Exploring the density tolerance yield potential paradigm

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Maize (Zea mays L.) breeders have been extremely successful in making continuous genetic improvement in commercial grain yield. In the US, over a 65-70 year period this progress amounts to approximately 2% per year or 117 kg/ha per year, with similar gains observed in Canada during the hybrid era (80 kg/ha per year). The genetic improvement over the past 65-70 years is the result of changing physiological attributes of the corn plant. But not all physiological aspects have changed. 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. Surprisingly, in light of the 'positive' unintended consequences of selection, is that yield potential did not change. Why has plant population density shown genetic improvement through intensive breeding efforts, while yield potential has remained unchanged? This proposal explores the relationship between plant population density tolerance and yield potential. Future gains in maize grain yields will no doubt come about through continued evolution of breeding methodologies and philosophies. Benefits derived via the proposed research are acquisition of new knowledge and expertise that may result in a paradigm shift with regards to future maize breeding selection methodologies utilized by the Canadian maize breeding industry.