Agriculture Reference
In-Depth Information
5. Determining viability of dormant seeds.
Some kinds of seeds such as certain chaffy grasses and
native species are highly dormant, resulting in extremely low germination estimates, even after extended
prechilling periods. The tetrazolium test is able to determine viability of dormant as well as nondormant
seeds so the true viability of dormant seed lots can be determined. Tetrazolium results may be combined
with a germination test to obtain more complete information concerning the quality of a seed lot. With this
procedure, the germination test indicates the percentage of seeds that are immediately germinable, the TZ
test indicates percentage that are viable, while the difference represents the percentage that are dormant.
Another useful application is to use tetrazolium to determine whether ungerminated seeds remaining
after a germination test are dead or dormant. Such information facilitates making preliminary shipping and
marketing arrangements pending results of germination tests.
6. Determining viability percentages of lots to be blended.
When two or more seed lots with dif-
ferent germination percentages are to be blended, the proportions of each lot to be put in the blend can be
calculated on the basis of tetrazolium results, saving much valuable time.
7. Investigating causes of questionable germination results.
When two germination tests on the
same seed lot do not agree, a tetrazolium test will often indicate which germination test is out of line.
8. Estimating seed vigor.
With the use of proper interpretation criteria, the tetrazolium test can also
be used to provide a rapid evaluation of vigor. Procedures for this are further described in Chapter 8 and in
the AOSA seed vigor testing handbook (2009).
LIMITATIonS
As useful as the tetrazolium test is, it does have certain limitations that must be recognized. Among these
are: (1) its inability to distinguish dormant from nondormant seed, (2) its non-detection of fungal infesta-
tion, (3) its inability to detect certain types of fumigation injury, and (4) the training and skill required to
attain proiciency in TZ testing. Because of these disadvantages and the subjectivity in interpreting the TZ
results, it remains an unoficial test. Perhaps in the future, upon demonstration of consistency (repeatability)
among test results, the TZ test will gain oficial acceptance. Until then, it will continue to provide an unof-
icial, albeit invaluable service to the seed industry.
fACILITIES, EQuIPMEnT, And SuPPLIES
A minimum of equipment and supplies is required to conduct the tetrazolium test. The working space
should be well-lit and include a desk or counter space and comfortable chairs in surroundings that are
conducive to relaxed concentration. At least one heat controlled incubation chamber is needed for holding
samples during preparation, staining, and clearing. A cold chamber is useful for holding samples which
cannot be evaluated promptly after staining. Supplies needed include the following:
a. Seed moistening media: The usual beakers or germination boxes and media including blotters,
towels and ilter paper; tap or distilled water for soaking seeds.
b. Cutting and piercing devices: Single-edge razor blades, dissecting knives, scalpels, and needles.
c. Staining dishes: Syracuse watch glasses, petri dishes, beakers, or small disposable plastic or
paper drinking cups.
d. Seed magniiers: Stereoscopic microscopes, hand lenses or magnifying glasses for piercing or
cutting and evaluating small seeds such as bentgrass.
e. Miscellaneous items: Laboratory glassware, balance, forceps, medicine droppers and yes,
band-aids!
f. Tetrazolium solution of various concentrations (0.1 - 1.0%) and 85% (v/v) lactic acid solutions
for clearing seeds of some species such as Kentucky bluegrass and tall fescue for easier visual
evaluation.
