July 12, 2011


USDA maps genome of Septoria wheat pathogen


An international consortium headed by the US Department of Agriculture's (USDA) Agricultural Research Service (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.


Septoria infects plants in a manner that is different from fungi that have been studied more thoroughly, said Steve Goodwin, plant pathogist with the research service in West Lafayette, Indiana. The disease enters through natural plant openings, has a hidden period of about 12 to 14 days and 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 Septoria is right behind the diseases that garner national attention, such as Fusarium head blight, stem rust, or 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."


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


Septoria typically infects young seedlings that have recently emerged, creating lesions, and spreading to the higher leaves. It can affect yield and quality, Goodwin said, and control methods are typically fungicide sprays.


Igor Grigoriev, of the US Department of Energy's Joint Genome Institute in Walnut Creek, California, 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 genes in the pathogen and see how they interact, but added that there was no real timeline for the project.


"It's very hard to predict the results of scientific research," he said.


But having the genome sequence for the disease is attracting more funding and a larger community of researchers, he said, noting a conference in Mexico will be devoted to Septoria diseases in cereal crops in September.


Fungicide companies may be able to design compounds that target specific genes and work on specific fungi, but not affect other organisms, Goodwin said. A recessive resistance gene could lead to a toxin sensitivity gene in wheat, which could allow cultivars to be screened ahead of time and remove the sensitivity to certain diseases, speeding up the efficiency of wheat breeding programs.


Researchers will also examine the gene sequences of the fungus on plants at different times 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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