To learn more about the inner workings of downy mildew and to provide a foundation for grower outreach and assistance, Brad Day assistant professor of plant pathology at Michigan State University and his research team have embarked on a project to map the downy mildew genome.
The research is funded by Project GREEEN (Generating Research and Extension to meet Economic and Environmental Needs). Titled "From the Lab to the Field: Developing Genomic Tools to Determine Pathogenicity in the Cucumber Downy Mildew Pathogen Pseudoperonospora cubensis," has allowed researchers to learn more about how the disease works.
"In the past, growers have used pesticides to control downy mildew but, while they can be effective, there's a little bit of guesswork involved. By understanding how the disease works, we can make research-based recommendations on whether you should spray or just keep an eye on what is happening," Day explains.
He is also working with researchers from different topic areas to create tools that will use his genomic data to help growers identify the pathogens in their fields.
"I'm working with Mary Hausbeck, a plant pathologist, Robin Buell, a genomicist, and Evangelyn Alociliga, an agricultural engineer, to develop a hand-held biosensor device, which can swiftly identify the pathogen in the field," he said. "Based on that information, growers can implement whatever management strategy they need."
For Brad Day, downy mildew provided the perfect test subject for a study that integrated laboratory research with real world "in the field" application.
"I really wanted to develop genomic resources for a pathogen of significant interest to Michigan and around the world," he says. "Downy mildew is the perfect example of that, since it plays such a big role in Michigan agriculture and is also relatively new."
Downy mildew is an oomycete pathogen that affects cucurbits, a group of specialty crops, which includes cucumbers, watermelon, cantaloupe, gourd, squash and zucchini. After decades of management through resistance breeding, it reemerged on cucurbit farms in numerous states east of the Mississippi River, including Michigan, in the mid-2000s. According to Day, no one is exactly sure what led to the reemergence, but he hypothesizes that the pathogen may have traveled on wind currents from countries that have had problems with downy mildew or arrived in the United States via infected plant propagation material.
No matter how it arrived, growers have had to deal with the implications of that arrival for nearly six years. Controlling downy mildew costs Michigan growers nearly $6 million annually. It is especially worrisome to growers who are a part of the state's $250 million pickling cucumbers industry.
"Imagine never having dealt with downy mildew on your farm and then in the first year it shows up, you have to buy new equipment to spray pesticides on your fields plus the cost of the actual pesticide itself," Day said. "On top of that, downy mildew causes rapid defoliation of your plants within 10 days of infection. By that time, the only thing you can do to stop the spread of disease is till under your crop."
Thanks in part to Project GREEEN support, Day has been able to seek further funding to build on the data he has collected so far. He and his team are currently seeking funding from the United States Department of Agriculture to study how disease resistance occurs in cucumber. Downy mildew will be the "spotlight disease" of that project. The study will also look at the economic ramifications of disease in cucumber and how disease management can be enhanced by building a solid genomic foundation in the laboratory.
"Project GREEEN has been phenomenal," Day says. "By providing us with start-up funding, we've been able to hire additional graduate students and build a groundwork – both with data and cost-sharing – that has allowed us to be competitive in looking for other grants."
In the long term, he hopes his research will help growers understand the true nature of the downy mildew problem and allow them to respond rapidly and accordingly. He also looks forward to the day when genomic data will help growers become independent of fungicides.
"Fungicides can be economically and environmentally expensive. While they put stress on the pathogen for a little while, downy mildew could ultimately overcome that stress," Day explained. "We may reach a point where fungicides aren't effective and we won't have any other way to manage the disease. What we want to do is provide growers with short-term resources to control the problem, but also help them create long-term plans to move towards fungicide independence."
Project GREEEN, Michigan's plant agriculture initiative at MSU, is a cooperative effort between plant-based commodities and businesses together with AgBioResearch at MSU, MSU Extension and the Michigan Department of Agriculture and Rural Development to advance the state's economy through its plant-based agriculture. Its mission is to develop research and educational programs in response to industry needs, ensure and improve food safety, and protect and preserve the quality of the environment.
To learn more about Michigan's plant agriculture initiative at MSU, visit www.greeen.msu.edu.