Variety Identification Testing
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 a variety stated on a seed label matches what is in the bag.
The variety identification test that the Diagnostic Lab performs on wheat and oat uses protein extracted from the seed to determine the identity of the unknown seed sample. The process of electrophoresis is then performed on the sample. Electrophoresis involves the separation of a mixture of chemical components, in this case proteins, using a gelatinous support medium or gel. A small amount of sample is applied to the gel and an electric current is applied. The electrical current allows charged molecules such as seed proteins to migrate through the gel and to be separated. The proteins separate based on their size and/or 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. All gels the lab runs are visually scored and electronically photographed.
In the case of barley, 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. A DNA test uses a process known as the polymerase chain reaction or PCR. Seed DNA from an unknown barley sample is subjected to PCR using specific markers for the variety of interest. Multiple markers are usually required to distinguish barley 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. Customers
should have some idea as to what the variety or varieties the unknown sample is.
This information helps narrow the possible varieties for the unknown sample and
gives the lab some 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 of mixed variety samples or seed
lots. In order to determine exact percentages of varietal mixtures, single seed
testing is required. This would be considered a genetic purity test. Variety
identification tests for wheat or oat require a ½ lb sample. A bulked sample of
100 seed is tested. For barley variety identification tests, a 1 lb. sample is
required to be submitted for testing. It is important to note that the
Diagnostic Lab does not currently conduct variety identification testing on most
durum wheat varieties due to their high degree of genetic similarity.