Seed Dormancy – Class 11 | Chapter – 15 | Biology Short Notes Series PDF

Seed Dormancy: It is a condition in which seeds are unable to germinate, even in conditions that are ordinarily favorable for their germination. The favorable conditions for the germination of seeds include appropriate light, water, temperature, gases, mechanical constraints, seed coverings, and hormone structures. Dormancy is a stage in the life cycle of a seed during which its development, growth, and numerous other physical activities are momentarily stopped. 

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Reasons or Causes of the Seed Dormancy

There are certain major causes for the seed dormancy. Listed below are the few reasons for the seed dormancy.

  • Light
  • Temperature
  • Hard Seed Coat
  • Period after ripening
  • Germination inhibitors
  • Immaturity of the seed embryo
  • Impermeability of seed coat to water
  • Impermeability of  seed coat to oxygen
  • Mechanically resistant seed coat
  • Presence of high concentrate solutes

Importance of Seed Dormancy

Seed Dormancy is important for plants for the following reasons – 

  • Dormancy allows the seeds to survive in the soil for several years. This ensures a steady supply of new plants even after the older plants of the area have died off due to various natural calamities.
  • It promotes the preservation of seeds for later use by animals and humans.
  • Desert plants benefit greatly from the dormancy produced by inhibitors found in seed coats.
  • Dormancy allows the seeds to remain suspended without injury during cold or hot summer temperatures, as well as during drought.

Disadvantages of Seed Dormancy

The disadvantages of seed dormancy are – 

  • It takes a long time to overcome seed dormancy.
  • It contributes to the long-term viability of the weed seeds.
  • With a dormant seed, it becomes difficult to maintain a population on the field while growing a crop.

Types of Seed Dormancy

The seed dormancy is of following types:

Innate dormancy

It is the condition of seeds which is incapable of germination even if conditions suitable for seedling growth are supplied. This inability to germinate may be due in certain species to the embryo being immature at the time of dispersal.

Enforced dormancy

It is the condition of seeds which is incapable of germination due to an environmental restraint which includes, an adequate amount of moisture, oxygen, light and a suitable temperature.

Induced dormancy

This type of seed dormancy occurs when the seed has imbibed water, but has been placed under extremely unfavourable conditions for germination. Finally, seed fails to germinate even under more favourable conditions.

Methods of Breaking Seed Dormancy

The different methods of breaking dormancy are mentioned below:

The natural breaking of Seed Dormancy

Nature of dormancy stops when the embryo gets appropriate environment such as adaptive moisture and temperature. The seed coat that exists in many species becomes permeable due to the rupturing of smoothing action of natural agents like microorganism, temperature, and abrasion by the digestive tract of birds and animals that feed on these seeds. Other natural methods include:

  • Completion of the over-ripening period.
  • Leaching of inhibitors present in the seed coat.
  • Inactivation of inhibitors by the supply of cold, heat, and light.
  • Leaching of the excess and highly concentrated solutes from the seeds.
  • Production of growth hormones which can neutralize the effect of inhibitors.

Artificial Overcoming of Seed Dormancy

Some of the artificial methods used for breaking seed dormancy are listed below:

  • Action with hot water for termination of waxes, surface inhibitors, etc.
  • Rupturing of seed coats by filing, chipping, or threshing through machines.
  • Exposure to heat, cold or light, depending upon the type of seed dormancy.
  • By applying Hydraulic pressure for 5 to 20 minutes in order to weaken the tough seed coats.
  • Seed coats are treated with concentrated sulphuric acid for removing all traces of the mineral acid.

Treatment to Break Dormancy in Seeds

There are separate treatments to overcome dormancy, and they are further divided into the following groups:

  • Seed coat treatment: These treatments make a hard seed coat permeable to water or gases either by softening or cracking. This process is called scarification. The treatment can be either chemical or physical in nature.
  • Embryo treatments
    • Stratification: The incubation of seeds at an appropriate low temperature over a moist layer before transferring to a temperature suitable for germination.
    • High-temperature treatment: Incubation at 40-50 °C for a few hours to a few days may have an effect in overcoming dormancy in some species. For instance, rice seeds treated with hot water at 40°C for at least 4 hours.
  • Chemical treatments: Plant growth regulators or other chemicals can be used in induced germination growth regulators

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By Team Learning Mantras