Imagine a picturesque blueberry farm, with its lush bushes teeming with plump, vibrant fruit and its sun-kissed leaves dancing in the gentle breeze. However, an imminent transformation looms on the horizon.
Blueberry plants are currently facing a threat, as a powdery white substance is affecting their vibrant appearance and hindering their growth.
Powdery mildew, a disease caused by a fungus called Erysiphe vaccinii, is the main culprit behind this issue.
A new study conducted by North Carolina State University sheds light on the concerning worldwide expansion of Erysiphe vaccinii in blueberries.
Powdery mildew is causing a decrease in yield and an increase in the use of fungicides. This fungal disease is currently affecting blueberry production on various continents.
Global spread of fungal blueberry disease
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The fungus, originating in the eastern United States, has spread globally over the past 12 years, as stated in the study.
“We are witnessing the rapid global spread of this phenomenon as it unfolds before our eyes,” expressed Michael Bradshaw, an assistant professor of plant pathology at NC State University.
When plants become infected with powdery mildew, a white, powdery layer is formed on their surface. This layer is caused by the fungus responsible for powdery mildew.
The coating not only hinders the plant’s ability to absorb sunlight for photosynthesis but also deprives the plant’s tissues of vital nutrients.
The plant’s growth is hindered, leading to a decline in its overall health. This makes the plant weaker and less productive.
Bradshaw pointed out that there are other powdery mildews that impact plants such as wild berries or eucalyptus. However, it is important to note that these powdery mildews are genetically distinct from the ones currently spreading across the globe on blueberries.
Tracking the spread of powdery mildew
The researchers analyzed 173 infected blueberry leaf samples to investigate the transmission of powdery mildew disease. These samples comprised both historical specimens from herbariums, some of which were collected over 150 years ago, and more recent samples from different countries.
The team uncovered through genetic testing that the strains responsible for the current outbreaks are completely new and distinct from those found in older specimens. They were able to identify two separate introductions of the fungus into the blueberry-growing regions worldwide.
The first strain of the virus was detected in China, Mexico, and California, while the second strain was identified in Morocco, Peru, and Portugal.
According to Bradshaw, it is highly likely that humans played a significant role in spreading the fungus. This was done by inadvertently transporting infected nursery plants across borders.
Sending plant material across the world inadvertently spreads this fungus, emphasizing how the global plant trade can introduce harmful pathogens to new regions.
Impact of the disease on blueberries
Powdery mildew wreaks havoc on the blueberry industry, causing substantial financial losses that range from $47 million to a staggering $530 million annually.
The increased use of fungicides to prevent or manage the disease is the main reason for these costs, along with potential losses in crop yield.
The study also highlights the vulnerability of certain regions, such as the U.S. Pacific Northwest, to future outbreaks. This area possesses environmental conditions that create an ideal habitat for the disease, with the perfect combination of temperature and humidity. Surprisingly, however, no reports of the fungus have been documented in this region thus far.
To effectively curb the spread of the disease in these high-risk regions, it is crucial to implement proactive monitoring and management strategies. Taking immediate action is essential in preventing the disease from taking hold and causing further damage.
According to Bradshaw, the severity of diseases can be influenced by agricultural practices. He observed that growing blueberries in tunnels or enclosed areas seemed to result in worse disease outcomes compared to growing them outdoors without any covering, as seen in North Carolina.
Helping farmers manage powdery mildew
The researchers have created a public database aimed at assisting farmers in better managing powdery mildew. This database is designed to identify various strains of the fungus, allowing growers to input data about the fungus affecting their crops. By doing so, farmers can determine the specific strain present in their fields and make more informed decisions regarding treatment and prevention.
Understanding the characteristics of the strain they are dealing with, including its level of virulence and resistance to commonly used fungicides, is crucial information for farmers.
Farmers can make more informed decisions about disease control and crop protection by having access to these details.
According to Bradshaw, having a clear understanding of the genetics can provide valuable insights to farmers. This knowledge can help them identify the strain of the disease they are dealing with, determine its resistance to fungicides, and track its spread.
The global spread of powdery mildew is a pressing issue that needs immediate attention. This research emphasizes the necessity of enhancing monitoring and control strategies to effectively combat this emerging disease. By doing so, we can protect the blueberry industry and ensure its long-term viability.
The National Science Foundation (NSF) and Novo Nordisk Foundation provided support for the research.
