Search continues on ways to combat soybean diseases

Frances Gould, Schultz, Bruce  |  10/22/2014 2:22:05 AM

AgCenter plant pathologist Clayton Hollier sprays fungicides on soybean plants. He is examining the cumulative effects of all soybean diseases rather than concentrate on one disease at a time. (Photo by Bruce Schultz)

LSU AgCenter plant pathologists are researching various ways to help farmers deal with soybean diseases.

Trey Price and Ray Schneider are focusing their work on Cercospora leaf blight.

"We are basically looking for ways to break the disease life cycle and provide new management solutions for producers,"

Price said. Price is testing different fungicides, along with fungicide timing and rates. But, he said, the work has revealed that the Cercospora pathogen is resistant to strobilurin and benzimidazole and is widespread across the state.

"There has been recent interest in applying triazole and SDHI fungicides to soybeans," he said.

Popular triazole fungicides used in soybean include Alto, Domark, Folicur, Proline and Topguard, and SDHI fungicides labeled in soybean include Endura, Priaxor, and Vertisan. There are many products containing a strobilurin + triazole active ingredients.

"We are currently evaluating the efficacy of these fungicides in the field and the laboratory," Price said.

Another project is looking at disease resistance of different soybean varieties to find which fungicides work best for different varieties. In addition, the project will quantify loss potential for different diseases to determine if the losses from a disease justify the expense of a fungicide. "A particular disease may not cause significant losses and may not warrant the expense of a control measure," Price said.

Schneider reported good results from a foliar application of an iron solution to soybean plants at the R-5 stage. "We’ve gotten very high levels of almost complete disease control," he said. The iron treatment also results in a slight yield boost.

Schneider said he decided to try the iron solution after a tissue analysis revealed the highest disease suppression was occurring in plants with the highest iron content.

Apparently, the disease is sensitive to high iron levels and shuts down its production of toxins that damage the plant, Schneider said. But an additional year of testing is needed before any recommendations can be made to farmers.

Rodrigo Valverde is using viruses to artificially infect soybean breeding lines being considered as future varieties for Louisiana. "The results will provide information on the degree of resistance of these lines to the viruses, and the data will be useful for soybean breeding and variety recommendation," he said.

Previous research showed that soybean mosaic virus can lower yields when compared with healthy plants.

"However, so far the occurrence of this virus is not high enough to be of a serious problem," he said. "Peanut stunt virus is known to lower soybean yields elsewhere." A survey is being conducted to determine the occurrence of peanut stunt virus on commercial farms in Louisiana.

For the past four years, AgCenter plant pathologist Clayton Hollier has been studying the yield and quality loss potential from a complex of soybean diseases. "I’m taking all diseases into consideration and calculating the yield difference," he said

Instead of trying to determine the yield loss of a specific disease, Hollier wants to know how the entire disease spectrum will affect yield, similar to what a farmer’s field experiences. "I’m looking at the total package because that’s what the grower has to do," he said.

To conduct the study, Hollier uses different fungicide application timings as well as different fungicides to see what effects those variables have. Some plots are not treated to be able to compare the differences of the best treatments.

In the past year, Zhi-Yuan Chen’s laboratory has been working on ways of using genetics to increase soybean resistances to diseases, such as Cercospora leaf blight and soybean rust.

Josielle Rezende, a Ph.D. student working under Chen’s supervision, found that the Cercospora pathogen produces a protein to protect its cell wall. She has cloned the gene for making this protein and is testing whether mutants that do not make this protein have a reduced ability to infect soybeans.

She also is studying the soybean genome sequence database to look for a protein identified with the potential to protect soybeans from Cercospora and to see whether any soybean lines she has screened in the past for Cercospora resistance contain high levels of this protein.

Another Ph.D. student, Dongfang Hu, has been testing several soybean proteins for their contribution to resistance to soybean rust disease. She has also been trying different ways to suppress rust growth through a new genetic technology in plant disease control.

In addition, Hu is looking into gene expression differences between soybean rust-resistant and susceptible soybean lines to identify more candidate genes that could enhance soybean rust resistance.

"Overall, these efforts could offer new and more effective approaches to control soybean fungal diseases," Chen said.

Bruce Schultz

This article was published in the 2014 Louisiana Soybean & Grain Research & Promotion Board Report.

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