Seed dormancy breaking treatments.pdf

Seed dormancy breaking treatments
Seed Science & Technology
K Vanangamudi
ICAR ARS NET STO exams
TNPSC AO AAO HO ADH AHO exams
Location and cause for dormancy in certain species
Scarification for seed dormancy breaking treatments
Electrical seed treatment for seed dormancy breaking treatments
Soaking in water for seed dormancy breaking treatments
Stratification for seed dormancy breaking treatments
Temperature treatments for seed dormancy breaking treatments
Chemical methods for seed dormancy breaking treatments
Promoters - inhibitors concept for seed dormancy breaking
Soaking in chemicals for seed dormancy breaking treatments

1. ICAR AIEEA JRF & SRF for PG admissions
ICAR NET, ARS & STO (T-6) Exams
IBPS – AFO Exams

TNPSC
AO, HO, ADH, AAO, AHO EXAMS


SEED SCIENCE &TECHNOLOGY
DORMANCY BREAKING TREATMENTS


Dr. K. Vanangamudi
Formerly Dean (Agriculture), TNAU, Coimbatore.
Dean, Adhiparasakthi Agricultural College, Kalavai,
Professor & Head,
Seed Science & Technology, TNAU, Coimbatore.

2. Location and cause for dormancy in certain species
Species Location of
inhibitor
Name of inhibitor
Gossypium spp. Pericarp, testa Absicic acid (ABA)
Coriandrum sativum Pericarp Coumarin
Helianthus annus Pericarp, testa Hydrocyanic acid
Oryza sativa Hull Probably ABA
Triticum spp. Pericarp, testa Catechin, catechin tannins
Hordeum vulgare Hull Coumarin, Phenolic acids, scopoletin
Beta vulgaris Pericarp Phenolic acids, Possibly ABA, high
concentration of inorganic ions
Avena sativa Hull Unknown

1.1. Physical methods
1.1.1. Scarification
 Any treatment may be physical or chemical that weakens or softens seed coat.
 More applicable to Malvaceae and Leguminaceae group of seeds.
 Done by manual / physical, mechanical, acid, biological, thermal and fire etc.
1.1.1.1. Manual / physical scarification
 Seeds should be soaked in boiled water for 1-5 minutes to 60-80 minutes.
 Some crops like Bengal gram and Groundnut, hot water treatment for more than
1 minute is found injurious to seed.
 Most effective for large leguminous seeds.
1.1.1.2. Mechanical scarification
 Rubbing or abrasion of seeds against hard surface.
 Done to partially damage hard seed coat to overcome physical dormancy
 E.g. Bitter gourd - sand and seed should be 2:1 ratio and rubbed against hard
surface of seed for 5 to 10 min.

3.  Large quantities of hard coated seeds can be mechanically scarified using
concrete mixer with sharp gravel or sand.
 Special drum lined with abrasive material such as sand paper, cement or
crushed glass or fitted with abrasive disks may be made for this purpose.

Mechanical scarifier
1.1.1.3. Acid scarification
 Done to partially damage hard seed coat to overcome physical dormancy to
allow imbibition of water over part or entire seed surface, leading to metabolic
processes of germination.
 For malvaceae and leguminaceae group of seeds, use 100 ml H2SO4/kg of
seed for 2-3 min.
 To scarify seeds, pour undiluted acid until all seeds are wetted.
 Stir them for few minutes to one hour and immediately wash them thoroughly in
cool running water for 5-10 minutes

4.  Final washing with slaked lime solution to neutralize acidity of seed coat and
used water.
 Shade dry seeds unless wet sowing is preferred.
 E.g. Tree crops 1-3 hours, Rose seeds - treat the seed partially with acid and
then given with warm stratification.
Duration of soaking in concentrated sulphuric acid to overcome seed coat
dormancy in some legume seed.
Species Duration of acid pretreatment
Acacia nilotica >15 min
Albizia lebbeck 40 min (85%)
Cassia fistula 45 min (75%) - 90 min (84%)
Delonix regia 3-6 h
Leucaena leucocephala 30 min (95%)
P. juliflora 15-60 min (95-100%)


1.1.1.4. Bioscarification
 Subjecting seeds to pretreatment by making use of animals and
microorganisms
 Done to partially damage hard seed coat to overcome physical dormancy
 It is done in the following ways:
a. Animals
 Pods of Acacia nilotica are fed to penned sheep or goats and seeds are
collected from the droppings.
 Combination of moisture, warmth and chemical action of digestive juices
softens and renders hard seed coat permeable.

5. b. Insects
 Termites are an important agent for breaking seed coat dormancy in many parts
of tropics.
 Termites feed on seeds and help to remove exocarp.

c. Microorganisms
 Partial fermenting which causes damage to many seeds can be beneficial in
overcoming seed coat dormancy.
 Microbes decompose epicarp and mesocarp over a period of time.
1.1.1.5. Electrical seed treatment
 Rapid heating of seeds by exposure to radio-frequency (r-f) electric fields of
sufficiently high frequency and intensity done to improve seed germination by
reducing percentage of hard seeds and destruct insects or parasitic
pathogens.
 Samples of optimum moisture content are exposed to r-f electric fields usually by
placing between a pair of parallel metal plates which are part of an electronic
power oscillator.
 The r-f electric fields improve germination by increasing water absorbing
capacity of seeds by causing reduction in the percentage of hard seeds without
reducing the keeping quality.
1.1.1.6. Fire
 Method of subjecting dormant seeds to heat generated by fire.

6.  Light inflammable litter are spread over the fruits and then ignited.
 Done to partially damage the hard seed coat to overcome physical dormancy
 Further, smoke accompanies fire is also shown to induce germination.
 Generated heat also scorches pericarp of seed so as to improve seed coat
permeability.
 E.g. Seeds of Calluna vulgaris - dormancy is broken by fire.
1.1.1.7. Soaking in water
 Soaking of seeds in cold or hot water for a period ranging from few hours to
several days specific to crops.
 Done to partially damage hard seed coat to overcome physical dormancy.
 Germination of teak is often poor due to dormancy.
 Pre - treatment of the seeds by alternate wetting and drying of the seed for a
week is required to break dormancy before sowing.
 Seeds were kept in a gunny bag and dock the bag in water, preferably in a running
stream, for 12 hours, then spread seed in sunlight to dry for 12 hours.
 This has to be repeated for one w eek.
 Germination percentage varies from 30 to 50 % in moist teak and 5 to 10 % in
dry teak.

 Also helps to leach out inhibitors causing chemical dormancy.
 Ex. Coriander (Coumarin), Sunflower (Hydrocyanic acid)

7. 1.2. Physiological methods
1.2.1. Stratification
 Method of exposing imbibed seeds to lower temperature (cold stratification) or
higher temperature (warm stratification) for a period of time.
 Cold stratification is done to overcome physiological as well as morphological
dormancy, while warm stratification helps to overcome physical, mechanical as
well as morphological dormancy.
1.2.1.1. Cold stratification
 Seeds should be soaked in several times their volume of water before pre-chilling
at 3-5°C for 41 h.
 After soaking, water is drained off and moist seeds are stored at 3-5°C.
 Storage may be without any medium i.e. seeds as such or seeds may be mixed
with 2-4 times its volume of a medium such as moist sand, peat or a mixture
of these two.
 E.g. Cherry and oil palm seeds.
1.2.1.2. Warm stratification
 Soak seeds in several times of their volume of cold water at approximately 3-5°C
for 41 h.
 Drain off water and mix seeds with two to four times their volume of a
moistened, water retained medium such as sand, sand peat mixture or
vermiculite.
 Store at a warm temperature.
 A constant temperature of 20-25°C or alternating temperature of 20°C and 30°C
is suitable for many species.
 Open the containers weekly, mix seeds and if surfaces show signs of drying,
remoist with water spray.
 Period of treatment vary from 2 weeks to 16 weeks depending upon species.
 E.g. Paddy

8.  In case of oil palm, it requires temperature of 40-50ºC for 2 months for breaking
dormancy
 Partial digestion of the outer layers and final weakening of the inner layers
relieves the seeds of physical dormancy.
1.2.2. Temperature treatments
a) Low temperature treatments
 Plants which grow in temperate and cooler climates require a period of chilling for
breakage of dormancy.
 E.g. Apple seed dormancy can be released by low temperature treatment by
storing seeds at 5ºC.
b) High temperature treatment
 Normally high temperature treatments are exhibited by early flowering "winter"
annuals.
 E.g. Blue bell (Hyacinthoides nonscripta).
 Their seeds are shed in early summer and do not germinate until they have been
exposed to the heat during high summer.
c) Alternate temperature treatments
 Most of the plant species which grow in temperate and cool temperate regions
require alternate temperature for breakage of dormancy. (e.g.) Bull rush (Typha).
1.2.3. Light and phytochrome
 Red light promotes germination and far red light affects germination.

1.3. Chemical methods
1.3.1. Soaking in growth regulators
1.3.1.1. Gibberelleic acid
 GA is light substituting chemical.
 Can be used at concentration of 100 to 1000 ppm.
 GA3 is effective in stimulating germination in large number of species.

9.  GA4 and GA7 are even more active being effective at much lower concentration
than GA3.

 Inducement of seed germination by gibberellic acid in dormant seeds has been
attributed to various reasons
 Increases the growth potential of the embryo,
 Weakens structures covering the embryo through cell wall hydrolysis e.g.,
weakening of endosperm in tomato,
 Counteracts effects of ABA directly or indirectly,
 Releases photo dormancy by regulating phytochrome and
 Promotes germination in thermodormancy through ABA metabolism.
1.3.1.2. Kinetin
 Cytokinins are present in developing seeds and accumulate predominantly in
liquid endosperm
 Cytokinins are needed for the promotion of cell division in the embryo.
 In many species, cytokinins alone break seed dormancy.
 Cytokinins appear to contribute to promotion of dormancy release and subsequent
germination by enhancing ethylene biosynthesis.
 Kinetin will stimulate germination of certain seeds, but it will not completely
replace requirement of red light in lettuce seeds.
 Applied cytokinins (kinetin) have been reported to overcome high-temperature
dormancy in lettuce seed.

10. 1.3.1.3. Ethylene
 Ethylene chlorohydrins also been reported to increase germination of tree
seeds.
 Ethephon - an ethylene releasing compound stimulates germination of
dormant and non-dormant seeds, although in some cases it may inhibit or
have no effect on germination.
 Moreover, treatment of dormant seeds with ethylene induced a high percentage
of germination.
 Ethephon or ethylene alleviates primary dormancy and light induced
dormancy.
 Primary action of ethylene - promotion of radicle cell expansion in embryonic
hypocotyl, increased seed respiration or increased water potential.
 Endogenous ethylene may promote the germination of dormant seeds by
decreasing the sensitivity to endogenous ABA.
 Ethylene may counteract the inhibitory effects of ABA on seed germination by
interfering with ABA signaling.
 An excess of ethylene can bypass the GA requirement.
 Ethrel can be used for breaking the dormancy of cotton seed. The dormancy in
cotton seed is due to the presence of ABA in pericarp of seed.

Promoters - inhibitors concept
 For regulation of germination the promoters and inhibitors present in the seed
should be in a balanced manner.
 GA - translocation of food reserve materials to active site of meristematic
activity. GA also helps in cell division.
 Cytokinin - natural endogenous hormone which controls germination through
DNA to RNA transcription system.
 Abscisic acid is an inhibitor that can prevent germination by affecting RNA
synthesis.

11. 1.3.1.4. Fusicoccin
 A diterpene fluoride is a toxin produced by the fungus (Fusicoccin amygdali)
capable of breaking dormancy and to stimulate germination rate of embryos
isolated from dormant grains.
 Fusicoccin induces extra cellular acidification.
 Acidic external pH is able to enhance GA induced biological responses such
as aleurone a-amylase production.
1.3.2. Soaking in chemicals
1.3.2.1. Potassium nitrate
 Nitrogenous substances such as nitrate, nitrite, ammonia, thiourea.
 KNO3 broke dormancy by decreasing endogenous ABA.
 In seed testing, 0.2% is the recommended concentration (ISTA, 1996).
 KNO3 2% can be used for breaking dormancy of light requiring seeds
 E.g. Oats, Barley and Tomato.
1.3.2.2. Thiourea
 First chemicals shown to break seed dormancy of lettuce were thiourea.
 Nitrate and thiourea - possible regulators of seed germination in soils.
 Thiourea can be used for breaking dormancy for both light and chilling
treatment requiring seeds (e.g.) lettuce - thiourea @ 10
-2
to 10
-3
M is used.

12. 1.3.2.3. Hydrogen peroxide
 H2O2 - active oxygen source with relative long half–life and is able to diffuse
into plant tissue.
 By enhancing oxygen production, H2O2 can decrease ABA content and thereby,
promote germination.
Seed Treatment with other Growth Regulators/Chemicals
 Sulphidral compounds like 2 mercapto ethanol and 2,3 dimercapto ethanol can
also be used.
 Plant products like strigol (root exudation from striga parasite host plant) can
also be used for breaking the seed dormancy.