What is a Tetrazolium Chloride Test?
The TZ test is often referred to as a quick germination test because results are usually available within 24 to 48 hours.
How is the TZ Test Different From a Germination Test?
The TZ test is good for an early and quick snapshot of seed viability, but doesn’t replace the more comprehensive seed <germination test>.
That’s partly because the TZ test is not officially recognized by the CFIA (except for western wheatgrass where the TZ result can be added to the germination for a final germination total).
Why do a TZ Test?
Despite it being thought of as a “quick germ” test, a TZ test is actually more laborious to do than a proper germination test.
Ask for a TZ test if you:
- Need a rapid evaluation of seed viability.
- Detect seed weaknesses, before they show up in germination tests.
- Want timely guidance for quality control programs.
Keep in mind that a TZ test:
- Doesn’t tell you anything about fungal infection or chemical damage.
- Won’t reveal any seed dormancy issues.
How is a TZ Test Done?
Seeds to be tested are soaked in water overnight. Once imbibed, they’re cut in half with a scalpel to expose the embryo. The halved seeds are then put in a tetrazolium chloride solution, and observed for staining.
How are TZ Tests are Evaluated?
The amount staining tells the tale. Living tissue contains dehydrogenase enzymes, which reduce the tetrazolium chloride to formazan, a reddish, water-insoluble compound. This reaction only happens in or near living cells that are releasing hydrogen as they respire, so staining indicates the seed is living. But “living” is relative. Analysts look for three things:
- Normal red colour: indicates the seed tissue is sound and releasing hydrogen slowly, as it should.
- Dark red colour: indicates seed tissue that’s beginning to deteriorate. Essentially, dying cells are “breathing” faster, releasing hydrogen faster, which leads to greater staining.
- No colour: indicates dead seed tissue. No respiration means no hydrogen, so no staining.
Interpreting TZ test results requires considerable skill on the part of the technician, who has to balance what the staining patterns reveal against the results of a proper germination test, as well as what a visual inspection of the seed lot tells them about overall quality.
TZ Test Results
This test will give you an estimate of the maximum percentage of seeds that have potential to produce normal seedlings. Results are noted in the remarks section of the Certificate of Seed Analysis issued by the seed lab.
TZ + Germination Test?
When properly conducted, the results of TZ and germination tests conducted on the same seed lot are usually quite close, and certainly within the range of normal sampling variation. Indeed, a difference of between 3% and 5% is likely due to an unavoidable sampling variation error.
Still, differences are usually smaller when seed quality is high, in large-seeded crops and with uniform seed lots.