Four yeasts and three bacteria that live on flowering wheat heads, but cause no harm there, have been patented by the U.S. Department of Agriculture (USDA) as biological control agents in the fight against Fusarium head blight (FHB).
Caused by the fungus Fusarium graminearum, FHB is among the most costly diseases of cereal crops worldwide, including wheat, barley and oats. From 1998 to 2000, FHB epidemics in U.S. small grains inflicted an estimated $2.7 billion worth of losses, notes David Schisler. He is a plant pathologist with the Agricultural Research Service (ARS), USDA's chief scientific research agency.
The fungus infects wheat through its flower tissues, including anthers. But competition for space and nutrients there is fierce, according to studies by Schisler and colleagues at the ARS National Center for Agricultural Utilization Research in Peoria, Ill., and at Ohio State University (OSU) in Columbus. Indeed, some of the bacteria and yeasts that the researchers isolated from wheat anthers secrete antibiotics, or use other means, to keep the fungus at bay--to the wheat plant's benefit.
To exploit this "natural antagonism," Schisler and OSU colleagues Michael Boehm and Naseem Khan devised fermentation procedures to culture quantities of the beneficial microbes for application to flowering wheat heads. The four yeasts and three bacteria that have been patented (U.S. No. 7,001,755) were the "top picks" from about 700 microbial specimens the scientists evaluated for their fungus-fighting prowess. Of these seven, yeast strain OH 182.9 performed the best in field trials, reducing FHB's severity in spring, winter and durum wheats by 20 to 60 percent.
USDA's patenting of this approach to controlling FHB is a critical first step towards garnering the commercial interest necessary to develop the microbes as registered biological control products that can be used separately or in specific combinations on wheat or other cereal crops. Their development, along with more FHB-resistant wheat varieties, is especially appealing because the use of foliar fungicides is complicated by timing and availability by state.
