Imbibitional chilling

​Corn seed is vulnerable to damage from soon after pollination in seed field until planting in the field.  Each cell in the embryo has membranous tissue that could be damaged from insufficient moisture during embryo formation.  Fungal pathogens can infect the seed as it develops.  Delaying harvest, perhaps because of weather problems, can result in initiating an aging process of cytoplasm of cells.  Too slow a drying process, perhaps because of inadequate dry air movement within the seed facilities can also contribute to cell aging.  Excess heat during that drying also affect the membranes within the cells.  Rough handling of the seed can result in breakage of the pericarp, allowing faster imbibition of water when in the field.  Genetics of the female parent affects vulnerability to each of these factors.
 
These damages rarely affect all the seed within a lot.  There is a tendency for the damage to be greatest at both ends of the ear, with the flat sizes generally having the least damage.  It is not clear of the cause but perhaps the embryos in rounds have less physical damage protection.  It appears that the damage is not evenly distributed in all cells of the embryo. Individual plants that show malformation during germination often show major injury in shoot meristem, resulting in radical growth but no stem. Injury to cells in the hypocotyl area is believed to be the cause of shoot finally emerging but twisted and clearly behind in growth compared with adjacent seedlings.
 
Imbibition, in which water allow the dehydrated membranes to swell and activate will allow some damage to repair.  Adequate heat is important to generate the energy generated by undamaged cytoplasm to promote repair. Generally, temperatures below 50°F (10°C), inhibit membrane damage in the embryo.  Imbibition chilling can result in lowering emergence in the field.
 
Corn breeders select for multiple performance characteristics, including tolerance of potentially damaging seed production stresses.  Combining all the favorable characteristics is never perfect.  Seed production methods aim to reduce stresses but nature does not always cooperate.