The Tetrazolium Chloride (TZ) test is often called the quick germination test. It’s a chemical test used to determine seed viability, and results are usually available within 24 to 48 hours.
How is the TZ Test Different From a Germination Test?
The TZ test can give you an early and quick snapshot of seed viability but is not a replacement for the more comprehensive seed germination test.
In Canada, the TZ test is not officially recognized by the CFIA (except for western wheatgrass where the TZ result may be added to the germination for a final germination total). In the United States, the TZ test can be used as a replacement for a germination test, although a follow-up germination test is usually recommended.
This test has a long history. Early research and development done by Professor Dr. Georg Lakon, Dr. Helene Blat and professor Dr. W. Lindenbein, led to the formation of the tetrazolium committee with the International Seed Testing Association (ISTA) in 1950.
In 1974, Professor R.P. Moore became chairman of the committee. In 1983 he presented a handbook to the ISTA Congress in Ottawa, which has become the standard that all official seed laboratories use.
Why do a TZ Test?
Advantages of the TZ test are:
Disadvantages of the TZ test are:
How is a TZ Test Done?
How are TZ Tests are Evaluated?
Dehydrogenase enzymes present in living tissue reduce the tetrazolium chloride to formazan, a reddish, water-insoluble compound. This reaction occurs in or near living cells, which are releasing hydrogen in respiration processes.
Depending on size, all seeds are examined under a microscope at 10-30 power. Larger seeds, such as peas, may be examined without a microscope. Analysts look for three things:
An accurate interpretation of the TZ test depends on:
The TZ test is basically sound and widely used among many accredited laboratories in Canada and the United States as well as Europe. Accuracy of results depend largely upon the training, experience, education, background and other general qualifications of the analysts.
TZ Test Results
Regardless of how they are reported, TZ test results for viability give you an estimate of the maximum percentage of seeds that have the potential to produce normal seedlings.
Properly conducted TZ and germination test results are generally in close agreement and within the range of normal sampling variation. Differences of 3% to 5% may be due to an unavoidable sampling variation error.Differences between TZ and germination test results are usually smaller in high quality seed than in low quality seed, with large seeded crops than with small-seeded crops, and with uniform seed lots than with non-uniform lots.