Most new crop seed is tested after drying and shelling and before bagging. Systematic sampling is done after sizing. These samples are tested for genetic purity, warm germination and cold germinations. These results are used for bagging decisions. After sizing and seed treatments are made seed is moved to bagging. Again, systematic sampling is made. Those samples are then tested at least in a warm and cold test. The warm test result is used for the reported germination printed on the bag tag. Germination percentage is within a statistically acceptable range of the published percent germination on the tag and within the month as published.
Not all individual seed within the bag are at exactly the same state of quality- some deteriorating faster than others. This could be related to position on the ear, or within the seed field or handling of seed after harvest. If 5% of the seed did not germinate in a December warm test, a few more percentage may (or may not) be deteriorating in the next few months. Seed companies attempt to estimate this rate by considering the cold test results or perhaps special tests. Suspect seed lots may be retested a few months later.
Each corn seed is a living organism, vulnerable to ageing from membrane deterioration including within the mitochondria, that transfer the energy from stored carbohydrates into usable forms for metabolism needed for cell growth and multiplication. Damage to membranes because of partial metabolic activation prior to artificial drying can affect mitochondrial activity when germination is encouraged. Physical injury to the pericarp can allow imbibition to be too rapid for cell membranes of the dormant cellular components, resulting in breakage. These membranes can self-repair but do this best at warmer temperatures. Leakage from injured kernels attracts micro-organisms that can further inhibit the seed metabolism.
It is a challenge to all involved to correctly predict the percentage of seed that will emerge in the field. Warm tests are often done at 70°F (21°C) as a measure of viability for a week after moistened. Successfully germinated seedlings have clear development of the primary root and shoot. Percentage of seeds showing these structures become the warm test result. Some seed will be slow to push both structures within that time. Those showing only a root are generally called non-germinated and not included in the percent germinated. There is some judgement needed for classification of those that are slow to push out both structures. The cold germination test in which the moistened seeds are kept at 50°F (10°C) for one week before moving to the warm test environment further amplifies the effect of the seed deterioration on germination. Some seed lot samples will express high germination percentages in both warm and cold tests. Usually those showing marginally acceptable warm test results usually have much lower cold test results, assumedly because the individual seeds with membrane damage could not self-repair after imbibition at low temperatures.
Professional Seed Research, Inc. plants corn seed under about ½ inch of artificial soil mix for warm and cold tests. Seedlings are counted when most plants show the third leaf. Individual seedlings that only show the ‘spike’ emerging are counted as not germinated on the assumption that these individuals, if they do emerge in the field, will be non-competitive plants. Uniformity of emergence of the 400 seed sample is also scored in the warm germination report.
The ultimate objective for all involved in corn seed is to allow full expression of the genetics on grain yield and not allow seed germination to be a detraction from that potential.
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.