The
Need of Fast Tests
The Oregon Seed
Industry has been asking for faster methods of testing seeds in order to
meet the new global market demands. In the area of viability (i.e., the
determination if the seed is dead or alive, which indicates seed
germinability), the TZ test is an ideal method. It is accurate, fast and
inexpensive. The development of the TZ test to determine the percentage
of viable seeds within a seed lot has probably been one of the most
significant discoveries in the science of seed testing of this century.
Yet this test is still misunderstood and underutilized.
Since the seed
industry needs sound information within a short time, the TZ test could
become an answer to some of the problems that caused backlog in the
past. It is no surprise that this test is increasingly gaining a wide
recognition as an accurate and fast method to determine the seed
viability of field crops, grasses, vegetables, flowers, trees and other
seeds throughout the world. There is no doubt that the TZ test will
become a highly used technology beyond year 2000. The question is
whether we, in Oregon, are ahead of the curve.
The TZ test can
be used regardless of the dormancy level of the seeds in question.
Therefore, this method is of great importance for the Global Oregon Seed
Industry, which deals with grass seed characterized by various levels of
dormancy. This is why the
determination of seed viability by TZ has become more useful for seed
growers, cleaners, seed certification services, seed laboratories, seed
dealers, and buyers. It can help make sound business decisions in the
shortest possible time. For example, immediately after harvest (during
summer months), grass seeds posses a high level of dormancy. It takes
about 4 weeks to break the dormancy and complete a germination test for
a given grass sample after purity test is finished. In contrast, a TZ
test can be completed within a day or two. This creates a possibility of
making faster decisions based on the TZ test, which can be followed up
by a standard germination test.
The
Principle of the Test
TZ is a biochemical test,
which differentiates live from dead tissues of seed embryos on the basis
of dehydrogenase enzyme activity (respiration enzymes). Upon seed
hydration, the activity of de-hydrogenase enzymes increases, resulting
in the release of hydrogen ions, which reduce the colorless tetrazolium
salt solution (2,3,5-triphenyl
tetrazolium chloride) into a chemical red compound called formazan.
Formazan stains living cells with a red color, while dead cells remain
colorless. The viability of seeds is interpreted according to the
staining pattern of the embryo and the intensity of the coloration.
Seed viability is an
indication of the capability of seeds to germinate and produce a normal
plant under suitable germination conditions.
The Association of Official
Seed Analysts (AOSA) has detailed techniques of how-to conduct TZ test
for a wide range of species.
The
Advantages of the Test
1.
Rapid determination of viability/quality level of a seed lot.
This is highly relevant for the Oregon Seed Industry and any industry
that needs to make decisions about the viability level of a seed lot in
a short notice.
2. Accurate evaluation of seed viability, even if seeds are still
dormant. This is relevant for grass seeds and other seeds characterized
by high levels of dormancy, especially the first few months after
harvest.
3. Guidance in quality control of carry over seeds to detect seed
deterioration even before it can be detected by germination.
4.
Useful for researching and teaching the biology and physiology of
seed quality and deterioration processes.
Like any other
seed testing method, the TZ test requires special training and
experience. This may be the reason why this test has been underutilized
in the past. This situation has prevailed even though the new seed
market conditions demand faster seed viability tests. High level of
training and experience in testing seeds is not unique to the TZ test,
it is a basic requirement in the seed testing business. Any test such as
purity, germination, ploidy, endophyte, x-ray is required to be done by
a highly qualified and trained seed analyst. So, the need for
well-trained seed analyst to conduct a TZ test should not be a
limitation for its use.
Procedures
1.
Hydration: seeds must be completely imbibed in order to
initiate the
dehydrogenase enzyme activity. This process is needed to release
hydrogen ions, which reduces the colorless TZ solution to red formazan.
2.
Cutting or puncturing: This process permits the access of
the TZ solution to the embryos of seeds. For some species, e.g., clover,
cutting is not necessary, where the TZ solution can be added to the
intact seeds with a clearing agent (e.g., lactic/phenol solution).
3.
Staining: Seeds are placed in a TZ solution for a certain
period of time, as indicated in the TZ Handbook of AOSA, for complete
coloration. During this process hydrogen ions reduce the colorless TZ
solution to red formazan, which stain viable tissues with red color
while dead tissues remain unstained.
4.
Evaluation: Critical evaluation of the TZ staining pattern
and intensity is needed for accurate interpretation. Seed analyst should
be familiar with the structure and the anatomy of the seeds in question
to determine the staining pattern of the embryo (the most critical organ
during germination). This will enable the analyst to determine if seeds
have the capacity to produce normal seedling.
Implications
for the Future?
The tetrazolium test is
expected to be used more extensively in the future in grass seed
testing. This is because the new seed market is demanding seed quality
information in the shortest possible time. It is difficult to envision
that the time pressure will disappear. The question that may emerge in
the future is whether there is a faster test than the TZ to determine
seed viability. If not, the TZ test is here to stay. Probably it is the
seed testing technology gift of the 20th century to the seed
industry of the 21st century.
Is
the OSU Seed Laboratory Prepared to Conduct TZ Test?
The
OSU Seed Laboratory has had the capacity to provide TZ testing for many
years. It is prepared to respond to the Oregon Seed Industry needs in
the future. This service is
available for a broad range of species, including field crops, grasses,
vegetables, flowers, tree species, and others.
For
more specific information please contact:
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