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, Revised 2000.
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.