Corn seed ageing

​It initially surprises people accustomed to manufacturing inanimate objects, that seed are living organisms that change after production.  Furthermore, despite the fact that all of the seed within a seed lot may be genetically identical, each has its own physiological state at any specific time.  Some seed within that lot may be vigorous at a specific time, while others may be dead, and others may be weakened to the point that they germinate but only emerge from the soil at a later time.  Seeds do age but not all at the same rate.
 
Genetics influence the rate of ageing in corn seed.  Chromosomal DNA affects structural aspects of seed, affecting reactions to important environmental pressures such as drying rate, pathogen resistance and vulnerability to handling damage. DNA of mitochondria influence the respiration process needed for the energy to grow new tissue during germination.  Despite all seed of a single cross hybrid have the same chromosomal DNA and probably the same mitochondrial DNA if harvest from the same parent, each seed’s environment can be sufficiently different to affect the rate of ageing.
 
It is well established that seed production environments can include stresses that affect the rate of ageing in the field.  It may be drought stress after pollination or delay in harvest because of rain allowing the seed to remain at a higher moisture for a prolonged time.  A week delay in harvest may have a detrimental effect on seed’s ageing process.
 
Seed’s produced on a single ear do not have exactly the same environment.  Pollination within that ear in the seed field occurred within 4-5 days, as the first silks to emerge are towards the base of the ear.  They are not all equally exposed to pathogens.  Artificial drying rate is a major factor affecting the delay of ageing in corn seed.  Seed shape and location on the ear must have some interaction with the drying rate.  Further handling of the seed during shelling, seed treatment and bagging is not equal for each individual ear.  Seed producers attempt to handle seed gently and carefully to avoid damage, but some individual seeds inevitably are more affected than others.
 
Our company evaluates germination and emergence of corn seed samples.  Nearly always, if a sample has a low percent of dead seed, the emergence from our artificial soil mix is uniform.  As the seed percent of germinating seed decreases, the uniformity decreases as more seedlings do finally emerge, some only showing the ‘spike’ (coleoptile) while others have third leaf unfolded.  It is rare to samples in which the seed are only dead or vigorously alive.  It is much more common to see intermediate stages of ageing in samples with a few dead or samples in which nearly all seedlings are growing vigorously.
 
Seed producers attempt to manage genetics, production environments and testing to provide high performing seed for crop producers.  Ageing rate of seed is not always manageable and sometimes seed and crop producers get surprised.