Vigor tests are more sensitive measures of seed quality than the standard germination test. The standard
germination test result is the product of a “first” and “final” count. The first count is the time when most
seeds germinate and the seedlings are moved before they become too unwieldy. The second count
provides the opportunity for slow to germinate seeds to demonstrate their ability to germinate. The final
count is conducted at a “safe” time that provides sufficient opportunity for even the weakest seeds to
germinate. Seed vigor testing is not afforded this luxury. Most seed vigor tests monitor some aspect of
seedling or biochemical growth. It is important to differentiate between weak and strong seeds at the
earliest possible moment, so timing of seed/seedling evaluations must be precise. When 72 hours is
recommended, it should not be 76 hours. For example, the accelerated ageing test protocol
appropriately emphasizes that not more than one hour should elapse beyond the recommended
accelerated ageing period or the test results may be invalid. The flexibility in timing enjoyed by analysts
in conducting a standard germination test serves as a poor model for seed vigor test analyses.
Similarly, environmental factors such as moisture and temperature must be precisely controlled in vigor
tests because of their immense impact on the rate of seedling growth. It is interesting that no
specifications for either the type of substrata or the amount of water used have been indicated for most
seed vigor tests. Yet, both factors strongly influence the availability of water to the imbibing seed and
its subsequent rate of growth. We know, of course, that some laboratories prefer to conduct their
germination tests “drier” or “wetter” than others. Vigor tests that use a component of seedling growth as
a parameter of seed vigor should define the level of moisture used in the seed test.
Temperature requirements also influence the rate of seedling growth. In germination testing, a ± 1o
C
differential in seed germination is permitted. In some cases, seed analysts conduct germination tests at
either constant or even alternating temperatures. But, we know that types of germinators differ among
laboratories. Some are wet, others dry. Some recover more rapidly from alternating temperature
regimes and still others are better able to maintain a ± 1o
C. When conducting vigor tests, seed analysts
must understand the importance of uniform temperature maintenance throughout the duration of the test.
Explanations for differences in vigor test results, particularly among laboratories, should begin with
questions regarding the quality of germination equipment and assurance of accurate temperatures
throughout the test. Perhaps the best example of appropriate emphasis on temperature is provided for
the accelerated ageing test where temperatures are required to be within tolerances of ± 0.3o
C and