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Last Updated: Thursday, 21 April, 2005, 13:49 GMT 14:49 UK
Rice fungus genome mapped at last
Workers in a paddy field, BBC
Half the world's population relies on rice to survive
Scientists have unravelled the genome of the rice plant's gravest fungal menace, a crop wrecker that ruins the potential to feed millions every year.

Magnaporthe grisea is the first pathogenic plant fungus to have its life-code read, which could pave the way for new treatments for the disease.

The fungus' genome, which is published in Nature, has 11,109 genes, which is similar to other funguses sequenced.

The research was led by researchers at North Carolina State University, US.

"Controlling rice blast disease, which will help people throughout the world, is for the first time a realistic prospect," said Nick Talbot, from Exeter University, UK, who was part of the team sequencing the genome.

This research also has potential for protecting the environment
Duncan Macintosh, IRRI
Duncan Macintosh, a spokesman of the International Rice Research Institute (IRRI), agreed this is a major breakthrough.

"This is definitely going to make a big difference," he told the BBC News website. "It will take a few years for the importance of this research to fully come out, but it is a very important scientific step."

High pressure

M. grisea comprises windborne spores that stick to the leaves of the rice plant, thanks to a special adhesive on the spore tip.

As it germinates, the spore forms a dome-shaped structure called an "appressorium", or pressure cell, whose task it is to infect the plant.

The tiny organ produces extraordinary pressures to drive a penetrative peg beneath the leaf's protective waxy surface.

In young seedlings, rice blast often destroys the whole plant; in older plants, the grain is lost.

The fungus spore on a rice leaf, Exeter University
The spore forms a pressure cell, whose task it is to infect the plant
It is estimated that, every year, the rice blast fungus kills an amount of rice that would feed 60 million people.

"Rice blast is one of the most destructive diseases of rice because of its wide distribution and its destructiveness," Duncan Macintosh said.

In India, more than 266,000 tonnes of rice are lost each year, about 0.8% of total yield.

In Japan, the disease can infect about 865,000 hectares of rice fields. And in the Philippines, many thousands of hectares of rice fields suffer more than 50% yield losses, the IRRI says.

M. grisea's cousins also attack some 50 other kinds of grass plants, including wheat, barley and millet.

New fungicides

Details of the rice blast sequence have revealed that the fungus produces a group of proteins which may be highly susceptible to new fungicides.

It is hoped that targeting these proteins will lead to new substances that are able to control the disease.

Mr Macintosh also hopes a more targeted treatment may be better for the environment.

"This research also has potential for protecting the environment," he told the BBC News website. "The intent of everybody is to reduce the use of fungicides and harmful chemicals and that is exactly the kind of strategy that can be developed now we understand the rice blast fungus."

Gene sequencing is a fast-moving area of biotechnology. By identifying the genes of crop pests and seeing how they work, scientists can target ways of blocking them chemically or of breeding plants that are resistant to the invader.

Ideally, these solutions would be cheaper and environmentally safer than dousing crops with expensive, broad-spectrum pesticides.

Listen to how the genome was cracked

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