A new North Carolina State University study pinpoints the worldwide spread of a fungus that taints blueberry plants with powdery mildew, a disease that reduces blueberry yield and encourages the use of fungicides to combat disease spread. The findings could help blueberry growers predict, monitor and control the spread of powdery mildew.
The study shows that the fungus, Erysiphe vaccinii, has in the last 12 years or so spread from its point of origin in the eastern United States to multiple continents.
We’re watching this global spread happen right now, in real time.
As its name suggests, powdery mildew disease causes a white, powdery substance to cover host plants, stealing nutrients and retarding photosynthesis while keeping the host alive. Different species of this fungus affect different plants; wheat, hops, grapes and strawberries, among other plants, have been detrimentally affected by powdery mildew.
"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,” Bradshaw said.
In the study, Bradshaw and his colleagues examined historic and modern plant leaves plagued by powdery mildew. The collection includes 173 samples from North America, Europe, Africa and Asia; one sample analysed from a North American herbarium was collected over 150 years ago, while the foreign samples were all collected within the past five years. In this study, powdery mildew was first spotted outside North America on a farm in Portugal in 2012, as noted by a co-author of Bradshaw’s who was employed by a major berry company.
The researchers performed genetic testing on the fungal samples to trace the history and spread of powdery mildew disease. Interestingly, none of the old specimens have the same genetic makeup, or genotype, as the specimens currently spreading throughout the world.
The study showed that the disease originated in the eastern United States and was set loose globally in two different introductions. One strain of E. vaccinii found its way to China, Mexico and California, while a different strain wound up in Morocco, Peru and Portugal. Bradshaw thinks humans are responsible for the spread as nursery plants travelled to foreign shores.
“This is a hard organism to control,” Bradshaw said. “If you’re sending plant material across the world, you’re likely spreading this fungus with it.”
An emerging fungal disease is spreading across the globe and affecting the blueberry industry
Michael Bradshaw, et. al.