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Great Grain: A Look at the Continuing Evolution of Wheat

Some 12,000 years ago, nomadic hunter-gatherers in the Fertile Crescent – modern-day Israel, Jordan, Lebanon, western Syria, southeast Turkey, Kuwait, Iraq, and western Iran – took what is considered one of the most important steps in the evolution of human culture: They began harvesting, then replanting, naturally growing wild grasses, including the predecessor to wheat.

This reliable source of food, which also featured long-term storage capability, enabled the development of villages, then towns, cities, nations, and the growth of the human population from an estimated 1 million to more than 7 billion in only 11 millennia. Wheat has grown with and become the single most important food grain of that evolution, with modern world trade in wheat exceeding that of all other crops combined.

The first successfully cultivated wheats were einkorn, a diploid (paired chromosome) species, and emmer, a natural hybrid of two diploid wild grasses. While prehistoric farmers knew nothing of genetics, they nonetheless used cross-breeding – both accidental and deliberate – largely with wild grasses, and selection of the best grains to seed future fields. That led to stronger, higher yield and more edible new varieties of wheat – and the eventual demise of einkorn and emmer by the Bronze Age.

The new wheats were polyploid (more than two paired sets of chromosomes), resulting largely from cultivation processes and experimentation by growers. Tetraploid (four sets of chromosomes in each cell) varieties of domesticated wheat became predominant as human cultivation intensified and eventually were crossed (apparently by accident) with a wild diploid species, creating hexaploids (six sets of chromosomes).

Today, durum (hard) wheat is tetraploid, while the more common bread wheats are hexaploid. Bread wheat has no natural wild hexaploid progenitor, but is a farming-associated natural hybrid that has become the world’s leading crop.

Bikram Gill

Bikram Gill, Ph.D., is the director of the Wheat Genetics Resource Center at Kansas State University. He and his team have mapped the wheat genome and subsequently were able to identify a gene that prevents preharvest sprouting, a problem that can cause crop losses estimated at $1 billion annually. Credit: Kansas State University Division of Communications and Marketing, David Mayes

Wheat accounts for more than 20 percent of total human food calories and is the staple food for about 40 percent of the world’s population, primarily in Europe, North America, and western and northern Asia. About 95 percent is bread wheat, with the remainder being durum, used in pasta and semolina products.

Modern wheat falls into six classifications:

hard red winter

hard red spring

soft red winter

durum (hard)

hard white

soft white

The higher gluten content of hard wheats makes them best for making bread, rolls, and all-purpose flour, while soft wheats are used for flat bread, cakes, pastries, crackers, muffins, and biscuits. Wheat is easily digested by nearly 99 percent of the human population, is highly nutritious, is responsible for nearly 700 million tons of food produced each year, and can be grown in environments from near arctic regions to the equator, sea level to 13,000 feet.

Wheat accounts for more than 20 percent of total human food calories and is the staple food for about 40 percent of the world’s population.

Largely because of its dominant place in the human diet, wheat also has been the subject of numerous modifications, from the first human farmers who selected the best of the predecessor grains to cultivate, to “semi-dwarf wheat,” a disease-resistant, fertilizer-amenable strain with a shorter, thicker stock that could bear the increased weight of the grain. The resulting increase in reliable yield won developer Norman Borlaug the 1970 Nobel Peace Prize for the subsequent drop in world hunger and starvation.

By 1997, an estimated 81 percent of the world’s 530 million planted acres of wheat were growing semi-dwarf wheats. A U.S. Department of Agriculture (USDA) study the following year showed U.S. wheat yields averaging 41.7 bushels per acre; that peaked at 47.1 in 2014.

But Borlaug’s achievement was only one of many changes in wheat types and processing methods across the millennia, especially in the past century. Contrary to some claims, however, all result from cross-breeding different strains of wheat and related plants, not genetic engineering to introduce genes from unrelated species. In fact, many recent experiments and advances have involved controlled cross-breeding of modern wheat strains with some of the ancient wild grasses – or their existing equivalents – responsible for the evolution of early wheat in the first place.

In wheat research and development, a better understanding of the plant’s genetic structure allows scientists to identify and isolate those naturally occurring genes that have an impact on every aspect of the resulting crop’s viability, from grain size to pest and environmental resistance to yield – both per stalk and per acre – to ease of processing.

For example, Bikram S. Gill, Ph.D., director of the Wheat Genetics Resource Center (WGRC), created in 1979, and his team at Kansas State University have mapped the wheat genome and improved wheat germplasm to enable the creation of new varieties of wheat with characteristics designed for specific needs, such as enhanced insect and disease resistance. The only major food plant not previously sequenced, the wheat genome is nearly three times the size of the human genome.

The wheat genome sequence provides a foundation for studying genetic variation and understanding how changes in the genetic code can impact important agronomic traits.

Gill said the blueprint allowed researchers to study sequenced segments of the common wheat genome to find a naturally occurring gene, called PHS, that prevents preharvest sprouting, in which significant early rain causes the wheat grain to germinate too soon, leading to significant crop losses. Preharvest sprouting causes wheat crop losses estimated at more than $1 billion each year. And given its massive and complex genome, Gill said it would have been impossible to isolate PHS without sequencing the wheat genome.

“Preharvest sprouting is a very difficult trait for wheat breeders to handle through breeding alone. With this study, they will have a gene marker to expedite the breeding of wheat that will not have this problem,” Gill said.

In a Kansas State University news release, Kansas State associate professor of plant pathology Eduard Akhunov, a collaborator with the International Wheat Genome Sequencing Consortium, described the wheat genome blueprint as critical for plant science researchers and breeders.

“For the first time, they have at their disposal a set of tools enabling them to rapidly locate specific genes on individual wheat chromosomes throughout the genome,” he said. “This resource is invaluable for identifying those genes that control complex traits, such as yield, grain quality, disease, pest resistance and abiotic stress tolerance. They will be able to produce a new generation of wheat varieties with higher yields and improved sustainability to meet the demands of a growing world population in a changing environment.

“This is a very significant advancement for [the] wheat genetics and breeding community. The wheat genome sequence provides a foundation for studying genetic variation and understanding how changes in the genetic code can impact important agronomic traits. In our lab, we use this sequence to create a catalog of single base changes in DNA sequence of a worldwide sample of wheat lines to get insights into the evolution and origin of wheat genetic diversity.”

In August 2013, the National Science Foundation (NSF) named Kansas State University as the lead institution for the world’s first Industry/University Cooperative Research Center (I/UCRC) on wheat. As the first such NSF center for any crop plant, the Kansas State facility is focused on improving food production and disease resistance for wheat and other crop plants; it also serves as a primary training site for the next generation of researchers.

Co-directed by Colorado State University, NSF I/UCRC collaborators include Kansas State’s departments of agronomy, plant pathology, entomology, and grain science and industry; USDA’s plant science and wheat genetics units; the Kansas Wheat Commission and Kansas Wheat Alliance; and several corporations, including Bayer CropScience, Syngenta, Limagrain, Dow AgroSciences LLC, General Mills, and the Heartland Plant Innovation Center.

With the creation of the NSF I/UCRC, the Wheat Genetics Resource Center gene bank, comprising some 14,000 wild wheat species strains and 10,000 genetic stocks – the largest in the world – has relocated to the new Kansas Wheat Innovation Center. As a result, it has become the primary source for wild wheat species, genetic stocks, and genomic resources for researchers worldwide. And with current and future scientists working alongside industry and academic partners on new genetic research, Gill said, future global wheat breeding and crop yields will be significantly accelerated.

With wheat’s status as one of the top sources for food staples for the majority of the world, the advances made by cutting-edge research facilities such as the WGRC and NSF I/UCRC are key to feeding the planet’s 7 billion-plus people.

With an increasingly detailed understanding of wheat at the genetic level, future research also will be able to expand beyond plant resiliency and yield and into improvements in taste, wheat-based products, and even the possibility of using food crops to improve human health through so-called “functional food.”

“People as consumers are more interested in not only getting calories from food, but getting health benefits, as well,” Gill said.

Having the genome is only the beginning of the effort, however.

“The wheat genome only has 21 chromosomes, but each chromosome is very big and therefore quite complicated,” Akhunov explained in the Kansas State University news release. “The largest chromosome, 3B, has nearly 800 million letters in its genetic code. This is nearly three times more information than is in the entire rice genome. So trying to sequence this chromosome – and this genome – end-to-end is an extremely complicated task.”

But with wheat’s status as one of the top sources for food staples for the majority of the world, the advances made by cutting-edge research facilities such as the WGRC and NSF I/UCRC are key to feeding the planet’s 7 billion-plus people – a number some estimates predict will grow to 10 billion in the next four decades and reach nearly 11 billion by the end of the century, due to a combination of high birth rates in the developing world, continued improvements in infant mortality, and rising life expectancy worldwide.

“As the global population continues to rapidly increase, we will need all the tools available to continue producing enough food for all people in light of a changing climate, diminishing land and water resources, and changing diets and health expectations,” said Sonny Ramaswamy, Ph.D., director of USDA’s National Institute of Food and Agriculture, in the news release. “This work will give a boost to researchers looking to identify ways to increase wheat yields.”

Borlaug

Near some wheat plots in Kenya, Nobel Peace Prize winner Norman Borlaug, Ph.D. (second from left) consults with leaders from Kenya and CIMMYT (the International Maize and Wheat Improvement Center) about Ug99, a virulent strain of the wheat stem rust disease that poses a serious threat to wheat. Borlaug’s development of semi-dwarf wheat resulted in increased crop yields and a drop in world hunger. Credit: Photo by Kay Simmons

All of the changes already seen in modern wheat have significantly changed the very nature of wheat-based products; as a result, those eaten today, in the United States and around the world, bear little resemblance to those from only a few decades ago. The hardier wheat variants also have simultaneously increased the amount of the food grain available to importing nations and greatly expanded the ability of many more nations to become wheat exporters.

About half of all U.S. wheat is exported, but despite significant growth in global demand, the total U.S. acreage devoted to wheat has dropped by roughly one-third – nearly 30 million acres – since its peak in 1981.

“The number of major exporting countries that can supply these importers has expanded in recent years from the traditional exporters (the United States, Argentina, Australia, Canada and the European Union). Ukraine, Russia, and Kazakhstan have become significant but highly variable wheat exporters. These three Black Sea exporters together surpassed U.S. exports in 2009/10 and again in 2011/12 by 11.6 million metric tons (mmt) and 10.1 mmt, respectively. During the mid-1990s, their combined wheat exports were less than 5 mmt,” according to the U.S. Department of Agriculture’s “Wheat Baseline: 2014-23.”

“Since 1981 and 1982, when U.S. wheat exports accounted for about 45 percent of world exports, the U.S. export share has trended down, averaging about 20 percent over the last three years. … The five largest traditional wheat exporters (United States, Australia, the EU, Argentina, and Canada) are projected to account for more than 60 percent of world trade in 2023/24, compared with nearly 70 percent during the last decade. This decrease is mostly due to increased exports from the former Soviet Union. U.S. wheat exports are projected to generally be in a 28- to 30-million-ton range during the coming decade. However, the U.S. share of world exports declines over the projection period.”

As to the future, the “Baseline” report projects a continued expansion of world wheat trade by nearly 19 percent in the next 10 years, rising to 177.5 million tons, with import growth concentrated in developing nations where income and growing populations drive demand. That growth will be led by the 15 countries of the Economic Community of West African States, other Sub-Saharan African countries, Egypt, other countries in the North Africa and the Middle East region, Indonesia, and Pakistan.

However, the report also predicts a continuing decline in market share for American wheat growers.

“The U.S. wheat sector is facing long-term challenges as productivity gains and producer returns for competing field crops outpace those for wheat. Over the next 10 years, the planted area of U.S. wheat is projected to fall. Wheat yield enhancements are expected to continue to lag those for competing row crops, primarily corn and soybeans,” the USDA predicts.

“U.S. exports are expected to show little growth with the increased trade competition, particularly from Russia, Ukraine, and Kazakhstan. Furthermore, domestic food use, although growing, no longer provides the dynamic market growth experienced from the 1970s through the mid-1990s.”

Great Grain: A Look at the Continuing Evolution of Wheat

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  • United States
  • J.R. Wilson