Helping Cereals Resist Head Scab

Head scab annually causes millions of dollars' worth of losses in wheat, rye, barley, and other cereal crops in the Great Plains and Midwest.

All this damage is caused by the fungus Fusarium graminearum, which got nicknamed “head scab” because of the blisters or scabs it forms on the grain-bearing structure, or head, of grain plants.

The disease is cyclical, severely infecting crops one year and then disappearing for several years before reappearing again. A recurrence of severe infestations of head scab across the Great Plains and Midwest in recent years has sent plant breeders and researchers scrambling for new ways to combat the disease.

Plant breeders typically attempt to reinforce cereal crop defenses by breeding for greater resistance to the fungus. Thomas M. Hohn, a microbiologist in the ARS Mycotoxin Research Unit at Peoria, Illinois, says he and colleagues decided to look for the genetic equivalent of an Achilles’s heel in the fungus and found it.

They have successfully disarmed the fungus’ ability to produce its toxin, trichothecene, by identifying the gene that is responsible for the production of an enzyme, trichodiene synthase.

This enzyme enables the fungus to produce trichothecene. Scientists at the lab disabled the toxin-producing gene and were able to successfully demonstrate that the genetically altered fungus was less damaging to crops.

ARS scientists say this new knowledge of the importance of toxin production by the fungus will give wheat breeders more ammunition for fighting costly head scab.

"We know disease resistance in wheat and barley is based on several factors and that current wheat breeding strategies provide only partial resistance," says Hohn. "We believe our findings linking toxin production with the amount of disease caused by the fungus may be another tool for wheat breeders to use in combating this disease."  — By Dawn Lyons-Johnson, ARS.

USDA-ARS Mycotoxin Research Unit, National Center for Agricultural Utilization Research, 1815 N. University St., Peoria, IL