It may seem easy to have a corn germination test. Give the seeds water, they imbibe, and then after a few days the root and shot emerges. Count those that do and those that do not. However, whereas most of the seed is adequately viable, some may not be dead but have enough membrane damage that they are slow to get enough metabolism to produce undamaged seedlings at the same time as the rest of the sample. All labs attempt to control the environmental variables such as water and temperature but interpretation of these slower plants does become a potential variable.
Warm tests are performed at 70-75°F. Water is usually measured and applied automatically. The medium may be a paper fiber similar to a disposable diaper, a rolled paper towel, sand or special artificial soil mix as we do at Professional Seed Research, Inc. Despite attempts to be consistent between labs, and attempt to define damaged seedlings, there remains a range of results between labs when all are germinating samples from the same original bag of seed. If the average warm test germination of 30 labs is 98-100% then the range will be 95-100%. However if the average is near 90% the range will be at least 10%. Probably this is due to small differences in lab environments and interpretation and classification of the slow and damaged seedlings.
Damaged membranes can repair under warm temperatures but not very well when temperatures approach the 50°F used for cold tests. Cold test media vary between labs as they attempt to predict the emergence in the field. In fact, the cold tests generally are a better predictor than the warm tests but also the range of results between labs is also greater. Probably a major difference is the medium used for the tests. Some use field soil, partly to introduce Pythium, as an attempt to mimic field conditions. A potential problem of this medium can come from small differences in water holding capacity because this is rarely completely uniform. This can affect the oxygen available to the seed even within a test container. Labs do try to monitor both the medium as well as the water. The usual standard cold test is 7 days at 50°F and then 4-7 days at 70°F. Variation between labs when testing seed from the same bag is usually greater between labs.
Other lab tests such as the saturated cold, advanced aging and extended cold are probably most useful in predicting the future viability of older seed. The usual problem of these tests is establishing minimum standards. We know that seed deteriorate but the challenge is to know the slope of deterioration.
Ultimately a seed company needs to identify the lab method that best predicts field emergence and then make big efforts for uniformity within that lab. We are dealing with living organisms that vary in germination quality even when from the same seed field, being planted in variable field environments. As all involved in growing corn understand, the best effort does not always match with the real world of field moistures, temperatures and soil types.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.