13 June 2011

A team led by scientists from the U.S. Department of Agriculture (USDA) has fully sequenced the genome of the pathogen that causes the wheat disease septoria tritici blotch, which can cause significant yield losses.

According to the International Maize and Wheat Improvement Centre in Mexico, losses can reach as high as 50 percent if fungicides are not used to protect susceptible wheat lines. The disease is found in every wheat-growing area the world over. The researchers who sequenced the genome, published in PLoS Genetics, believe their work will lead to developing strategies to control the disease.

The pathogen that causes septoria tritici, Mycosphaerella graminicola, has a long "silent period;" a latent stage during which it takes nutrition from the living plant and evades the host plant's natural defences. Scientists previously did not have a good understanding of how the organism infects wheat, or how the wheat plant itself resists the pathogen. Sequencing the genome of the pathogen could help answer these questions, among others.

Agricultural Research Service (ARS) Administrator Edward B. Knipling said of the breakthrough, "Having a complete sequence of the M. graminicola genome will give researchers across the globe the tools necessary to mitigate the damage this pathogen causes to wheat crops."

"A lot of pathogens infect host plants by penetrating the plant's cell wall," said plant pathologist Stephen Goodwin at the ARS Crop Production and Pest Control Research Unit in West Lafayette, Ind. "But this organism grows into the plant's natural openings, the stomata, which are normally used for gas exchange. The pathogen then grows in between the cell walls without triggering defense responses that are designed to stop infection."

The pathogen goes into its "silent period" and then switches to a pathogenic (disease-causing) stage. "We don't know what happens in that switch from the latent phase to the pathogenic phase," Goodwin said. "The gene sequence will allow scientists to look at the expression of all of those genes involved in the transition period."