Measures of Dispersion and Variability: Range, QD, AD and SD
Quality control of seeds
1. QUALITY CONTROL OF SEEDS
OBJECTIVES :
To supply quality seeds in the market.
To determine the quality problem
To obtain information about the planting value of the seeds, etc
METHODOLOGY : By performing different tests in the laboratory.
The report presents the following topics
(i) Seed Sampling
(ii) Physical Purity Analysis of the Seed
(iii) Germination tests of the seed
(iv) Moisture content of the seed
By
D.N. MADHUSHREE
AMITY UNIVERSITY, AIOA
2. SEED SAMPLING
The size and number of seed samples received in the laboratory is quite
large. They need to be reduced to obtain working samples for carrying
out various tests. That means the results can only show the quality of
the seeds that is taken for analysis.
It is important that the submitted samples representative of the lots
from which they are drawn, otherwise calculations based tests results
inaccurate and lead to costly errors.
OBJECTIVE :
To obtain a sample for testing in which the constituents are present in
the same portion as in the seed lot.
Seed lot is a specified quantity of seed of that is physically and
uniquely identifiable (according to the ISTA definition).
TYPES OF SAMPLES:
• Primary sample: it is the small portion taken from one point in the
lot.
• Composite sample: it is formed by combining and mixing all
primary samples taken from the lot.
• Submitted sample: it is the sample submitted to the seed testing
laboratory. The size of the submitted sample is specified in the seed
testing rules.
• Working sample: it is the sub sample taken from submitted sample
in the laboratory, on which one of the quality test is made.
→ The following information will be mentioned in the label of samples
which is to be checked and noted in a record that is maintained by the
laboratory :-
(i) kind of seed
3. (ii) Variety
(iii) Lot number
(iv) Date of the test
(v) Lab test number
(vi) Sellers name and address
Samples that are tested for Germination are packed in a cloth bag,
whereas for moisture content determination, samples are packed
separately in moisture proof bags.
MINIMUN SAMPLING INTENSITY FOR SEED LOTS IN
CONTAINERS
Containers Number of primary samples
1-4 3 samples from each container
5-8 2 samples from each container
9-15 2 samples from each container
16-30 15 samples in total
31-59 20 samples in total
60 or more 30 samples in total
→ Take 3 representative samples in the prescribed manner and mark
and seal.
• 1 sample to be delivered to the person from whom it has been taken,
• 2nd to be sent for analysis to the Seed Analyst of the area,
• 3rd to be retained for any legal precedings
At least 2 persons should be present and obtain the signature of both
the witnesses
METHOS OF OBTAINING WORKING SAMPLES
4. There are many methods that are used for obtaining working samples
for analysis by reducing the submitted sample. Some are mentioned
below
(i) Mechanical method :
In this method mechanical dividers are used
The submitted samples is passed through the divider to make
the seeds mixed and blended.
By repeating this process with one half remaining each time
the sample is reduced to desired size.
There are several types of mechanical dividers viz., Boerner
divider Centrifugal or Gamet divider.
(ii) Random cup method :
In this method few small cups are placed in tray.
After the mixing the seed is poured uniformly over the tray.
The seeds that fall into the cup re taken as the working
sample.
This is used when working samples of about 10g is required.
(iii) Hand halving method :
In this method the seeds are 1st poured on a clean surface or
newspaper and thoroughly mixed.
By using hand we divide the seeds into 2 parts.
Now each half is divided into 4 parts, and then for 8 parts.
The halved portions remain and alternate portion are used.
This process is repeated till we get a required working
sample.
5. PURITY ANALYSIS OF SEED
PHYSICAL PURITY TESTING
Physical purity test tells us about the amount/ proportion of the pure
seed present in the seed lot as well as the amount of other crop seed,
weed seed, inert matter by weight in %.
OBJECTIVE:
(i) To identify various species of the seeds and inert particles
comprising the sample.
(ii) To know the % composition by weight of the sample that
has to be tested
Thus, it helps in:
i. Improving the plant stand (by increasing the pure seed component).
ii. Raising a pure crop (by eliminating other crop seed and weed
seeds).
iii. Raising a disease free-crop (by eliminating inert matter).
iv. In the use of seed drill (by selecting uniform particles).
IMPURITIES
Other crop seeds : The seeds that are of the crops other than the kind
examined.
Weed seeds : It includes those seeds which are generally recognised as
Weeds.
Inert matter : Inert matter shall include seed units and all other matter
and structures not defined as pure seed or other seed.
APPARATUS : Aids such as magnifiers, reflected light, sieves and
blowers are used in separating the working sample into its components
parts.
6. Hand lenses and binocular microscopes are used for accurate
identification and separation of small seed units.
Sieves are used in separating trash, soil and other small particles in
the working sample.
Seed blowers are used to separate light-weight materials such as
chaff and empty florets in grasses from the heavier seeds.
METHOD OF PURITY ANALYSIS :
1. Obtaining working sample
Since the size of the seed lot that is received for testing is large,
we need to reduce it to obtain a working sample to carry out
various test.
There are many methods to obtain working sample which is
already explained in the previous activity (seed sampling).
2. Separation
In this method the impurities which include the weed seeds, other
crop seeds, inert matter are separated from the working sample.
Aids such as spatula or forceps, work-board, purity dishes are
used in this process.
3. Identification
After the separation of impurities from the concerned seed is
completed , we identify and note down each kind of the inert
matter, weed seeds and other crop seeds.
The sample is examined to check whether it conforms to the name
under it was submitted.
4. Weighing of purity components
All the 3 components are weighed .
If there is loss or gain between the weight of the three
components and the original samples, other test is conducted.
7. 5. Check or duplicate test
A duplicate test is carried out of two half sample and one whole
sample, if the difference exceed the permissible tolerance,
another analysis is done.
GERMINATION TEST
OBJECTIVE :
To know the viability or the seed quality and to predict its
performance in the field.
To obtain information about the planting value of the seed
sample.
The first step is to draw a working sample from the submitted sample.
This is done by taking samples from different parts of the different
bags.
ESSENTIAL MATERIAL:-
A. Substratum : The substratum serves as moisture reservoir and
provides a surface or medium for which the seeds can germinate
and the seedlings grow. The commonly used substrate are sand,
germination paper and soil.
1. Sand
• Size of sand particle- Sand particles should not be too large or too
small. The sand particles should pass through 0.80 mm sieve and
retained by 0.05mm sieve.
• Toxicity- Sand should not have any toxic material or any pathogen. If
there is presence of any pathogen found then the sand should be
sterilized in an autoclave.
8. • Germination tray-When we use the sand, germination trays are used
to carry out the test. The normal size of the tray is 22.5 x 22.5 x 4 cm.
The tray may either zinc or stainless steel.
Method of seed placement:
I. Seed in sand(S)-Seeds are planted in a uniform layer of moist
sand and then covered to a depth of 1 to 2 cm with sand.
II. Top of sand (TS)-Seeds are pressed in to the surface of the sand.
Spacing: We must give equal spacing on all sides to facilitate normal
growth of seedling and to avoid entangling of seed and spread of
disease. Spacing should be 1-5 times the width or diameter of the seed.
Water: The amount of water to be added to the sand will depend on
size of the seed. For cereals, except maize, the sand can be moistened
to 50% of its water holding capacity. For large seeded legumes and
maize sand is moistened to 60% water holding capacity.
2. Germination paper
Most widely used paper substrates are filter paper, blotter or towel
(kraft paper). It should have capillary movement of water, at vertical
direction (30 mm rise / min.). It should be free from toxic substances
and free from fungi or bacteria. It should hold sufficient moisture
during the period of test. The texture should be such that the roots of
germinating seedlings will grow on and not into the paper.
Methods of seed placement:
I. Top of paper : Seeds are placed on one or more layers of moist
filter paper or blotter paper in petri plates. These petri plates are
covered with lid and placed inside the germination cabinet. This
is suitable for those seeds which require light.
9. II. Between paper (BP): The seeds are germinated between two
layers of paper. The seeds are placed between two layers of paper
and rolled in towels. The rolled towels are placed in the
germinator in an upright position.
B. Germination apparatus
1. Germination cabinet / Germination room- This is called
chamber where in temperature and relative humidity are
controlled. We can maintain the temperature, relative humidity
and light required for different crops.
2. Room germinator- It works with same principle as that of
germinator. This is a modified chamber of larger one and the
worker can enter into it and evaluate the seedlings. Provisions are
made to maintain the temperature and relative humidity. This is
used widely in practice.
3. Seed counting board- This is used for accurate counting and
spacing of seeds. This consists of 2 plates. The basal one is
stationary and top one is movable. Both top and basal plates are
having uniform number of holes viz., 50/100, when the plates are
in different position. After taking the sample, the top plate is
pulled in such a way that the holes are in one line so that the fixed
number of seeds falls on the substratum.
4. Vacuum seed counter- Consists of a head, pipe and wall. There
are plates of 50 or 100 holes which can be fitted to the head.
When vacuum is created the plate absorbs seeds and once the
vacuum is released the seeds fall on the substrate.
10. 5. Impression board- Made of plastic / wood with 50 or 100 holes
/ pins. Here the knobs are arranged in equal length and space. By
giving impression on the sand it makes uniform depth and
spacing for seed.
EVALUATION OF GERMINATION TESTS
The germination test is evaluated as
and un-germinated seeds
Normal seedlings
Abnormal seedlings
Hard seeds
Fresh Dead seeds
ISTA classified the seedlings into different categories based on the
development of essential structures.
I. Normal seedlings
Seedlings which has the capacity for continued development into
normal plant when grown in favourable conditions of soil, water,
temperature and light.
II. Abnormal seedling
Seedlings which do not show the capacity for continued development
into normal plant when grown in favorable condition of soil, water,
temperature and light.
→Types of abnormal seedlings:
Damaged seedlings- Seedlings with any one of the essential structures
missing or badly damaged so that the balanced growth is not expected.
Deformed seedlings- Weak or unbalanced development of essential
structures such as spirally twisted or stunted plumule or hypocotyls or
epicotyls, swollen shoot, stunted roots etc.
11. Decayed seedlings- Seedlings with any one of the essential structures
showing diseased or decayed symptoms as a result of primary infection
from the seed which prevents the development of the seedlings.
III. Hard seedlings : Such which do not absorb moisture till the end
of the test period and remain hard (e.g.) seed of leguminaceae and
malvaceae.
IV. Fresh and un-germinated seedlings : Seeds which are neither
hard nor have germinated but remain firm and apparently viable
at the end of the test period.
Seeds at the end of the test period are neither hard or nor fresh or
have produced any part of a seedling. Often dead seeds collapse
and milky paste comes out when pressed at the end of the test.
SEED MOISTURE CONTENT
The seed moisture content (mc) is the amount of water in the seed. It is
usually expressed as a percentage on wet weight basis in any seed-
testing laboratory. The seed moisture content is the most vital
parameter, which influence the seed quality and storage life of the seed.
Seed moisture content is closely associated with several aspects of
physiological seed quality. For example, it is related to seed maturity,
optimum harvest time, mechanical damage, economics of artificial seed
drying, seed longevity and insect and pathogen infestation.
OBJECTIVE: To determine the moisture content of seed
IMPORTANCE : It influence the seed quality and storage life of the
seed.
EQUIPMENTS : Analytical balance, desiccator, notebook to record
details.
DETERMINATION OF SEED MOISTURE CONTENT :
12. The seed moisture content can be measured directly by loss or gain in
seed weight. These include
1. Desiccation method
2. Vacuum drying method
3. Direct weighing balance
4. Phosphorous pentaoxide method
5. Oven-drying method
6. Distillation method
7. Microwave oven method
PROCEDURE FOR OVEN DRYING METHOD :
(i) First we weigh an empty numbered container along with its
lid using an analytical balance, and note down in a
notebook.
(ii) Then we add 5g of the prepared seed in the container and
weigh it.
(iii) Again we note down the new weight of the container, and
place it aside carefully.
(iv) This is continued for all samples in the same way.
(v) When all the samples have been weighed into numbered
containers , we place them in the oven at 101-105 c.
(vi) After 16-17 hours, remove the containers from the oven and
place them in a desiccator to cool at room temp.
(vii) After it cools down we weigh the containers and note the
weight in a notebook
CALCULATION OF THE MOISTURE CONTENT :
Wt. of fresh seeds- wt. of dry seeds
% of moisture content = ------------------------------------------------------
--- x100
Wt. of fresh seeds
