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in germination test results with the recognition that these seeds will not contribute to vigor testing values.
Whatever the best answer, guidelines for the treatment of seed dormancy in vigor testing are needed.
Vigor test design . There are also variables that inluence interpretation of results based on the design
of the vigor test. For example, most vigor tests evaluate individual seeds/seedlings and then provide a
composite value such as a percentage for the seed lot. Others, such as the conductivity test are a bulk test
where all seeds are treated in the same way at the same time and the results expressed as an average value
for all seeds. This vigor test design has merit because it is more rapid and less expensive to conduct than
individual seed analyses. However, the results must be interpreted with caution. The general understanding
of a conductivity result is that it represents an average value applied to each seed. However, it is also pos-
sible that there might be one bad “leaker” in the seed lot while the remaining seeds are excellent. This bad
“leaker” would increase the conductivity reading and the result would suggest that all seeds were average
when, in fact, the seed lot is of overall excellent quality.
Choice of vigor test. Another approach to vigor test design is based on recognition that most vigor
tests determine speciic facets of seed quality. For example, the accelerated aging test provides an indication
of the storability of a seed lot while the conductivity test evaluates membrane integrity. Both components
are important determinants of seed vigor. As a consequence, it has been proposed that greater information
concerning seed quality could be acquired by conducting a battery of vigor tests and summarizing the
results as a single vigor index. This approach is sound, but it is dificult to successfully implement. One
reason is that it is uncertain whether equal weight should be given to values provided by each of the vigor
tests or whether certain test values provide more vigor information than others. Perhaps a user may decide
that cold test results provide more sensitive vigor information than conductivity results, but by how much?
Another reason why vigor test indices have not become more common is related to the cost:beneit ratio.
The increased information provided by additional vigor tests may not be suficient to warrant the increased
cost and time required to generate the data.
Duration that results are valid . Seldom is there a discourse about the length of time that vigor test
results can be considered valid, but this dialogue should begin. The U.S. Federal Seed Act mandates that
seeds in open storage must be retested for germination after ive months, or 24 months when hermetically
sealed. Because vigor tests are more sensitive determinants of seed quality, it is assumed that retest intervals
for vigor would be shorter than for germination. But by how much? Are certain vigor tests better able to
determine seed vigor than others? If so, would this time frame vary according to the test used? What inlu-
ence would the seed storage environment have on the validity of vigor test results over time?
Need for standards . Neither the ISTA nor AOSA Vigor Test Handbooks advocate the need for stan-
dards when interpreting the results of a vigor test. This idea has merit for the following two reasons. First,
a seed testing laboratory should have a standard seed lot for which vigor test values are known that is either
routinely or anonymously introduced into the testing regime. Because seed vigor testing requires precise
environments and analyst interpretations, these standards identify when test results may be altered or “out
of tolerance” due to conditions external to the seed. Second, standards can also be employed in comparing
results among laboratories for tests that are dificult to standardize. For example, the use of local soils in
a cold test makes comparison of test results among laboratories dificult because soils vary in their patho-
gen levels and water holding capacities. Both of these factors have a major impact on cold test results.
However, if the laboratories comparing seed lots use the same seed standard, they might be able to express
the results on a percentage basis relative to the standard. Thus, a seed lot may have a cold test result of
35% and the standard may be 45% in laboratory A. At laboratory B, the cold test may be less stressful and
produce results of 70% for the seed lot and 90% for the standard. While these absolute values are different,
they become the same when computed on the basis of the standard seed lot (Laboratory A: 35/45 = 0.77;
Laboratory B: 70/90 = 0.77).
The 2009 revision of the AOSA Vigor Testing Handbook has addressed many standardization issues
of vigor testing.
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