A century of corn breeding to boost yields in the US Midwest may also have made the crop more vulnerable to the warmer temperatures expected from climate change.
The amount of corn grown in the US more than fivefold in the 20th century through a combination of cultivation, agricultural intensification and favorable temperatures. But the warmer and drier weather expected to arrive due to climate change threatens to slow or even reverse those gains.
“It’s pretty serious,” says Patrick Schnable at Iowa State University. “If you look at mid-projections, corn yields are going down.” The worst-case scenarios predict a yield drop of as much as 50 percent by 2100.
To investigate whether corn breeders could develop more hardy varieties, Schnable and his colleagues looked at data from corn crop trials in four Midwestern states between 1934 and 2014, along with temperature data from the same years. The trials involved nearly 5,000 different varieties, allowing the researchers to track the influence of both climate and breeding on yield.
They found that after decades of breeding, maize varieties became more tolerant of moderately high temperatures between 32˚C and 34˚C (89.6˚F and 93.2˚F). However, many varieties became less tolerant of intense heat above 38˚C (100.4˚F), indicating a genetic trade-off between breeding for a 20th-century climate and a 21st century.
“The trade-off there is bad news if you’re in a high-temperature area,” says team member Aaron Kusmec at Iowa State University, though it’s unclear exactly why it happens, he says.
Such intense heat is rare in the Corn Belt, but could become more common with climate change, he says Ethan Butler at the University of Minnesota. The fact that corn adapts differently to moderate and intense heat shows that “the exact magnitude of the warming is going to make a very big difference,” he says.
While the trade-off suggests that breeding varieties that can tolerate both moderate and severe heat will be more challenging, the amount of genetic variation in response to temperature means that careful breeding or genetic engineering could address this vulnerability. “Corn is so flexible,” says Schnable. “It’s pretty extraordinary.”
PLoS Genetics
DOI: https://doi.org/10.1371/journal.pgen.1010799
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