Germination

 ​Corn seed planting time is approaching in the northern hemisphere. The processes of successful producing and storage of the seed will soon come to fruition.  The selection of seed parents, care in the seed field of the last season and then the drying, shelling and storage all have an affect on reaching the goal of getting a uniform emergence in this next stage of growing corn.
 
Cells in a developing embryo are sufficiently mature to germinate in only 15 days after pollination if separated from the endosperm.  Early germination (vipipary) is inhibited by the presence of the plant hormone, abscisic acid, in the endosperm which negates the growth stimulant hormone, gibberellic acid, in the embryo.  This allows normal seed desiccation as water is replaced with starch deposits and eventual seed germination inhibition because of low water content.  Seed producers know that each genotype differs in the percent moisture to be used to harvest for optimum seed quality.  Generally, for most corn dent hybrids, that moisture is higher (+/-36%) than normal black layer moisture of 32%.  From there the moisture level must be rapidly decreased to less than 13 % to prevent excessive aging caused by damage to the cell membranes.  It is the art and science of the seed producer to bring the moisture down rapidly without using excess heat which also could damage the membranes.
 
Intactness of the pericarp affects the speed of imbibition of water in the soil.  Allowing the membranes surrounding each cell as well as the cell internal membranes to swell back to normal size with minimum injury is essential to their functions.  Cell membranes being the main structural component of embryo cells needed for energy conversion from starch in the mitochondria and translation of DNA to proteins, have a major effect on the germination quality of seeds.  Genetics of mitochondrial membranes, at least partly affected by the mitochondrial DNA, are probably one of the major reasons that seed quality varies between hybrid parents.  Mitochondria of the seed are replications of those in the female parent.  This is the major reason why choice of which hybrid parent becomes the seed parent.
 
Another major factor affecting on seed quality is the growing environment in the seed production field.  Stress, from drought or disease during the seed maturation period shows later in seed germination quality.  Such seed often becomes evident in germination tests done 4-5 months after seed harvest, sometimes in contrast to tests done only a few months earlier.  It is as if these seed had some membrane pre-harvest injury that when added to normal aging during these 4-5 months surpassed the minimum for normal germination.  These individual seeds either fail to germinate or are slower to emerge than other seed in the same seedlot.