PARIS, April 20: Scientists have unravelled the genome of the rice plant’s greatest fungal menace, a harvest-wrecking foe that each year destroys the potential to feed 60 million people. Magnaporthe grisea is the first pathogenic plant fungus to have its genetic code unravelled, a feat that the researchers hope will open the way to newer, smarter and less damaging weapons against this menace.
M. grisea, also called rice blast, 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 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 metres — to drive a penetrative peg beneath the leaf’s protective waxy surface.
The fungus then colonises the leaf, producing greyish 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,” the Manila-based International Rice Research Institute (IRRI) says on its website.
In India, more than 266,000 tons of rice are lost each year, about 0.8 percent of total yield. In Japan, the disease can infect about 865,000 hectares of rice fields. In the Philippines, many thousand hectares of rice fields suffer more than 50 percent yield losses, says IRRI.
M. grisea’s cousins also attack some 50 other kinds of grass plants, including wheat, barley and millet.
The fungus’ genome, published on Thursday in the British weekly science journal Nature, suggests the organism has 11,109 genomes, which is in the same ballpark as other funguses that have been sequenced.
The fungus is believed to be able to secrete 739 proteins, twice as many 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.
The research was led by Ralph Dean of North Carolina State University, heading the International Rice Blast Genome Consortium.
Gene sequencing is a fast-moving area of biotechnology. 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.
—AFP