According to the International Maize and Wheat Improvement Center 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 in the world, including the United States. The research, published in PLoS Genetics, may lead to strategies to control this disease.

The USDA scientists work for the Agricultural Research Service (ARS), USDA's chief intramural scientific research agency.

The pathogen that causes the disease, 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 defenses.

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.

"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," said ARS Administrator Edward B. Knipling.

M. graminicola employs "stealth" pathogenicity, the ability to infect the host plant without the plant mounting an adequate defense response, if any at all.

"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."

Goodwin led the sequencing effort and is a lead author of the paper, along with Igor V. Grigoriev of the U.S. Department of Energy's Joint Genome Institute in Walnut Creek, Calif., and Gert H. J. Kema of the Plant Research International B.V., Wageningen, The Netherlands.

The international research team also included scientists in Australia, Brazil, France, Germany, Iran, Mexico, Switzerland, and The United Kingdom.