Agriculture Reference
In-Depth Information
7
Tetrazolium
Testing
No seed laboratory can afford to operate and meet the needs of the modern seed industry without offering
tetrazolium (TZ) testing services to its customers. Proits in the modern seed industry often demand rapid
information about seed quality (viability) that can be provided only by the tetrazolium test. It is the classic
quick test
in that it provides a rapid determination of seed viability. It can also provide valuable insights
into reasons for loss of viability, such as injury caused by frost, sprouting, chemical treatment, mechanical
damage, structural abnormalities and other factors. Perhaps no other test can provide so many insights into
reasons for loss in viability and seed quality. Although tetrazolium test results may not be considered ofi-
cial for the purpose of seed law enforcement labeling in North America (AOSA Rules), the test is used by
many seed certiication agencies and is widely supported by farmers and the seed industry. Furthermore, it
is an invaluable method of rapidly evaluating seed lots before decisions are made about further condition-
ing, treatment, or disposition. Consequently, it represents one of the most practical and important of all tests
conducted by seed testing laboratories.
History
The tetrazolium test was developed and perfected in Germany during World War II by Dr. George Lakon.
Dr. Lakon was born in Greece but worked in Germany most of his professional life. Previous work by
Lakon and others had established the “topographical” method of biochemical seed testing in which it was
demonstrated that speciic embryo structures had to be alive for the seed to germinate normally. However,
the most useful chemicals for indicating viability, selenium and tellurium, were toxic to humans, which
limited the usefulness of the test. With the substitution of non-toxic tetrazolium by Lakon, the “topographi-
cal tetrazolium test” was established, and Lakon's irst publication on the method appeared in 1942. The
method is now widely accepted and used successfully throughout the world.
PrInCIPLES
In performing the tetrazolium test, the analyst critically examines the embryo and associated structures
of the seed to determine its potential for developing into a normal seedling under conditions suitable for
germination. This determination is based on the embryo's staining reaction when placed in a tetrazolium
solution, together with the physical condition of associated seed structures such as broken radicle tips,
decomposed endosperm or cotyledons.
To successfully conduct a tetrazolium test, the analyst must have a knowledge of seed and seedling
structures (e.g., the shape and location of the embryo, the type of storage tissues, the nature of seed coats,
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