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Genome of 'stealth' pathogen unlocked



Progress made on disease that affects wheat around world


By MATTHEW WEAVER


Capital Press


Researchers at the USDA Agricultural Research Service say they are closer to understanding a global wheat pathogen.


An international consortium headed by ARS recently announced that it has sequenced the genome for the pathogen that causes Septoria tritici blotch, found in every wheat-growing area of the world.


S. tritici infects plants in a manner that is different from fungi that have been studied more thoroughly, said Steve Goodwin, ARS plant pathologist in West Lafayette, Ind. The disease enters through natural plant openings and has a "hidden" period of about 12 to 14 days. It grows between cells, turning off plant defense responses or failing to trigger them.


"It's kind of a stealth pathogen," Goodwin said. "It gets in there very sneakily until it's ready, and then it mounts an attack the host can't overcome."


He said S. tritici is right behind the diseases that garner the most attention, such as fusarium head blight, stem rust and stripe rust.


"If you don't have those, the next one you have is septoria," he said. "It's in the top three diseases of wheat in terms of economic importance worldwide."


S. tritici is a particular problem in Russia and Europe, or regions where the weather is cool and wet and other diseases are under control.


It typically infects seedlings that have recently emerged, creating lesions and spreading to the higher leaves. It can affect yield and quality, Goodwin said. Fungicide sprays are used to control it, he said.


Igor Grigoriev, of the U.S. Department of Energy's Joint Genome Institute in Walnut Creek, Calif., has been sequencing the genomes of other fungi in the same class.


"We think we will be able to derive those features that make them pathogens," Grigoriev said.


Grigoriev said the next step is to determine the function of the genes in the pathogen and see how they interact.


Having the genome sequence for the disease is attracting more funding and more researchers, Goodwin said. A September conference in Mexico will focus on the disease.


Fungicide companies may be able to design compounds that target specific genes and work on specific fungi, Goodwin said.


Researchers will also examine the gene sequences of the fungus on plants at different times, trying to figure out what genes they express as they interact.


"That will give us a better idea of what the fungus is doing to cause disease and what the plant is doing to cause resistance," Goodwin said.



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