This document discusses seed dormancy, which prevents seeds from germinating under unsuitable conditions. It defines seed dormancy and describes its merits of preventing pre-harvest sprouting and allowing seeds to survive adverse conditions. The document also classifies seed dormancy and discusses mechanisms like seed coat impermeability and hormone levels. Methods for breaking dormancy include scarification, stratification, temperature treatments, washing, and chemical treatments.

1. Submitted By :
B. Pavan Kumar Naik
Redg. No. 180805200001
M.Sc Horticulture
(Vegetable Science)

2. INDEX
Introduction
Definition of Seed dormancy
Merits and Demerits of Seed dormancy
Classification of Seed dormancy
Mechanism of Seed dormancy
Breaking of Seed dormancy

3. 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 seed
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.

4. What is Seed Dormancy?
Seed dormancy is defined as a state in which seeds are
prevented from germinating even under environmental
conditions normally favorable for germination. These
conditions are a complex combination of water, light,
temperature, gasses, mechanical restrictions, seed coats,
and hormone structures

5. Merits of seed dormancy
 Dormancy prevents pre-harvest sprouting of seeds in the
standing crop when there is rain at maturity stage or
when crop lodges into water in the field.
 Dormant seeds often remain viable for longer period than
non-dormant seeds.
 It allows the seeds to survive adverse climatic and
seasonal conditions.
 Seed dormancy introduces temporal delay in the
germination process that provides additional time for
seed dispersal over greater geographical distances.

6. Demerits of seed dormancy
 Freshly harvested dormant seeds cannot be used
immediately for sowing.
 Seed dormancy is a problem for plant breeders going for
advancing pedigree lines in off-season.
 Seed analysts face difficulty in determining germination
potential of seed samples having dormancy.

7. Dormancy in cultivated plants
In the process of domestication
of plant species, selection
has usually been exercised
for seeds which germinate
relatively promptly and
uniformly. Thus seed
dormancy has been
minimised in crop plants.
Seed dormancy is
widespread in crop plants.
The vegetables like brinjal,
carrot, beet, lettuce, etc.
possess seed dormancy for
variable periods.

8. Classification of seed dormancy:
1. Primary and secondary dormancy
2. Exogenous, endogenous and combined dormancy
 Primary and secondary dormancy:
The former being the state of seed as shed from the mother
plant and the latter being dormancy induced in a mature
and imbibed seed by certain environmental conditions
unfavourable for germination. Primary and secondary
dormancy are also known as organic and induced
dormancy, respectively.

9.  Exogenous, endogenous and combined dormancy:
In exogenous dormancy, the dormancy factor exists in the
structures surrounding embryo. The exogenous dormancy
includes physical, mechanical and chemical dormancy
depending upon the physical and chemical property of
seed coat.
In endogenous dormancy, the dormancy factor resides in the
embryo. The endogenous dormancy is determined by
specific anatomical peculiarities (morphological
dormancy) and physiological peculiarities (physiological
dormancy) of the embryo itself.
In combined dormancy, the dormancy factors are present
both in the seed coat and embryo.

10. Mechanism of seed dormancy
(Khan, 1977)
• Barrier effects of seed coats and permeability
changes:
The degree of dormancy in seeds has been associated with
hardness and impermeability of seed coats which could be
due to physical and chemical characteristics of the seed coat
and impermeability to water, gases and solutes.
• Barrier effects of seed coats and permeability
changes:
The degree of dormancy in seeds has been associated with
hardness and impermeability of seed coats which could be
due to physical and chemical characteristics of the seed coat
and impermeability to water, gases and solutes.

11. • Selective role of hormones:
A number of studies showed that presence of inhibitors
results in dormancy and release of dormancy resulted
from high level of promoters. The inhibitor-promoter
concept has been popular with many workers. The
promoters include plant hormones, namely gibberellins,
cytokinins (kinetin), ethylene, etc. The hormonal concept
developed with the demonstration that some of the
promoter hormones alleviated the effects of inhibitors in
the seed, their role in light reaction and in certain seeds
they could substitute stratification requirement for
germination.

12. Active vs inactive form of phytochrome:
The concept that light induces synthesis, activation and
destruction of bio-reactive chemicals involved in seed
dormancy got a boost by the discovery of the active
(Pfr) and inactive (Pr) forms of phytochrome. It appears
that seeds exhibiting positive photoblastism do so by
absorbing red spectrum of white light, while non-
photoblastic seeds perceive mainly far-red region. In
both the cases, red (Pr) and far-red (Pfr) photo-
reversibility occurs to maintain a specific ratio of those
two forms of phytochrome.

13. Shift in oxidative pathways:
It has been observed that certain respiratory inhibitors,
which reduce oxygen consumption, are effective
dormancy breaking agents. The operation of Krebs
cycle in the seed which is supra-optional in its activity,
consumes all the available oxygen to the exclusion of
other oxygen requiring processes that lead to breaking
of dormancy. Application of certain respiratory
inhibitors may shift the pathway to PPP (pentose
phosphate pathway) which utilises less oxygen thus
making available oxygen for operation of dormancy
breaking reactions. (e.g. arsenite, amino oxyacetate,
etc.)

14. • Molecular genetic control: The concept of genetic or molecular
control of dormancy was inspired by the monumental work of
Jacob and Manod (1961). Several reports have indicated
oligogenic or polygenic control of seed dormancy in different
species.
Measurement of dormancy: Seed dormancy is measured in terms
of period of dormancy and intensity of dormancy. Period of
dormancy is usually measured as the number of days taken from
the day of harvest to achieve full germinability (G100) or
germination (%) equal to the minimum certification standards.
Intensity of dormancy is measured as the percentage of non-
germination at the time of harvest or as the dose of dormancy
breaking treatments required to break dormancy completely.
Biochemistry of dormancy: Several chemicals have been found to
be associated with seed dormancy. Certain chemicals are found
to induce or cause dormancy in seed. Some important ones are
abscisic acid (ABA), phenolic compounds like hydroxybenzoic
acid, ferulic acid, sinapic acid, etc. The common chemicals
which break dormancy and promote germination are gibberellins
(GA), cytokinins, ethylene, etc.

15. Breaking of seed dormancy
Scarification: Dormancy caused due to hard or impermeable
seed coat can be broken by scarification of the seed coat.
Scarification can be done mechanically either by rubbing
the seed with sand paper or by help of scarifier. Chemical
scarification is done by treating seeds with concentrated
HCl or H2SO4 for a specified time followed by thorough
washing. e.g. pulses, cotton, seeds of forest trees, etc.

16. Stratification: Dormancy in seeds of many woody and
herbaceous species is broken when hydrated seeds are
exposed to relatively low temperatures (00 to 200C) for 3
to 7 days.
High temperature treatment: Dry heating of seeds at 400–
550C temperature for several days have been found
effective in breaking dormancy in paddy, groundnut, etc.

17. Alternating temperature treatment: Alternating low and
high temperature treatment on imbibed seeds has been
found effective for breaking dormancy in many species.
e.g. brinjal, Malus sylvestris, etc.
Washing: Washing of dormant seeds by water has been
reported to break dormancy, probably due to leaching of
dormancy factor from the seeds. e.g. ragi, groundnut,
etc.
Dry storage: The embryo of seeds of certain species is not
fully developed even at harvestable maturity stage and
requires some more time after harvest (after ripening
period) for full development of embryo. Dry storage of
such seeds for few days will break dormancy and
promote germination.

18. Chemical treatments: Various chemicals and growth
hormones, viz. Gibberellins, cytokinins, ethylene, KNO3,
thiourea, HNO3, cyanide, etc. have been found to break
seed dormancy in different species. The concentration of
the chemicals and mode of treatment varies in seeds.
Polymorphism of dormancy: In sunflower, the seeds
formed in the peripheral portion of the head/capitulum
may not be dormant while those formed in the central
portion are dormant. This is known as polymorphism in
seed dormancy.