Testing for corn seed quality
The fact that all individual seeds in a seed bag or a seed lot are not identical in terms of seed quality presents a problem for seed testing and seed companies. This problem gets greater as the more of the seed deteriorates as it gets difficult to judge those that do manage to push out the root and shoot from the seed. The ‘official’ practice is to designate those with torn or misshapen coleoptile or first leaf are called abnormals, and are usually equated as non-germinating in some labs. This is done under the assumption that these plants will emerge late or not at all when in the field.
Warm test methods vary, even with attempts to have similarity in materials, temperatures, watering and counting. Referee samples sent to 30+ public and private labs all testing seed from the same commercial bag of seed show a range of percent germinations of perhaps 5% when the average is high and 10% when the average among the labs is passing but below 95%. To accommodate this lab to lab variance, the legal range in actual germination printed on the tag on a bag of seed is 6% if the tag states 95% germination. Logical, systematic sampling of a seed lot and earnest efforts to test via the warm test still struggles to measure every seed’s germination quality.
Cold test germinations are generally the most consistent predictor of emergence in the field. This seems to apply at least in the temperate zone because corn is generally planted soon after soil temperatures are higher than 50°F. The principle of cold test is that when seed imbibes but is unable to repair damaged membranes, the seed will either die, or not germinate with the non-damaged seed. Methods for cold tests vary more among labs as each one attempts to mimic field conditions, many by adding soil to the test. This can cause some problem because the water holding capacity affects oxygen available for respiration in the seed. PSR Inc. uses an artificial soil mix with a surfactant to minimize this problem. The many slight differences in methods among labs adds to the range of results that shows when each lab tests referee samples. Ultimately a seed producer needs to choose the lab and procedure that most consistently predicts the genetic potential of their product that will not be affected by seed quality. And this is not easy. This spring, living seed of slightly varying germination quality will be placed in varying environments with everyone’s intent to get maximum performance by the end of summer.
Surely, testing of inanimate, manufactured objects instead of biological living things like seed is more defined but trying to understand the interactive dynamics of corn in its environments is more fun!
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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.