Different species may be source of Cercospora diseases

Frances Gould, Bogren, Richard C.  |  10/14/2016 5:43:16 PM

LSU AgCenter mycologist Vinson Doyle examines cultures of Cercospora isolated from soybean seed. DNA will be extracted from these cultures to be used in further research. Photo by Rick Bogren


Scientists have long believed Cercospora leaf blight and purple seed stain are caused by the pathogen Cercospora kikuchii. A group of LSU AgCenter researchers led by Sebastian Albu, however, recently discovered that a different species of Cercospora is causing leaf blight and purple seed stain in Louisiana. That discovery is leading researchers in a new direction.

Cercospora flagellaris has been isolated from a wide range of host species, said Vinson Doyle, an AgCenter mycologist. Unlike kikuchii, it’s considered a “generalist” that lives on multiple host plants.

Doyle and graduate student Zac Carver are now looking for sources of inoculum on other host plants by surveying alternative hosts beyond soybean field borders.

Researchers may have underestimated the causes of Cercospora leaf blight and purple seed stain and are now investigating if more than one source of the pathogen may be responsible for the different diseases. “We want to determine if the cause of purple seed stain is seed-borne or originates elsewhere,” Doyle said.

The researchers believe the pathogen is on the seed coat or just under it, he said, so they’re using chlorine gas as treatment to disinfest the seed. “We’re looking at the safe length of time that will eliminate the pathogen without affecting seed germination or seedling vigor.”

Doyle is working with plant pathologist Trey Price at the Macon Ridge Research Station to determine if pathogens on seed from different areas of the country remain in the plants after planting and during development.

Price planted seeds from Arkansas, Illinois and Tennessee, and the researchers will sample the leaves and seeds to see if the pathogens match the ones initially on the seeds.

“We want to see if the inoculum comes with the seed or is airborne from other hosts,” Doyle said. “We may be able to find alternatives to mitigating disease without widespread use of fungicides, especially if the pathogen is seed-borne.”

This new research approach has three objectives: first, to disinfest seed to see if it reduces disease severity; second, to determine the genetic relationship between isolates from seed and those that show up on blighted leaves; and third, to identify alternative host plants for C. flagellaris.

Rick Bogren

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