Germination testing is used to assure that seed quality will not detract from final performance in the field. Warm germination tests are done by rolled towel, Kimpak and sand test. Each lab has some variation of these tests and results are used as a basis for the germination percentage posted on the tag for a bag or other container of commercial seed. Cold tests are also used for all commercial seed lots and is generally considered equally or more important predictor of field emergence, especially because most corn is planted as soon as soil temperatures approach 50°F. Various labs also have other tests in attempt to refine the evaluation of seed quality within a seed lot.
Attempts to standardize the testing systems among labs has been done by various groups including the International Seed Testing Association (ISTA) and Society of Commercial Seed Technologists. Despite efforts to standardize among labs it is common for results of testing referee samples when drawn from the same commercial bag to have a wide range. One example, a referee corn test sent to 30+ public and private labs resulted in warm test range of 86 to 98 and cold test range of 78-93%. This range is not because labs are making errors but it is more a problem that not all seed in a sample are of equal quality. Some are vigorous, some are a range of less vigorous and some are dead. It would be easier, and more consistent between labs if seed within a sample were either dead or alive.
The problem comes with those less vigorous seed. How do you predict which ones will emerge in the field? Will they emerge so far behind the neighbor plants that they won’t compete? Each lab attempts to classify those late germinating seed. Those that only show a root and not a shoot are classified as non-germinating. Those with torn coleoptile or first leaf are usually classified as ‘abnormal’ and most, I think, equilibrate them to non-germinating. The problem becomes more difficult with the seed that germinate slower than the others in the group. These individual seed are at some stage of deterioration but do eventually establish a shoot and root in the lab germination test. I think labs vary in how these seeds are classified are probably are expressed differently with different test methods. As the quality of seed deteriorates and the percentage of germinating seeds decreases, so does the percentage of seed with late germination increases. As a result, the differences among labs also increases.
Ideally a lab first works for consistency within the lab method and then attempts to relate the results to field performance. The latter requires multiple reps and locations and perhaps multiple hybrids as well.
We want things to be simple but it is amazing how often biology is not.
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.