Agriculture Reference
In-Depth Information
THE TETrAzoLIuM TEST AS A VIGor TEST
Perhaps no person (other than Lakon) has done more to champion the use of the TZ test than Dr. R. P. Moore,
Professor Emeritus at North Carolina State University. He saw the test as the ideal 'window' through which
one could look to recognize high seed quality and, perhaps more importantly, to understand the reasons for
poor seed performance. Possibly his greatest legacy was his development and promotion of the TZ test as
a way to evaluate seed vigor, especially for large-seeded legumes. Generations of seed analysts and seed
industry professionals have studied and adopted his techniques, not only to learn methods of vigor testing,
but to learn a lasting knowledge and appreciation of seed quality.
The Moore method of vigor testing is exempliied by its use in soybean vigor testing. This method
classiies seed into different levels of vigor: strong=3, medium=2, weak=1, and dead or nonviable=0. These
categories are illustrated and described in Chapter 8 (see Figure 8.6). From a total of 200, the seeds can be
divided into the four numerical categories (above) which can be multiplied by the number in each category
to develop a TZ vigor index. Strong seed lots could theoretically have an index as high as 600, but most
would fall between 400 and 500, depending on the quality of particular lots.
Although this method has been perfected for soybeans and other large-seeded legumes, the principles,
if not the exact procedures, should be applicable to the development of procedures for evaluating vigor in
other species. However, the exact procedures would have to be developed and tested over a period of time
and testing experience. The AOSA Seed Vigor Handbook (2009) contains detailed procedures on using the
TZ test as a vigor test.
ACCurACy of TETrAzoLIuM TEST rESuLTS
The percent viability obtained by the tetrazolium test should be the percent germination expected when
non-dormant seed is germinated under favorable conditions. Favorable germinating conditions assume the
proper use of fungicides for seed lots that are susceptible to mold infection in germination tests.
Properly conducted tetrazolium and germination test results are generally in close agreement for non-
dormant seeds and within the range of random sampling variation. Differences of 3-5% may be due entirely
to unavoidable sampling error. Differences in results are usually smaller with high quality seed than with
medium or low quality seed, with large-seeded crops than with small-seeded crops, and with uniform seed
lots than with non-uniform lots. When discrepancies occur, retests by both methods may help to establish
the causes. Differences between tetrazolium and germination test results, when they occur, may be due to
one or more of the following reasons:
1. Sample differences.
Wide variations in uniformity due to sampling are especially frequent in
chaffy grasses, range grasses with many immature seeds, mechanically injured, hulled lots, and
blended lots.
2. Improper germination testing techniques.
Improper moisture, light, and temperature, or other
conditions may result in erratic germination of seed lots especially sensitive to these factors.
3. Improper tetrazolium testing techniques.
There can be considerable latitude in methods of
staining, but interpretation of results is much more critical.
4. Dormant seed.
It must be recognized that tetrazolium results indicate viability rather than germi-
nability. Viable seeds may be germinable or they may be dormant, and the tetrazolium test does
not differentiate between dormant and non-dormant seeds. Thus, in those seed lots with deep-
seated dormancy, tetrazolium test results are considerably higher than germination test results.
Tetrazolium test results should closely approximate the total of germination plus dormant seed
percentages.
5. Hard seeds.
Hard seed content may vary between the two tests, but the total tetrazolium plus
hard seed percentage should approximate the total germination plus hard seed percentage. To help
