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(09/01/26) BATON ROUGE, La. — For many years, farmers have battled leaf spot diseases caused by fungi in the genus Cercospora. And for almost as many years, plant pathologists have studied the diseases, searching for fungicides, growing practices and other ways to limit their negative effects on crops.
There are many species of Cercospora. Researchers have long struggled to distinguish one species from the next, however, which complicates efforts to learn about disease behavior and identify possible solutions.
Modern technology is shedding new light on these species, pointing toward connections that scientists didn’t always realize existed. But where exactly are those overlaps? And how can that information be leveraged to develop better control methods for farmers?
LSU AgCenter plant pathologists Vinson Doyle and Jonathan Richards are trying to answer those questions. They recently were awarded a five-year, $1.5 million grant from the National Science Foundation to support the project.
The scientists are retracing the steps of forebears in plant pathology who sought to differentiate between the many species that comprise the Cercospora genus.
This group of fungi includes species that cause diseases that have been perennial concerns for farmers. They generally present as leaf spots that can stress and defoliate plants, leading to losses in yield, quality and, ultimately, profits. Cercospora leaf blight, for example, is a frequent problem in soybeans in Louisiana.
Much of the current understanding of Cercospora stems from the research of Charles Chupp, a Cornell University plant pathology professor who worked with vegetable farmers in New York. In the 1940s, he set out to determine which species affect which plants, name them and describe them — a science referred to as taxonomy.
Many of the species looked similar under a microscope, so Chupp separated them based on the plants they infected and the appearance of the spores they produced. By the time he published a monograph on the genus in 1953, Chupp had described or redescribed a whopping 1,419 distinct species.
“There was this assumption that if you find one thing on one plant and you find something else that looks the same but on a different plant, that there are actually two different species,” said Doyle, chair of the AgCenter Department of Plant Pathology and Crop Physiology.
It was groundbreaking work in its day, but Chupp’s host-specific framework has fallen apart in the past 10 to 15 years. Modern molecular tools have revealed that some Cercospora species infect more than one host plant, and multiple species sometimes infect the same host — upending the old taxonomic model.
Today’s scientists know that species with different names may in fact be one and the same. But there’s no comprehensive list of which hosts share the same pathogens, not only creating confusion for researchers but also hampering their ability to develop the most effective control strategies.
“What that means from a practical perspective is you can’t just focus on what the disease is in that particular crop system and ignore everything else around it because it might be coming from other plants that you’re not managing at all,” Doyle said. “This comes back to the questions of what species are out there and on what host plants? What diseases are they causing?”
Chupp explored the same issues decades ago. Taxonomy back then was part art, Doyle said — the scientist would study collections of specimens and interpret them, deciding where the boundary lay between one species and another. Today’s technology reduces the amount of human error and subjectivity in the equation.
“We have a lot more information now, and we have tools that were not available to Chupp at the time — the DNA sequencing tools in particular — and they provide a much more objective way to answer these questions,” Doyle said.
Developing a stable taxonomy based on DNA is the primary goal of Doyle and Richards’ project. To do this, they’ll track down a sample of each species and sequence it — a high-tech way of documenting its DNA makeup.
“We can understand which genes each species has and how much overlap there is between these different species,” Richards said. “For example, if we’re interested in understanding how multiple Cercospora species have evolved to infect soybean, we can compare the genomes of all these different Cercospora species and identify genes that might be specific to species that have the ability to infect soybean.”
Richards hopes to use the same process to find out how species have adapted to different environments over time as well as the mechanisms they use to infect plants.
He and Doyle anticipate uncovering new links between species and hosts, which has implications for research areas like fungicide resistance and population variability.
That’s useful information for scientists and farmers, so Doyle and Richards want to be sure others can access their findings. They plan to build a database of Cercospora species and their characteristics. Ignazio Carbone, a North Carolina State University plant pathologist who is collaborating on the project, will develop the data platform.
Because the project is foundational in nature, it transcends the silos that have traditionally accompanied plant disease research, which tends to be crop specific.
“This allows us to work across lots of different crop systems, lots of different geographic areas and bring all this information together so that we can start to sort it out,” Doyle said.
For Richards, the project holds the potential to see an economically important, much-studied genus of fungi through a new lens.
“There are tons and tons of Cercospora species that are out there that are maybe not agriculturally relevant but are prevalent in the wild. A lot of the work that’s been done has only given us a really small fragment of the picture,” Richards said. “The results from this project are going to give us a much broader view of the diversity within this genus at the genome level.”
LSU AgCenter plant pathologists Vinson Doyle, left, and Jonathan Richards look at a sample of Cercospora cultures in their laboratory. Photo by Olivia McClure/LSU AgCenter
This leaf has lesions resulting from infection with one of the many disease-causing species in the genus Cercospora. Photo by Olivia McClure/LSU AgCenter
LSU AgCenter plant pathologists Vinson Doyle, left, and Jonathan Richards look at microscope imagery of Cercospora spores. Photo by Olivia McClure/LSU AgCenter
