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Exploring the density tolerance, yield potential paradigm

Principal Investigator: Elizabeth Lee

Research Institution: University of Guelph

Timeline: September 2010 – September 2015


  • Determine if planting density tolerance and yield potential are mutually exclusive biological processes.
  • Evaluate the genetic variation for yield potential in the elite germplasm pool.
  • Investigate whether genetic improvement in density tolerance is in part due to increasing the proportion of the spikelets that develop normally.
  • Investigate how genotype by environment (GxE) affects kernel number per plant and influences the proportion of normal spikelets on an ear initial.
  • Investigate whether the genetic variation that gives rise to the Long Ear phenotype in the Iowa Long Ear Synthetic (BSLE) population reduces the proportion of spikelets that develop atypical morphology.


  • The improved understanding of GxE effects on kernel number may lead to improved corn breeding programs.

Scientific Summary:

Grain yield in maize is directly proportional to the kernel number and has increased nearly 7-fold in less than 70 years of intensive breeding efforts. Accompanying this nearly 7-fold increase in grain yield was an equally impressive enhancement in general abiotic stress tolerance: plant population density stress, nitrogen stress, cold temperature stress, water stress, weed competition, and herbicide tolerances have been enhanced during this period. What is most surprising is that this was an unintended consequence of selection for increased grain yield. Equally as surprising, in light of the ‘positive’ unintended consequences of selection, is that the yield potential of the plant (the number of kernels) under ‘optimal conditions’ has not changed. Why? This question was the focus of this research project.

We have shown with this research that it is possible to increase both yield potential and density tolerance, as they are not antagonistic or mutually exclusive processes. We also demonstrated that despite 70+ years of selection, the elite Iodent germplasm pool still contains genetic variation for yield potential. There may also be genetic variation for yield potential in the elite Stiff Stalk germplasm pool, but it was not present in the sample that we used. Furthermore, the genomic regions associated with yield potential are distinctly different than the regions involved in density response. These findings suggest that we still have the ability to make genetic progress in grain yield. We also showed with this research that there is a relationship between the number of properly developed florets and kernel number, but that this relationship breaks down across years, suggesting that there are other factors involved in determining kernel number. Finally, we demonstrated that Long-Ear genetics represents a novel source of genetic variation that increases the amount of pre-silking biomass that is accumulated, which may serve to further enhance genetic gains in grain yield in the shorter growing seasons.

Funding Partners:

Natural Sciences and Engineering Research Council of Canada

Project Related Publications:

Jaroenchai, C. (2017). Potential of Long-Ear Genetic Background to Improve Short-Season Maize Hybrids. [PhD dissertation, University of Guelph].

MacKenzie, J.O. (2015). An Examination of Genetic Improvement to Floret Number and Morphology of Maize. (Zea mays L.). [MSc thesis, University of Guelph].

Moum, G. (2015). Year and Plant Population Density Effects on Ear Initial Development and Grain Yield. [MSc thesis, University of Guelph].