Seed deterioration and emergence

​Corn seed germination quality is always temporary.  Female seed parent genetics, especially that of the mitochondria, area factor.  Seed with dormancy because of low moisture content remains alive as long as the mitochondria have a low level of respiration to maintain membrane integrity, it becomes more difficult if kept in humid environments at temperatures greater than 50°F.  We have seen many examples of seed kept on farms because 2019 weather prevented planting.  Some will show in the field this spring.
 
Perhaps, for the first 8 centuries of corn culture, the percent of seedlings emerging from seed planted was not as significant as the amount and type of grain produced.  Planting in hills or even by planters at low densities, favored genetics that produced larger ears if adjacent seed did not germinate.  Modern terminology attempts to identify hybrids that adjust of lower density by producing larger ears defining them as ‘flex’ ear types.  It is doubtful that there are only two types, flex and non-flex, but hybrids do have different tendencies when plants are less dense.  There are hybrids that will tend to go barren if planted too dense and there are others that will only show competitive yields if planted at high densities.  There are some that do not cut back on kernel numbers if crowded but will develop high percentage of stalk rot if planted too thick.  Recent years of corn culture in the USA has led to hybrids that tolerate planting a 33% higher density than 40 years ago- and give more stable high yields than hybrids of that era.
 
These modern hybrids may have genetics for more photosynthesis per acre, at least due to increased leaf area, but also consistent silking when under the stress from competing plants.  This may also favor selection of hybrids with less ‘flex’ and consequently a need for higher plant density.  Although best knowledge of the ideal plant density in any season only becomes apparent after harvest, there is more pressure now than 40 years ago to have a uniform emergence percentage of 90+% every season.
 
Every seed within a single cross hybrid may be nearly genetically identical, but not with identical germination quality and not planted in identical microenvironments.  Highest quality seed will tend to emerge uniformly, and seed producers make large efforts to produce such seed.  However, even with best genetics, timely seed harvest and care in handling the seed it is rare that field emergence is perfect.  It is a challenge to produce all seed lots with great quality and for testing systems to correctly predict the field emergence the following spring.