Very early fungicide applications provide control for Cercospora Scientists researching solutions to variety of soybean diseases

Frances Gould, Van Osdell, Mary Ann  |  11/18/2010 3:14:53 AM

Cercospora leaf blight is the No. 1 disease facing Louisiana soybean producers. LSU AgCenter researchers are working on a variety of methods for combatting this disease.

Very early applications of fungicides, long before symptoms develop, provide a surprising level of disease control for Cercospera leaf blight, according to LSU AgCenter research.

Dr. Ray Schneider and Dr. Zhi-Yuan Chen, LSU AgCenter plant pathologists in Baton Rouge, have developed a DNA protocol to monitor the infection process.

"This project relates directly to work done by a graduate student," Schneider said. "He sampled and analyzed several of the fungicide treatments and found that infection occurs during vegetative growth, and we later confirmed that very early applications of several fungicides, long before symptoms developed, provided a surprising level of disease control."

This work will be expanded substantially in 2010, Schneider said, during which the process of identifying fungicides and application rates and timing to control this disease will begin. "If our earlier findings are confirmed, we will need to develop recommendations and possibly combine an early fungicide application with an insecticide or herbicide," he said.

Currently, Chen’s lab is focusing on determining whether seeds could be the source of Cercospora leaf blight disease and is exploring new ways to prevent the fungus from producing the Cercospora toxin that causes the disease.

"My part of the research on soybean rust has been to identify specific proteins that increase in production upon rust infection and are present in higher levels in soybeans with demonstrated resistance to Louisiana soybean rust spores," Chen said. "We have found a couple of such proteins in the past two years using a molecular technique called proteomics. The importance of these two proteins in soybean resistance to rust disease is being evaluated in the greenhouse."

Chen said the research involves reducing production of those two proteins by plants. Then if the resulting plants show increased susceptibility to rust infection, which proves the importance of the proteins, Chen will develop ways to increase the production of these proteins to enhance soybean resistance to rust and possibly other fungal diseases such as Cercospora leaf blight, he said.

Schneider said data from a multiyear geographic information systems project has shown certain soil nutrients are related to decreased incidence and severity of Asian soybean rust.

"Analyses are still ongoing, but it appears that magnesium, boron, copper and possibly other nutrients affect disease development," Schneider said, adding, "We will be attempting to manage this disease and Cercospora leaf blight by applying these minerals in different concentrations and combinations."

The LSU AgCenter researcher said another project led to substantially reducing rust severity with single applications of selected fungicides when they were applied before infection took place.

The findings relate to the researchers’ discovery that latent infection may last for six weeks or longer.The LSU AgCenter researcher also cites substantial progress in work with green stem disorder.

"We evaluated several possible causal factors, including the herbicide Roundup, the fungicide Headline, water deficits and cultivars," he said. "By far, the most significant factor is cultivar. So it seems likely that it may be possible to breed or select for cultivars that are resistant to this disorder."

LSU AgCenter plant pathologist Dr. Boyd Padgett confirmed those findings with similar work at the AgCenter’s Macon Ridge Research Station, Schneider said.

Padgett said research is conducted to assess the effects of diseases on yield and quality. Yield loss assessments are targeted for Cercospora leaf blight, Asian soybean rust, frogeye leaf spot, pod diseases and aerial blight.

Dr. Svetlana Oard, an LSU AgCenter plant molecular biologist, takes a genetic approach in identifying disease-resistant genes in other plants and is working toward developing resistant soybeans.

"We have completed antibacterial and antifungal bioassays on the previously selected true-breeding lines of a model plant, which was transformed with an antimicrobial peptide," Oard said. "Our best line showed up to a 60 percent increase in resistance to a fungal pathogen, Fusarium. Such a success using an antimicrobial peptide, which is safe for human and animal consumption, was shown for the first time."

Furthermore, seven transgenic soybean plants were produced last year using "our invented gene," Oard said. First-generation seeds were obtained, and seedlings are growing in a greenhouse and being tested using DNA-specific assays.

"We already identified two independent lines with considerable levels of our gene production in leaf tissues," Oard said. "Thus, we were successful from the first time in constructing the gene for soybean transformation.

"Not too many people can make the same statement, especially because we are dealing with a small peptide," she added.

In another project, LSU AgCenter scientist Dr. Rodrigo Valverde is evaluating damage and yield losses caused by soybean mosaic virus and bean pod mottle virus, alone or in combination with other viruses.

All the LSU AgCenter research is aimed toward improved production practices and monitoring techniques that can help reduce damage done by diseases, Padgett said.

Disease losses to Louisiana soybeans were 13.4 percent or 5.67 million bushels in 2009, he said. –Mary Ann Van Osdell

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