The Purdue Plant and Pest Diagnostic Laboratory

What's Hot at the P&PDL
May 4, 2012

Be on the lookout for a new wheat disease

Kiersten Wise, Associate Professor, Field Crops Extension Specialist, Department of Botany & Plant Pathology

Last week the University of Kentucky released an article documenting the discovery of a new disease of wheat in the United States called wheat blast. The article can be accessed at this link: http://news.ca.uky.edu/article/uk-researchers-find-important-new-disease. Wheat blast is caused by the fungus Magnaporthe oryzae (Pyricularia grisea), and has caused moderate to severe yield loss in wheat in Brazil since its detection in the mid 1980s.

Wheat blast was confirmed in Kentucky in 2011, and was limited to a single occurrence of the disease in one research plot in Princeton. No disease was confirmed in any commercial field in Kentucky in 2011. We have not confirmed the disease in Indiana to date, but this is a key time to scout for wheat blast. Symptoms of wheat blast are very similar to those of Fusarium head blight (FHB), and farmers and consultants should look for bleached heads at head emergence and early flowering. Wheat blast symptoms typically appear BEFORE symptoms of FHB, and heads will not have the orange or pink spore masses of the fungus that causes FHB. If wheat blast symptoms are suspected, collect several heads from each field and send samples to the Purdue Plant and Pest Diagnostic Lab (PPDL) for confirmation.

So why are we detecting wheat blast in the U.S. now? Researchers at the University of Kentucky suspect that fungal evolution may be the cause of the find. Variants of the fungus that causes wheat blast also cause a blast disease on rice, and gray leaf spot on annual and perennial ryegrass. Perennial ryegrass is a common turfgrass, and annual ryegrass is a popular cover crop species. Mark Farman at the University of Kentucky has studied the wheat blast fungus found in Kentucky and determined that it is more similar to the fungus that causes gray leaf spot on annual ryegrass than the fungus that causes wheat blast in South America. This suggests that the detection in Kentucky occurred as a result of the fungus evolving and expanding its host range from ryegrass to wheat, rather than an introduction of the fungus from South America.

Research is ongoing at several universities in the U.S. to understand the disease and determine how to best manage it should the need arise. We currently do not know the potential impact of this new disease in U.S. wheat, but early detection and documentation of the disease in Indiana will help us to prepare management strategies for the future.

Click image to enlarge

Wheat blast
Photo courtesy of Paul Bachi, UKY

Closeup of wheat blast
Photo courtesy of Paul Bachi, UKY

Fusarium head blight (scab) also results in bleached heads and can be mistaken for wheat blast

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service