What is Seed Dormancy?
Survival and proliferation of seeds to ensure the production of healthy offsprings depends on the evolution of successful strategies of germination.
During evolution, dormancy serves as a defense mechanism to survive in extreme conditions related to temperature, drought, salinity.
Unfavorable circumstances prevent seeds germination and this state is called “dormancy”. Amen in 1963 defined dormancy as “endogenously controlled but environmentally imposed and it is the temporary suspension of growth accompanied by reduced metabolic activity and relatively independent of ambient environmental conditions”.
Dormancy provides a resting period for the preparation of germination by avoiding seed germination even in the presence of required conditions.
Classification of Seed Dormancy
According to Amen description, seed dormancy can be divided into the following types-
• Primary dormancy/innate dormancy: This is a type of dormancy initiated before the dispersion of seeds from a mother plant. It is further classified as-
i. Exogenous dormancy– it depends on the nature of the seed coat and the presence of inhibitors on the seed coat.
ii. Endogenous Dormancy– Either due to the malfunction embryo or presence of inhibiting chemicals i.e. phenols, ABA which restrict the metabolic activities inside the embryo.
• Secondary dormancy: exposure to inappropriate light and temperature introduces irreversible dormancy.
Factors Affecting Seed Dormancy
• Genetic factors
• Chemical that inhibits germination
• Immature seed embryo
• Resistance of seed coat to water
• Resistance of seed coat to oxygen
• Solute concentration
• Dormant embryo
• Period after ripening
Seed Dormancy Breaking Methods
Overtime can break dormancy naturally in seeds that are dormant at the time of harvesting.
Whereas some species need pre-treatment to exit dormancy.
Seed coat dormancy breaking method:
• Breaking of seed coat dormancy includes piercing, knife filling, chipping, etc.
• Scarification is a useful method to break seed coat dormancy.
• Removing seed covering also helps in overcoming seed coat dormancy.
• Leaching out of inhibitors by soaking seeds in excess water can also break seed dormancy.
• The use of concentrated sulphuric acid is also suggested by ISTA based on species.
• The boiling of seeds can also accelerate imbibition and remove the waxy covering of the seed coat.
Embryo dormancy breaking method:
Embryo dormancy can be broken by several recommended methods discussed in the following paragraph.
• Cold treatment (cold stratification): In this method, moist seeds are exposed to cold temperature (3-5 degree celcius) for days to weeks, after treatment seeds are allowed to germinate.
• Heating: In appropriate conditions seeds are exposed to high temperature (40 degree celcius) before germination.
• Hormone treatment: treatment of gibberellic acid is recommended to break embryo dormancy.
• Light: some species are sensitive to temperature and light cycles.
• Potassium nitrate: KNO3 treatment can break dormancy.
Advantages of Seed Dormancy
• Dormancy helps seeds to escape unfavorable climatic conditions and allow germination only in appropriate environments.
• Seed coat dormancy enhances the rate of survival during water stress.
• Dormancy enable the artificial storage of seeds
• Due to dormancy seeds manage to remain alive for a long time in soil.
• In unfavorable environments dormancy helps in the dispersal of seeds in other places.