Cold germination testing

Purpose of germination testing is to avoid emergence problems in the field.  All labs, private and public, attempt to have methods to accomplish this objective.  It is complicated.  A potential problem can be from a sample inadequately representing a seed lot that may include 1000 bags with 80,000 kernels per bag.  Seed sizes within a seed lot may not have the same germination quality. Not all seed lots deteriorate at the same rate, making the timing of the testing in relation to field planting can be a factor. Labs strive for consistency within the lab and many use similar methods, but subtle differences apparently influence results.
 
We participate in a referee testing in which corn seed from the same commercial bag is sent to 30-40 private and public labs for tests.  In one year’s example, the average corn warm test germination was 95.1% but the range among the 45 labs was 90.3-98.4%.  The cold tests ranged from 75-94.6% among 27 participating labs.  The germination listed on the seed bag tag could legally be 95% because seed law is based on warm test results that allow for that much variance, acknowledging all the variables involved.
 
Labs conduct a cold test in which the corn seed is planted on a paper, soil, sand or artificial soil medium, watered and kept for 7 days at 50°F before exposed to a minimum of 70°F for 4-7 days.  The principle involved is that this temperature inhibits the metabolism needed to repair damaged membranes further damaged with imbibition.  The higher initial temperatures of the warm test immediately after imbibition will allow repair of the membranes and thus normal germination and emergence.  The medium, especially concerning water-holding capacity and oxygen availability does also have an effect.  There is some confusion as to definition of saturated cold tests but it is intended to have water interfering with oxygen availability.
 
Studies that we have participated attempting to compare tests with actual field emergence generally show the cold test is the most reliable predictor of field emergence.  Over many reps, fields and years the cold test usually has the closest correlation with field emergence and that correlation value is often about 70%. Obviously other field factors also influence emergence.
 
Our company (PSR) performs many tests for companies and growers.  400 seeds are planted in an artificial soil mix prepared for us.  It includes a surfactant to allow even distribution of water and yet enough aeration for seeds to respire.  Cold test samples are planted, watered and placed in a 50°F cold room for 7 days.  Samples then are placed on a greenhouse bench heated with a minimum of 70°F until the third leaf is visible for most seedlings.  All labs struggle with classification of the few seed that emerge late and perhaps show some injury in the first leaves.  Our policy is to characterize those seed that only show the ‘spike’ when most are at 3 leaves as not germinating.  We assume that even if these individuals do germinate late in the field, they will be non-performing plants because of competition with adjacent plants.
 
PSR warm tests tend to give lower results than many labs, but not the lowest among referee labs, probably because of our characterization of the late emergers and especially with marginal quality lots.  Our cold tests tend to be about average of the wide range of lab results.