University of Kentucky College of Agriculturespecialists are encouraging Kentucky wheat producers and crop consultants to scout their fields for a new disease that could have important implications for future crop years.

UK soil scientist Lloyd Murdock found wheat blast on a single wheat head May 18, 2011 at a UK Research and Education Center research plot in Princeton. No additional instances of the disease were found even after extensive scouting of the involved research plots and neighboring fields by UK researchers. It is likely, however, that additional infected heads existed, but at levels too low to make detection possible.

Wheat blast is a disease that is recognized as an emerging threat worldwide. Caused by the fungus Magnaporthe oryzae/Pyricularia grisea, the disease was first detected in southern Brazil in 1985 and has since become a problem in several of its neighboring countries.

Crop losses of 40 percent are common and cases of 100 percent loss have been reported. Currently, there are no commercially available resistant varieties and fungicidal programs targeting wheat blast have generally been ineffective.

The Kentucky find is the first known occurrence of wheat blast outside of South America. However, a related pathogen has caused a disease called gray leaf spot on annual ryegrass in Louisiana and Mississippi since the 1970s and on perennial ryegrass in much of the humid regions of the United States since 1992.

Annual ryegrass is a common forage crop in the South, and it is also recognized as a weed in Kentucky wheat fields.

Perennial ryegrass is grown as a turfgrass in Kentucky, as well as an infrequent forage grass. There is also a disease common in rice produced in the Mid-South called rice blast. Although rice blast is caused by the same fungus, isolates of the fungus known to infect rice do not infect wheat and vice-versa. Thus, rice producers who grow wheat in extreme southwest Kentucky and surrounding states are not at increased risk from the wheat blast fungus.

UK plant pathologist Mark Farman has spent most of his career studying the fungi that cause the blast and gray leaf spot diseases. He sequenced the genome of the isolate found at the UK Research and Education Center and compared it to the genetic structure of isolates found on ryegrasses and from South American wheat blast.

Farman found the annual ryegrass pathogen and the wheat blast pathogen discovered at the Research and Education Center to be genetically very similar. This led him to think that the annual ryegrass pathogen gained the genetic ability to infect wheat.

The UK wheat blast pathogen’s genetic structure was most different from the wheat blast pathogen known to affect South American wheat.

His results, thus far, suggest that the blast fungus found on the Kentucky wheat head has probably been around for at least a decade or longer on annual and perennial ryegrass and perhaps on wheat, and almost certainly was not imported with grain originating from South America.

This is important, because it means the new find is not an exotic pathogen. Farman said the pathogen is usually host-specific, meaning the fungus that attacks annual ryegrass normally will only attack annual ryegrass or its close relative, perennial ryegrass. This is the first time he’s seen this pathogen able to “jump” hosts.

Samples of the fungus collected from Kentucky wheat were also sent for testing to Gary Peterson, a researcher with the U.S. Department of Agriculture’s Agriculture Research Service. He confirmed the fungus collected from wheat found in Princeton was able to infect wheat.

Moreover, he found the Kentucky isolate was similar in its ability to cause disease as isolates that cause wheat blast in South America.