Seed technology

Introduction
• Crop production is the commercial activity that enables man to produce such
plant materials that satisfies his various needs.
• It also enables him to commercially exploit the improvement of crop
genotype achieved thought well planned and sustained breeding programs.
• The crop has to be raised using various propagules.
• A propagule is an any plant part that gives rise to a new plant.

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• The type of propagules used for raising a crop will depend mainly of the
flowing two considerations:
1. The ease with which the propagules are obtained for planting a unit area
and the cost thereof.
2. The performance of the crop as affected solely by the nature of the
propagules used.

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• The various propagules are obtained either through sexual (true botanical
seed) or asexual (tubers, rhizomes etc.) reproduction.
• in crop production all parts which are capable of developing into an other
such plant are seed including stems ( sugarcane), leaf (Bryophyllum spp),
modified stem (onion), and true seed it self such ( cereals and legumes).

Stem propagation of
sugarcane
Leaf propagation of
Bryophyllum spp
Modified stem
propagation of onion

True Seed
• A true seed is a productive unit that develops from ovules and contains an
embryo and food reserves which are located either in embryo it self or some
external storage tissues.
• in other words, a true seed is a plant part having the following three
components (1) a living embryo, (2) food reserve or endosperm, and (3) a
protective coat or coats.

Definitions of Seed
• Seeds may be defined in many ways:
1) A seed is fertilized ripened ovule.
2) the part of flowering plant that contains the embryo and develops into a new plant if
sown.
3) Anatomically a seed is an embryo plant consisting of rudimentary stem and root together
with a supply of food sufficient to stablish a plant in new locations, all encased in
protective coat.
4) A seed is a unit of reproduction of flowering plants in general.
5) Agronomically, seed or a seed material or propagule is a living organ(s) of the crop in
rudimentary form that is used for propagations.

Origin and Evolution of True Seed
• Seeds are originated with the origin of seed bearing plants.
• the oldest seed bearing plant that has bean discovered in fossils is dated around 350
MYBP from the Hampshire formation of Randolph county, west Virginia USA.
• scientist call this plant Elkinsia polymorpha it carries seeds 5-6mm long capsule
terminating bifurcating bunch system.
• the earliest angiosperm seed of two species Caspiocarpus paniculiger or
Ranunculaecarpus quinquiecarpellatus (from USSR) are reported to be from Albania
around 150 MYBP.
• It is only after 65 MYBP that modern angiosperms having large seeds appear.

Elkinsia polymorpha Caspiocarpus paniculiger Ranunculaecarpus quinquiecarpellatus
Earliest seed plant
350 MYBP
Earliest angiosperm seed
plants 150 MYBP

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• The seed of gymnosperms and angiosperms differ in the development of
integuments and surrounding fruit tissues. The origin of two integuments is
known to be associated with the angiosperms.
• The storages tissues tissue in gymnosperms in megagametophytes. In
angiosperms, gradually thus function was taken by endosperms.
• The origin and evolution of endosperms has resulted the following three
situations:

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i. the endosperm is formed and retained as a food reserves reserve tissue in
the mature seed.
ii. The endosperm is formed but it is absorbed before the embryo is mature
e.g. cotton and sunflower.
iii. the endosperm nuclear division are terminated early where the embryo
always develops firmly appressed to the chalazal end of the embryonic
sack.

IMPROVED SEED
• Propagules of improve varieties are know as improved seed.
• improved seeds is of high genetic and physical purity and possess high
germination potential.
• The term genetic purity indicates the proportion of seed belonging to the
variety in question in a given seed lot. Therefore genetically pure seed lot has
seeds of only that particular genotype.
• As a proportion of seeds of other varieties/genotypes of the concerned
crop increases in a seed lot, the genetic purity of the seed lot declines.

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• Physical purity refers to the freedom of seed lot from physical matters, such as dust,
pebbles, straw, weed seeds, and shrivels and damaged seeds.
• A seed lot must carry germination potential capable of producing an effective crop stand.
• genetic purity, physical purity and germination potential are often referred as the quality
parameters of seed.
• Thus improved seed is the seed of high yielding varieties, which is of high genetic and
physical purity and has high germination.
• If the improved seed has to be certified, it has to be the seed of variety that has been
notified for cultivation by recognized notification agency.

CLASSES OF IMPROVED SEED
• Seed production is continues process. Each year a huge quantity of seed is
required to meet the demand of crop production.
• This huge quantity of seed of improved varieties cannot be generated in a
single season or year. In addition quality and cost of the seed hast to be kept
at an acceptable level.
• Therefore seeds of improved varieties are produced in several stages, each
stage generates a particular class of seed.

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• These classes and stages are recognized in order to:
1. facilitate seed production while maintaining genetic and physical purities and;
2. ensure the continues supply of quality seed at reasonable price.
• the modern classification of improved seed are:
i. Basic or nucleus seed
ii. Breeder seed and;
iii. Certified seed.
• Each seed class further subdivide into subclasses and stages.

Basic or Nucleus Seed
• Basic or nucleus seed is the original or first seed ( propagating material) of a
variety available with the producing breeder (= the breeder, who developed
the variety in question) or any other recognized breeder of the crop.
• Basic seed has 100% genetic and physical purity along with high standards
of all other quality parameters.
• Nucleus seed is multiplied and maintained by selecting individual
pods/spikelet/plants and growing individual pods/spikelets/plant progenies.

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• Nucleus seed is subdivided into two subclasses: (1) nucleus seed stag I (NSSI) and
(2) nucleus seed stag II (NSSII).
• Nucleus seed stage I is obtained as follow:
The true-to-type plants/ears/pods are selected from a field of a nucleus seed of the
variety in question; their seeds are grown in separate progeny rows, and seed true-to-
type rows are composited to constitute NSS I seeds.
• When NSS II is to be produced, seeds from the true-to-type are harvested
separately and grown in separate progeny plots. true-to-type plots are selected and
their seed are composited to obtain NSS II.

Breeder Seeds
• Breeder seed is the progeny of nucleus seed and is the source for initial and
recurring increase of foundation seed.
• Breeder seed production is directly controlled by the originating plant
breeder who developed the variety, or any other institution or qualified
breeder recognized by the authorities.
• Breeder seed is genetically so pure to guarantee that the subsequent seed
class shall confirm to the prescribed standards of genetic purity.

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• Breeder seed can be subdivided into the following groups: Breeder seed stage
I and Breeder seed stage II.
• Breeder seed stage I is the progeny of nucleus seed while stage II breeder
seed is the progeny of stage I breeder seed.
• Breeder seed stage II is allowed only under the conditions when the breeder
seed is in extremely short supply and it needs to be multiplied as breeder
seed to continue the seed chain in an effective manner.

Certified Seed
• Certified seed is the seed which is certified by any seed certification agency
that recognized by the government.
• Certified seed consists of the following two classes.
1. certified foundation seed and;
2. Certified seed.

Certified foundation seed
• Certified foundation seed is the progeny of breeder seed or the certified foundation seed it
self.
• When seed is the progeny of breeder seed, it is called foundation seed stage I, while it is
called foundation seed stage II when it is the progeny of certified foundation seed.
• It is important that only certified foundation seed stage I can be multiplied to generate
certified foundation seed stage II. Certified foundation seed stage II cannot be used to
produce foundation seed, it can be used only for production of certified seed.
• Production of foundation seed stage II is undertaken only when it is clearly expressed by
the seed certification agency that the breeder seed is in a short supply and stage II
foundation seed has to be produced to meet the seed demand.

Certified Seed
• Certified seed is the progeny of foundation seed and its production is so
handled as to maintain specified genetic identity and purity standards as
prescribed for the crop being certified.
• Certified seed can also be the progeny of certified seed provided, this
reproduction does not exceed three generations beyond foundation seed
stage I.
• Certified seed stage II cannot be used for further seed multiplication.

Class of seed Colour of tag
Basic or Nuclues seed (Stage I* and Stage II1) Tag is not used certificate given by the concerned
breeder.
Breeder Seed (Stage I* and Stage II1) Golden Brown
Foundation Seed (Stage I* and Stage II1) White
Certified Seed (Stage I* and Stage II1,2) Blue ( Shade ISI No.104, Azure blue)
Color of Tags Used For Different Classes of Seeds
• * Obtained by bulking seeds from true-to-type spikelets/pods selected from field of nucleus seed.
• 1 Progeny of stage I seed; produced only when stage I seed is not sufficient to meet the demand.
• 2 Product from such stage I certified seed that was produced from stage I foundation seed. It cannot
be produced from stage I certified seed that is the progeny of stage II foundation seed.
•

Nucleus seed
Stage I
Breeder Seed
Stage I
Nucleus seed
Stage II
Foundation
seed stage I
Certified seed
Stage I
Breeder Seed
Stage II
Foundation seed
stage II
Certified seed
Stage II
FARMER
FIELD

CONCEPT OF SEED QUALITY
• Seed quality comprises a wide range of inter related attributes of seeds.
• From a seed technological perspectives high quality seed must have the following
characteristics:
1. High purity in terms of species and cultivar.
2. High germination
3. High vigour
4. Uniform size
5. Absence of seed borne diseases
6. Optimum moisture content

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• The ultimate seed quality is the result of these attributes and their
interactions with each other. These attributes can be represented as those as
those belonging to the :
1. inner core ;
2. Middle core and;
3. Outer core of seed quality.

The inner core
• The inner core of seed quality consist of the most important seed quality
attribute, i.e., the genotype represented by the seed.
• A seed lot can be called a quality seed only when it belongs an improved
variety, i.e., a variety notified by the official notification agency of the
country under question.
• The variety may have been developed by a foreign country, but it must be
recognized and notified by the host country in/for which seed production is
being done.

The middle core
• The middle core of seed quality comprises the next most important group
of attributes of seed quality, such as; genetic purity, physical purity, minimum
acceptable germination and vigour or health.
• genetic purity is the most important attribute of the middle core.
• A genetically pure seed lot must have all the seeds of same genetic make up
of the variety in question.
• Genetic purity is negatively influenced by factors like; natural crossing,
mutation, mechanical mixture and developmental variation.

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• the accepted official method of testing the genetic purity of seed lot is grow out
test, which involves raising a population of plant in field using a representative
sample of seed lot and then observing for difference among them. Some other
modern testing genetic purity techniques are; electrophoresis and DNA finger-
printing.
• Physical purity along with freedom from weed seeds and other crop seeds is
important for raising a good crop.
• Seed vigour also influences crop performance and the quality of seed produced by
the crop.

The outer core
• The outer core of seed quality caries the attributes such as, seed health, seed
moisture, seed size and seed colour.
• Seed health refers to the presence or absence of disease causing agents or insect
pests.
• Seed moisture is associated with longevity of seed. In general, the lower is the seed
moisture (%), the longer is the seed life. In addition high seed moisture also
promotes insect pest attack.
• Uniform seed size and/or colour gives the seed lot a better look and leads greater
price/satisfaction to the grower.

1) Genetic Potential
1) Seed Health
2) Seed Moisture
3) Seed Size
4) Seed Colour
1) Genetic Purity
2) Germination
Potential
3) Physical Purity
4) Seed Vigour

SEED STRUCTURE
AND COMPOSITION
Chapter two

•Sepals
•Petals
•Stamens
•Pistil

• Usually green; leaf-like
structures that protect the
flower, as it forms and
emerges.
SEPALS

• The group of sepals on a
flower are called calyx.

• Located just inside
the sepals
• Leaf-like and often
very colorful
• Attract pollinators
PETALS

• The collection of
petals on a flower are
called corolla.

• The sepals and the
petals of a flower.
(Not the
reproductive parts)
are called the
Perianth.

• Stamen and pistil together
are called the reproductive
parts of flower or essential
parts.
• Found at the center of the
flower

• Stamen is the male
reproductive parts of a
flower
• Arranged around the
female parts

• Part of the stamen
that produces and
holds pollen are
called anther.

• Stalk that holds up the
anther is the filament

• The female part of the
flower is the pistil.
• It consist if the stigma,
style, ovary and ovules.
PISTIL

• Stamen is found at
the end of the pistil
• Has a sticky surface
to catch pollen

• The neck of the pistil
is called Style.
• it holds the stigma
• it has the tube that
pollen grains pass
through to reach the
ovules

• Ovary is the part
of the pistil that
contains the
ovules
Ovary

• The part of the
flower in which the
eggs are produced
and seeds develop
is the ovules.

Pollination
• the transfer f pollen grains from anther to the receptive stigma of a flower
is called pollination.
• In the case of angiosperms the ovules are enclosed in the ovary of carpel
such type of pollination is called indirect pollination.
• Pollination is an important biological phase of a sexually reproducing plants.
• It the pre-requisite for fertilization.

Types of pollination
• There two types of pollinations which are self-pollination and cross-pollination.
• Self pollination is possible only in case of bisexual flowers. In this there is a transfer
of pollen grains from an anther to stigma of a same flower or between two flowers
of borne by the same parent plants. In this case, only one parent plant is concerned
to produce off-springs.
• Cross-pollination is the transfer of pollen grains from the anther to stigma of the
other flower borne by the separate parent plants of the same kind of allied species.
Here the pollination takes place between two flowers present of different plants of
the same kind.

Reason for self-pollination
• For self pollination following are the reasons.
1. The bisexual flowers of certain plants never open.
2. Simultaneous maturation of male and female organs in bisexual flower forces the pollen
grain to fall directly on the stigma.
3. Due to movement of petals the anther contacts the stigma.
4. Incomplete dichogamy some times brings self pollinations
5. When cross pollination fails the stigma bends down ward and touches to facilitate self-
pollination.
• Continue self pollination, generation after generation, has how ever, results in weaker
progeny.

Reason for Cross-pollination
• For the cross pollinations following are the reasons.
1. Some plants produce unisexual flowers only, either staminate (male) or pistilate (female) flowers. This is called
dioecious nature of plant
2. Ripening of male and female sex organs of a flowers at different types causes cross pollination. This process
is called dichogamy.
3. In a bisexual flowers the flowers, if both the sex organs mature at a same time self pollination is preened by
the arrangement of sex organs at a different height.
4. In some bisexual flowers pollen grains are not able to germinate. This condition is called self sterility.
5. In some plants when stigma receives pollen from same flower as well as from an other flower same time the
foreign pollen germinates earlier than its own. This condition is called pollen prepotency.
6. in some plants the sigmatic lobes may be very sensitive. When once cross pollinated these lobes move and
come closer to prevent self pollination further.

Agents for cross-pollination
• As the pollen is not capable of locomotion, pollen cannot take place
spontaneously. There the act of pollination involves the help of certain
external agents.
• The structure of flower and its relation to external agents reveals the
pollination mechanism.
• The usual agents are wind water and animal. According three types of
pollination are recognized and they are: Amenophily, hyrdophily and
zoophily.

Amenophily
• Pollination brought by wind is called Amenophily.
• Plant bearing Amenophilous flowers may be short (grass) or tall (palm). these flower certain characteristics to ensure wind pollination.
1. they are not showy
2. They don’t have scent or nectar.
3. The inflorescences may be spikes, catkin or spadix.
4. They produce large quantities of dusty pollen grains.
5. Stamen has long dropping filaments.
6. The anther shows versatile fixation for easy dehiscence.
7. the pollen grains are usually small, dry, smooth, very light in weight and in some cases they are winged.
8. some times the pollen is released with some forces.
9. Usually wind pollinated flowers branched brush like stigma for catching the pollen form air.

Hydrophily
• In such plants water bring pollination. Here the pollen is carried on the surface and
also inside water.
• The ripened male flower detach from the plant and float on water. The female
flower when mature come to the water surface and they touch each other.
• After the pollination the female flowers are pulled down and fertilization takes place
in the water.
• Pollination can also take place in water. Some plants liberate needle like pollen grain
from anther and appear suspended in water. The long stile with sticky stigma can
catch the suspended pollen grains to facilitate the pollination.

ZOOPHILY
• This type of pollination is carried by bird. such plants are very few in number.
Usually the pollen is large in size, brightly cloured and produce nectar. Small birds
while feeding the nectar of the flower effect the pollination.
• In some plants pollination is brought by bats, snakes and snakes also.
• pollination by insects is found great majority of the flowers. Bees, flies, butterflies
and moths are common insects involved in the process. they visit flowers for honey
and pollen.
• The flowers show certain adaptations to attract the insects like colour, nectar size
and scent.

The advantages of crosspollination
• It results in healthier offspring and better adaptive to the struggle for
existence.
• It produce abundant viable seed
• It produce seed of high geminated capacity seeds
• it produce new varieties which are more adaptable to their environmental
conditions.

Pollination and crop plants
• According to the type of pollination that carried out in them the plants are classified into
four types
1. Naturally self pollinated crops where cross pollination is less than 5% like; wheat, barley,
outs, a groundnut and tomatoes.
2. Frequently self pollinated crops where cross pollination is more than 5% here the self
pollination is the common like; rice
3. Naturally cross pollinated crops where self pollination is less than 5% like; rye, alfalfa,
carrots and coriander.
4. Frequently cross pollinated crops where cross pollination is more than 5% here the cross
pollination is the common like; cotton.

Seed Structure
• There are three major structure of seeds,
1. Embryo,
2. Endosperm and
3. Seed coat
• These are described in the following sections:

Embryo
• The living embryo is the most important of seed and it consist of two structures (i)
embryonic axes and (ii) cotyledons.
• The embryonic axis is composed of three parts, namely (i)radicle (embryonic root),
(ii) the hypocotyl (the point of attachment of cotyledons) and (iii) plumule ( the
shoot apex with the first true leaves).
• These three parts of embryonic axis are easy to identify in dicots, but in monocots
(especially the family of Gramineae) their identification is difficult.
• In monocots there is only one cotyledon which is educed and modified to form the
sculentum. The basal sheet of cotyledons is elongated and to the shape of
coleoptile, while in some cases the hypocotyl is modified to form mesocotyl.

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• The base of hypocotyl sheathing is the radicle is termed as coleorhiza.
• The size and shape of embryo varies from species to species. In endospermic
(monocot and dicot) seeds the embryo occupies much lesser space in the seed than
non-endospermic seeds.
• In some species such as citrus each seed contains more than one embryo, this
condition is called polyembryony.
• Polyembryony may occur dueto (i) cleavage of fertilized egg cell to for many zygote
initials, (ii) development of one or more synergids into embryos, (iii) present of
many embryo sacs per ovule, and (iv) different forms of apomixes and adventitious
embryo.

• Based on the presence or absence of a well developed endosperm in the mature seed, seeds
may be grouped into two classes as follow (i) endosperm, and (ii) non-endospermic seeds.
• In some crops like cereals castor bean and the endospermic legumes (Fenugreek, carob,
honey-locust etc.) endosperms are relatively larger and carry substantial food reserves in the
mature seed.
• In such seeds, stored food materials absorb the cytoplasmic contents during seed
development. Therefore the majority of cells in the endosperms of such mature seed are
non-living.
• The endosperm is surrounded by a layer of living cells that that constitute the leurone
layer.
Storage Tissue or endosperms

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• The leurone layer does not store does not store many reserves but is responsible for
release of enzymes that mobilize the endosperm food reserves.
• Some seeds despite having an endosperm, are called non-endospermic seeds. This is
because of the following reasons:
a) the endosperm may be broken and only remnant of that developed during seed
formation e.g. Soybean and peanuts.
b) The endo endosperm is only one to few cell layers thick. e.g. lettuce.
• In such crops the cotyledons serve as the storage organ.

Seed coat or Testa
• The seed coat or testa is outer most layer of a seed and is often the only protective
barrier between the embryo and external environment.
• The seed coat consist of an outer and inner cuticle, impregnated with waxes and
fats and one or few layers of protective cells.
• In some species, crystal ( calcium oxalate or carbonate) containing cells are present
in seed coat, and reserve as protective barriers by discouraging insect predations.
• The seed coat of pulse are hard impermeable to water and capable of restricting
metabolism and growth of inner issues.

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• The testa of seed across species show considerable variation for color and texture.
These feature are often used taxonomic classification of seeds. How ever these
features some times overlap under the environment and genetic influences during
development; therefore they do not offer a reliable distinguishing criterion.
• Almost all seed a scar like point called helium. This is the point at which a seed
remains joined with funiculus.
• The micropyle, which is a small hole at one end of hilum is present in seed coat
of any species.

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• Some times hair or wings are also present in testa these structures help in
seed dispersal.
• seed coat may also pear our growth of helium regions like trophiole, which
controls movement of in and out of seed, and the aril which contain
chemicals.

Composition of Seed Storage Constituents
• Seed is the carrier of life to the next generation of concerned species. The living
embryo with in the seed is able to survive till the onset of favorable environment
largely due to the presence of large quantity of food as a storage reserve.
• The reserve also serve as the source of food for germinating seedling till it becomes
capable of surviving independently.
• The principle constituent of seed storage reserves are carbohydrates, fats and oil,
and protein. Occasionally seed also contain toxic or nutritionally un wanted
chemicals such as, alkaloids, phytin, lectins, proteinase inhibitors etc.

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• The major food reserve of seeds are presence either in embyro ( especially
cotyledons) or endosperm.
• In cereals the major (60-85%) constituent is carbohydrates, while in oil seeds
it is oil (40-65%).
• Legumes, how ever, contains substantial amount of carbohydrates, but they
are rich source of protein.
• In some cases such as maize the food reserves is stored in in both embryo
and endosperm.

Crop Storage tissue Protein Oil Carbohydrat
es
1. Cereals
Wheat, barley, rye,
Maize,
oats
Endosperm (non-embryonic)
10-14
10-12
12-14
2-3
5-6
6-10
75-77
80-82
60-65
2. Pulse/legumes
Pea, broad bean
Soybean
Cotyledon (Embryonic)
Cotyledon (Embryonic)
22-26
35-40
1-6
15-20
50-56
25-30
3. Oilseeds
Rape seed
Castor
20-22
18-20
45-50
60-66
18-22
Trace
Composition of seeds of some crop species

DEFINATIONS
• Seed dormancy is defined as a state in which seeds are prevented from
germinating even under environmental conditions normally favorable for
germination.
• OR
• Seed dormancy is the internal or innate inhibition of germination of
otherwise normal or viable seed even when present under most favorable
conditions required for its germination.

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• Dormancy is a mechanism to prevent germination during unsuitable ecological conditions,
when the probability of seedling survival is low.
• True dormancy or innate dormancy is caused by conditions within the seed that prevent
germination under normally ideal conditions.
• Often seed dormancy is divided into two major categories based on what part of the seed
produces dormancy: exogenous and endogenous.
• There are three types of dormancy based on their mode of action: physical, physiological
and morphological.
• One important function of most seeds is delayed germination, which allows time for
dispersal and prevents germination of all the seeds at the same time.

Categories of Seed Dormancy
Exogenous dormancy
• Exogenous dormancy is caused by conditions outside the embryo and is often broken down
into three subgroups:
a. Physical dormancy:
• Dormancy that is 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.

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• 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.
• Generally, physical dormancy is the result of one or more palisade layers in
the fruit or seed coat.
• These layers are lignified with malphigian cells tightly packed together and
impregnated with water-repellent

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Mechanical dormancy
• Mechanical dormancy occurs when seed coats or other coverings are too
hard to allow the embryo to expand during germination.
• In the past this mechanism of dormancy was ascribed to a number of
species that have been found to have endogenous factors for their dormancy
instead. These endogenous factors include low embryo growth potential.

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Chemical dormancy
• Includes growth regulators etc., that are present in the coverings around the
embryo. They may be leached out of the tissues by washing or soaking the
seed, or deactivated by other means.
• Other chemicals that prevent germination are washed out of the seeds by
rainwater or snow melt.

Endogenous dormancy
• Endogenous dormancy is caused by conditions within the embryo itself, and
it is also often broken down into three subgroups:
a. physiological dormancy,
b. morphological dormancy and
c. combined dormancy,
• Each of these groups may also have subgroups.

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Physiological dormancy
• Physiological dormancy prevents embryo growth and seed germination until chemical
changes occur.
• These chemicals include inhibitors that often retard embryo growth to the point where it is
not strong enough to break through the seed coat or other tissues.
• Physiological dormancy is indicated when an increase in germination rate occurs after an
application of gibberellic acid (GA3) or after Dry after-ripening or dry storage.
• Physiological dormancy is broken when inhibiting chemicals are broken down or are no
longer produced by the seed; often by a period of cool moist conditions,

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• Conditions that affect physiological dormancy of seeds include:
• Drying: some plants including a number of grasses and those from seasonally arid regions
need a period of drying before they will germinate, the seeds are released but need to have a
lower moisture content before germination can begin. If the seeds remain moist after
dispersal, germination can be delayed for many months or even years.
• Photodormancy or light sensitivity affects germination of some seeds. These photoblastic
seeds need a period of darkness or light to germinate. In species with thin seed coats, light
may be able to penetrate into the dormant embryo. The presence of light or the absence of
light may trigger the germination process, inhibiting germination in some seeds buried too
deeply or in others not buried in the soil.

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• Thermo-dormancy is seed sensitivity to heat or cold. Some seeds including
cocklebur and amaranth germinate only at high temperatures .
• Many plants that have seeds that germinate in early to mid summer have
thermo-dormancy and germinate only when the soil temperature is warm.

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Morphological dormancy
• In morphological dormancy, the embryo is underdeveloped or undifferentiated.
• Some seeds have fully differentiated embryos that need to grow more before seed
germination, or the embryos are not differentiated into different tissues at the time
of fruit ripening.
• Immature embryos: some plants release their seeds before the tissues of the
embryos have fully differentiated, and the seeds ripen after they take in water while
on the ground, germination can be delayed from a few weeks to a few months.

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Combined dormancy
• Seeds have both morphological and physiological dormancy.
• Morpho-physiological dormancy occurs when seeds with underdeveloped
embryos, also have physiological components to dormancy.
• These seeds therefore require dormancy-breaking treatments as well as a
period of time to develop fully grown embryos.

CAUSES OF SEED DORMANCY
1. Hard Seed Coat
• Seeds of many species possess hard seed coat.
• Most of these seeds belong to the family. Leguminosae and Malvaceae. Such seeds
remain dormant.
• Hard seed coat prevents germination due to following reasons: (a) Hard seed coat
prevents the entry of water into the seed. (b) Hard coat obstruct exchange of gases,
especially oxygen. Oxygen is necessary for respiration. (c) Hard seed coat causes
mechanical resistance. Thus radicle does not come out.

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2. Immature Embryo
• The embryo is fully developer inside the seed in most of the plants before shedding
from the parent plant.
• But development of the embryo is incomplete at dispersal in few cases like
Fraxinus and Anemone. Such seeds remain dormant and fail to germinate. Such
seeds imbibe water and the development of the embryo is completed in a few
weeks.
• Then the embryo is fully developed Now the seed can germinate under favorable
conditions.

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3. Light Sensitive Seeds
• There two type of seeds for light sensitivity:
a. Positive photoblastic seeds: Seeds of most of the species germinate equally well
both in the dark and in light. Therefore light is not necessary for germination.
However, seeds of some species like lettuce remain dormant in the dark an they do
not germinate till these are exposed to light. These are called positive photoblastic
seeds. Therefore dark inhibits germination in these seeds.
b. Negative photoblastic seeds: Seeds of some species like phlox. Nemophila and
Silene remain dormant when exposed to light. They germinate only in the dark.
These are called negative photoblastic seeds.

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4. Chilling Requirement
• Seeds of many temperate trees remain dormant and do not germinate after
harvest. Its examples are apple, walnut and pinus. Such seeds need chilling
temperature (1 -5 degrees) for a few weeks.
• This requirement is met in nature. These seeds lie buried in the soil during
winter therefore they get chilling temperature. But some seed become
dormant in nature. And they need artificial chilling.

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5. Dormancy due to growth inhibitory chemicals
• There are several naturally occurring compounds which inhibit germination of
seeds.
• Seeds of many species contain several phenolic compounds. These phenolic
compounds are ferulic acid, parasorbic acid and coumarin.
• These compounds are present in the embryo or in the seed coats. They inhibit the
germination.
• Sometimes, an inhibitory hormone abscisie acid prevents germination.

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6. Excessive Salts
• In Atriplex plants the seeds contain a high concentration of solutes which
do not allow the embryo to resume its growth.

BREAKING DOWN OF DORMANCY
Naturally
1. Weakening of tough and impermeable seed coats by microbial action.
2. Rupturing or weakening of seed coats by mechanical abrasions.
3. Action of digestive enzymes present in alimentary canals of birds and other
animals which happen to feed on their fruits.
4. Leaching of inhibitors present in the seed coat.
5. Inactivation or oxidation of inhibitors by heat, cold and light.

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6. Production of growth hormones which can counteract the effect of
inhibitors.
7. Completion of over-ripening period.
8. Attainment of maturity of embryo in case the dormancy is due to
incomplete development of embryo.
9. Leaching of solutes in Atriplex where dormancy is caused- by high osmotic
concentration inside the seeds.

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Artificially
1. Rupturing of seed coats or scarification by abrasion through machine threshing, filing,
chipping, vigorous shaking, etc.
2. Hydraulic pressure of up to 2000 kg for 5-20 minutes for weakening the tough seed coats.
3. Treatment with hot water or fat solvents for dissolution of surface inhibitors, waxes, etc.
4. Treatment with concentrated sulphuric acid for a short period followed by thorough
washing to remove all traces of the mineral acid.
5. Stratification or subjecting the moist seeds in the presence of oxygen to periods of low or
high temperature.

BIOLOGICAL IMPORTANCE SEED
DORMANCY
1. Dormancy allows the seeds to remain in suspended animation without any
harm during drought, cold or high summer temperature.
2. The dormant seeds can remain alive in the soil for several years. They
provide a continuous source of new plants even when all the mature plants
of the area have died down due to landslides, earth quake, floods,
epidemics or continued drought.
3. It helps the seed to get dispersed over long distances through unfavourable
environment or inhospitable area.

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4. The small seeds with impermeable seed coat belonging to edible fruits
come out of the alimentary canals of birds and other animals uninjured
e.g., Guava.
5. Dormancy induced by the inhibitors present in the seed coats is highly
useful to desert plants. The seeds germinate only after a good rainfall which
dissolves away the inhibitors. The rainfall ensures the seed a proper supply
of water during its germination.
6. It follows storage of seeds for later use by animals and man.

Definition of Germination
• Germination in plants is the process by which a dormant seed begins to
sprout and grow into a seedling under the right growing conditions.
• Seed germination is the resumption of active growth of the embryo that
results in the rupture of the seed coat and emergence of the young plant.
• When a viable seed absorbs water under favorable environment, respiration
protein synthesis, and other metabolic activities begin and lead to embryo
emergence after some time; such seed is called germinated.

Types of Germination
Epigeal germination
• In this, the cotyledons are raised out of the soil and generally become green
and photosynthetic.
• In dicots, they are pushed up by rapid extension of hypocotyl before growth
of the epicotyl.
• Epigeal germination occurs in bean, caster, mustard, tamarind, sunflower
etc.

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Hypogeal germination
• In this type of germination, the cotyledons remain underground.
• Hypocotyl growth is restricted. The epicotyl grows to raise the first leaves
out of the soil.
• Hypogeal germination occurs in dicotyledenous seeds of gram, pea, mango,
ground nut e.t.c and in monocotyledons like rice, maize, wheat e.t.c.

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Viviparous germination
• This is a special type of germination occurring in mangrove plants.
• These plants generally grow in salty lakes, sea coasts and deltas. Here, the seed
germinates while still attached to the parent plant.
• The embryo emerges out of the fruit with a massive radicle pointing downwards.
Due to increased weight, the seedling separates from the parent plant and
establishes itself in the muddy soil below.
• – Example: Rhizophora

Factors Affecting Germination
A. Abiotic (external) Factors:
1. Light
2. Temperature
3. Aeration (Oxygen)
4. Soil type and depth of sowing
B. Biotic (internal) factors:
1. Viability of seed
2. Dormancy period
3. Other factors:

Abiotic factors
1. Light
• Generally seeds require darkness to germinate. However, lettuce, tobacco, tomato and many
grasses seed to light exposure to germinate.
• These seeds require the red portion of the light spectrum, while far red light inhibits
germination.
• Many small seeds with low amounts of storage reserves (such as lettuce) show such a red
light requirement.
• These seeds must not be buried below the soil so deeply that light cannot penetrate.
Although research suggests that even a few minutes of exposure will allow the germination
to occur.

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2. Temperature
• As with most reactions germination generally occurs faster when at warmer
temperatures. However there is sometimes a need for cool temperatures to
break dormancy.
• Stratification is one strategy that is employed in woody species in particular.
It requires a moist, cool period that degrades growth inhibitors that prevent
germination. Once the inhibitors are degraded and all other conditions are
met then germination will occur.

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• The temperature for germination to occur is quite different than the
temperature requirement to break dormancy.
• Generally the temperature for germination correlates to the temperature
needed for successful plant growth. Seeds of cool season crops germinate
best at temperatures between 32 and 50 degrees Fahrenheit (0 – 10 Co ).
(Examples: celery, lettuce, peas.) Warm season crops germinate best at
temperatures between 59 to 79 degrees Fahrenheit (15 – 26 Co).

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3. Oxygen
• Another requirement for germination is aeration (oxygen).
• Respiration rates for germinating seeds are very high, therefore adequate oxygen is
necessary.
• The germination percent of most seeds will be retarded if the oxygen percent goes
below 20 percent. (Normal air is 20 percent oxygen.)
• Seedbeds that are over-watered or poorly drained will cause the oxygen supply to
become limited, so the germination percent will diminish.

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4. Soil type
• Soil type is widely affected on seed germination, there are so many
parameters of soil affecting on seed germination.
• In that factors, soil salinity, acidity, salt concentrate, EC of soil, soil porosity,
water holding capacity, texture of soil also affect on seed germination.
• Most problematic factor is water holding capacity of soil water holding
capacity.

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5. Depth of Sowing
• Proper planting depth is a direct correlation to seed size.
• The general rule of thumb is larger seeds can be planted more deeply than small
seeds. This is due to the energy needed to emerge. Larger seeds have greater food
reserves from which to draw energy for respiration and growth. They are able to
emerge from greater depths.
• Soil types also affect the planting depths. The surface of sandy soils tends to dry out
quickly, so seeds planted in these soils should be planted deeper, than in loam soils.

SEED AND
SEEDLING VIGOUR
Chapter five

FACTORS AFFECTING SEED VIGOUR
• To achieve maximal seed vigour of a given cultivar in seed production,
efforts must focus on:
• Producing a seed crop in the best possible environment for development of
vigorous seeds
• Harvesting as soon as possible after physiological maturity (PM)
• Handling, conditioning, and storing seed to minimize damage, slow
deterioration

INITIAL SEED QUALITY
• High initial viability of seeds maintains their quality in storage longer than those
with less initial viability.
• Vigorous and undeteriorated seeds can store longer than deteriorated seeds.
• Seeds that have been broken, cracked, or bruised due to handling deteriorate more
rapidly in storage than undamaged seeds.
• Cracks in seeds serve as entrance to pathogens causing consequent deterioration.
• Seeds that have been developed under environmental stress conditions (such as
drought, nutrient deficiency and high temperatures) become more susceptible to
rapid deterioration.

NUTRITION
• The structural and textural status of the soil, its fertility level, pH, microbial environment.
• In the nutrition of seed crops, nitrogen, phosphorus, potassium and several other elements
play an important role for vigorous seed production.
• It is advisable to know and identify the nutritional requirements of seed crops and apply
adequate fertilizers.
• Adequate fertilization results in good seed development and maturation.
• Adequate supply of nitrogen is very important for a good healthy seed development.
• Severe nitrogen deficiency in carrot, lettuce, and pepper resulted in poor seed development.

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• High dose of nitrogen reduces development in seed due to accumulation of
germination inhibitors
• A good supply of phosphorus helps in good seed development.
• Phosphorus deficiency retards overall growth and development.
• It should be applied in the soil before sowing
• Excess quantity of nitrogen prolong the growing period and delays the seed
maturity so time of application of nitrogen is important.
• In some crops dressings at flowering tends to delay in seed ripening.

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• In certain crops, a side dressing of phosphorus is also applied at the time of
flowering.
• The P reserves in the seed in the form of phytic acid and acts as a antioxidant.
• Potassium plays an important role in flowering and seed development.
• Helps in synthesis of proteins and fat in oil crops.
• Severe deficiency of potassium in pepper resulted in a higher percentage of
abnormal seed production.

TEMPERATURE
• Most of the crops require moderate temperatures for flowering and pollination such that
good seeds are formed.
• Too high temperatures cause desiccation of pollen resulting in poor seed set.
• If hot dry weather conditions prevail during flowering many crops such as vegetables,
legumes and fruit trees fail to set vigourous seeds effectively.
• Vegetables, legumes, fruit crops require cool conditions to flower and pollinate normally.
• Though oil crops can withstand hot periods during flowering, very high temperatures result
in premature flowering, and production of poor quality seeds.
• Very cold temperatures may also damage seed quality especially in the early phases of seed
maturation.

AFFECT OF TEMPERATURE ON SOME
CROPS
• Very low temperature (0⁰C and below)damages ripening of corn seed. (Rossman,
1949).
• In Lettuce koller (1962) noted that when the seeds matured at high temperatures,
germination was less at 26⁰C in the dark than the corresponding low temperature
matured seed.
• Temperature differences during ripening also altered the dormancy patterns of
wheat (Van Dobben, 1947; Kramer, Pest, Witten, 1952).
• In Mungbean, Dharmalingam (1982) showed the late summer sowing in Tamil
Nadu resulted in the production of high % of hard seeds.

MOISTURE STATUS OF SOIL
• For good-quality seed, a relatively dry climate during the ripening phase is preferred.
• Even for a wetland crop like rice, a dry climate during grain ripening phase produces seeds
of good quality
• Adequate soil moisture is essential for good seed development.
• Soil with high moisture due to high irrigation or high rainfall may lead to seeds of low
nitrogen and protein content in case of wheat.
• Drought during flowering might interfere with fertilization, thus seed vigor is reduced.
• Weight and size of seed which are usually correlated with vigour, are reduced by drought
during seed development and maturation.

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• extreme water deficit stimulates premature desiccation, and affect the quality
of seed. as such seeds badly affected by pre-harvest rains should not be
stored for planting purposes.

PLANT PROTECTION CHEMICALS
• Herbicides and pesticides applied to the soil or to the growing crop may affect the
development of seed and influence its quality. If the concerned herbicide or
pesticide is not easily biodegradable.
• Increase in the protein content of wheat with sub herbicidal doses of Simazine
(Ries, Schweizer, and Chmiel, 1968).
• Ramamoorthy (1990) studied the effect of Fluchloralin, Pendimethalin and
Oxyfluoren applied and observed tat there was no effect on vigour of groundnut
seeds before storage but after storage the use of herbicides other than fluchloralin,
resulted in better seed vigour.

HARVEST FACTORS
• Seed quality is highly affected by harvesting and handling methods.
• Harvest and post-harvest deterioration comprises threshing, processing machinery,
seed collection, handling, transporting and drying.
• Mechanical damage is one of the major causes of seed deterioration during storage.
• Very dry seeds are prone to mechanical damage and injuries.
• Such damage may result in physical damage or fracturing of essential seed parts;
broken seed coats permit early entry and easy access for microflora, make the seed
vulnerable to fungal attack and reduce storage potential (Shelar, 2008).

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• Soybean seeds germination dropped from 93% for seed harvested on October 9 to 48% for
seed harvested on December 11.
• The field emergences of 3 categories of soybean seeds, namely non broken, lightly broken,
and moderately broken, were 96, 72, 52 percent, respectively (Moore, 2007) indicating the
poor performance of even lightly injured seed subjected to stress conditions in the field.
• The thin coat of flat seeded sesame poses a problem even with manual harvesting and
processing in India and significant reduction of vigour is encountered following
storage.(Atkin, 1998).
• Rain soaked and subsequently dried soybean lead to substantial loss of vigour in storage
(Saha and Basu, 1984).

FIELD WEATHERING
• Adverse environmental conditions during seed filling and maturation result in forced seed
maturation, which is associated with low yields, leading to a significant decrease in quality and an
extensive reduction in the crop productivity (Franca- Neto et al., 2005; Pádua et al., 2009).
• After physiological maturity if the seeds are retained on mother plant seeds will deteriorate,
physiological changes in seed may lead to formation of rigid seeds or off colour seeds in pulse
crops (Khatun et al., 2009).
• Harvest delays beyond optimum maturity extend field exposure and intensify seed deterioration.
• Weathering not only lowers seed germination, but also increases susceptibility to mechanical
damage and disease infection. Timely harvesting avoids prolonged exposure to moisture, and is
the best means of avoiding weathering.

POST-HARVEST FACTORS/STORAGE
FACTORS
• Storability of seeds is mainly a genetically regulated character and is influenced by quality of the
seed at the time of storage, pre-storage history of seed (environmental factors during pre and
post-harvest stages), moisture content of seed or ambient relative humidity, temperature of
storage environment, duration of storage and biotic agents (Shelar et al., 2008; Baleseviæ-Tubic et
al., 2005; Khatun et al., 2009; Biabani et al., 2011).
• Damage of seed during storage is inevitable (Balesevic-Tubic et al., 2005). These environmental
conditions are very difficult to maintain during storage. The seed storage environment highly
influences the period of seed survival.
• After planting of deteriorate seeds, seedling emergence may be poor and transmission of
pathogens to the new crop may occur.
• Lower temperature and humidity result in delayed seed deteriorative process and thereby leads to
prolonged viability period (Mohammadi et al., 2011).

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• The rate of seed deterioration is highly influenced by environmental (temperature, relative
humidity and seed moisture content) and biological factors (such as fungi that create their
own biological niche) (Ghassemi-Golezani et al., 2010).
• Seed longevity is determined by seed moisture, temperature and seed attributes that are
influenced by genetic and environmental interactions during seed maturation, harvesting and
storage (Walters et al., 2010).
• Several other factors such as environmental conditions during seed producing stage, pests,
diseases, seed oil content, storage longevity, mechanical damages of seed in processing,
fluctuations in moisture (including drought), weathering, nutrient deficiencies, packaging,
pesticides, improper handling, drying and biochemical injury of seed tissue can affect vigour
of seeds (Krishnan et al., 2003; Marshal and Levis, 2004; Astegar et al., 2011.

EFFECT OF ORGANISMS ASSOCIATED
WITH SEEDS
• Organisms associated with seeds in storage are bacteria, fungi, mites, insects and
rodents. The activity of these entire organisms can lead to damage resulting in loss
of vigour and viability or, complete loss of seed.
• There are several factors which favour infection fungi and promote their infestation
such as moisture content of seed and interspace relative humidity, temperature, pre-
storage infection and storage pest.
• Most storage fungi belong to Penicillium and Aspergillus genera. They induce seed
deterioration by producing toxic substances that destroy the cells of seeds.
• Mechanically damaged seed allow quick and easy access for micro flora to enter the
seed (Shelar et al., 2008).

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• To minimize the risk of fungi invasion, seeds have to be stored at low moisture
content, low temperature, and RH.
• Researches show that all storage fungi are completely inactive below 62% relative
humidity and show very little activity below about 75% relative humidity upwards,
the amount of fungi in a seed often shows an exponential relationship with relative
humidity.
• The storage bacteria require at least 90% relative humidity for growth and therefore
only become significant under conditions in which fungi are already very active.

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• There is no insect activity at seed moisture contents below 8%, but if grain is
infected, increased activity may generally be expected up to about 15% moisture
content.
• The optimum temperature for insect activity of storage insects ranges from 28 to
38°C.
• The temperatures below 17 to 22°C are considered unsafe for insect activity.
Although it is usually preferable to control insect and mite activity by the
manipulation of the seed environment, i.e., use of fumigants and insecticides.

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• The main problem of chemical control is the adverse effect of chemicals on
seed viability and vigour, and some of them are dangerous to handle.
• However, fumigants which have been used successfully include methyl
bromide, hydrogen cyanide, phosphine, ethylene dichloride and carbon
tetrachloride in 3:1 mixture, carbon disulphide and naphthalene.
• Insecticides – used in seed storage include DDT, lindane and Malathion.

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