Scientists announced Thursday that they are approaching a milestone in humanity’s ability to improve bread wheat.
One of the most common and most versatile crops on the planet — the main food staple for a third of the world population — wheat is remarkably good at adapting to change. But efforts to grow higher-yielding, more nutritious and more resilient wheat in response to population growth and climate change have been slow for one simple reason. Its genes are a big, complicated mess.
Many scientists thought that it would be impossible to map the genome of wheat — to figure out how its genes are ordered so that specific traits can be more quickly identified. But a group made up of scientists, breeders and growers say that they’re more than halfway there and that an entire sequence is on the horizon.
Genome sequencing has revolutionized the process of breeding corn and rice, experts said, and is especially important given the stress that climate change will put on the food supply as the world’s population booms.
“Human civilization rests on a small handful of crops, all of which were developed with much more stable weather conditions than we see now,” said Patrick Schnable, an Iowa State University professor who worked on the genome sequencing of corn. “In a world with climate change, we need to help those crops adapt quickly.” And to do that, he said, one needs the genome sequence.
“I was told by a breeder that it was the single most valuable thing the government has ever done for them,” Schnable said. The genetic information has been used to increase crop yields and make crops more resilient to stresses such as pests and weather change.
The same has been true for rice. “It’s accelerated the discovery of the genes involved in many traits, including those for higher yield and disease resistance,” said Jan E. Leach, a Colorado State University professor who is not involved in the study. “It’s always boggled my mind how ridiculous it is to not have [a complete genome] for wheat,” she said, “so this is great news.”
Thursday’s announcement reported that about half of bread wheat’s genome has been sequenced, which might not sound impressive. But until recently, scientists had something like 5 percent of the information, said Kellye Eversole, executive director of the International Wheat Genome Sequencing Consortium (IWGSC), which organized the research.
She compared the sequencing thus far to a partially completed map. After starting with an empty map and a list of roads, she said, the researchers now have about half the highways in place. “It’s not very well ordered,” she said. “You might know there’s a Route 1, and that it’s in Virginia, but you don’t know exactly where it is. But it’s a guide, and it’s accelerating us towards that complete map.”
A second study, also published Thursday, provided a nearly full sequence for one wheat chromosome. “It’s like they took the state of Maryland,” Eversole said, “and positioned all of its roads and even the houses.” With about 94 percent of the information in place, she said, this single chromosome is proof that the whole genome can be decoded.
Why all the confusion? Bread wheat is complex — the result of multiple cross-breedings over thousands of years in farmers’ fields. Although some varieties of wheat are diploid (with two sets of chromosomes), like humans, bread wheat is made of three diploid genomes combined. And each of the three genomes contains nearly twice as many genes as the human genome. The two most common varieties of rice, which were sequenced in 2002, contain as many as 50,000 and 55,615 genes each. Bread wheat contains as many as 124,000.
Despite the lack of genetic knowledge, wheat farmers and engineers breed wheat to produce desired traits all the time. And wheat’s large number of redundant genes allows it to switch traits from generation to generation, even without human help.
“Bread wheat already exhibits a lot of adaptation,” said Jane Rogers, who worked on the Human Genome Project and serves as a co-director of the IWGSC. “It’s one of the most well-adapted plants on the planet. It grows in the greatest variety of soil types and climates and has the ability to respond to different pests and diseases.”
With a complete sequence, which the IWGSC hopes to produce within three years, scientists can better understand how wheat manages its adaptations — and encourage some that suit human needs.
“Knowing what genes are on which chromosomes will allow us to accelerate breeding by putting the right genes into the right wheat populations,” Eversole said, “In the long term, this means more rapid progress for wheat.”
And it’s not just about genetic engineering, she said. Understanding the genetic interactions behind the visible traits that farmers observe in their crops will help them breed more intelligently. “When you can look at related species and understand why they’re different,” Eversole said, “it allows you to use them together more efficiently.”
Scientists involved in the IWGSC project released a related paper Thursday to just that effect, examining how species of wheat are interrelated.
The rice genome is already being put to practical use. In May, the 3000 Rice Genomes Project released the sequences of 3,000 strains of rice to the general public. The 13.4 terabytes of data, researchers told news media, would help fight global hunger and food scarcity through improved crop yields.
Of course, Eversole said, genetic information is just one piece of the puzzle. “You need to look at bread wheat’s relationship with other plants, microbial communities and the environment,” she said, to name just a few factors in a wheat field’s success. “So this is just a foundation.”