Hunt for soybean disease resistance uses molecular biology

Frances Gould, Bogren, Richard C., Benedict, Linda F.  |  11/11/2013 11:19:07 PM

Under the watchful eye of Zhi-Yuan Chen, graduate students Josielle Rezende, left, and Dong fang Hu introduce Cercospora leaf blight disease resistance-related genes into soybean plants using a gene gun. (Photo by Rick Bogren)

Cercospora leaf blight is the No. 1 fungal disease in Louisiana soybeans. The disease, which has appeared only in the past five to 10 years, has no resistance in any soybean lines, according to LSU AgCenter plant pathologist Zhi-Yuan Chen.

The Cercospora fungus survives in infected seeds and plant residue, and spores form on the residue surface during warm, humid weather, experts say. The spores are wind-blown or rain-splashed onto new soybean tissue where infection occurs. Seeds also can carry the fungus.

The foliar disease can remain latent in growing soybean plants for several weeks before they show symptoms. In severe cases the disease can cause defoliation, and it is associated with the green stem disorder.

In an attempt to solve the lack of resistant plants, Chen has been using molecular tools to find ways to make soybeans resistant to the disease.

"There are no known resistant lines that we can use to learn how soybeans defend themselves against Cercospora leaf blight infection using the available molecular tools," Chen said.

Instead, Chen’s research team in the Department of Plant Pathology and Crop Physiology has been focusing on identifying genes that produce cercosporin, a toxin from the disease organism that can suppress a plant’s defense mechanism.

So far, he has identified two genes using proteomics – the branch of molecular biology that studies the full set of proteins encoded by a genome – and gene disruption studies.

These genes appear to be important for cercosporin production by the pathogen. The genes are currently being tested for their ability to suppress the toxin and the resulting fungal infections. If they actually do what the researchers believe, these genes will be introduced into new soybean lines to produce resistant varieties.

Chen’s laboratory team also has identified several genes that potentially can play an important role in soybean resistance to soybean rust infection. They currently are testing these genes using a virus-induced gene silencing approach.

"Preliminary data show that soybeans with reduced expression of these genes are more susceptible to soybean rust infection, indicating that enhancing the expression of these genes in the future could provide better protection against soybean rust diseases," Chen said.

Rick Bogren

(This article was published in the 2013 Soybean and Grain Research & Promotion Board Report.)

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