About seed dormacy

1. Topic : Dormancy
Ravi Yadav
Department of horticulture(Vegetable Science)
CoA,Tikamgarh(M.P)
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2. Content
•Introduction,meaning,definition
•Classification of seed dormancy
•Factors causing dormancy of seeds
•Methods to overcome seed dormancy
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3. Dormancy
Introduction, meaning, defination
• Dormancy: is a period in an organism's life
cycle when growth, development, and (in animals)
physical activity are temporarily stopped.
• This minimizes metabolic activity and therefore
helps an organism to conserve energy.
• Dormancy tends to be closely associated
with environmental conditions.
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4. Dormancy
Introduction,meaning,defination
• During the developmental cycle of the plant, at
some phase certain structures like buds, tubers,
seeds, go through a period of temporary
suspension of growth activity, such a state is called
dormancy.
• It is derived Dormant word.
• Dormant means sleeping
“Seed dormancy is defined as a state
in which seeds are unable to germinate even under
Environmental conditions normally favorable for
germination.”
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5. Classification of seed dormancy
Types of dormancy include:
a) Primary dormancy: Physical dormancy
Mechanical dormancy
Chemical dormancy
• Secondary dormancy: Physiological dormancy
• Morphological dormancy
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6. Primary dormancy
• Exogenous dormancy is a result of factors imposed
form outside the embryo for example the seed coat
and or the fruit parts.
• This material surrounding the embryo may inhibit
imbibition of water, or limit oxygen to the embryo,
or prevent inhibitor leaching or conversely supply
inhibitors to the embryo.
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7. Physical dormancy
• Dormancy that is caused by an impermeable seed
coat.
• It is the result of impermeable layer that develops
during maturation and drying of the seed or fruit.
• It prevents the seed from taking up water or gases.
• As a result, the seed is prevented from germinating
until dormancy is broken.
• Generally, physical dormancy is the result of one or
more palisade layers in the fruit or seed coat.
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8. Mechanical dormancy, Chemical
dormancy
• Mechanical dormancy:
• Mechanical dormancy occurs when seed coats or
other coverings are too hard to allow the embryo
to expand during germination.
• Chemical dormancy-
• Presence of inhibitors within the seed (seed coat)
can cause dormancy.
•E.g.: Coriander seed pericarp contains Coumarin
•Paddy hull contain Abscisic acid
•Tomato juice circulic acid
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9. Physiological dormancy
• Physiological dormancy prevents embryo growth
and seed germination until chemical changes occur.
• Photo dormancy: light sensitivity affects
germination of some seeds. These photoblastic
seeds need a period of darkness or light to
germinate.
• Thermo dormancy : seed sensitivity to heat or cold.
• Some seeds germinate only at high temperature
like Amaranth.
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10. Morphological dormancy
• In morphological dormancy, the embryo is
underdeveloped or undifferentiated.
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11. Factors causing dormancy of seeds
• Hard seed coat
• Dormancy due to temperature
• Immature Embryo
• Light Sensitive Seed
• Dormancy due to growth inhibitory chemicals
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12. Dormancy due to hard seed coat
• Testa of some seeds are hard and multilayered
(Leguminaceae, Solonaceae).
• Hard seed coat prevents the entry of water into the
seed.because waxy coating(Lignin,cutin) in seed
coat. Breaking seed coat ;soil fungus,Bacteria.
• seed coat impermeable to oxygen.Ex-Xanthium,
Oat.
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13. Dormancy due to temperature
• Some seeds require chilling treatment for
germination.
• Examples are apple, walnut,pear,cherry. Such seeds
need chilling temperature (1 -5 ºC) for few weeks.
• Immature Embryo
• Embryo is not matured at the time of harvesting for
maturity of such embryo, resting period is required.
• Example: Caltha palustris,apple,pea,cherry
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14. Light Sensitive Seed
• There two type of seeds for light sensitivity:
• Positive photoblastic seeds: Seeds of some species
like lettuce,tabboco,carrot. remain dormant in the
dark, they germinate when they are exposed to
light.
• Negative photoblastic seeds: Seeds of some
species like Phlox, Nemophila and Silene remain
dormant when exposed to light. They germinate
only in the dark.
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15. Dormancy due to growth
inhibitory chemicals
• There are several naturally occurring compounds
which inhibit germination of seeds, like Coumarin,
Cyanides,Ammonia, Dinitrophenols, Organic acid,
Aldehydes, Alkaloids, Fluorides.
• Example: Tomato fruit pulp – Circulic acid, Caffeic
acid and Ferulic acid which induce dormancy.
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16. Methods to overcome seed
dormancy
• Mechanical scarification
• Impaction
• Cold stratification
• Removal of inhibitors
• Treatment with growth hormones
• Specific light requirement
• Pressure
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17. Mechanical scarification
• Scarification : Any treatment i.e. physical or
chemical that weakens the seed coat.
(A)Piercing
• Chipping
• Rubbing
• Chilling: cabbage, sunflower.
• Pre-drying: maize, lettuce.
• Pre-soaking: bean.
(B)Acid Treatment:
Sulphuric acid, nitric acid.
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18. Stratification
• Treatment of seed at low temperature
Under, well aeration moist condition.
• Temperature 0-10 centigrade
• Growth promoting hormones increases
and Growth retarding hormones
decreases.
Ex: Rosaceae (Peach,Apple,Cherry etc)
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19. • 4. Removal of inhibitors: Growth inhibiting
chemicals removed by repeated washing with
water. Ex sugerbeet, xanthium etc.
• 5. Treatment with growth hormones: Gibberellins
substitute the cold treatment requirement in many
seeds. Cytokinin promotes germination of many
seeds.Gibberelic acid @ 0.05% 1L. Water.
• 6. Pressure: Dormancy can be broken by exposing
seeds to high atmospheric pressure. E.g. Sweet
Clover or lucern seeds subjected to hydraulic
pressure of 200 atm favors the increase in
germination at 18 ºC.
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20. Thank you for lessening ………….
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