Germination

• Germination is the process by which plants, fungus and bacteria emerge from seeds and spores, and begin growth.
• The most common example of germination is the sprouting of a seedling from a seed of an
• angiosperm or gymnosperm.
• In a more general sense, germination can imply anything expanding into greater being from a small existence or germ.

Types of Germination

• Epigeal Germination: The cotyledons rise above the soil surface. Most dicots undergo epigeal germination.
• Hypogeal Germination The cotyledons remain below the soil surface. All monocots have this type of germination and few dicots.

Seed Viability

• Viability is defined as the capability of a seed to germinate and produce a normal seedling.

Environmental conditions affecting seed germination

(1) Water: soften the seed coat, radicle elongates easily.

(2) Temperature: The larger difference (10º) between day and night favors to germination

(4) Light: light favored seed（lettuce cv. Grandrapids） germination controlled by red light（660 nm） and far-red light (730nm).The seeds germinate well under darkness but poorly under light.

Requirements for Germination

• Oxygen most critical, required for respiration
• High levels of CO2 inhibitory
• Nitrogen no effect

Pattern of Germination

• “Trigger agent” – factor that elicits germination but whose presence is not required throughout (e.g., light, temperature); shifts balance from inhibitor to promoter
• “Germination agent” – factor that must be present throughout germination (GA3)

Sequence of events for germination

Ø Radicle protrusion is the final sequence of germination

Ø Seedling becomes autotrophic

Ø Germination is ended by visible primary root growth