Corn Conundrum

Highly productive corn varieties have more trouble adapting to changing environmental conditions, so more balanced breeding may be needed

When in place, plants have no choice but to adapt to their environments, responding to stresses like drought or pests by changing how they grow. On a broader scale, crop breeders need to be able to develop new varieties that are adapted to a new location or changing growing conditions in the same area.

Both types of adaptation rely on a pool of possibilities, the combinations from which one can choose. For the individual plant, those possibilities depend on the genome it was born with. For breeders, that pool of possibilities is the whole range of genomes of cultivated crops, which they can blend together to create new varieties.

CALS researchers wanted to know whether the last 100 years of selecting for corn that is acclimated to particular locations has changed its ability to adapt to new or stressful environments. By measuring populations of corn plants sown across North America, they could test how the corn genomes responded to different growing conditions. What they found is that artificial selection by crop breeders has constricted the pool of possibilities for North American corn varieties.

A drone’s eye view of research plots for an experimental field maize hybrid grain trial at UW-Madison’s West Madison Agricultural Research Station. Photo by Dustin Eilert

In a recent issue of Nature Communications, agronomy professor Natalia de Leon MS’00 PhD’02, her student Joe Gage PhDx’19, and colleagues at several institutions concluded that the existing corn varieties are strong and stable, but they are less flexible in their ability to respond to various stresses. At the same time, these corn populations might have a reduced ability to contribute to breeding programs that seek to create new varieties adapted to novel environments.

“Over the last 100 years, people have definitely improved cultivars,” explains de Leon, the senior author of the report. “What we were trying to do in this study is to measure whether by doing that we have also limited the ability of the genotypes to respond to environments when they change.”

By intensively breeding for high yield — in Wisconsin, for example — those plants might lose the flexibility to respond to environments that are very different from Wisconsin growing conditions. To test this idea, de Leon and her colleagues at 12 agricultural universities in the U.S. and Canada devised a large field trial with more than 850 unique corn varieties growing in 21 locations across North America. There were more than 12,000 total field plots where researchers measured traits like yield and plant height while recording weather conditions.

The massive experiment is possible only because of a collaboration called Genomes to Fields, which is led by de Leon, UW–Madison agronomy professor Shawn Kaeppler BS’87, and others. The project stretches across 20 states and parts of Canada. This provides precisely the range of various field conditions required to tease apart the different contributions of the genomes and of the environments to the final traits of the corn.

De Leon and her collaborators found that the regions of the corn genome that have undergone a high degree of selection — for example, gene regions that contribute to high yield in a particular location — were associated with a reduced capacity of corn to respond to variable environments compared to genomic regions that weren’t directly acted on by breeders. The upshot is that the modern corn varieties are very productive in the environments they are grown in, but they might have a harder time handling changes in those environments.

“The data seem to point to the idea that by selecting genotypes that are better suited to be more productive, we are eroding variability that might be important as we move into a world where climate might be more erratic and where we might need to move cultivars into places where they haven’t been grown before,” de Leon says.

Yet this loss of flexibility is an inherent trade-off for highly productive cultivars of corn, she says.

“When you try to adapt cultivars to many different environments, you end up with plants that are not great anywhere,” de Leon says. “The cost of maintaining this plasticity is to the detriment of maximum productivity.”

“So we have to strike the right balance in the long term,” she says.