Seed type and characterstics

1. TYPE AND CHARACTERSTICS OF SEED
 Seed are the protectors and propagators of their kind. Thus farmers
entire crop depends on the quality of seed they use for sowing or
planting.
 Seed may be defined as a fertilized ovule consisting of intact embryo,
stored food and seed coat which of viable and has the capacity to
germinate. It may also be called as a “unit of reproduction of flowering
plants and may be described as a plant embryo, in a dormant state,
surrounded by a food supply and protective outer skin or seed coat.”
 Seed is the living link between parent and its progeny. Biologically, seed
is the ripe fertilized ovule and a unit of propagation / reproduction of
flowering plants. Agronomically, a seed material or propagule is the
living organ of crop in rudimentary form use for propagation. It can be
any part of the crop from which a new crop will grow.

2. CLASSES OF SEED
After harvest the seed is subjected to analysis and germination test. The
standards of certification of each crop differ, but in all cases they result in the
sale of quality seeds to the farmers. Four classes of pure seeds are recognized
by the International Crop Improvement Association.
Breeder or Nucleus seed:
It is directly controlled by the organizing or sponsoring plant breeder or
institution. It provides for initial or recurring increase of the foundation seed.
This is the seed that is produced directly under supervision of plant breeder.
Foundation seed:
This includes elite seed, would be seed stock (seeds, tubers, bulbs, plants etc.)
that are so handled as to maintain specific genetic identity and purity that
may be distributed by representatives of an experimental station. Foundation
seeds are the source of all other certified seed classes, either directly or
through registered seed agencies. It as also known as mother seed.

3. Registered seed:
This is the progeny of the foundation seed that is so handled as to maintain
satisfactory genetic identity and purity and has been approved by the
certifying agency. This class of seed is of a quality suitable for production of
certified seed. It can be produced by the farmer and other growers under
special contract with the certifying agency.
Certified seed:
This is the progeny of foundation, registered or certified seed that is so
handled as to maintain satisfactory genetic identity and purity that is
approved by certifying agency. This is the seed designed for the use by the
farmers for crop production. Two classes of certified seeds are produced i.e.
F1 and F2 .
Hybrid seed:
It is the seed produced by crossing two or more homozygous inbred lines to
obtain a desirable type with high yield potential. Only F1 generation of
hybrids is recommended for use as seed for commercial production.

4. Characteristic of good seed
The seeds in its real meaning must possess the following characters:
1. It must be true to its type.
2. The seeds must be healthy, pure and free from all the inert materials and
weed seeds.
3. The seeds must be viable, the germination capacity is up to the standard
and it has been tested recently.
4. The seeds must be uniform in texture and structure.
5. The seeds must be truthfully labeled and produced under due care and
strict supervision so that it does not degenerate quickly.
6. The seed must not be affected by any seed born disease.

5. According to their nature and precaution which seed are produced they are
classified into:
TYPE OF SEED COLOUR OF TAG
1. Breeder seeds or nucleus seeds Gold/ Yellow
2. Foundation seeds White
3. Certified seeds Blue
4. Registered seed Purple
5. Truthfully labeled seeds -
QUALITY OF SEED:
Viability and vigour are two important characters of seed quality. Viability
can be expressed by the germination percentage which indicate the number
of seedlings produced by a given number of seeds. Vigour of seed and
seedlings is difficult to measure, Low germination percentage, low
germination rate and low vigour are often associated. Seeds with low vigour
may not be able to withstand unfavorable condition in the seedbed. The
seedling may lack the strength to emerge if the seeds are planted too deep or
if the soil surface is crusted.

6. Germination is measured with two parameters:
 The germination percentage and germination rate.
 Vigour is indicated by the higher germination percentage, high
germination rate and quicker seedling growth.
Germination percentage is the number of seeds germinated to no. of seeds
planted and its expressed in two ways:
1. The number of days require to produce a given germination percentage.
2. The average number of days required for radicle or plumule to emerge.
SEED PRODUCTION
Purity of seed is important and it has to be maintained during seed
production. Impurities of seed occur due to cross pollination, from a
mechanical mixture etc. Purity of seed is maintained by isolation and
roguing.

7. ISOLATION
Contamination by cross pollination with a different but related cultivar has
to be prevented. It is primarily achieved through distance, but it can also be
attained by enclosing plant or growing of plants in cases, enclosing individual
flowers or removing male flower parts and then employing artificial
pollination. Isolation distance of different field and vegetable crops vary
according to the crop, according to type of seeds and different category of
seeds to be produced like foundation, certified.
Separation of different cultivars is needed to production of self- pollinated
plants to prevent mechanical mixing of seeds during harvest. The main
distance usually specified between plots is 3 meters.
ROUGHING
Off type plants are to be removed before flowering so as to avoid
contamination of off type plants which may arise because recessive genes are
present in heterozygous conditions even in highly homozygous cultivars.
Volunteer plants arising from accidentally planted seeds or from seeds
produced by earlier crops is another source of contamination.

8. CULTIVAR
It is a contraction of cultivated variety. Cultivar is synonymous with variety. A
variety is a subdivision of a species with some special characteristics. There
are several varieties in rice (Oryza sativa) such as Saket- 4, Samba mahsuri,
Sarju-52 and each variety has different characteristics regarding tillering,
plant height, duration, grain quality etc. A cultivar is also a unique population
of plants but it is artificially maintain by human efforts and is named. Many
cultivars cannot continue to exist without human effort. A cultivar should have
proper name so that it can be identified.
HIBRIDIZATION
A hybrid line is the F1 generation of two inbred lines. Hybridization may be
made between two inbred lines (single cross) or two single crosses (double
cross) and inbred line and an open pollinated cultivar (top cross) or between a
single cross and inbred line (three way cross). Inbred lines are true breeding
cultivars that result from enforced self- pollination of selected parent plants
followed by continued selection to a desired type in succeeding generation.
Once are desired has been selected it is maintained by growing plants in
isolation and allowing them to cross pollinate or self- pollinate naturally.

9. SEED ANALYSIS
Optimum crop stand establishment depends upon quality of seed used and
soil environment in which it is sown.
SEED TESTING
It is the procedure for obtaining reliable information on five aspects of seed
quality, viability, purity, vigour, seed health and presence of noxious weed
seed.
VIABILITY TESTING
Seed viability is the capacity of non-dormant seed to germinate under
favorable conditions. Petri dish/ Rolled towel test is done to test the viability
of seed.

10. TETRAZOLIUM TEST
It is the calorimetric test in which a bio chemical reaction causes the test
solution to change colour under certain conditions. Tetrezolium (2,3,5-
triphneyl tetrazolium chloride) solution is colourless but changes to red
insoluble compound called formagan upon being reduced by hydrogen ion.
Viable seeds will change colour to red and dead or non- respiring seeds
remain colourless. This test is quick and reliable.
SEED PURITY
It is the percentage of pure seed (seed without contaminants) in the sample
tested. Contaminants include seeds of other crops, weed seed and inert
matter.
PURE LINE SEED
Pure line seed (PLS) is the percentage of desired cultivar that will
germinate. It is the function of both percent purity and percent germination
it is calculated in percent.
Percent (PLS) = (% Germination x % Purity) / 100

11. SEED VIGOUR
It indicates the properties of seed that determine its potential for rapid,
uniform emergence and development of normal seedlings under a wide range
of field conditions. It is influenced by genetic factors and external
environmental condition during seed development and maturity. An
environment of high temperature and humidity adversely affects seed vigour.
SEED HEALTH
It evaluate the presence of pathogens and insect pest on the seed. Seed health
may be evaluated visually (change in testa, colour, presence of spores etc.)
after incubating on an appropriate medium for disease development. It can
also be determined by biochemical test such as enzyme linked
immunosorbent assay (ELISA).

12. SEED DORMANCY
In induced or secondary dormancy, some seeds may achieve dormancy due
to interaction of seed with environment (temperature). Such dormancy may
continue even after the removal of seed from such environment. When non
dormant imbibed seeds are buried deep in soil, inadequate light,
temperature, excess carbondioxide or a combination of these may induce the
dormancy. Such dormancy lasts until the seed experiences such conditions
necessary to break it.
ENFORCED DORMANCY
Some seeds have dormancy thrust upon them due to conditions of inadequate
oxygen, excess carbondioxide, cold temperature, ethylene etc. induced by
human or nature is called enforced or environmental dormancy. Non
dormant seeds fail to germinate under such forced unfavorable condition.
Weed seeds buried deep in the soil are put under enforced dormancy.

13. RELATIVE DORMANCY
Certain varieties of lettuce germinate well at 20o C or below. However, they
are dormant at high temperature (thermal dormancy) and require light for
germination.
EPICOTYL DORMANCY
Some species of plants show epicotyl dormancy, combination of root and
epicotyl dormancy or double dormancy as in the case of Sanguinaria sps.
This can be overcome by moist storage at 1.0 to 10o C for two to three months
after the seed has germinated to form a root.
MULTIPLE DORMANCY
Some seed required passage of one cold period for the after ripening of
radicle and embryos. During the next summer, the radicle emerges and
become established. However, the epicotyl remains dormant until the passage
of another cold period.

14. ENVIRONMENTAL CONTROLS OF SEED DORMANCY
The environmental controls of seed dormancy are:
1. Temperature: Some seeds required low temperature to break dormancy.
Temperature as low as 10oC is sufficient for breaking dormancy. Low
temperature treatment can depress the inhibitor content of dormant
seeds and high temperatures. Generally increase the dormancy of seeds
rather than improving germination.
2. Light: Light requirement of seeds may serve to bring about germination
when the seeds reaches soil surface or surrounding vegetation has been
disturbed. It is a common requirement for germination of many weed
seeds.
3. Water: The seed coats may contain large amounts of some osmotic
materials which can restrict the amount of water entering the embryo
through osmotic means. Water itself can relieve dormancy in many types
of seed specially from seed coat. Drying can relieve dormancy in some
cases as in tomato seeds.

15. VIABILITY OF SEEDS
Viability is the capacity of seed to germinate to maintain its normal life
process, capacity of growing or maintaining its living state. A viable seed can
germinate under favourable conditions, provided dormancy is removed. A
viable seed may be dormant or non-dormant. Under optimum conditions, a
viable weed seed germinates with in ten days while crop germinates within 7
days.
LONGEVITY OF SEEDS
Longevity or duration of seed viability depends on storage environment and
the genetic constitution of the seed. A given storage environment may
lengthen the life span of one species and shorten that of another. Even when
the seeds is intact with parent plant, the seeds may deteriote with time
depending on the weather and other biotic factors. Relatively dry weather is
favourable for good seeds. The maturity stage at harvest is the major factor
responsible for part of the variation in viability and seed side. Seed may be
non- viable due to various reasons, like mechanical injury, insect, disease
damage and aging.