LSU AgCenter researchers are taking a variety of approaches to combat soybean diseases.

The studies are seeking to develop new disease-resistant varieties, identify existing varieties that offer resistance or find specific characteristics of plants that seem to bolster disease resistance. The research also is aimed toward improved production practices and monitoring techniques that can help to reduce the damage done by such maladies as Asian soybean rust, Cercospora leaf blight and others.

"Varieties in the LSU AgCenter’s official soybean variety tests at the Northeast, Macon Ridge and Dean Lee research stations are being evaluated for disease resistance," Dr. Boyd Padgett said of one prong of the research. "Reactions for all diseases are recorded on varieties entered in these tests – and are used in making recommendations and ratings of the varieties."

Padgett also is responsible for leading projects to evaluate commercially available and experimental fungicides for soybean disease management and to quantify disease losses in selected soybean varieties to determine when fungicides are necessary.

As part of that work, 184 treatments were evaluated in 2008 tests on research stations and other test sites.

Among the early observations, Padgett said some experimental compounds looked promising for improving stand and yield when compared to the untreated plots.

"This project provides valuable information to producers on variety performance against diseases, as well as fungicide efficacy and the distribution of soybean diseases in the state," he said.

Meanwhile, other members of the team of LSU AgCenter researchers combating soybean diseases are pursuing a variety of avenues.

"Our team continued to evaluate and refine tactics and strategies for managing Asian soybean rust, in particular," said LSU AgCenter soybean expert Dr. Ray Schneider, who is one of the research leaders.

Schneider said some of the work has shown the latent period for Asian soybean rust may be as long as six weeks – much longer than the previously assumed period of 10-14 days.

"Our work with multiple plantings of different maturity groups indicated latency – the period between penetration of the leaf surface and when symptoms become apparent – may last for as long as six weeks," he stressed, explaining the findings suggest that disease indications observed at the mid-R5 growth stage could be the result of infection at the R1 stage.

"Given that fungicides are most effective when they are applied before infection, in 2008 we demonstrated that a single application at R1 with a triazole fungicide was more efficacious than multiple applications beginning at R3 and that there was little benefit to multiple applications when the first application was made at R1," he said, adding that the experiments are being repeated and expanded in 2009.

"If these findings are confirmed, the practical implication is that Louisiana producers who get rust on a yearly basis may wish to spray at R1 for season-long control of this disease," Schneider explained.

The situation will be complicated by the possible need to spray later in the season for Cercospora leaf blight or aerial blight, but Schneider said the researchers also are evaluating time of infection and latency with Cercospora.

Comprehensive field experiments in Baton Rouge and Winnsboro are addressing that issue, according to Schneider, who said Dr. Zhi-Yuan Chen also is assessing infection with DNA protocols to try to better define when initial infection takes place.

"The objective of this part of our soybean project is to detect soybean Cercospora leaf blight disease before the purple leaf symptom appears and to understand how the disease is being spread," Chen said. "We have designed specific molecular probes... and found the presence of the fungus in healthy leaves before soybean plants enter the reproductive stages of growth."

In addition to working on Cercospora leaf blight disease, Chen’s lab has been evaluating several soybean proteins through molecular techniques for their importance in soybean rust resistance. These proteins were found highly induced when rust infects soybean plants.

Dr. Svetlana Oard also is taking a genetic approach. In her case, it involves identifying disease-resistant genes in other plants and working toward developing resistant soybeans.

"Last fall we sent two transformation vectors we designed and engineered to soybean transformation facilities, and they are producing 10 transgenic soybean plants per vector," Oard explained. "We expect to get first-generation seed this fall and start testing the soybeans with these vectors to see if they work."

Oard stressed the research still has a long way to go, but she indicated it was promising, based on experiments with model plants that indicate the possibility of "up to a 50 percent increase in fungal resistance."

In the meantime, the researchers will continue working on a variety of other avenues, such as how amendments like potassium chloride may help fend off disease and developing disease forecasting models to safeguard the state’s soybean industry.
 –Tom Merrill

Checkoff funds for these projects: $195,806