SEED SCIENCE AND TECHNOLOGY
SEED TESTING
Seed Testing refers to evaluation of
seed in terms of purity and germination. Seed testing is done to determine the
quality of seed for planting purposes. Seed testing is essential for seed certification,
because analysis of purity and seed viability are prerequisites for the process
of seed certification. Three important tests, viz, 1) Purity Test, 2)
Germination Test, and 3) Seed Moisture Test are carried out in the seed testing
laboratories. In India there are 60 seed testing laboratories which are located
in different states.
1. Purity Test
This test is useful in determining the
physical purity of seed. A composite sample which is true representative of a
seed lot is used for seed testing purpose. From the composite sample, a small
sample known as working sample (generally 25%) is drawn for testing purpose.
International Seed Testing Association (ISTA) rules are adopted for seed
testing. As per ISTA Rules, the sample is separated into three components, viz.
(1) pure seeds, (2) inert matter, and (3) other seeds.
(1)
Pure seeds: It refers to the seeds
of variety under testing.
(2)
Inert matter:
In
includes broken or damaged seeds, leaf bits, straw, soil particles, stones etc.
(3)
Other seeds: In includes seeds of
other variety of a crop, other crop seeds and weed seeds.
Name of the crop
|
Objectionable weeds
|
Scientific name
|
Wheat
|
Hirankhuri
|
Convolulus
arvensis
|
Rice
|
Wild rice
|
Oryza
sativa var fatua
|
Mustard/Rapeseed
|
Satyanashi
|
Argemone
mexicana
|
Methi
|
Sanji
|
Melilotus
spp.
|
Lucerne
|
Dodder
|
Cuscuta
spp.
|
Berseem
|
Chicory or kansi
|
Chicorium
intybus
|
Lettuce
|
Wild lettuce
|
Luctuca
seriola
|
Okra
|
Wild okra
|
Abelmoschus
spp.
|
Cucurbits
|
Wild cucurbits
|
Cucurbita
spp.
|
The
percentage of above three components is worked out on weight basis and reported
in the seed testing report. The physical purity of 98% is required in majority
of crops for certification purpose. Moreover, the sample should be free from
seeds of other variety of the crop and from objectionable weed seeds. The objectionable weeds are either wild relatives of a
crop or such weed species whose seeds cannot be separated from the seeds of
main crop. List of some objectionable weeds of different crops is presented in above
table.
2. Germination Test
Germination
refers to emergence of normal seedlings from the seeds under ideal conditions
of light, temperature, moisture, oxygen and nutrients. Germination test is essential
to determine planting value of the seed. Germination test indicates ability of
seed to develop in to normal plants under normal field conditions. Germination
is expressed in percentage. As per ISTA rules, the sample is divided into five
components, viz. (1) Normal seedlings, (2) Abnormal seedlings, (3) Hard seeds,
(4) Fresh ungerminated seeds, and dead seeds are described below:-
(1) Normal seedlings:- It includes seedlings with normal
growth of root and shoot. The minor defects in the structure are ignored if the
seedling growth is vigorous.
(2) Abnormal
seedlings:- Such seedlings
do not have capacity to develop in to normal plants. This group includes
defective seedlings that lack either cotyledon or primary root and have stunted root
(3) Hard seeds:- The seeds which do not absorb water are
known as hard seeds. Such seeds are common in Leguminosae and Malvaceae. Seed
coats of such seeds are impermeable to water.
(4) Fresh
ungerminated seeds:-
These are viable seeds, absorb water but do not germinate and remain fresh in
germination test.
(5) Dead seeds:- These
are unviable seeds.
Germination test
is conducted in replications and average value is worked out. Normal seedlings
are used for reporting of germination percentage. Seed incubator is used for
germination purpose. The seed viability is also tested with a chemical known as
tetrazolium
chloride. For this test, first seeds are soaked in water for 24 hrs. the
seeds are then split longitudinally in to two halves and dipped in to 1%
aqueous solution of tetrazolium chloride in the petri dish for four hrs. Then
these seeds are taken out and washed with fresh water. Only viable seeds takeup
the stain and the dead seeds remain colorless. Counting of stained seeds will
give germination percentage. This is the rapid method of germination test.
3. Moisture Test:- Seed moisture is
tested with the help of MOISTURE METER.
Knowledge of seed moisture is essential for seed storage.
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