An example of frogeye leaf spot lesions. LSU AgCenter file photo

Over the course of the last few years, LSU AgCenter plant pathologist Jonathan Richards has been focusing his research on screening different soybean varieties for resistance to frogeye leaf spot, a disease that has the potential to adversely affect yield by reducing leaf area and causing defoliation.

Richards and his team have been screening a different collection of soybean varieties and have identified three or four varieties that seem to have a high level of resistance.

“We identified what's likely the Rcs3 resistance gene, one that has been previously identified, that is considered a broad-spectrum resistance gene because it's effective against all the races present in the United States,” he said. “The linked genetic markers we have identified will be useful in soybean breeding programs.”

However, according to Richards, novel races may arise that overcome that resistance gene, which highlights the need to continue doing the work to identify new sources of resistance.

Richards said that, preliminarily, he’s excited that his team may have found some new resistance genes towards frogeye leaf spot, which they will continue to research this year.

“One of my students is working on that project,” he said.

Richards says another big focus of the last few years has been to optimize and develop new ways to phenotype or screen soybean lines for resistance. One of those ways is through an image analysis workflow.

“It uses machine learning to detect differences between healthy tissue and diseased tissue,” he said. “So, we can use that workflow to take pictures of the diseased leaves and it will tell us how many lesions there are on the leaves, how big those lesions are and what percentage of the leaf is covered by disease.”

Richards said this can supply his team with the information to map these resistance genes more precisely in different soybean populations.

In the past, much of Richards’ team’s focus has been on conducting greenhouse or growth chamber experiments, but from 2020 to 2022, they’ve developed plots at the Macon Ridge and Dean Lee research stations to diversify their studies.

“The experiments we have in the field were primarily to confirm some of the findings that we were getting in the growth chamber and the greenhouse where we found a few lines that look to be highly resistant,” he said.

They found that, overall, there was a high correlation with the resistance that was effective in the greenhouse studies also being effective out in the field.

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.”

Richards said that although they haven’t had any results yet, the plan for the next year is to look at differences in gene expression between resistant and susceptible soybean lines in an effort to understand what genes a resistant plant uses that a susceptible plant doesn't.

“By understanding these different genes or different pathways that are involved, we can be more informed of how we can utilize host genetic resistance,” he said.