ROCHESTER, NEW YORK--The fungus Fusarium graminearum can devastate a wheat crop, killing plants and contaminating the survivors with a toxin that sickens humans and animals. Without any effective way to stop the blight, farmers stagger varieties and time of planting to cut their risks. But microscopic help may be on the way: A bacterium can fight the fungus and dramatically reduce toxin levels, researchers announced yesterday here at the annual meeting of the American Phytopathological Society.
Winter wheat spends more than 8 months putting down roots and growing leaves in preparation for its 6-week burst of activity to make grain. But just a few days of rain while the wheat blooms make the plant vulnerable to the fungus, commonly known as wheat scab, which can cut yield by up to one-third. "It's a devastating disease that can take a seemingly beautiful, lush crop down to nothing in a matter of 2 weeks," says Marcia McMullen, a plant pathologist at North Dakota State University in Fargo. And farmers suffer a double blow because they get less money for the remaining wheat if it is contaminated with so-called vomitoxin (also known as deoxynivalenol) produced by wheat scab. Sometimes their loads are even rejected outright.
To counteract this threat, scientists at the Brazilian Wheat Research Center in Passo Fundo, Brazil, have been isolating and testing thousands of different microbes for activity against wheat scab and other fungi. They sent three of the most promising to plant pathologist Gary Bergstrom of Cornell University and his colleagues, who sprayed the organisms on the heads of wheat plants that were then exposed to the fungus in greenhouse tests. The best results came from the bacterium Paenibacillus macerans: Plants sprayed with that microbe not only yielded 15% more grain than their untreated counterparts did, but they had dramatically lower levels of vomitoxin--less than one-tenth the levels seen in control plants. "We never would have guessed we'd see such a dramatic drop," says Bergstrom.
But North Dakota's McMullen cautions that finding microbes that are effective against a pest is just a first step. "The organisms must be tested in the field, where all kinds of things can happen," she says, adding that a way to deliver P. macerans effectively to crops must also be developed. Field testing is already under way in Brazil and planned for next summer at Cornell, Bergstrom says.