Powdery mildew spreads globally through migration and trade

By Ally Roden

Wheat is an essential staple food across the world and is crucial for global food security. Amid the invasion of Ukraine, global wheat supply has taken a dive. July’s World Agricultural Supply and Demand Estimates (WASDE) from the USDA reports U.S. wheat exports are projected at 800 million bushels, down from 2021.

Meanwhile, the FAO’s forecast for global cereal production was raised by 7 million tons in July from June and is estimated at 2.8 million tons globally. Unfortunately, that number is down — .6% short of the world output in 2021.

A common threat to many crops are fungal diseases that can cause economic losses and famine. Powdery mildew is known as one of the most damaging pathogens that reduces crop yields.

Knowledge is Power

Major investments have been made into the breeding of mildew-resistant varieties of grain to prevent infestation. The pathogen must be a prime match with the host to infect the crop plant. When there are resistant varieties, the fungus is unable to attack.

Powdery mildew is continuously and rapidly adapting to new hosts, making it vital for scientists to gain a better grasp of the pathogen. Historical data is key, as ″powdery mildew is as old as wheat itself, but until now, it was not known how it had been able to spread worldwide on different grains,″ according to a release.

The Key to Wheat Mildew’s Success

The University Research Priority Program (URPP) Evolution in Action at the University of Zurich researchers Thomas Wicker and Beat Keller uncovered the secret of wheat mildew’s success in a study. The research team analyzed the genetic composition from 172 powdery mildew strains sourced from 13 countries over 5 continents.

″With our analyses we were able to prove that the mildew first appeared around 10,000 years ago in the Middle East, which is also the birthplace of agriculture and modern wheat,″ said Alexandros Georgios Sotiropoulos, PhD candidate at the Department of Plant and Microbial Biology. ″In the Stone and Bronze Ages, agriculture spread to Europe and Asia. The pathogen was also spread to these new regions through human migration and trade. Around 300 years ago, European settlers introduced powdery mildew along with wheat to North and South America.″

New Data Comes to Light

Data proved what scientists predicted: when wheat was introduced to new spots across the globe, powdery mildew followed and underwent hybridization throughout the journey. The wheat genetically mixed with each local powdery mildew species and developed hybrids that can adapt better to local agricultural environments.

″This appears to be the cause of the rapid evolution of powdery mildew’s pathogenicity,″ explained Kentaro Shimizu, co-director of the URPP. ″A particularly clear example of this is seen in the many American wheat varieties brought to Japan over the past 120 years for cross breeding with traditional East Asian wheat. The powdery mildew from the U.S., which was also imported, hybridized with the resident Japanese mildew strains, and the resulting hybrids successfully attacked newly bred wheat varieties.″

Researchers used theoretical analyses to investigate the spread of powdery mildew that were developed to inspect 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 offers great potential and has implications for modern crop breeding,″ concluded Shimizu.