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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