Problem Statement: In 1996 and 1997, much of the $5-billion/year U.S. wheat export market was threatened by the supposed discovery of a fungus, Tilletia indica (which causes the disease Karnal bunt) in wheat crops in Arizona and a small part of California. It is estimated that about one third of countries that might buy wheat from the United States will not buy Karnal-bunt-infected wheat. During the U.S. national Karnal bunt survey of 1996, T. indica-like fungal spores (teliospores) were found in wheat grain washes from the south-eastern United States. However, no bunted i.e. blackened and foul-smelling, wheat seeds were found. Ryegrass seed infected with a similar fungus sometimes gets harvested along with the wheat. Initially, available tests incorrectly identified this fungus as Karnal bunt. As a result, in 1996-97, restrictions were placed on the movement of suspect wheat from Alabama, Georgia, Florida, and Tennessee.

Methods: An incorrect identification was suspected by taxonomists because no bunted wheat kernels were found but the wheat grain wash samples in the south-eastern United States were testing positive for the Karnal bunt fungus using the then-available molecular test. After close taxonomic re-examination of the bunt fungi family using light and scanning electron microscopy of the spores, it was determined that the Tilletia species on the ryegrass was an unnamed species new to science. With these techniques, it was determined that, with experience, visual characteristics could be used to tell the two fungi apart.

Outcomes and Impacts: The new techniques quickly showed that 100 percent of each of the wheat samples collected from south-eastern farms in 1996 were contaminated with the new fungus (named T. walkeri) and not Karnal bunt. As a result, in March 1997, restrictions on the movement of the suspect wheat were lifted. Federal plant quarantine officials now use the new technique as a first cut, to decide if possible quarantine actions are needed.

If Karnal bunt had been incorrectly confirmed in the south-eastern US wheat crop, it would have indicated that Karnal bunt was widespread in the US and that all wheat produced in the US was potentially infected. This would have threatened the entire US $5 billion export market, with disastrous consequences.

Lessons: Taxonomic expertise allowed for the distinction between the different fungal species. The correct identification of a new fungus led to the lifting of the ban on movement of the wheat crops from the south-eastern United States and prevented the wholesale rejection of all wheat export produce from the US. What could have been a trade and agricultural disaster was avoided.