How bread and wheat gave rise to a civilization of 8 billion people

A major international study has unveiled new insights into how bread wheat played a pivotal role in transforming the ancient world, ultimately becoming the iconic crop that sustains a global population of eight billion today.

“Our findings shed new light on an iconic event in our civilization that created a new kind of agriculture and allowed humans to settle down and form societies,” said Brande Wulff, a wheat researcher at King Abdullah University of Science and Technology (KAUST) and one of the lead authors of the study.

Importance of global collaboration 

Study co-author Cristobal Uauy, a group leader at the John Innes Center, said this work exemplifies the importance of global collaboration and sharing of data and seeds across countries. 

“We can achieve so much by combining resources and expertise across institutes and across international boundaries,” said Uauy.

Secret of bread wheat’s success 

The research, conducted by the Open Wild Wheat Consortium (OWWC), points to the genetic diversity of a wild grass called Aegilops tauschii as the secret to bread wheat’s success. 

Bread wheat is a hybrid of three wild grasses, containing three genomes (A, B, and D) within a single complex plant. Aegilops tauschii, an otherwise unremarkable weed, provided bread wheat with its D-genome when it hybridized with early cultivated pasta wheat in the Fertile Crescent between eight and eleven thousand years ago.

This chance hybridization near the southern Caspian Sea sparked an agricultural revolution. The cultivation of bread wheat quickly spread across diverse climates and soils, as farmers eagerly adopted this dynamic new crop, known for its high gluten content that produces a more elastic and airy dough ideal for breadmaking.

Rapid spread of bread wheat 

The rapid spread of bread wheat across such a wide geographical range has long puzzled researchers.

Bread wheat does not exist in the wild, and the hybridization event that introduced the D genome into the plant’s existing A and B genomes created a genetic bottleneck, significantly reducing the new species’ genetic diversity compared to the surrounding wild grasses. 

Furthermore, wheat is an inbreeding species, meaning it self-pollinates, which would typically suggest that bread wheat might struggle to thrive outside its original Fertile Crescent environment. So how did it become so widely cultivated and globally dominant?

Focus of the research

To solve this mystery, the international research team assembled a diversity panel of 493 unique accessions spanning the geographical range of Aegilops tauschii, from northwestern Turkey to eastern China. 

From this panel, the researchers selected 46 accessions that reflected the species’ traits and genetic diversity to create a Pangenome – a comprehensive genetic map – of Aegilops tauschii.

Using this Pangenome, they scanned 80,000 bread wheat landraces – locally adapted varieties – held by the International Maize and Wheat Improvement Center (CIMMYT) and collected from around the world. 

Genetic variability of wheat bread

The data revealed that approximately 75% of the bread wheat D-genome is derived from a lineage (L2) of Aegilops tauschii that originates from the southern Caspian Sea. The remaining 25% of the D-genome comes from lineages across the species’ range.

Simon Krattinger, co-lead author of the study, noted that this 25% influx of genetic material from other lineages of tauschii has contributed to and defined the success of bread wheat.

“Without the genetic variability that this diversity brings, we would most likely not eat bread on the scale we do today. Otherwise, bread wheat today would be a regional crop – important to the Middle East – but I doubt that it would have become globally dominant without this plasticity that enabled bread wheat to adapt,” said Krattinger.

Distinct lineage of Aegilops tauschii

A previous study by the OWWC had revealed the existence of a distinct lineage of Aegilops tauschii, known as L3, which is geographically restricted to present-day Georgia in the Caucasus region – about 500 kilometers from the Fertile Crescent. This L3 lineage is significant because it has contributed the best-known gene for dough quality to bread wheat.

In this study, the researchers hypothesized that if this gene was introduced to bread wheat in a manner similar to how Neanderthal DNA was integrated into the human genome, they would find landraces in the CIMMYT collections with a higher proportion of this L3 lineage. 

Indeed, their data showed that wheat landraces collected from the Georgian region contained 7% L3 introgressions in their genomes – seven times more than the bread wheat landraces collected from the Fertile Crescent.

“We used the L3 tauschii accessions as a guinea pig to track and trace the hybridizations using 80,000 bread wheat landraces,” Krattinger said. 

“The data beautifully supports a picture where bread wheat emerges in the southern Caspian, then with migration and agricultural expansion it reached Georgia, where gene flow and hybridizations with the peculiar, genetically distinct and geographically restricted L3 accessions resulted in the influx of new genetic material.”

“This is one of the novel aspects of our study, and it confirms that using our new resources, we can trace the dynamics of these introgressions in bread wheat.”

Broader implications of the study 

Beyond solving this age-old biological mystery, the new Aegilops tauschii open-source Pangenome and germplasm made available by the OWWC are already being used by researchers and breeders worldwide. 

The data will help experts discover new disease resistance genes that will protect wheat crops against long-standing agricultural threats like wheat rust. Researchers are also mining this wild grass species for climate-resilient genes that can be bred into elite wheat cultivars.

At the John Innes Center, researchers worked closely with colleagues from KAUST, employing bioinformatic approaches to track the levels of DNA contributed to bread wheat by the L3 lineage of Aegilops tauschii. 

“The study highlights the importance of maintaining genetic resources such as the BBSRC-funded Germplasm Resources Unit here at the John Innes Center, which maintains historic collections of wild grasses that can be used to breed valuable traits such as disease resistance and pest resistance into modern wheat,” Uauy concluded.

The study is published in the journal Nature.

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