Agriculture Reference
In-Depth Information
In addition, seed companies use vigor test results to educate their sales staff, identify speciic market
areas (for example, no-till), test competitor's seed lots, or defend the company through litigation. Some
companies provide seed vigor information directly to the customer at the time of seed purchase.
The seed consumer also beneits from seed vigor information in various ways. For example, it helps
the consumer decide on the fair price of a seed lot. Beyond purchase price, however, the seed consumer can
also use vigor test information to determine how early in the season to plant, the quantity of seeds to use for
satisfactory emergence, the expected uniformity of stand for subsequent secondary tillage and/or pesticide
operations, the conditions of environmental stress such as cold, drought, soil compaction, and so forth, that
might be tolerated, and how plentiful and uniform a harvest can be anticipated.
STAndArdIzATIon of SEEd VIGor TESTS
Criteria for Vigor Tests
Vigor tests are more sensitive measures of seed quality than the standard germination test. The standard
germination test result is the product of a “irst” and “inal” count. The irst count is the time when most
seeds germinate and the seedlings are removed before they become too unwieldy or bulky. The inal count
is conducted at a “safe” time that provides suficient 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. For example, the accelerated aging test
procedures emphasize that not more than one hour should elapse beyond the recommended accelerated
aging period or the test results may be invalid. The lexibility 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 physiological/biochemical deterioration. It is
interesting that no speciications for either the type of substrata or the amount of water used have been indi-
cated for most seed vigor tests prior to the publication of AOSA's 2009 Vigor Handbook edition. Yet both
factors strongly inluence 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 deine the
level of moisture used in the seed test. More standardization of factors affecting vigor test results have been
addressed in the 2009 AOSA Vigor Testing Handbook revisions.
Temperature requirements also inluence the rate of physiological stress and seedling growth. In ger-
mination testing, a ± 1°C differential in seed germinators is permitted. In some cases, seed analysts conduct
germination tests at either constant or alternating temperatures. But germinators differ in relative humidity
among laboratories; some are wet, others dry. Some recover more rapidly from alternating temperature
regimes and still others are better able to maintain ±1%. When conducting vigor tests, seed analysts must
know the importance of uniform temperature maintenance throughout the test. Explanations for the dif-
ferences in vigor test results, particularly among laboratories, should begin with questions regarding the
quality of germination test equipment and assurance of accurate temperatures throughout the test. Perhaps
the best example of appropriate emphasis on temperature is provided for the accelerated aging test where
temperatures are required to be within tolerances of ± 0.3°C and speciic types of commercial equipment
are recommended for the conduct of the test (Hampton and TeKrony, 1995). These precise descriptions are
excellent models for other vigor test protocols.
