A brand new study from North Carolina State University identifies the worldwide spread of a fungus that taints blueberry plants with powdery mildew, a disease that reduces blueberry production and the spread of the disease. Encourages using fungicides. These findings may also help blueberry growers predict, monitor and control powdery mildew outbreaks.
The study shows that the fungus, over the past 12 years, has spread from its original location within the eastern United States to multiple continents.
“We're seeing this global spread happening right now, in real time,” said Michael Bradshaw, assistant professor of plant pathology at NC State and corresponding creator of a paper describing the research.
As its name suggests, powdery mildew causes a white, powdery substance to cover host plants, stealing nutrients and inhibiting photosynthesis, keeping the host alive. Different species of this fungus affect different plants. Wheat, hops, grapes and strawberries, amongst other plants, have been adversely affected by powdery mildew.
“There are other closely related powdery mildews that affect plants like wild berries or eucalyptus, but they're genetically different from the plants that grow on blueberries worldwide,” Bradshaw said.
In the study, Bradshaw and his colleagues examined the leaves of historical and modern plants affected by powdery mildew. The collection includes 173 specimens from North America, Europe, Africa and Asia. A specimen analyzed from a North American herbarium was collected 150 years ago, while the foreign specimens were collected throughout the last five years. In the study, powdery mildew was first observed outside of North America in 2012 at a farm in Portugal, as noted by one among Bradshaw's co-authors who was employed by a big berry company.
The researchers performed genetic testing on fungal samples to find out the history and prevalence of powdery mildew disease. Interestingly, not one of the older samples have the identical genetic make-up or genotype, because the samples currently spread world wide.
The study showed that the disease originated within the eastern United States and was released globally in two different introductions. One strain reached China, Mexico, and California, while a distinct strain spread to Morocco, Peru, and Portugal. Bradshaw believes humans are accountable for the spread as nursery plants make their approach to foreign shores.
“It's a difficult organism to control,” Bradshaw said. “If you're sending plant material around the world, you're spreading this fungus with it.”
Interestingly, the study also showed that the fungus present in blueberries in other countries reproduces completely asexually. Reproduction doesn't require each sexual versions of the fungus, while fungi reproduce each sexually and asexually within the United States.
The study also worked with a significant company and farmers to offer estimates of the worldwide cost of powdery mildew of blueberries, showing the fee of spraying fungicides to forestall or reduce powdery mildew. The study estimated the fee to the worldwide blueberry industry at between $47 million and $530 million annually.
Finally, this study provides some early warning signals to key blueberry-producing regions, corresponding to the US Pacific Northwest. Conditions are ripe for powdery mildew to take hold and spread, however the disease has not yet found its way there.
“Disease spread can also be affected by agricultural conditions,” Bradshaw said. “Some areas that grow blueberries in tunnels, or enclosed areas, have worse disease outcomes than areas that grow blueberries outdoors without any cover, such as in North Carolina.”
Bradshaw added that the researchers used a useful gizmo that might help farmers and other researchers discover strains.
“Identifying the fungus that causes powdery mildew in blueberries is difficult, so we enter our data into a public database developed by Ignazio Carbone, a co-author at NC State. This platform allows growers to enter their data. “allows them to do and know what specific strains are of their fields,” Bradshaw said. “This is vital because understanding the genetics can alert farmers to what strain they've, whether it's proof against fungicides, and the way the disease is spreading, in addition to the virulence of specific strains.”
appears within the paper. Funding was provided by the National Science Foundation under award numbers 2315953, 2200038, 2031955, and 2308472. This work was also supported by the Novo Nordisk Foundation under grant numbers NNF19SA0059360 and NNF19SA0035476.