PRINCIPLES OF CROP PRODUCTION
ABT-320
(3 CREDIT HOURS)
LECTURE 08
DETERMINING SEED QUALITY
SEED CLASSIFICATION
SEED TREATMENTS
FACTORS AFFECTING SEED GERMINATION
DETERMINING SEED QUALITY
Seeds of high quality should be:
• true to its kind or variety --> these are varietal purity characteristics
• contain a minimum of impurities --> these are seed lot characteristics
• have high establishment rates in the field --> this is seed viability
So the 3 main criteria for describing seed quality are:
1. VARIETAL PURITY CHARACTERISTICS
Varietal purity is about the genetic purity or the purity of the cultivar. It can be
described by its physical, chemical and crop characteristics.
• PHYSICAL CHARACTERISTICS
Every variety has seeds with specific length and width, shape, size, color and
aroma. These characteristics can be tested by calculating the 1000 grain
weight, measuring color using the naked eye or a colorimeter and so on.
• CHEMICAL CHARACTERISTICS
Various chemical tests can also be used to see the difference between
varieties. Amylase content, alkali digestion color, gel consistency and brown
rice protein are all different between varieties.
• CROP CHARACTERISTICS
Most of the time, a variety has always the same plant height, time to maturity,
plant color and plant growth habit. (Small variations may occur especially in
harsher environmental growing conditions.)
2. SEED LOT CHARACTERISTICS
A description of the seed lot includes the level of impurities, seed size, and
damaged, deformed or diseased seed.
• IMPURITIES
Impurities are weed seeds, seeds of other crops or species, and inert material
such as stones, dirt or twigs. It is expressed on a percentage basis by weight.
• SEED SIZE
Plumpness and/or fullness are usually good seed characteristics. They mean that
the seed has the potential to produce vigorous seedlings under favorable
conditions.
• DAMAGED, DEFORMED OR INFECTED SEED
High quality seed should be free from seed-borne diseases, insects and other
extraneous matter. They should also be free from various types of mechanical
injury that reduce germination and seedling vigor.
3. SEED VIABILITY
The viability of the seed in the field will depend mainly on its stored moisture
level, germination potential and its vigor.
• MOISTURE CONTENT (MC)
Moisture content has a big influence on the life and vigor of the seed. The
MC should be less than 14% and preferably less than 13% if stored for a long
time.
• GERMINATION (IN %)
This is the proportion of the total number of seeds that are alive. This is
tested by counting the number of seeds that germinate.
Many varieties have a dormancy period immediately after harvest. Stored
under traditional open systems the germination rate of most rice seed begins
to go down fast after 6 months.
3. SEED VIABILITY
• SEED VIGOR
Seed vigor gives a very good idea of the possible field performance, and
subsequently, the field planting value.
While the speed of germination varies slightly across varieties, seeds
should absorb moisture and within 2 days produce a root and a first leaf in
4 days. Then the seed has germinated. How well the germinating seed
continues to grow and survive determines crop establishment.
Seed vigor is all these things that determine the level of activity and
performance of the seed during germination and seedling emergence.
Seed vigor is an important factor in seedling establishment.
• Seeds low in vigor produce weak seedlings that are susceptible
(=vulnerable) to environmental stresses.
• A high level of vigor in seeds provide for early and uniform stands which
give the growing seedlings good resistance against various environmental
stresses.
SEED CLASSIFICATION
A plant breeder develops a new variety – it is very good and every farmer
wants the variety. The seed marketing companies want the seed to meet
the high demand from the farmers. In this chain from plant breeder to
farmer, there are a number of steps and, at each step the system must
ensure that the original variety is truthfully produced.
NUCLEUS STOCK
• When a new variety is released there is very little seed. There may be only
a handful of seed selected by the breeder from individual plants. This seed
is the basis of a variety and is known as the Nucleus Stock. This nucleus
stock must be managed with great care so that all seed produced from it
remains true to the new variety. This is the most important step and is the
responsibility of the plant breeder who developed the variety.
• The nucleus stock seed is not available to farmers. The next step in the
chain from plant breeder to farmer is that the plant breeder develops
Breeder Seed.
BREEDER SEED
• Breeder seed is the seed of the highest purity of the new variety. It is produced
by the breeder and provided by the breeder’s institution to agencies for
further multiplication. If you are from a non-governmental organization
(NGO) seed business or a private company that is producing seed, you may
need to purchase breeder seed from a research institution. Breeder seed is the
most expensive seed to buy.
• As a private company or an NGO business you need breeder seed or
foundation seed. Once again your interest is quality.
FOUNDATION SEED
• Foundation seed is the seed produced from growing breeder seed. It is
produced by trained officers of an agricultural station to national
standards and handled to maintain the genetic purity of the variety. It may
be produced by a government seed production farm or a private
organization – this will depend on the regulations of the country.
Foundation seed is less expensive than breeder seed.
• If your interest is to have quality seed to grow paddy, you will not be
interested in buying breeder seed or foundation seed. You need registered
seed or truthfully labeled seed.
REGISTERED SEED
Registered seed is produced from growing foundation seed. It is grown by
selected farmers in a way that maintains genetic purity. Production has
undergone field and seed inspections by Seed Inspectors to ensure
conformity with standards.
CERTIFIED SEED
Certified seed is produced from growing foundation or registered seed. It
is grown by selected farmers to maintain sufficient varietal
purity. Production is subjected to field and seed inspections prior to
approval by the certifying agency. Harvest from this class is used for
producing again.
QUALITY DECLARED SEED
Truthfully labeled seed or Quality Declared Seed is produced from
foundation, registered or certified seed. It is not subjected to inspection
by a certifying agency. As this seed is not inspected, its quality is
dependent on the good reputation of the farmer who has grown the seed.
His good name in the village is important.
TODAY’S MODERN SEED TREATMENTS
• Modern seed treatment products offer control of target pests and
diseases and ensure the establishment of healthy and vigorous plants.
Their formulation and industrial application also contribute to
improvement in growers’ and workers’ safety and stewardship of the
environment.
• Today’s modern seed treatment products have to meet not only efficacy
standards but also safety and environment standards. The newest active
substances and formulations provide long-lasting, broad spectrum,
control of pests and diseases (depending on the specific active
ingredient).
• Modern formulated seed treatment products are precisely blended
products consisting of several active ingredients, special wetting agents,
colorants and sometimes bird repellents which are rigorously tested for
their safety to the seed, the users and the environment.
GOOD SEED TREATMENT PRACTICE
• The seed industry and seed treatment applicators use an array of quality
management systems to optimize the application process. These quality
systems define the treatment process, handling of treated seed, worker
protection, environmental stewardship and provide the information
required to facilitate the safe and legal treatment of seed and the disposal
of treated seed.
• Seed treatment requires adequate standards and good application
methods. These should be agreed upon between the involved parties on a
case-by-case basis to insure producer, applicator, seed and environmental
safety in the most cost efficient manner.
SEED TREATMENT
Seed treatments, in broad terms, are the application of biological, physical
and chemical agents and techniques to seed that provide protection to
seeds and plants and improve the establishment of healthy crops.
THE ROLE OF SEED TREATMENT
• Diseases and pests affecting crops can have devastating consequences in
agricultural and horticultural production if not properly managed.
• Breeding is an excellent tool to build resistances against pests and
diseases in the plants. However, breeding alone does not address all of the
agronomic challenges, therefore crop protection products are often
needed and used for good crop management. These crop protection
products can be applied during the growth of the crop but can also be
added to the seed as a seed treatment. Seed treatments have played and
are still playing a significant role in the history of mankind, in staving off
hunger and starvation by improving the establishment of healthy crops.
EVOLUTION OF SEED TREATMENTS
• Some of the first recorded seed treatments are the use of sap from onion
(Allium spp) and extract of cypress in the Egyptian and Roman periods.
• Salt water treatments have been used since the mid-1600s and the first
copper products were introduced in the mid-1700s. Other key milestones
were the introduction of arsenic, used from 1740 until 1808 and the
introduction of mercury, used from 1915 until 1982. Until the 1960s seed
treatments had been only surface disinfectants and protectants. The first
systemic fungicide product was launched in 1968. This systemic fungicide
had not only seed surface activity but also moved into the plants
protecting the young seedlings from airborne pathogens. Since the 1990s
the crop protection and seed industries have developed and adopted new
classes of fungicide, insecticide, and nematicide chemistry, expanding pest
control while reducing user and environmental impact.
• The seed and seed treatments industries have a long history of
partnership and dedication in providing growers with high quality seed.
Today the seed must be as pest- and disease-free as possible and the
treatment must provide protection against pests and diseases during
germination, emergence and growth of the plant.
SEED TREATMENT AND INTEGRATED PEST
MANAGEMENT
• The FAO International Code of Conduct on the Distribution and Use of
Pesticides (Revised version) adopted in 2002 defines Integrated Pest
Management (IPM) as meaning “the careful consideration of all available
pest control techniques and subsequent integration of appropriate measures
that discourage the development of pest populations and keep pesticides and
other interventions to levels that are economically justified and reduce or
minimize risks to human health and the environment. IPM emphasizes the
growth of a healthy crop with the least possible disruption to agroecosystems and encourages natural pest control mechanisms”.
• Seed treatments can be used as a primary tool in a successful Integrated Pest
Management Program for sustainable agriculture since they target the pests
and diseases with smaller amounts of active ingredients per hectare and are
not introduced into the atmosphere. In many cases, without the use of seed
treatment, growers would have great difficulty in controlling certain seedborne and early season seedling pests and diseases and would have to resort
to more expensive and less environment-friendly methods.
HOW SEED TREATMENTS ARE APPLIED?
• Seed treatment is a term that describes both products and processes. Processes
range from basic dressing to coating and pelleting. In all cases, the basis of good
application techniques is to deliver the product to the seed at the correct dose
and as uniformly as possible from seed to seed.
• Seed Dressing: The most common method of seed treatment. The seed is either
dressed with a dry formulation or wet treated with a slurry or liquid formulation.
Dressings are applied both on-farm or in specialized seed treatment facilities.
• Seed Coating: A special binder is used with a formulation to enhance adherence
to the seed and begin to impact seed size and shape. Coatings require advanced
treatment application technology.
• Seed Pelleting: The most sophisticated seed treatment technology, resulting in
changing the physical shape of a seed to enhance plantability and handling.
Pelleting requires specialized application machinery and techniques and is the
most expensive of the applications.
HOW SEED TREATMENTS ARE APPLIED
Depending on the type of desired treatment, various machines can be
used. The more complex the treatment, the more cost is involved. Many
modern treatment machines can deliver specific formulation and dosing
by way of a direct injection process. The most sophisticated treatment
machines can deliver the various formulations and additives as layers on
the seed, which allows precise placement of the active ingredient.
MEETING USERS’ EXPECTATIONS
• Regulatory authorities, seed distributors and seed users have established
high standards for the seed and seed treatment industries regarding the
quality of a seed treatment and its application to the seed. The
expectations are that the treated seed will be easy to plant and that the
seed treatment will be effective in the field, safe to the applicators, the
growers and the environment.
• The industry recognizes that seed treatment must provide “added seed
value” (e.g. better emergence, higher seedling establishment, improved
crop health, higher yields and improved crop quality). It expects seed
treatments to be easy to handle and apply to seeds, to complement and
protect genetic improvements, to function as part of IPM (Integrated Pest
Management), to be safe and cost effective in use and to reduce personal
and environmental risks.
• Seed treatments, compared to conventional application of crop protection
products, offer convenience to the grower, saving time and energy and
reducing application efforts.
ENVIRONMENTAL FACTORS AND
SEED GERMINATION
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Water
Temperature
Oxygen
Light
SEED WATER UPTAKE
• Seed-soil contact varies with seed size, shape.
• Small seeds and smooth coated seeds most efficient in H2O uptake.
• Increased soil contact; larger surface area/volume ratio.
OXYGEN AVAILABILITY IN SOIL
• Found to vary from 19% to 21% in a wide range of conditions (time of year,
tillage, soil depth, soil type)
• Exception may be when seeds are encased in soil particle aggregates,
sealing them off from gas exchange with the soil environment
OXYGEN SOLUBILITY IN WATER
• O2 solubility increases with decreasing temperatures (twice as much 02
available to seeds at 5oC than at 40oC)
• Literature on O2 role in seed dormancy is sometimes conflicting,
inconclusive because of these solubility differences.
EFFECTS OF LIGHT ON SEED
GERMINATION
• Light can promote or inhibit germination
• Sensitivity to light is important to seed banks and other ecological
responses, providing a mechanism for optimal timing of seedling
establishment
SOWING TIME
PRIMARY SYMPTOMS
Excessively high or low temperatures or moisture stress at heading
indicate a possible problem of sowing date. Wheat is most sensitive to
temperature and water stress during the flowering and heading stages.
SOWING TIME
Sowing at the wrong time exposes the crop to temperature and moisture
extremes.
There is an optimum time for sowing for every location determined
primarily by weather and availability of the field and irrigation water, but
also by the variety that is being used and the likely timing of serious
disease in the area. The best sowing time is that which gives the highest
yield within the local limitations. It is usually decided on by working
backwards from the date that is best for anthesis. Once the best sowing
time has been determined, any delays in sowing at that date can reduce
yield. Yield loss from delays will generally be greater in hotter regions.
SOWING TIME
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The most suitable variety will be one that fits its growth stages into the
available time. When deciding on variety and calculating your sowing date
you should bear in mind the following risks:
Frost from spike emergence through early grain filling should be avoided.
High temperature during anthesis and early grain filling is best avoided.
Avoid overcast and misty conditions during 2 weeks before to 1 week after
anthesis - solar radiation should be high for this period.
Irrigation water should be available from stem elongation through anthesis
to early grain filling.
Avoid varieties that run to head too quickly before producing tillers unless
the available season demands a very short duration crop.
Think not only of the current crop. Work out the best compromise planting
times for all sequential crops in the rotation so that annual production is
optimized.
THE END