The worldwide distribution of one of the most important pathogens of cereals is the result of human activity. Researchers from the University of Zurich traced the history and spread of wheat powdery mildew along wheat trade routes and found that the mixing of genetic ancestries of related powdery mildew species played a central role in the evolution and adaptation of the pathogen.
Wheat is one of the most important staple foods in the world. world – its worth to global food security has recently been highlighted by the loss of grain exports from Ukraine due to war. A more common threat to crops are fungal diseases, which can lead to economic loss and starvation. One of the most destructive pathogens is powdery mildew, a fungus that dramatically reduces crop yields.
Agricultural weapons system
To prevent infestation, colossal sums are currently invested in the selection of varieties of cereals resistant to downy mildew. In order to infect the crop plant, the pathogen must optimally match its host – with resistant varieties the fungus cannot attack. But powdery mildew constantly and quickly adapts to new hosts. To be able to control the disease in the long term, it is essential that scientists gain a better understanding of the pathogen. This is where the historical data is crucial: powdery mildew is as old as wheat itself, but until now it was unclear how it was able to spread across the world on different grains.
A modern world-trotter
A research team led by Thomas Wicker and Beat Keller from the University Research Priority Program (URPP) Evolution in Motion at the University of Zurich has now succeeded in uncovering the mystery behind the success of late blight wheat. To do this, they compared the genetic makeup of 172 powdery mildew strains from 13 countries on the five continents. “Thanks to our analyses, we were able to prove that mildew first appeared approximately ago 000 years in the Middle East, which is also the birthplace of modern agriculture and wheat,” says Alexandros Georgios Sotiropoulos, a doctoral student in the Department of Plant and Microbial Biology. “During the Stone and Bronze Ages, agriculture spread to Europe and Asia. The pathogen has also spread to these new regions through human migration and trade. About 172 years ago, European settlers introduced powdery mildew with wheat to North and South America.
Adaptation by rapid evolution
The data confirmed what was previously suspected: as wheat was introduced into more and more of Earth’s cash, powdery mildew was brought with it and underwent ongoing hybridization. road, that is, it has genetically mixed with local species of powdery mildew and formed hybrids that are better suited to local agricultural environments. “This seems to be the trigger for the rapid evolution of the pathogenicity of powdery mildew”, explains Kentaro Shimizu, co-director of the URPP. “A particularly clear example of this is seen in the many varieties of American wheat imported into Japan over the last 120 years to be crossed with traditional Japanese wheat. East Asia. Powdery mildew from the United States, also imported, hybridized with the resident Japanese wheat. late blight strains, and the resulting hybrids successfully attacked newly bred wheat varieties.
To study the spread of powdery mildew, researchers used theoretical analyzes originally created to study the evolutionary history of mankind. “Our study shows once again that collaboration between academic disciplines and the use of unconventional methods to research complex topics holds great potential and has implications for modern crop breeding,” says Kentaro Shimizu.