The Tetrazolium Test provides a quick estimate of seed viability.
With results within one to two days this test can be very
helpful when time is a factor or for species which have very
long germination requirements.
Tetrazolium testing originated in Germany during the early
1940's. George Lakon and colleagues discovered that embryonic
tissues had to be alive and respiring in order for the seed
to germinate normally. Their early biochemical work led to
the development of a 'topographical' staining method for determining
seed viability. The early experiments used toxic chemicals
such as selenium and tellurium to indicate viability, which
limited their usefulness in seed testing. In 1942, Lakon developed
a method using less-toxic tetrazolium as the viability indicator.
Source: Tetrazolium Testing Handbook, Contribution No.29,
When your seed arrives, we mix it down to obtain a working
sample and randomly select 200 pure seeds for testing. Most
crop kinds are then placed on moist blotters overnight to
imbibe water. The next morning we cut or poke the seeds (depending
on the type and size of seed) and then immerse them in tetrazolium
chloride solution and incubate. The amount of time and temperature
required for staining varies depending on the species being
tested. When the staining is complete the solution is drained
and the seeds are examined under the microscope.
Evaluation of the tetrazolium test requires experience and
a sound knowledge of seed structures. This test is very labour
intensive and is largely dependent on the level of expertise
of the analyst. At Seed Check we are highly experienced in
this area and find our results correlate very closely to germination
results in most cases. The tetrazolium test is not a test
accredited by the Canadian Food Inspection Agency and may
not be used for grading purposes except as stated in the Methods
and Procedures for Testing Seed.
4.7.7 Tetrazolium testing
Tetrazolium test results may be used as the basis
for grading of fall planted cereals, but must be confirmed
by a standard germination test. For Western wheatgrass,
a tetrazolium test is to be conducted to estimate the
percentage dormant seeds (See Sec. 4.7.2). For other crop
kinds, tetrazolium test results are to be used for information
only, not as the basis for grading.
Chemical and fungicide damage is not detectable by the
TZ test. A standard germination test is usually considered
more accurate than a tetrazolium test but not necessarily.
Native seed which can be highly dormant and unresponsive in
laboratory conditions may have a more accurate result via
the tetrazolium test. A germination test is recommended in
addition to a TZ, particularly if you are planning to sell
your seed based on your TZ result.