Blueberries may be small, but they're facing a big problem: powdery mildew. This sneaky fungus has a knack for ruining crops and encouraging the use of fungicides to fight its spread, spelling trouble for your favorite summer snack.
A new study from North Carolina State University has pinpointed the spread of the fungus worldwide. The findings could help farmers predict and control the spread of powdery mildew.
In the last 12 years or so, the fungus Erysiphe vaccinii has advanced from its point of origin in the eastern United States to several continents.
True to its name, powdery mildew causes a white, powdery substance to coat the leaves of plants, siphoning nutrients and hindering photosynthesis while keeping the host plant alive.
There are different species of the fungus that affect different plants, such as wheat, hops, strawberries, and grapes.
"There are other closely related powdery mildews that affect plants like wild berries or eucalyptus, but these are genetically different from the ones spreading across the world on blueberries," said Michael Bradshaw, a co-author of the study and an assistant professor of plant pathology at NC State.
In the study, Bradshaw and colleagues examined historic and modern plant leaves afflicted with powdery mildew. They analyzed 173 samples from North America, Europe, Asia, and Africa.
One sample from a North American herbarium was collected more than 150 years ago, while the foreign samples were all collected within the last five years. Powdery mildew was first observed outside of North America on a farm in Portugal in 2012.
The research team performed genetic testing on the fungal samples to uncover the history and the spread of powdery mildew.
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They found that none of the old specimens contained the same genetic makeup as the specimens currently invading the world.
The disease originated in the eastern U.S. and spread globally through two separate introductions. One strain made its way to China, Mexico, and California, while another reached Peru, Portugal, and Morocco.
The researchers believe humans are responsible for the spread by transporting nursery plants to other parts of the world.
The study also showed that the E. vaccinii fungus found in blueberries in other countries reproduces asexually, but in the U.S., it reproduces both sexually and asexually.
Furthermore, the researchers worked with farmers and a large company to estimate the global cost of powdery mildew to blueberries.
They considered the cost of spraying fungicide to prevent or minimize powdery mildew. The global cost to the blueberry industry is estimated to range between $47 million and $530 million annually.
Finally, the study detailed early warning signals of powdery mildew to look out for in major blueberry-producing areas, like the U.S. Pacific Northwest.
The disease has not taken over the area yet. The team also utilized a tool that can help identify E. vaccinii strains, which is really helpful for farmers.
"That's important because understanding the genetics can warn farmers about which strain they have, whether it is resistant to fungicides, and how the disease is spreading, as well as the virulence of particular strains," Bradshaw said.