In the third year of a three-year project aimed at developing RNA-based alternatives to traditional fungicides, Zhi-Yuan Chen and his team have made promising progress in improving the delivery and stability of double-stranded RNA (dsRNA) treatments for soybean diseases in their field trials at the LSU AgCenter’s Central Research Station.

One of the biggest challenges has been the poor delivery of dsRNA into soybean plants. To address this, the team tested various chemical adjuvants — additives used in commercial fungicides — to help the dsRNA stick to the leaf surface and penetrate the waxy cuticle.

“Last year, we were mainly testing different dsRNAs with or without adjuvants.” Chen said. “Basically, we needed to reduce the amount of dsRNA sprayed in the field for effective disease management by boosting their uptake by plants through the use of adjuvants to make it more economical.”

He found two of the agents helped the dsRNA get into the leaf based on the analysis of samples they completed recently.

“From last year’s limited small-scale field trials, we saw that dsRNAs with these adjuvants helped suppress pathogen growth and reduce symptoms,” Chen said.

The other major challenge is the instability of dsRNA under field conditions.

“The weather conditions, like rain, wash off things that are sprayed on the plants,” Chen explained. “The UV sunlight and microbes on the leaves really destroy the dsRNAs we sprayed onto soybean in a matter of days.”

During the winter, the team also explored the use of magnesium ferric and other nanoparticles to encapsulate the dsRNA, protecting it from environmental degradation. The latter nanomaterials were obtained through collaborating with a professor in the LSU Department of Chemistry.

“The idea is that the nanoparticles act as a physical barrier. When UV light shines on them, it doesn’t get to the dsRNA. But with enough moisture, the dsRNA is slowly released,” he said.

Graduate student Sunira Marahatta conducted the greenhouse trials to test the effectiveness of these nanoparticles.

She had soybean plants growing in the greenhouse, sprayed with dsRNA — some mixed with nanoparticles — and after two weeks, she collected the leaves to compare disease symptoms. She then extracted DNA from the leaves to see any differences in fungal growth among soybean leaves treated with dsRNA with or without nanoparticles.

Using a specialized DNA quantification machine, Marahatta was able to measure the amount of fungal DNA in the soybean tissue.

“That machine can tell us how much fungal DNA is inside the total DNA of the soybean,” Chen said. “Statistically, we should be able to separate them. If it’s effective, we should see less fungal growth inside the soybean leaves compared
to the controls.”

Chen noted that the greenhouse results were inconclusive.

“The help from nanoparticles is not very clear,” he said. “Statistically, we did not see a difference between with and
without nanoparticles.”

He said that the lack of environmental stressors in the greenhouse may have limited the nanoparticles’ effectiveness. New field trials planned will test their performance under real-world conditions.

Soybeans were planted at the Central Research Station in early May, with additional plantings scheduled through June to capture different stages of disease development.

“That way we can catch the soybean disease in different stages and do the treatments,” Chen said.

Ultimately, the goal is to develop a cost-effective, environmentally friendly alternative to fungicides.

Graduate student Sunira Marahatta is working with LSU AgCenter plant pathologist Zhi-Yuan Chen to improve the delivery and stability of double-stranded RNA (dsRNA) for practical management of soybean fungal diseases. Marahatta stands next to a specialized DNA quantification machine that she uses to accurately measure the amount of fungal growth in the soybean tissue. Photo by Tobie Blanchard