Longmont, Colorado, and Gilroy,
California
February, 2009
 Source:
Eurofins STA Today newsletter
By Linda Barbosa
There are occasions when a
customer may note variability between germination tests. These
may be between tests from the same lab or different labs. There
may be differences between a label, especially if several months
old, and a current lab test. There are several possible causes
for this variability. First, let us look at the background of
seed testing. Most tests in the United States are preformed
following the AOSA rules. These rules were developed from years
of experience in seed testing and research. Until recently these
were established by government and university labs. The goal of
the AOSA rules is to standardize seed tests to ensure uniformity
among testing laboratories providing accurate information to the
owners of the seed.
Sampling
Independent labs count on
the customer to provide a sample that has been drawn
correctly from the bulk. A composite sample must be drawn
from several locations within the container or containers,
and then divided down to a representative sample. No lot is
perfectly uniform and variability can be found between
samples, especially if the samples are not well-mixed
composites of the lot. This is often the most frequent cause
of differences in germination between samples. Clients
should refer to the AOSA rules for correct sampling
procedures for all seed quality tests.
Live Products
Seeds are live products
that are dynamic and change with conditions and this may
also account for differences between laboratory germination
tests. AOSA rules have tolerance tables that take these
facts into account and provide directions for determining an
allowable deviation between tests. Thus, tests on the same
sample that vary a few to several points may actually be
within allowable deviation.
Age of the Seed Lot
Producers and dealers will
track the history of lots to note unexpected differences
and/or gradual declines. It is not unusual to see a low germ
if a company is checking the quality of an older lot.
However, an outside testing lab does not have access to this
history information and therefore is dependant on the
company to inform them if a recent germination is a dramatic
change from the history of the lot. With this information,
repeat tests can be done to verify the current condition of
the lot.
Sample Conditions
The conditions under which
a sample is stored or shipped can also greatly influence the
germination. Two samples that are properly obtained from a
lot at the same time can give radically different
germinations if they are stored or shipped under greatly
varying conditions.
Test Conditions
Variability of test
conditions can also affect the germination result. Although
germination labs follow AOSA rules in setting up test
conditions, slight deviations in the test conditions can
cause additional stress on seeds, which can affect the
germination result. It is possible that the test can be
planted too wet, too dry, or put into the wrong temperature.
Labs are expected to monitor their germinator temperatures,
planting conditions and employee methods in an effort to
reduce these variables and maintain consistent quality
between tests.
Selection of test protocol
The AOSA rules offer
protocol options for the same crop. The lab selects the
protocol they feel will provide the best option for maximum
germination.
The rules may allow a test to be preformed in a rolled paper
towel or if dormancy is suspected on top of a blotter with
light provided. Some protocols offer the option of
prechilling and applying KNO3 to the planting media to
overcome suspected dormancy. A company may decide to test
all of their lots using the same method so that a comparison
can be made across all lots. There also may be a choice of
equally valid temperatures that can be used in the test.
Some labs may disinfect untreated seed with a fungicide
while others may not.
Eurofins STA Labs strives to
provide our clients with consistent and reliable results through
continual training of our employees and active participation in
comparative testing with other labs. There will always be
variability in results between labs but our goal is to assure
our clients that we constantly strive to ensure that our test
conditions and test evaluators are consistent test to test, and
day to day.
At Eurofins STA Labs we will replant all questionable tests
immediately at the request of the client. If we notice a problem
in the test conditions we will replant automatically at no
charge to the client. If a result is unexpectedly low, our
procedure is to contact the customer and discuss the results
with them. At that point a decision can be made to retest the
sample, obtain a new sample and test it, or not to retest at
all. |
