Agriculture Reference
In-Depth Information
ment. In the case of the conductivity test, improved performance due to seed treatments, the degree of mor-
phological damage, the inluence of soil microorganism attack and other factors are often not adequately
assessed.
Another strategy is to simply divide seed vigor tests into categories based on the component of vigor
that is measured. For example, Woodstock (1973) separated vigor tests into
physiological
and
biochemical
groupings. Physiological tests measure some aspect of germination or seedling growth while biochemical
tests evaluate a speciic chemical reaction such as enzymatic activity or respiration which is related to the
seed's germination and hence, vigor capability. McDonald (1975) concurred with this separation system but
added one additional grouping, a
physical
category which included seed size, shape and density - factors
long associated with seed vigor because of their indication of seed maturity.
Others have suggested classifying vigor tests into
stress
and
quick
test categories (Pollock and Roos,
1972). A stress test consists of subjecting a seed to one or more of the environmental stresses it might
encounter under ield conditions. Stress conditions can include high temperatures and relative humidity
such as the accelerated aging test, low temperatures with or without soil, such as the cold test or cool ger-
mination test, or placing seeds under osmotic stress using solutions such as polyethylene glycol. Quick tests
are considered to be tests which evaluate some chemical reaction associated with seed vigor and can be con-
ducted within a short time when compared with stress tests. Examples are the tetrazolium test, conductivity
test, and various tests associated with enzymatic activity.
The 2009 AOSA Vigor Testing Handbook revision groups tests based on similarity of procedure. They
are:
1. Aging tests including accelerated aging, saturated salt accelerated aging and controlled deteriora-
tion tests;
2. Cold stress tests including the cold test (tray, rolled towel and deep box methods), the saturated
cold test and the cool germination test;
3. Conductivity tests including electrical conductivity, single seed conductivity and potassium leak-
age tests;
4. Seedling performance tests including speed of germination, seedling growth (linear and dry
weight) and computer imaging tests; and
5. Tetrazolium vigor tests.
Criteria for Seed Vigor Tests
Although many seed vigor test methods have been proposed in the past as legitimate approaches to measur-
ing certain aspects of seed vigor, only a few have attained routine use in seed testing. For seed vigor tests
to be accepted for routine use by seed laboratories, they must meet the following criteria (McDonald, 1975;
1980):
1. Inexpensive
. Due to limited budgets in seed testing laboratories, it is important that a vigor test
require reasonably priced equipment and supplies.
2. Rapid
. Every seed laboratory has periods of peak activity when seed samples arrive for testing
simultaneously. During these periods, the addition of another seed quality test in conjunction
with the routine germination and purity analyses places a further burden on the analyst. So, it is
important that the vigor test be conducted rapidly to keep time spent by the analyst on a test to a
minimum. Further, a vigor test which is not rapid will tie up needed germinator space as well as
delay the reporting of results to the seed producer.
3. Uncomplicated
. A vigor test which requires sophisticated equipment and intricate procedures
can be expensive. It may involve extensive training of analysts or may necessitate the hiring of
