Photosynthesis, grain yield and stalk rot of corn

​Competition between roots and grain for products of photosynthesis can result in root death followed by premature wilting and death of the corn plant. This is followed by collapse of stalk tissue, followed by invasion by stalk rotting fungi. Increasing grain yield while maintaining stalk quality obviously requires increasing photosynthesis either per plant and /or per acre.  We have seen progress in this during the past 30 years by increasing the leaf area per acre, reducing the grain per plant but increasing the grain per land area.  Selection for better stalk quality along with grain yield under higher plant density also could be selecting the genetics for improved photosynthetic efficiency.
 
Some genetic input to leaf structure that affect capturing more light could be effective.  Chromosomal genetics and chloroplast genetics affect the number of chloroplasts and their productivity.  Mitochondrial genetics influences the efficiency of converting the carbohydrates into useful energy need to drive cellular physiology as well as building of the plant structures. Some beneficial characters such as leaf disease resistance are visible, but much is not obvious. A recent paper (Plant Physiology:10.1104/pp.18.00176) identifies mutants affecting the opening and closing the stomata, which affects the loss of water when open but also allows the CO2 movement into the leaf for carbohydrate synthesis.  There must be multiples of other mutants to critical aspects of increasing net photosynthesis per acre that are available but unknown. 
 
We currently mostly select for these mutants by yield testing for improved grain yield and stalk quality.  We don’t know the specifics of what genetics are responsible, but we have witnessed that this improvement has occurred and expect that it will continue even if we do not which mutations in corn’s 30000-40000 genes were mostly responsible. 
 
Agronomic practices are also contributing to improved yield and stalk quality affecting total plant physiology.  Weather also contributes as it affects the plants directly, nullifying some genetic advantages and favoring others.  Fortunately, the breadth of genetic variability available in this species allows general improvement in grain production.