In Louisiana’s hot and humid climate, fungal diseases can thrive. LSU AgCenter scientists are working on novel ways of controlling disease problems on soybeans by looking beyond chemical control and investigating the possibility of interfering with the pathogens’ genes when they infect soybean.

The research that AgCenter plant biologist Zhi-Yuan Chen is conducting doesn’t involve genetic modification of the plant, which would incur heavy regulation. Instead, he is looking at spraying genetic material — a double-stranded RNA (dsRNA) — on plants to disrupt disease formation, which he called a new frontier in plant disease management.

Chen and his students have identified genes that are important for the pathogen to infect the plant and are seeing effective disease control with dsRNA to suppress the expression of these genes in some instances.

“We have demonstrated that in growth chambers and greenhouses by spraying those double-stranded RNAs targeting those genes that they can reduce the disease symptoms very clearly,” Chen said.

But issues arise when the researcher attempts to replicate this in the field. Chen said when the dsRNA gets put into natural field conditions it can break down quickly — rain can wash it away or ultraviolet rays from sunlight can break it apart.

Chen plans to stabilize the spray by binding the dsRNA with iron- and magnesium-based nanoparticles as the carrier. He also is planning to use adjuvants that act as surfactants that help the spray stick to the leaf surface or break down that waxy layer of the leaf to help deliver more of the dsRNA into the plant.

Sunira Marahatta, a graduate student in Zhi-Yuan Chen’s lab, examines the differences of frogeye leaf spot disease symptoms among soybean plants four weeks after they were sprayed with dsRNA with or without adjuvants in a field trial at the Doyle Chambers Central Research Station on Sept. 22, 2023. Photo by Zhi-Yuan Chen.

Additionally, he is researching ways the dsRNA can be taken up systemically by the plant to help with disease issues that might infect the plant in areas the spray can’t reach such as the roots.

This mode of disease management, such as for controlling Cercospera leaf blight in comparison to traditional fungicide approach, has several advantages.

“When we use any fungicide on a pathogen, you will always have some off-targeted effects,” Chen said, giving examples of a mosquito spray killing similar insect species in addition to mosquitoes.

With Chen’s approach, off-target effects wouldn’t be an issue because the dsRNA sequence is very specific to one gene in the pathogen. He said the molecule itself is not toxic the way a chemical is.

“It would only act against the pathogen and its very close relatives,” Chen said.

Using dsRNA could also help combat issues with herbicide resistance in plants. Chen said the sequence is long — about 500 base pairs long. If the pathogen tries to mutate, the mutation would just be on one or two pairs and wouldn’t greatly affect the efficacy of the dsRNA. If mutations occur in more places, he can select a new pathogen sequence to target.

“We are much nimbler in responding to all those changes,” Chen said.” We can make a dsRNA to target a different sequence in a couple of weeks. But for regular conventional pesticide or fungicide, it would take five to 10 years to develop chemicals and then have to go through EPA approval.”

Chen is working to get this disease defense system to a level that is economical. Chen said his long-term goal with this research is to develop a cost-effective, sustainable and long-lasting alternative to breeding and fungicide application in managing soybean diseases.