Agriculture Reference
In-Depth Information
Presentation and Interpretation of Vigor Test results
Still unresolved is how to best present seed vigor test results. Tests, such as the cold and accelerated aging
tests, which provide results on a percentage basis, lend themselves to immediate acceptability by seed
users because of their similarity with germination test results. Yet other tests are just as valuable but the
presentation of results is more problematic. For example, the tetrazolium test is one of the most useful seed
vigor tests, but how should the colorful, topographic staining patterns be presented to the consumer in a
meaningful way? The conductivity test, too, is an important test of seed vigor for many crops. However, the
data are presented in µS/cm/g seed. To the uninformed consumer, what does that value mean, particularly
as it applies to ield emergence? More importantly, since there is an inverse relationship with seed quality,
higher readings mean poorer quality seeds which is a conclusion opposite from what most people would
expect. Some have suggested that the interpretation of results would be assisted by providing arbitrary
categories. Readings below 25 µS/cm/g are acceptable, readings above 43 µS/cm/g are unacceptable and
those in between are considered marginal. At irst glance, this appears an acceptable alternative but how
does one classify a seed lot with a reading of 24.9 µS/cm/g and another seed lot with a reading of 25.1 µS/
cm/g; particularly in cases of litigation? Are these lots signiicantly different in quality as the arbitrary clas-
siications would lead one to believe?
This example provides the forum necessary to initiate a discussion of interpretation of vigor test
results. Inevitably, as any new test is formulated, the consumer using the information asks what the data
mean. In seed vigor testing, this question is often related to some component of ield performance and we
have been guilty of this association. It should be emphasized that it is not the responsibility of the seed ana-
lyst to interpret vigor test results and analysts exceed their role when they speculate what the values of any
particular test mean in terms of subsequent performance. The analyst's role is to accurately present the test
data and allow the consumer the responsibility of interpreting whether the seed lot is of acceptable quality
based on his/her own standard(s): a time-honored process known as
caveat emptor.
Another concern in interpretation is the implied association between vigor test results and ield per-
formance. For example, assume that a seed lot with a standard germination of 90% and a cold test of
65% might be thought to produce a stand of 90% under ideal conditions and 65% under stress conditions.
However, it should be emphasized that vigor test results do not forecast stand emergence. At most, the test
allows the customer the opportunity to determine that one seed lot is superior to another, which can be
proven only when environmental stress is encountered. In some years, the stress may be so severe that very
few seeds emerge, even for the most vigorous lot. In other years, vigor results may actually be better cor-
related with stand establishment. The important point is that analysts should avoid predicting or forecast-
ing ield performance of a seed lot based on vigor test results. It can be said only that one seed lot should
perform better than another. How much better depends on the amount of environmental stress encountered.
CLASSIfICATIon of SEEd VIGor TESTS
Types of Seed Vigor Tests
Various classiication systems have incorporated strategies that separate vigor tests into groupings based on
the parameters monitored. For example, Isely (1957) divided vigor tests into
direct
and
indirect
tests. Direct
tests imitate the ield environment in some ways and the ability of the seed to emerge under simulated stress
ield conditions. The cold test is an example of a direct test because it subjects seeds to adverse conditions
by placing them in cold, wet soil where direct stress from microorganisms and imbibition occurs. However,
direct tests have been criticized because they ignore differences in seed quality when seeds are exposed to
favorable soil conditions. Indirect tests, in contrast, measure speciic physiological components of seeds.
For example, the conductivity test is an indirect test because it monitors cell membrane leakage. Indirect
tests, however, fail to evaluate all the physical and physiological factors which determine ield establish-
