Scientist making progress toward unlocking mysteries of bacterial panicle blight

Frances Gould  |  1/23/2014 9:42:25 PM

Graduate student Hari Sharan Karki inoculates research plots at the Rice Research Station with bacterial panicle blight . The project is part of a study being conducted by LSU AgCenter plant pathologist Dr. Jong Ham to determine if a chemical mechanismcan be used to protect plants from the disease.

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LSU AgCenter pathologist Dr. Jong Hyun Ham is trying to unlock the mysteries of bacterial panicle blight – and he is making progress with encouraging signs.

Ham said he is studying the pathogen cells to learn how and why they turn on and off the chemical systems that result in bacterial panicle blight. The pathogen cells somehow sense when conditions are good for the disease (high temperatures, especially at night, dry weather at the grain-filling stage and high population levels of the pathogen), and those cells release chemicals, or fatty acid-type compounds, to alert neighboring cells.

"Through that mechanism, they signal to other cells to produce the virulence factor," Ham said.

That factor is a poisonous chemical called toxoflavin that quickly will kill its host and enable the bacterial panicle blight pathogen cells to feed on the nutrients.

Chances are that bacterial panicle blight pathogen cells can be found in any rice field, but those pathogen cells don’t start the process that leads to the disease unless the proper environment is present.

Ham is looking at the bacteria’s genetic structure to see what genes make toxoflavin. Once that is found, the gene can be turned off through development of mutants, he said, but international plant pathology regulations restrict such research to greenhouse studies only.

The bacteria’s genetic makeup includes DNA that turns off toxoflavin production, Ham said, and he hopes to find the responsible gene, too.

The LSU AgCenter scientist hopes to find a chemical that can fool the bacteria, preventing it from releasing the toxic substance, he said.

Ham is working with LSU AgCenter rice breeder Dr. Steve Linscombe to develop a rice variety resistant to bacterial panicle blight. He said a progeny descended from a cross between the variety Bengal and LM-1, a mutant line of Lemont, has shown resistance to bacterial panicle blight and sheath blight. This progeny line showed more resistance than LM-1 and higher yields than Bengal or LM-1.

He said genome sequencing and genetic mapping are being used to identify genetic markers related to the disease resistance. Ham said some bacterial panicle blight pathogen cells do not produce toxoflavin, and testing is being done to see if a population of those nonvirulent cells can be used to inoculate a plant and prevent the virulent strain from establishing itself. He said results from a test last year were encouraging, but this year’s outcome was not as promising.

Testing also is underway on the use of ascorbic acid, vitamin C, which appears to prevent the bacteria from causing bacterial panicle blight. The disease is proving to be like the layers of an onion, according to Ham, who explained, "The more we study this disease, the more complicated it appears to be."

(This article was published in the 2014 Louisiana Rice Research Board Annual Report.)


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