The world's population keeps growing, but the amount of wheat farmers worldwide are able to grow per hectare has leveled off.
According to a new study, that's because breeders and researchers have reached the limit of how much grain the wheat plant can produce.
The authors say achieving higher per-hectare yields of the world's third-most important cereal crop in the coming years will require a major scientific breakthrough.
Researchers looked at yields from wheat varieties bred by companies and universities across the North American Great Plains dating back to 1959.
"In the 50 years of breeding history, we've essentially almost doubled our genetic potential for yield," says wheat geneticist Bob Graybosch with the U.S. Department of Agriculture and the lead author of the new study in the journal Crop Science.
Peaked in the '90s
Unfortunately, Graybosch says, "There's got to be an upper limit on how much they can do, and it maybe looks like we're approaching that upper limit."
Data from Great Plains breeders show their varieties reached peak yields in the early-to-mid-1990s and have been leveling off ever since.
Graybosch says the last major leap forward in wheat genetics took place in the 1960s, and scientists will need to make another leap forward in order to keep up with population growth.
However, he notes that the study only talks about the crop's genetic potential - the plant's innate ability to produce grain.
"If we need more wheat," he says, "we can produce a lot more wheat."
Farmers in his state of Nebraska could double or triple the crop by using more irrigation or fertilizer. But that would be expensive.
Graybosch says farmers looking to produce more simply based on improvements in the crop's genetic potential may be out of luck.
"The farmers that are growing dry-land wheat may see the same yields from now on," he says. "They may not see increases in yield under dry-land conditions because we simply are shuffling the same genetic deck out there."
Many scientists acknowledge that wheat yields worldwide are not increasing fast enough to keep up with population growth. But they disagree on whether plant breeders have actually pushed wheat to its grain-producing limit. Breeders at some institutes outside the U.S. are still making improvements in the plant's genetic potential.
The reason yields have flattened out in the Great Plains, according to Brett Carver at Oklahoma State University, is that breeders have had to focus on developing resistance to diseases that plague the crop.
"We spend so much more time now looking at those yield-depressing factors that we tend to gravitate away from just going on the offense: breeding for yield outright," Carver says. "When you spend more time on defense, that's less time on offense."
Hans Joachim Braun directs the global wheat program at the International Maize and Wheat Improvement Center based in Mexico. He says wheat production worldwide has flattened out, but that it has more to do with farming practices than genetics. However, Braun adds, breeders will need to step up their efforts because demand for wheat is expected to grow by 50 to 70 percent by mid-century.
"And this is a real challenge, because wheat is very sensitive to higher increasing temperature. And if the temperature goes up as predicted due to global climate change, they may have maybe 20 to 25 percent less yields."
So even if there is genetic potential left in the wheat plant, Braun says feeding more mouths while fighting the effects of climate change will pose a major challenge to crop research for decades to come.