent when first green leaves expand, ending germination phase.

Worked Example

A farmer tests 200 bean seeds. After 24 hours soaking, seeds imbibed water and average mass increased from 0.40 g to 0.75 g, increase = 0.35 g or 87.5 percent. After 7 days at 25 degrees Celsius with water and air, 172 seeds show radicle emergence. Germination percentage = 172 divided by 200 times 100 = 86 percent. Dormant or dead = 28 seeds = 14 percent. If seed coat is scarified, repeat test shows 186 germinated = 93 percent, improvement = 7 percentage points, showing coat dormancy effect. In hypogeal pea same test would keep cotyledons below soil surface.

Common Misconceptions

• Misconception: Dormant seeds are dead. Correction: Dormant seeds are alive with low metabolism and can germinate after specific triggers break dormancy.
• Misconception: Seeds need soil and sunlight to germinate. Correction: Most need water, oxygen and temperature only, light is needed only by some small seeds, soil is not essential as seen on moist cotton.
• Misconception: All seeds germinate with cotyledons above ground. Correction: Pea and maize show hypogeal germination where cotyledons remain underground.

Real-World Applications

Seed banks store seeds dormant at low moisture and temperature for years for crop conservation. Farmers scarify hard seeds like pulses and soak seeds to get uniform germination and better crop stand. Nurseries use cold stratification for apple and other temperate seeds requiring winter chill. Weed managers predict weed emergence because dormant weed seeds in soil germinate in flushes after rain.

Seed dormancy is a live resting state caused by coats, inhibitors or immaturity, broken by scarification, water and temperature cues, allowing germination where radicle emerges first in epigeal or hypogeal patterns.