Genetic tests provide the ability to determine the quality of a seed lot beyond standard visual quality tests the Seed Lab is capable of offering. Together, both labs provide the best determination of seed lot quality available.
Genetic purity testing is an important test used to determine precisely the genetic purity of a sample. This test is similar to a variety identification test except that individual seed are tested. Results are presented as a percentage of each distinctive component identified in the sample. This test is useful when it is necessary to know exact amounts of other varieties, off-types, etc. in a sample. Currently, wheat is the primary crop tested. Customers should contact the department for pricing information.
The Diagnostic Lab has performed variety identification testing in cereal crops since 1994 utilizing either Polyacrylamide Gel Electrophoresis (PAGE) or Polymerase Chain Reaction (PCR) tests, depending on the crop. Beginning in 2010, the Field Seed Program began requiring variety ID testing for certification of all seed lots spring wheat, barley and field peas.
Electrophoresis is capable of detecting whether two or more different varieties are mixed together. Seed producers or retailers may request this test to verify which bin a particular lot of seed was stored in or to determine whether a mixture has occurred. With most new varieties protected by plant variety protection laws, this type of test becomes a valuable tool for PVP enforcement. The department uses this test during the regulatory inspection process to verify that the variety name stated on a seed label matches what is in the container or bin.
Electrophoresis separates proteins using a gelatinous support medium or gel. This test is used to identify wheat and oat varieties compared to known checks. The test uses protein extracted from the seed to determine the identity of the unknown seed sample. A small amount of sample is applied to the gel and an electrical current is applied that causes charged molecules such as seed proteins to migrate through the gel. The proteins separate based on their size and/or electrical charges. A special stain is used to visualize the banding pattern or ‘fingerprint’ for a particular variety. Known control samples are run with unknowns for positive identification. Sample mixtures or other varieties can be identified from the sample fingerprint. Gels are visually evaluated and electronically photographed.
In the case of barley and field pea, a seed DNA test is conducted. High genetic similarity of many barley varieties released over the past several years has resulted in the need to use an alternative test for variety identification. A DNA test uses a process known as polymerase chain reaction or PCR. Seed DNA from an unknown sample is subjected to PCR using specific markers for the variety of interest. Multiple markers are usually required to distinguish barley and pea varieties from each other. PCR products are then visualized using electrophoresis and a stain specific for DNA. As with a seed protein variety identification test, known control samples are tested with unknowns. Sample mixtures and other varieties can be determined from this test.
For all variety identification tests, sample information is important. For seed certification, we maintain a library of common varieties that are used as controls. For samples of unknown identity, customers should have some idea as to the identity of the unknown sample. This information helps narrow the possible varieties for the unknown sample and gives the lab a starting point as to what varieties to test the unknown against. In the case of barley, information such as whether the sample is a 2 or 6-rowed variety, rachilla hair type, etc. is also useful information. Prior to testing barley samples, a rachilla hair check is often performed to aid in identification.
Both the seed protein and seed DNA tests use bulked seed analysis and do not determine exact percentages in samples of mixed varieties. In order to determine exact percentages of varietal mixtures, single seed testing is required. That would be considered a genetic purity test.
Variety ID testing is required for all lots of spring wheat, barley and field peas submitted for final certification.
Adventitious presence is a term used to describe when one type of commodity, grain, or seed is mixed with small amounts of another commodity, grain, or seed. This commingling is generally unintentional and accidental and includes both biotech and non-biotech products. Adventitious presence can occur when a biotech product, such as a herbicide tolerant soybean, is accidentally mixed into a non-biotech product like a conventional soybean variety. Adventitious presence could also occur when two non-biotech or two biotech products are mixed.
Flow Strip Test
Flow strip tests are antibody based tests that use a support structure in the form of a stick that has imbedded antibodies for a specific trait. The flow strip is placed into a liquid sample and is allowed to absorb. A positive result is indicated if lines develop on the strip after a few minutes. Many different biotech traits can be detected using this type of test including herbicide and insect resistance. Some of the crops that can be tested for biotech traits in this manner include canola, corn, cotton, and soybean. Flow strip tests usually take less than 30 minutes.
ELISA stands for Enzyme Linked Immunosorbent Assay and is another type of antibody based test similar to a flow strip test. In this test, a plate is used that contains wells coated with a specific antibody that targets an antigen or protein of interest. In the case of adventitious presence of biotech crops, the protein could be produced by the Roundup gene in biotech soybeans. The antibody captures the protein and then allows the user to detect the protein on a plate reader. The department currently conducts ELISA tests for the detection and quantification of low levels of glyphosate (Roundup Ready®) soybean (less than 3%) in conventional soybean. ELISA tests can be performed in less than one day.
Flow strip tests and ELISA tests detect proteins that are produced by a biotech trait. A DNA test actually targets the gene of the biotech trait or regions next to the gene using the process of PCR (polymerase chain reaction) to detect this area of interest. This test is very specific and can be used in a qualitative form (presence or absence) or a quantitative form (exact percentage) of a particular biotech trait. Many different biotech traits can be detected in this manner including those from corn, cotton, canola, and soybean. DNA tests are sensitive and can detect small amounts of biotech traits in a sample. DNA tests can be performed in 1-2 days depending upon the sample. The Seed Department currently conducts a qualitative DNA test in soybean for the presence or absence of the Roundup Ready gene.
Herbicide bioassay tests can also be used to detect an adventitious presence in a sample. Most herbicide tolerant crops have bioassay tests that are designed to verify that a seed source has a minimum acceptable level of herbicide tolerance. These same tests can be used to identify the presence of a herbicide tolerant trait in a conventional sample. Bioassay tests usually take 7 days to complete. The Seed Department offers several different types of herbicide bioassay tests including Roundup Ready soybean and canola, Liberty Link canola, and Clearfield wheat, canola, and sunflower.