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Evaluation of Tetrazolium (TZ) Tests on Small Vegetable Seeds
A presentation by Nancy Vivrette, RST, Ph.D.
Ransom Seed Laboratory

Viability tests can provide valuable information about seed quality.  A viability test determines if a seed is dead (non-viable) or alive (viable).  There are many ways to measure viability.  A viability test can be a direct measurement, such as a standard germination test, or an indirect estimate.  A germination test determines if a seed will produce an intact seedling that is likely to produce a plant in the field (normal) or a seedling with damaged or missing parts that is not likely to produce a plant in the field (abnormal).  Only normal seedlings are included in the reported percent germination in a standard germination test. Direct viability tests have the best correlation with field emergence under optimal conditions when dormancy is not present. 

There are also indirect methods to estimate viability, such as a TZ test (tetrazolium chloride).  This test estimates the viability of seed by correlating the degree of stain with respiring or living tissue in the embryo.  There are limitations to the methods which estimate seed viability.  To better understand the usefulness of the viability estimates, it is important to understand the sources of differences in results between direct measures of viability such as a germination test and indirect estimates of viability such as a TZ test.

The questions addressed here are: 

  • Using TZ to estimate viability, which kinds of abnormal seedlings are able to be easily detected and evaluated as non-viable in comparison to a direct germination test? 

  • Which kinds of abnormal seedlings detected in a germination test would be missed in a TZ test to estimate viability?

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