2. Contents
• Introduction
• Causes of Seed Dormancy
• Types of Seed Dormancy
• Methods of breaking seed dormancy
• Importance of Seed Dormancy
• References
3. Introduction
• Seed Dormancy is a condition where seeds will not
germinate even when the environmental conditions
such as water, temperature and air are favourable for
germination.
• Dormant = not active or growing but able to become
active later.
• The main reason behind this condition is that they
require a period of rest before being capable of
germination.
4. • Seed refers to the fertilized, matured ovule that contains
an embryonic plant, food reserves, all enclosed within a
protective seed coat.
5. Causes of the Seed Dormancy
• Light
• Temperature
• Hard Seed Coat
• Period after ripening
• Germination inhibitors
• Immaturity of the seed embryo
• Impermeability of seed coat to water
• Impermeability of seed coat to oxygen
• Mechanically resistant seed coat
• Presence of high concentrate solutes (lower the osmotic potential)
7. Primary Dormancy
Exogenous dormancy is a result of factors
imposed from 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.
8. Therefore exogenous dormancy may be physical or chemical.
• Physical dormancy: seeds with such dormancy fail to germinate due to
seed coats that are impermeable to water. Eg the Malvaceae family- okra.
• Chemical dormancy: chemicals that are present in the flesh of fruits and
seed coverings may inhibit germination . Eg ABA in flesh and seed
coats.
Endogenous dormancy (physiological) results from
characteristics of the embryo that prevent germination .
The basis of this type of dormancy is that the embryo lacks
the growth potential.
Growth potential is the force exerted by the radicle to
penetrate the seed coat.
9. Types of endogenous dormancy
• Physiological
Seeds cannot germinate unless they have received a dormancy breaking
treatment.
• Morphological
Found in seeds with underdeveloped embryos that must differentiate before
germinating.
• Morphophysiological
Physiological dormancy developed in seeds with underdeveloped embryos
(morphological dormancy).
Photodormancy : seeds requiring light or the absence of
light (darkness) are referred to as photodormant or
photoblastic.
Combinational dormancy is a result of the combination
of exo and endogenous dormancy. The seed coat may be
hard coupled by physiological dormancy (lack of growth
potential).
10. Secondary Dormancy
• Secondary dormancy is due to germination conditions. It
is a further adaptation to prevent germination of an
imbibed seed if other environmental conditions are not
favourable. These conditions can include unfavourably
high or low temperature, prolonged darkness and water
stress. It is of two types:
• I) Thermo dormancy: High temperature induced
dormancy.
• II) Conditional dormancy: Change in ability to germinate
related to time of the year.
11. Methods of breaking Seed
Dormancy
• Seed coat treatment: Scarification
• Embryo treatments:
• Stratification
• High temperature treatment
• Chemical treatments: Hormonal treatment
12. 1. Scarification
• Scarification is the process of breaking, scratching,
mechanically altering or softening the seed covering
to make it permeable to water and gases.
i. Mechanical Scarification: Chipping hard seed coat
by rubbing with sand paper, cutting with a file or
cracking with a hammer are simple methods useful
for small amount of relatively large seeds.
14. ii. Acid Scarification: Dry seeds are placed in containers
and covered with concentrated Sulphuric acid (H2SO4) or
HCl in the ratio of one part of seed to two parts of acid.
The acid treated seeds can either be planted immediately
when wet or dried and stored for later planting.
Large seeds of most legume species, brinjal and tomatoes are
reported to respond simple sulphuric acid treatment.
15. iii. Hot water Scarification: Drop the seeds into 4-5 times
their volume of hot water with temperature ranging
from 77 to 100oC. The heat source is immediately
removed, and the seeds soaked in the gradually cooking
water for 12 to 24 hours. Following this the unswollen
seeds may be separated from the swollen seeds by
suitable screens. Then seeds are sown immediately.
iv. Warm Moist Scarification: The seeds are placed in
moist warm medium for many months to soften the seed
coat and other seed coverings through microbial activity.
This treatment is highly beneficial in seeds having double
seed dormancy.
16. 2. Stratification
• Seeds of some trees and shrubs from the temperate
zone do not germinate unless they are exposed to
chilling temperatures. E.g peach and apple.
• This can be accomplished artificially by a practice
called stratification.
• As the chilling process prolongs levels of ABA
decrease as levels of GA rise.
17. The following procedure is usually successful:
1. Put sand or vermiculite in a clay pot to about 2-3 cm from the top.
Place the seeds on top of the medium and cover with 1 cm of sand
or vermiculite.
2. Wet the medium thoroughly and allow excess water to drain
through the holes in the pot. Place the pot containing the moist
medium and seeds in a plastic bag and seal.
3. Place the bag in a refrigerator. Periodically check to see that the
medium is moist, but not wet. Additional water will probably not be
necessary.
4. After 10 to 12 weeks, remove the bag from the refrigerator. Take
the pot out and set it in a warm place in the house. Water often
enough to keep the medium moist.
5. When the young plants are about 5-7 cm tall, transplant them into
pots to grow until time for planting at their permanent sites.
18. 3.Leaching of inhibitors
• It is established fact that some inhibitors and
phenolic compounds are present in seed coverings of
many species, which inhibit germination. Therefore,
soaking of seeds in the running water for 12-24
hours or placing them in water for few hours help in
leaching off the inhibitors and phenolic compounds,
which help in easy seed germination.
19. 4. Pre- chilling: In seeds of certain plant species, dormancy
can be overcome by pre-chilling treatment. In this
treatment, the imbibed or soaked seeds are kept at a
temperature of 5-100C for 5-7 days before sowing. After
that seed can be sown in the field immediately.
5. Pre-drying: This is also a useful practice in some seeds to
overcome seed dormancy. In this treatment, the dry seeds
are subjected to a temperature of 37-400C for 5-7 days
prior to sowing. After this, seed can be sown in the field.
20. 6.Treatment with chemicals: Some compounds other
than hormones are also used to break dormancy but their
role is not clear. Thiourea is one example known to
stimulate germination in some kinds of dormant seeds.
The seeds are soaked in 0.5 – 3 per cent solution of
thiourea for 3-5 minutes. Afterwards seeds are rinsed with
water and are sown in the field. Similarly, potassium
nitrate and sodium hypochlorite also stimulate seed
germination in many plant species.
21. 7. Hormonal Treatment
• Among various hormones, GA3 is commercially used for
breaking seed dormancy in different types of seeds. The
concentration of GA3 depends upon the kind of seed but
generally a concentration of 200-500 ppm is most widely used.
• Cytokinin is another group of hormones used for breaking
physiological dormancy and stimulating germination in seeds of
many species. Kinetin and BA(6-benzyle aminopurine) are
commercial preparations of cytokinin used for breaking seed
dormancy. Soaking seeds in 100 ppm solution of kinetin for 3-5
minutes is highly effective concentration for overcoming seed
dormancy of many species. Etheral also stimulates germination
in seeds of some species.
22. Crop Chemical/hormone Concentration
Apple Thiourea 5000 ppm
Kinetin 25 ppm
GA 50 ppm
Ethrel 100-200 ppm
Pear GA 150 ppm
Thiourea 5000 ppm
Peach Thiourea 5000 ppm
GA 400 ppm
BA 400 ppm
Walnut GA 250 ppm
Ethrel 1000 ppm
Recommended concentrations of growth hormones in temperate fruits
for increasing seed germination:
23. Hormonal changes during stratification:
A reduction of ABA
Increased synthesis of cytokinin and gibberellins
Reduction in hormone synthesis in preparation for
germination.
In general, gibberellins promote germination in dormant
seeds, while ABA inhibits germination.
Pre-sowing treatments with certain seeds not only reduce
the stratification requirement and improve the seed
germination but also enhances seedling growth in a
number of temperate fruits.
24. Importance of Seed Dormancy
1. It follows the storage of seeds for later use by animals and man.
2. It helps in the dispersal of the seeds through the unfavourable
environment.
3. Dormancy induced by the inhibitors present in the seed coats is
highly useful to desert plants.
4. Allows the seeds to continue to be in suspended animation without
any harm during cold or high summer temperature and even under
drought conditions.
5. Dormancy helps seeds to remain alive in the soil for several years
and provides a continuous source of new plants, even when all the
mature plants of the area have died down due to natural disasters.
25. References
• Textbook of Plant Physiology- V. Verma
• Textbook of Basic Horticulture- Jitendra Singh
• http://ecoursesonline.iasri.res.in/pluginfile.php/101
028/mod_resource/content/1/Lecture_-_2.pdf
• https://www.slideshare.net/MaitriThakor/seed-
dormancy-213436624
• https://slideplayer.com/slide/13548671/
