Seed dormancy Seed Dormancy Terms & Terminology Seed Dormancy Classification Primary Dormancy Secondary Seed Dormancy

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K.VANANGAMUDI
Formerly Dean (Agri.), TNAU
Dean, Adhiparasakthi Agricultural College, Kalavai
Professor & Head, Seed Science & Technology
Tamil Nadu Agricultural University,
Coimbatore
Tamil Nadu
CELL WALL
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ATP
PLASMA MEMBRANE
Plasma
membran
Cell
wall
Nucleus
Vacuole
Cytop
H2O
CYTOPLASM

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TERMS AND DEFINITIONS
 Dormancy – general meaning : lack of
growth due to any external or internal cause.
 Seed dormancy : Failure of a viable seed to
germinate even when given favourable
environmental conditions.
 Quiescence : Condition in which seed can
germinate upon absorption of water. No
internal germination barriers exist.

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TERMS AND DEFINITIONS
oAfterripening : Physiological processes that occur in the
seed after harvest that enables germination to take place.
oPrimary dormancy : Dormancy which develops when the
seed is attached to the plant and exists when first
harvested.
oSecondary dormancy : A condition that develops to
prevent germination after the seed has been detached
from the plant and is exposed to specific unfavorable
environmental conditions

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TERMS AND DEFINITIONS
Endogenous dormancy: Any cause of dormancy related to the
embryo e.g. immature development or chemical inhibitors
Exogenous dormancy: Mechanical resistance, physical
impermeability, inhibitors or light sensitivity associated with seed
coat
Double dormancy or combined dormancy: Two or more
dormancy types occur in the seed e.g. fleshy/dry fruits with
chemical inhibitors combines with hard endocarp,

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TERMS AND DEFINITIONS
Thermo- dormancy: Type of dormancy induced by high temperature
(Hartmann et al. 1997).
Photo – dormancy: Most seeds having photo dormancy germinate only
under light conditions. Such seeds are therefore also called light sensitive
(Fig.1)
Red light, 660-760nm
White light (sunlight): Red/ far-red: 2/1
Pr -------------------------------------------------Pfr
(Dormant) (Non dormant)
Far red light, 760-800nm

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SEED DORMANCY TYPES
I. Primary dormancy
A. Exogenous dormancy – Due to factors outside the
embryo
a. Physical
b. Mechanical
c. Chemical
B. Endogenous dormancy – Due to factors within the
embryo itself
1. Morphological
a. Rudimentary
b. Linear
c. Undifferentiated

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2. Physiological
a. Non-deep
b. Intermediate
c. Deep
C. Combinational (two kinds of dormancy)
II. Secondary dormancy
1. Thermo-dormancy
2. Photo- dormancy
Contd…

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EXOGENOUS DORMANCY - PHYSICAL
Seed coats are impermeable to water and oxygen
Legumes are an example.
The cause of physical dormancy is the structure of the
outer cell layer which becomes impermeable to water.
Macrosclereid cells, a mucilaginous outer cell layer or
a hardened endocarp are the reasons that seed coats
become impermeable to water

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MECHANICAL DORMANCY
Seed coats are too hard to allow the embryo to expand
during germination.
Causes: Structure of seed coats or remaining fruit.
Occurs in olive.
In nature – coats are softened by environmental agents
such as acid in guts, microorganisms, warm, and moist
environment and forest fires.

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MECHANICAL DORMANCY….
Overcome
Abrasive action
Scarify with Sandpaper
Hot Water
Acid scarification @ 100ml commercial grade
sulfuric acid/kg of seed
Fire (Melts Resins In Cones)
Use immature fruits.
Softening of hard seed coat: water & O2 enter easily
Once scarified water can get in.
Have to be careful because the seed is also more
susceptible to damage by microorganisms.
SST 613 PRE- SOWING SEED MANAGEMENT

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CHEMICAL
3. Chemical
Presence of chemical inhibitors in the outer coverings
of many fruits and seeds.
Occurs in fleshy fruits, hulls, and capsules of many dry
fruits.
Examples: Apples, citrus, grapes, teak, coriander,
spinach
Overcome:
Water soaking and leaching
Heavy Rains
Use of Hormones (GA3)
Chilling for a few days

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Endogenous dormancy - MORPHOLOGICAL DORMANCY
Embryo is not fully developed at time of ripening.
Need additional embryo growth after the seed is
separated from the plant.
Ranunculus, poppy, woody species such as holly,
date palms.
Often combined with other kinds of dormancy such as
hard seed coats.

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MORPHOLOGICAL DORMANCY: TYPES
Rudimentary: Pro-embryo stage, Ranunculaceae,
Papaveraceae, Araliaceae
Linear: Torpedo stage, Umbelliferaea, Ericaceae, Primulaceae
Undifferentiated: Orchids
To overcome:
After ripening
Alternate warm and cool temperatures
GA3
Extended period at high temperatures
Date palms often takes several years to reach full
embryo development & germinate.
Often high temperatures (100oF) will accelerate this

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PHYSIOLOGICAL - NON-DEEP
Often short – termed 1 month to 6 months e. g. Lettuce.
Disappears as the seed is stored.
Two kinds
Photo-dormancy
Thermo-dormancy
May be due to
1. Inhibitors
2. Control of gas exchange (oxygen).
But this light requirement can be substituted by cool
temperatures - growing the seeds in the dark below 73ºF.

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NON-DEEP….
To overcome
Hormones
ABA
Kinetin
GA3
Photodormancy appears to be through phytochrome.
Sunlight (R:FR=2:1) results in phytochrome in the
active form.
Under foliage (R:FR=0.12:1 to 0.70:1) far red
dominates resulting in phytochrome in the inactive form

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INTERMEDIATE
Control mechanism to be in seed coat and tissue
around embryo e.g. temperate trees, Conifers.
Embryo itself is quiescent, not dormant and germinate
if excised.
Excised embryos exhibit physiologically dwarfing – stunted
growth, rosette – like structure.
To overcome
Chilling
Cold Stratification for 1 – several months.
Exposing pre moistened seed @ 0-5oC
Will respond to GA3 treatment.

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DEEP DORMANCY….
To overcome:
Natural stratification
Stratification : moist chilling
Presoak in water to 50% moisture and kept at 35-45ºF.
Note : If temperature is too high, secondary dormancy is
induced. Then, another chilling period is required.
For apple the temperature is 17ºC (62ºF)

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SECONDARY DORMANCY
Secondary Dormancy
It prevents the seed from germinating after it absorbs
water.
Caused by
temperature extremes,
prolonged darkness,
prolonged light,
water stress, or oxygen extremes.

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Dormancy Character-
istics
Example Dormancy breaking
stimulus
Natural Seed
handling
Immature
embryo
Physiologically
immature
embryo
Fraxinus,
Gingko
biloba
Post – dispersal
development
After
ripening
Mechanical
dormancy
Embryo
emergence
restricted due to
hard seed coat
Pterocarpus,
Terminalias
Melias
Decomposition
of hard
structures by
termites
Mechanical
cracking of
hard coat
Physical
dormancy
Imbibition
impeded due to
impermeable
seed coat
Leguminosae
, Myrtaceae
Abrasion by
sand, high
temperatures,
ingestion by
animals
Mechanical
scarification,
boiling water
or acid
scarification

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Dorman-
cy
Characteristics Example Dormancy breaking stimulus
Natural Seed
handling
Chemical
dormancy
Chemical inhibitory
compounds that
prevent germination
Berries, drupes
and pomes
Leaching by rain,
decomposition of
fruit pulp
Removal of fruit
pulp plus leaching
with water.
Photo
dormancy
Seeds fail to germinate
unless exposed to
appropriate light
regimes.
Temperate
species, Betula,
humid tropical
pioneer,
Spathodea,
Eucalyptus
Exposure to white
light or red light
likely to promote
germination
Exposure to light,
during
germination, light-
dark cycle of
variable duration
Thermo
dormancy
Temperatures control Fagus,Quercus,
Pinus, tropical-
sub tropical
pioneers
Exposure to low
winter temperature,
bush or forest fires,
diurnal fluctuating
temperature
Stratification or
chilling
kiln or light
burning,
fluctuating
temperature