Dormancy refers to the inability of a viable seed to germinate under favorable conditions. It allows seeds to delay germination until conditions are optimal for seedling survival. There are several types of dormancy based on its physiological cause, including dormancy caused by impermeable seed coats, underdeveloped embryos, or inhibitory compounds in seeds. Dormancy ensures seeds do not germinate at inappropriate times and helps plant populations survive unpredictable environments. Various natural and treatment methods can be used to break dormancy, promoting synchronized and optimal germination. Understanding dormancy is important for seed production, testing, storage, and breeding programs.

1. Dormancy
 Inability of a viable and mature seeds to germinate even under favourable
environment is known as seed dormancy.
 Dormancy may also be defined as a process by which physiological activities
become capable of ceasing entirely, in a reversible manner, usually manifested
in the cessation of growth.
 The period of rest after harvest that is necessary for germination is sometimes
referred to as after ripening period.
 The period of dormancy varies from a few days to several months depending
on the plant species.
 The inability of seed/organs to grow due to chemical/anatomical features of the
seed has been variously termed as ‘true dormancy’, ‘primary dormancy’, rest,
innate dormancy, ‘constitutive dormancy’ and ‘organic dormancy’.
 It has been argued that the term ‘dormancy’ should be restricted to such cases
and be preferred other terms.
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2.  In contrast, the failure of seeds/organs to grow under unfavourable
environment has been referred to as ‘dormancy’, ‘enforced dormancy,
‘imposed dormancy’ and ‘quiescence’.
 In cases where dormancy is induced in non dormant seeds due to
unfavourable conditions, the phenomenon is referred to as ‘secondary
dormancy’ or ‘induced dormancy’, the latter being more preferable.
 Induced dormancy persists even when the seeds are exposed to favourable
environments; it has to be overcome by exposure to specific treatments.
 In addition to seeds, dormancy involves a variety of plant organs, such as, stem
tubers (Solanum spp.), bulbs (Allium, Tulipa), corms (Gladiolus), rhizomes
(Convallarias)and the turions of aquatic plants (Hydrocharis, Stratiotes).
 Besides plants, dormancy is also encountered in animals and microorganisms,
such as, bacteria, fungi, algae, protozoa, nematodes, amoeba, insects,
vertebrates etc.
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3. BIOLOGICAL SIGNIFICANCE OF DORMANCY
 The survival of natural populations depends mainly on their ability to exploit
the favourable and avoid the unfavourable weather conditions to which they
are cyclically exposed in their natural habitats.
 The state of dormancy equips organisms to escape the detrimental effects of
adverse natural environments, thereby enhancing their chances of survival.
 During dormancy, physiological activities, particularly those concerned with
growth, cease entirely.
 Other metabolic activities, such as, photosynthesis, protein synthesis,
water exchange and respiration may be suspended.
 The dormant state thus leads to a greatly reduced dependence of the
organisms on their environments. Consequently, their tolerance to adverse
environments is greatly enhanced.
 The dormancy in seeds and buds is often associated with the formation of
specialized organs, tissues and structures, which play specific roles in
increasing their tolerance to adverse environments.
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4.  Plants with a long history of domestication generally show much less seed
dormancy than wild or recently domesticated species. Thus crop domestication
has promoted rapid seed germinability.
 Premature germination of seeds within ears/pods/fruits when the seed/crops are
exposed to a wet weather (favourable for germination) just before harvest is
termed as vivipary.
 Certain degree of seed dormancy is often deliberately selected in order to
prevent preharvest sprouting in cereals.
 However, seed dormancy may present problems in the determination of seed
germination immediately after harvest, which is essential for seed certification.
In such cases, one would have to resort to some effective treatments to
overcome the brief seed dormancy.
 Knowledge of dormancy helps us in understanding the survival of
individuals/populations under natural conditions, provides cheap and highly
effective means for the protection of crop produce from deterioration due to
preharvest sprouting and enables us to conduct reliable germination tests in
such species that exhibit dormancy.
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5. TYPES OF DORMANCY
 There are several mechanisms that generate seed dormancy. As a result of this,
several classifications, based on the factors conditioning the dormant state, have
been proposed. The most commonly quoted classification is that of Crocker
(1916) who described seven types of dormancy:
1) Embryo immature or not fully developed,
2) Seed coat impermeable to water,
3) Seed coat presents mechanical resistance to germinating embryo,
4) Seed coat poorly Permeable to gases,
5) Dormancy due to metabolic block within the embryo itself,
6) Combination of the above factors,
7) Secondary dormancy induced when seeds are imbibed under unfavourable
environment.
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6.  Harper (1957) and Roberts (l972) have divided dormancy into three types: (1)
innate, (2) induced, and 3) enforced
 Nikolaeva (1969, 1977) has proposed detailed classification of dormancy, three
broad groups: (1) exogenous, (2) endogenous, and (3) combined
 These have been further subdivided
 1. Exogenous dormancy: Due to some features of located outside the embryo but
within seed.
(a) Physical impermeability of coat to water.
(b) Inhibitors present within seed coat.
(c) Mechanical resistance of seed coat to germinating embryo.
2. Endogenous dormancy: Features present within the embryo.
(a) Underdevelopment of embryo
(b) Physiological condition of embryo coupled with its impermeability to gases.
 3. Combined dormancy: Due to factors located in the seed both within and
outside the embryo
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7. COMPREHENSIVE CLASSIFICATION
1) Exogenous dormancy:
(a) impermeability of seed coat to water,
(b) impermeability of seed coat to gases,
(c) mechanical resistance of seed coat to germination,
(d) inhibitors present in seed coat and/or endosperm
2) Endogenous dormancy:
(a) incomplete embryo development,
(b) inhibitor present within the embryo,
(c) light-dependent dormancy,
(d) low temperature requirement
3) Combined dormancy
4) Secondary dormancy.
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8. 1. Impermeability of Seed Coat to Water
 Hard seed coat: Leguminosae, Malvaceae, Chenopodiaceae,
Convolvulaceae, Solanaceae, Liliaceae etc.
 The impermeability of water is due to the Testa, which is hard.
 The presence of outer and inner cuticle, fatty or waxy layers, and of
thickened protective layer makes the Testa impermeable to water.
2. Impermeability of Seed Coat to Gases
 In many cases, dormancy is related to the insufficient intake by seeds of
atmospheric gases, especially oxygen, due to the impermeability of seed
structures enclosing embryo Such cases of dormancy occur in many
species of Gramineae, Leguminosae, fruit crops, forest trees etc.
 In many cases, degradation of inhibitors is enhanced under oxygen,
which is very important in overcoming dormancy.
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9. 3. Mechanical Resistance of Seed Coat to Germination
 Growth of embryo is checked due to extremely hard seed/fruit
structures, such as, seed coat, endosperm, pericarp etc., e.g., Acacia
spp., Juglans nigra etc.
 It has been observed that the tensile strength is greater for seeds with a
larger radius of curvature.
4. Inhibitors Present in Seed Coat/Endosperm
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10.  5. Incomplete Embryo Development
In many plant species, dormancy is due not development of embryo to their
normal size, e.g., in the members of the families Palmaceae, Magnoliaceae,
Azaliaceae, etc.
a) Underdeveloped embryos which are non-dormant and begin to grow after
the seeds are placed under favourable moisture and light conditions.
b) Partially developed embryos which are dormant. Dormancy breaking
conditions, e.g., high or low temperature required before and/or during the time
of embryo growth.
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11. 6. Inhibitors Present within the Embryo
Germination can commence only when these inhibitors are leached out of the
embryo, e.g., Xanthium, etc.
 1. Photoblastism: The phenomenon of improvement or suppression of
germination by exposure to light is known as photoblastism. Light may
promote (Betula spp., Lepidium virginicum, Nicotiana tobacum, Lactuca
sativa etc.) i.e. negatively photoblastic or break dormancy (Phacelia
tonacetifolia, Nemophila insignis etc.) i.e. positively photoblastic.
 2. Stratification: The exposure of seeds to a period of low or high
temperature leading to elimination of dormancy is called stratification
(Copeland, 1976). E.g., Members of families Rosaceae, Olearaceae,
Aceraceae, Celastraceae etc.
In general, seeds require low temperature treatment, but in some, e.g., nut grass
(Cyperus rotundus), seeds require high temperature (40°C) treatment on a
moist medium for 3-6 weeks. In a majority of cases stratification occurs in the
temperature range of 0-10°C. In some species, stratification is an essential
requirement, while for others it may only speed up germination and seedling
growth.
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12.  The response of seeds to cold is reversible and depends on their moisture level
before imbibition.
 The duration of cold stratification varies from few hours to few days in cases of
non-deep dormancy.
 In general, young seeds require longer periods of stratification than aged seeds.
7. Combined Dormancy
 Dormancy is produced by a combination of two or more factors, which act in
complementary fashion, In Fraxinus excelsior seeds, dormancy is generated
due to a combination of immature embryo, restriction on oxygen supply and a
chilling requirement.
8. Secondary Dormancy
 In many species, dormancy is induced in normally germinable seeds due to their
exposure to one or more unfavourable conditions, such as, excessive moisture,
adverse light or temperature regimes; this is known as secondary dormancy.
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13. METHODS OF BREAKING DORMANCY
 1. Natural Breakdown of Dormancy
 In nature, dormancy terminates when embryo gets suitable environment, such
as, adequate moisture, aeration and temperature. The impermeable seed coats
present in many species become permeable due to the rupturing or softening
action of natural agents like microorganisms, high or low temperature, humidity,
fire and abrasion due to wind or digestive tracts of birds and animals, which
feed on these seeds.
 Birds and herbivorous animals feed on seeds. In the digestive tracts of animals,
the seeds may lose their inhibitors or the permeability of their coats may be
enhanced due to the action of digestive enzymes and/or microorganisms.
 It is generally accepted that in case of birds, mechanical scarification of seed
coats is the major factor; it occurs by the grinding action However, digestive
acids play a crucial role in softening the seed coat in the digestive tracts of other
animals. Improvement in seed germination following a passage rough birds’
digestive tract was clearly demonstrated by feeding seeds to captive birds.
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14. 2. Treatments to Break Dormancy
 The methods either aim at breaking/softening of seed coats or at promoting
seed germination through stimulation of embryo and there are three broad
groups: (i) seed coat treatments, (ii) embryo treatments (iii) miscellaneous
approaches.
1. Seed Coat Treatments
 These treatments are either physical or chemical in nature, and aim at
making hard coats permeable to water and/or gases by either cracking or
softening them; the process is usually referred to as scarification.
 Such treatments would overcome dormancy due to hard seed coat causing
impediments to water/oxygen uptake/ no emergence.
 Seed coat treatments may be of 1) wet, and (2) dry treatments.
1. Wet Treatment: These treatments utilize either, (a) chemical or (b) thermal
action
(i) Chemical action. This is achieved by the use of sulphuric acid,
alcohol, acetone, oxidizing agents etc.
(ii) Thermal action. Seeds are treated with hot or boiling water, or
liquefied gases like liquid nitrogen, liquid oxygen etc.
2. Dry Treatment. The seed treatments include application of mechanical, or
thermal actions.
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15. i) Mechanical action: Manual and mechanical scarification, action to modify
seed coat properties.
(ii) Thermal action. Dry heat, radiations, electromagnetic waves and field
temperature fluctuations use thermal effects to alter seed coat properties.
Scarification must be done with caution and care in one of the following ways.
1. Scarification may be achieved by rubbing the seeds on a sand paper
manually by using a mechanical scarifier; This treatment is effective in
species ,like ‘subabool’ (Leucaena .cephalla), green gram (Phaseolus
arueus) etc.
2. The seed coat may be pierced by a needle or a small incision may be made jn
to the abaxial end of the seed, e.g., in bitter gourd (Memordica charantia).
3. Seed coat may be completely removed by breaking, e.g., Hevea spp. The
treatment may be slow, time taking and tedious.
4. The seed may be soaked in a concentrated or dilute solution of sulphuric acid
for 1 to 60 minutes, followed by thorough washing with tap water to
remove all traces of acid, e.g., in cotton (Gossypium spp.).
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16. 5. In some species, e.g., lentil, Bengal gram etc., soaking the seeds in hot water
(80°C) for 1-5 minutes effectively softens their seed coats. But seeds of
some species may be highly sensitive to this treatment, e.g., a treatment
of more than 1 minute reduces the germinability of Bengal gram seeds.
Mechanical scarification, especially, manual scarification, is the most
commonly used technique and is relatively safer but, quite often tedious.
2. Embryo Treatments
When dormancy is due to factors located within the embryo, such treatments
have to be applied that are capable of inducing the embryo to resume growth.
Some of the common treatments are
1. Stratification: Stratification is the incubation of seeds at a suitable low
temperature (usually, 0-5°C) over a moist substratum before transferring
them to a temperature optimum for germination; it is a common embryo
treatment designed to overcome dormancy. It is commonly used in crops
like cherry (Prunus cerasus), mustard (Brassica campestris), species of
family Rosaceae (2-6 months at 5-10°C), etc.
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17. 3. Chemical Treatments. Alternatively, growth regulators or other chemicals
may be applied to induce germination. E.g. GA3 (100 ppm commonly used) and
kinetin (10-15 ppm), potassium nitrate (0.2%) and thiourea (0.5 to 3%).
Potassium nitrate breaks the dormancy of seeds requiring light and allows them to
germinate in dark e.g., in case of oats, barley, tomato, etc.
Thiourea breaks the dormancy of seeds requiring light and/or chilling, e.g., in
lettuce (effective concentration 10-2 to I 0 M). Cichorium, Gladiolus etc.
3. Miscellaneous Treatments
Exposing the seeds of many species to red or white light leads to a termination of
dormancy. For example, lettuce seeds exposed to red light at 660 nm or to white
light are induced to germinate. Generally, seeds are placed initially in red light,
and they are subsequently transferred to dark or white light for germination.
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2. High Temperature Treatment. In some species, incubation at 40- 50°C for
few hours to 1-5 days may be effective in overcoming dormancy. Care should
be taken that the moisture content of seeds should be less than 15%. For
example, rice (Oryza sativa) seeds having less than 15% moisture are incubated
at 40-50°C for 4-5 days for overcoming dormancy.

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19. RELEVANCE OF DORMANCY TO SEED PRODUCTION
 Seed dormancy is relevant to seed production activities from several angles. It
may influence (I) seed multiplication, (2) seed testing, (3) plans of seed
programme (4) progress of researches related to seed productions and (5)
breeding of crops necessary to evolve new cultivars.
1. Seed Multiplication
 Dormant seeds of weeds/other crop species/other varieties of the same crop
would remain in the soil and would keep appearing in the seed crops for some
years to come. Thus a prolonged dormancy of seeds may pose a problem in the
maintenance of seed purity and impose the burden.
 In contrast, a total lack of dormancy may lead to a deterioration in viability
during storage or in seed quality due to preharvest rains. Non- dormant seeds
sprout in the ears or pods and become unfit.
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20. 2. Seed Testing
 The determination of germination percentage is a vital aspect of seed testing
process. Dormant seeds, especially those showing prolonged dormancy, cause
inconvenience to seed Scientists, seed producers and planners as their
germinability can not be determined easily, readily and reliably. But rapid
viability tests, e.g., tetrazolium test, assess their viability, which would be a poor
indicator of their germinability due to the presence of dormancy.
 Successful germination tests in such cases may require specific pre treatments to
overcome dormancy.
 In addition, germination data so obtained may not be a reliable indicator of the
germination achievable later under the field Conditions
3. Planning of Seed Program
 Rapid multiplication of seeds of newly released varieties is essential for a quick
exploitation of their potential. A rapid seed multiplication programme may often
involve growing of two or three crops in a Year by raising off-season crops.
Facilities for large scale treatments to overcome dormancy would become a
must if genotypes possessing dormancy are to be ordered in such programmes.
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21. 4. Research Activities
 Seed scientists and plant breeders desire to take as many generations each year as
it is feasible. Therefore, recognition of dormancy in freshly harvested seeds and
development of appropriate methods for overcoming it are very important.
 It may be seen that the presence of dormancy is desirable from one angle, but is
undesirable from another viewpoint. In a given crop species, the appropriate level
of dormancy would depend upon the balance between the contradictory needs for
protecting it from preharvest sprouting and for taking two or more crops in a year.
 In many situations, a brief period of dormancy may be desirable as long as it can
be effectively and reliably terminated by some rapid, simple and inexpensive
treatment.
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