What is Fusarium graminearum, the fungus US authorities say was smuggled in from China?

Two Chinese researchers are facing federal charges for allegedly smuggling Fusarium graminearum, a destructive fungus, into the U.S. last summer. The fungus causes Fusarium head blight, a disease that leads to significant losses in cereal crops like wheat and barley, costing the U.S. agriculture industry an estimated $1 billion annually. While the fungus already exists in the U.S.