Seed dormancy is an evolutionary adaptation that prevents seeds from germinating during unsuitable ecological conditions. There are three types of inherent dormancy: physical, physiological, and morphological. Physical dormancy is caused by an impermeable seed coat and prevents water uptake. The impermeable layer develops during seed maturation and drying. Physical dormancy can be broken by scarification methods like acid treatment, mechanical abrasion, or hot water soak that weaken the impermeable seed coat.

1. PHYSICAL
DORMANCY

2. SEED DORMANCY
Seed dormancy is an evolutionary adaptation that
prevents seeds from germinating during unsuitable
ecological conditions that would typically lead to a
low probability of seedling survival.
Dormant seeds do not germinate in a specified
period of time under a combination of
environmental factors that are normally conducive
to the germination of non-dormant seeds.
 Seed dormancy can be divided into two major
categories based on what part of the seed produces
dormancy: Exogenous and Endogenous.
There are three types of inherent dormancy based
on their mode of action: Physical, Physiological and
Morphological.

3. EXOGENOUS DORMANCY
Exogenous dormancy is caused by
conditions outside the embryo and is
often broken down into three
subgroups:
Physical dormancy
Mechanical dormancy
Chemical dormancy

4. PHYSICAL DORMANCY
• Dormancy caused by an impermeable seed coat is known as physical
dormancy.
• Physical dormancy is the result of impermeable layer(s) that develops
during maturation and drying of the seed or fruit.
• This impermeable layer prevents the seed from taking up water or gases.
• As a result, the seed is prevented from germinating until dormancy is
broken.
• Physical dormancy is believed to have developed more than 100 million
years ago.
• Physical dormancy has been identified in the seeds of plants across 16
angiosperm families like Anacardiaceae,Asteraceae, Cucurbitaceae,
Fabaceae,Malvaceae

5. REASON FOR THE PHYSICAL DORMANCY
• Generally, physical dormancy is the result of one or
more palisade layers in the fruit or seed coat.
• These layers are lignified with malpighian cells tightly
packed together and impregnated with water-
repellent.
• Specialised structures, which function as a "water-
gap", are associated with the impermeable layers of
the seed to prevent the uptake of water.
• The water-gap is closed at seed maturity and is
opened in response to the appropriate environmental
signal.
• Breaking physical dormancy involves the disruption of
these specialised structures within the seed, and acts
as an environmental signal detector for germination.

6. • For example,In PY-dormant Fabaceae species (Rosids) the
lens (strophiole) is the spezialized structure localized in the
hilum region that controls water-impermeability.
• In PY-dormant Anacardiaceae species (Rosids), e.g. Rhus
spp., the endocarp consists of three water-impermeable
palisade layers (macrosclereids, osteosclereis,
brachysclereids) and the outer crystalliferous layer.
• Different types of chalazal plugs/caps are the specialized
structures that control water-impermeability of other seeds,
e.g. in PY-dormant species of Bixaceae, Cistaceae, and
Malvaceae.
• Therefore, palisade layers in the fruit perform the functional
role of preventing water uptake.

7. TREATMENT TO BREAK PHYSICAL DORMANCY
• In natural systems, physical dormancy is broken by
several factors including high temperatures, fluctuating
temperatures, fire, freezing/thawing, drying or passage
through the digestive tracts of animals.
• But the commonly followed method is
SCARIFICATION
• Acid
• Mechanical
• Physical treatment – hot water treatment

8. SCARIFICATION
• Any treatments may be physical or chemical that
weakens or softens the seed coat is known as
scarification.
• This method is more applicable to Malvaceae and
Leguminaceae group of seeds.
ACID SCARIFICATION
• By using concentrated H2SO4 @ 100ml/kg of seed for 2-3
minutes treatments dormancy can be overcome in the
seeds.
• The duration of treatment will vary and it depends on
type and nature of seed coat.
• E.g. Tree crops 1-3 hours, Rose seeds, treat the seed
partially with acid and then given with warm
stratification.

9. MECHANICAL SCARIFICATION
• Seeds are rubbed on a sand paper or with a help
of mechanical scarifier or by puncturing on seed
coat with the help of needle to enhance / increase
the moisture absorption by seeds.
• E.g. Bitter gourd for sand scarification, sand and
seed 2:1 ratio should be followed. Rub against
hard surface of seed for 5 to 10 minutes.
HOT WATER TREATMENTS
• It is effective in case of leguminous seeds.
• The seeds should be soaked in boiled water for
1-5 minutes in 60-80 °C.