On a research plot, Brenda Tubaña’s soil health team is testing several biostimulant products. Photo provided by Brenda Tubaña

“A management tool that can potentially target multiple soybean diseases,” is the primary goal for LSU AgCenter plant pathologist Jonathan Richards and his team. They have been analyzing differences in gene expression between resistant and susceptible soybean varieties.

Specifically, Richards and his team are interested in understanding the role of phytohormone signaling pathways in the resistance response during frogeye leaf spot disease development. By characterizing which pathways are activated in resistant soybeans and at what stage of infection, Richards aims to design a control method to induce resistance.

“Resistant soybean varieties activate specific genetic pathways, which susceptible varieties do not have, or are unable to turn on,” he said. “By understanding which genes or pathways are important for resistance, we can be better informed on how to improve soybean varieties and use host resistance.”

Richards said resistance pathways can be induced in plants through various chemical applications, but these treatments can have varying effects depending on the specific pathogen.”

“This is why we want to first get a firm understanding of which pathways are important for frogeye leaf spot resistance,” he said.

In addition to examining soybean gene expression, Richards and his team have been focusing on expression of genes in the fungal pathogen.

“Fungi that cause plant diseases have genes, called effectors, that help them infect the plant and suppress the plant immune system,” he said. “Our research has identified a set of effectors that are highly expressed during infection, indicating that they might play an important role in causing disease.”

Richards mentioned that other fungal pathogens of soybeans, such as those that cause Cercospora leaf blight, possess related genes that may function similarly. Richards says that by identifying these common genes, targeted interventions can be developed to suppress their expression and inhibit infection by multiple fungal pathogens.

Complementing his work on host and pathogen gene expression, a primary focus of his research of the last five years has been towards the identification of host resistance genes. According to Richards, novel races may arise that overcome currently deployed resistance genes, which highlights the need to continue doing the work to identify new sources of resistance. His team continues to screen soybean germplasm with the goal of identifying and mapping novel resistance genes that can be used to increase the durability of frogeye leaf spot resistance.

Host genetic resistance is important because if his team can use a soybean variety that's resistant to different fungal diseases, that reduces the reliance on other management practices, such as fungicide applications, which can save producers time and money.

“Especially for some of these pathogens like the one that causes frogeye leaf spot,” he said. “Some of these chemicals aren’t effective anymore, so we need to use other strategies, like genetic resistance to help control the disease.”