It is sad that we, and corn seed, age. The mechanisms between us and them may be similar in that mitochondria are probably involved in all deteriorating living cells. These organelles which can number a few hundred in a cell, are the main sites for transformation of stored carbohydrates into useable energy for other cell functions. Mitochondria have their own DNA and are composed largely of membranes. Dehydrated seed results in mitochondria functioning at a very low level resulting in being unable to repair deteriorating membrane structures. While at very low kernel moisture levels (6-14%?) and cool temperatures (less than 50°F (?) further damage is limited. Precise moisture percentage and temperature for best storage of maize seed probably varies for genotype and seed condition but the general concept remains.
Seed imbibition of water is a physical phenomenon with little inhibition from the pericarp or seed coat. Seed treatments added to seed can slow down the imbibition, apparently giving the renewed mitochondrial function more time to repair damaged membranes. On the other hand, only increasing kernel moisture slightly can cause more membrane damage to occur, but not repaired. Increasing moisture more while at low temperatures (50°F) has the same effect. Corn seed planted in cold soils will imbibe water but the low temperature inhibits normal cell function, including repairing mitochondria. Those individual seeds with the most mitochondrial damage are likely the ones that struggle to germinate when the soil temperatures do heat up.
Seed producers are aware of the significance of inadvertently adding a small amount of moisture, such as from a seed treater before bagging by designing their process to limit the water and allowing for drying after application. I recall a case in the Thailand in which a new fungicide seed treatment was applied to control downy mildews but the humid environment did not allow the seed to dry after application. Seed germination quality quickly deteriorated as a result. Accelerated aging test of corn seed is based upon placing seed in an environment of 100% humidity and 113°F for 3 days, then planting in germination test to record the reduced germination. It is intended to predict the viability of the seed after storage. It is notable that even under this condition, all seed within the sample are not equally affected. Some germinated normally, some eventually and some not at all. This is typical of normal, well treated aging seed lots. Each individual seed is in a slightly different condition. We expect maximum performance when emergence is uniform. Seed quality is a factor influencing this trait.
We all want things to be simple but it is amazing how rarely this happens.
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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.