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.
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