Work to combat Cercospora continues


Nelomie Galagedara, a graduate student, checks a spore trap being used in work on Cercospora leaf blight. Photo by Sara Thomas-Sharma

LSU AgCenter plant pathologist Sara Thomas-Sharma is looking for new ways to control an old problem in Louisiana soybeans: Cercospora leaf blight.

Cercospora has long been the prime foliar disease in soybeans throughout the South. The disease usually sets in as plants enter reproductive stages of development, meaning it can affect seed production and lead to yield and quality losses.

These symptoms are caused by a toxin called cercosporin, which is produced by the Cercospora fungus.

“It’s toxic universally, so all kinds of cells die with it, but the fungus does not die in the process of producing the toxin,” Thomas-Sharma said. “So we are trying to understand how the fungus is able to resist the toxin. How is it not killing itself when it is killing the plant?”

Research has shown that the cells of other kinds of fungi contain lipid droplets that sequester toxins and prevent damage. Thomas-Sharma wants to find out if Cercospora cells function similarly.

“My interest is seeing if there are chemicals that can inhibit lipid droplet formation, which would then make the fungus perhaps kill itself or not produce enough cercosporin to damage plant cells,” she said.

Thomas-Sharma also is following up on the findings of a previous project conducted by fellow AgCenter plant pathologist Vinson Doyle. This work aims to determine if spore traps can be used to detect peak times for spore transmission and help target fungicide applications and whether those applications are economical.

Though it previously was thought that seeds brought the Cercospora fungus into fields, Doyle’s work has suggested that weeds can serve as hosts to Cercospora, which can then spread via airborne spores to neighboring soybeans.

Thomas-Sharma also recently completed a project looking at whether foliar iron applications can help control Cercospora. The applications didn’t seem to work, but the project sparked an idea for future research.

In examining soybean plants, Thomas-Sharma found that iron content is the highest in the lower leaves, while Cercospora tends to be most prevalent in leaves that are higher on the plant. Also, the disease comes in during reproduction, when nutrient balances are changing.

“We still think nutrients are playing a role in how this disease is seen in the field,” she said. Olivia McClure

8/17/2022 8:32:17 PM
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