Magnaporthe grisea is the first disease-causing plant fungus to have its genetic code unraveled. Researchers hope it will open the way to newer, smarter and less damaging weapons against the menace. Also called rice blast, M grisea, comprises windborne spores that stick to rice plant leaves.

As it germinates, the spore breeds a dome-shaped infection structure called an ``appressorium,'' whose task is to infect the plant.

The tiny organ produces extraordinary pressures - equivalent to those experienced in a deep-sea dive to 750 meters - to drive a penetrative peg beneath the leaf's protective waxy surface.

The fungus then colonizes the leaf, producing grayish spindle-shaped lesions from which more spores emerge, helped by rain or dew, and which then go on to infect other plants.

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

``Rice blast is one of the most destructive diseases of rice because of its wide distribution and its destructiveness,'' said the Manila-based International Rice Research Institute. In India, more than 266,000 tonnes of rice are lost each year, about 0.8 percent of total yield. In Japan, about 865,000 hectares of rice are at risk and in the Philippines many thousands of hectares suffer more than 50 percent yield losses.

Cousins of M grisea attack 50 other kinds of grasses, including wheat, barley and millet.

The fungus' genome, published today in British weekly science journal Nature, suggests the organism has 11,109 genomes - in the same ballpark as other funguses that have been sequenced.

Where M grisea is at its most impressive is the diversity of its genes.

The fungus is believed to be able to secrete 739 proteins - twice as many as in other researched funguses - in order to penetrate and infect its host. Eight genes alone are used to synthesise cuticle-degrading enzymes called methyl esterases.

By identifying the genes of crop parasites and seeing how they work, scientists can target ways of blocking them chemically or of breeding plants that are resistant to the invader.