Hybrid seedling sensitivity to temperatures

​Moving corn from its tropical origin to temperate zones required adaptations for many characters. One character needed to advantage of the full summer season, including in some areas of the USA, was to plant as early as possible to avoid pollination problems caused by extreme heat during flowering and to avoid killing frost stopping grain filling.  It is common to observe that every field does not emerge and seedlings equally fast, but the many environmental factors complicate drawing conclusions as to cause.  Was it seed quality or was it due to soil content difference? 
 
One study (https://dl.sciencesocieties.org/publications/cs/articles/55/2/851) attempted to compare hybrids under controlled temperature and environments for leaf and root weights under differing temperature environments. Results supported the hypothesis that hybrids did differ in tolerance to cold temperatures after planting.  Methods and results in this presentation cited are a good read.
 
There are genetic differences for tolerance to cooler, early seasons, but the significance must be always be put in perspective of final hybrid performance. This character is only one of many influencing the performance of best hybrid for a season.  It among the many genetic-environmental reasons that rarely is the same hybrid the best in all fields or in all years. Genetics, seed production and environments interact each year as we have taken this species of tropical origin to temperate (and tropical) fields around the earth.