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Fighting blast disease: Rice pathogen sequenced

Scientists have sequenced one of the most devastating agricultural pathogens in the world, a fungus called Magnaporthe grisea. The fungus causes blast disease in rice, a scourge that destroys enough rice crops to feed 60 million people annually. The pathogen's remarkable ability to overcome plant defenses has stymied efforts to fight the disease.

The effect of melanin on the fungal germ tube and apressorium under hypertonic (a) and hypotonic (b) conditions.

Magnaporthe grisea is the first fungal plant pathogen whose genome has been made publicly available. Together with the draft rice genome sequences published earlier this year, the new information will help researchers develop better and cheaper methods of protecting plants than the currently available fungicides. The key may be to understand how the pathogen so successfully invades its host.

A joint team of researchers from the International Rice Blast Genome Consortium and the Whitehead Institute for Genome Research in Cambridge, Massachusetts finished the draft sequence in July. They plan to publish a completed version, along with annotation, later this year.

Scientists are currently investigating the genes and proteins involved in the rice's recognition of and response to pathogens. The hope is that they could then manipulate the plant's response to invasion by introducing resistant genes.

"We would like to equip the rice so it doesn't produce signals to stimulate the pathogen to attack," says Ralph Dean, who spearheaded the project at North Carolina State University's Center for Integrated Fungal Research in Raleigh.

Dean says the biggest surprises in Magnaporthe's approximately 40-million-base-pair genome are the differences between its non-pathogenic fungal cousin Neurospora crassa. These variations in the genetic code will be used to explore what makes Magnaporthe so toxic to plants.

"By comparing the non-pathogenic and pathogenic fungi, scientists can start to look at the components that determine pathogenicity," says Robert Zeigler of Kansas State University in Manhattan, Kansas.

American long grain rice.

Zeigler has studied the effects of rice blast disease throughout the world, including the Philippines, and the Kingdom of Bhutan in the Himalayan Mountains, where rice is cultivated at one of the highest elevations in the world. He says most rice is susceptible to some strain of the pathogen, and the disease can destroy entire yields of crops.

"They call it blast disease for a reason," says Zeigler. "It's a complete meltdown. The plants look like they've been hit by a flame thrower."

The crippling nature of rice blast disease makes it a potentially dangerous biological weapon in agriculture. The Centers for Disease Control and Prevention in Atlanta, Georgia list rice blast as a significant biological agent, and Dean says it is "certainly an issue of concern" to global food security. He adds that access to the genome could possibly help to identify where and how an agent is introduced in the event of an attack.

Once thought to be a threat only to developing nations, rice blast has emerged as a growing concern throughout the United States. Certain strains attack other grasses such as wheat, barley and turf grass. It can ravage entire golf courses and even the grass growing in your own backyard.

For more information, visit the Magnaporthe grisea genome project here.

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Scientists sequence genome of rice-killing fungus. Press release, North Carolina State University, Raleigh, NC (July 25, 2002).

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