Dissecting the Genetics of Complex Agronomic Traits for Crop Improvement

Maize, like many crops, is extremely diverse, especially when compared to mammalian diversity.  In the case of maize, that diversity is the product of evolution and adaptation over the last five million years.  There are more than 100 million common genetic variants distributed across the maize genome, which makes any two maize varieties far more genetically varied than humans and chimps are from one another.  This tremendous diversity has already allowed maize to respond to selection in amazing ways, but it also provides the potential for creating a more sustainable crop that satisfies some of the desperate nutritional needs facing many parts of the world.

By conducting some of the world’s largest complex trait studies and sequencing genomes (Genome Wide Association Studies, GWAS), we have evaluated what controls flowering, hybrid vigor, as well as a range of basic morphological traits.  In almost all of these cases, we found that the functional diversity of maize generally results from numerous genes of small effects.  In a few cases—notably the less complex traits involving nutritional quality (provitamin A content)—there are variants with large effects.  Importantly, once these effects have been identified in diverse germplasm, accurate predications can be made to drive breeding. 

The combination of the significant diversity inherent in maize, and the ability to manipulate both targeted small and large effects suggests that we will be able to tailor-make varieties of maize to respond to specific and changing needs, whether that be drought tolerance in one part of the world or a particular pest threat in another.  With advances in molecular marker techniques and new mathematical models, we can accelerate breeding three fold, even for the most complex traits. Plant breeding has the opportunity to play an important role in sustainability and human nutrition.  The challenge we now face is understanding how this remarkable variation interacts with numerous environments and ensuring that we maintain diversity in these rapid breeding efforts.