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The overall objective of the research is to identify and quantify physiological mechanisms that influence grain yield of maize grown in a production environment, using a top-down approach. In this approach, studies of a phenomenon are started at the canopy-level of organisation and may proceed to lower levels of organisation (e.g., leaf carbon exchange rate, enzyme kinetics, gene expression) if warranted. Specific objectives of the research focus on mechanisms associated with the efficiency of maize production (i.e., agronomy) and the efficiency of genetic improvement in maize (i.e., maize breeding).
One major focus of the program has been the physiological bases for genetic yield improvement. Genetic yield improvement in maize has been in the order of 1.5% per year during the past 7 decades in North America. Results of our research have shown that stress tolerance has been the major factor that has contributed to the genetic yield improvement in maize. Indeed, potential rates of important physiological process apparently have not changed. Our current research is focused on differential effects of low night temperature during the grain-filling period on leaf carbon exchange rate (CER) among maize genotypes and the identification of differences in gene expression associated with the CER response. We also have reported evidence that heterosis confers stress tolerance and we are examining the physiological bases for heterosis in maize.Quantification of maize yield potential has been another long-term focus of the program. The two- to three-fold discrepancy between maize yields reported occasionally for maize grown under commercial production environments (e.g., grain yield > 21 Mg/ha) and average North American maize yield, challenges our understanding of plant physiology, in general, and of the physiology of maize production, in particular. We have been using computer simulation of maize growth and development, and measurements of potential-production processes to estimate the effect of yield-limiting factors. It is possible that processes genetically altered to improve stress tolerance are the same as those that are altered by means of environmental manipulation under extremely high yielding conditions.
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