Seed dormacy.

Seed dormacy.

Seed dormancy refers to the condition/ period when the variable seeds donot germinate when planted even when provide with favourble condition of germination.

Causes of seed dormacy

Hard seed coats

This prevents the entry of water and oxygen between the seeds. It also prevents the emergency of   the plumule and radical.

Immature seeds.

Immature seeds have immature embryo which cannot germinate when planted.

Presence of used coat hair which prevents the absorption of oxygen by the seeds e.g barley seeds.

Presence of germination inhabitants that prevents the germination of sees e.g  Absicic acid.

Death of the embryo due to over storage.

Shortage  of growth stimulating hormones e.g gibberellins

Physical factors e.g light and temperature.

Some seeds are negatively photo plastic and their germination is inhabited by presence of light e.g onions, tobacco seeds donot germinate unless there is enough light and they are said to be positively photoplastic.

 Methods of breaking seed dormacy

By soaking the seeds in growth stimulating hardness.

By pre- chilling i.e seeds are exposed to very low temperatures for a short period of time before planting in normal conditions.

Soaking seeds in cold water overnight to soften the testa before planting in normal conditions.

Mechanical breaking of the seed coat (scarification) here the seeds are cracked or pricked with some paper or with pin to break the testa so that water and oxygen can go through the seeds.

Heat treatment

The seeds are soaked in hot water at about 80oc for 3 – 5 minutes before taken for planting.

Chemical treatment

Here the seeds are soaked in chemicals e.g sulhpuric acid, potassium Nitrate urea. They are then washed in water before planting.

Teaming off the brush covering the seed coats. This will allow the entry of oxygen into the seed.

Advantages of seed dormancy

  • It enables the seeds to wait for favourable conditions before germination
  • Allow sufficient time for dispersal of seeds to enable them colonize new areas.
  • Prevents death of the entire population in bad times since some would not have germinated
  • Prevents pre- harvest germination especially of cereal crops
  • Facilitates proper storage of crop produce (seeds).

Disadvantages

It increases the chances of seed destruction by pts because of their prolonged stage in the dormant phase.

It leads to the decrease in the food reserves in the seed.

Types of seed dormacy

Primary dormancy

This occurs if seed cannot germinate immediately after their dispersal

Secondary dormancy

This usually occurs when seeds enter dormancy after failing to get favourable   conditions

Questions

Write down the condition necessary for germination of seeds.