MU researchers find fungi buildup in glyphosate-treated soybean fields

"MU researchers find fungi buildup in glyphosate-treated soybean fields"

Information Specialist
University of Missouri
December 21, 2000
COLUMBIA, Mo. - A four-year study by University of Missouri researchers has found that Roundup herbicide applications change the microbial composition of soil in the field. They observed increases in fungi on the roots and in the soil around the roots of soybean plants, with "potential implications in future management." "Experiments conducted in 1997 through 2000 at two Missouri locations revealed that Roundup Ready soybeans receiving glyphosate at recommended rates had significantly higher incidence of Fusarium on roots within one week of application compared with" soybeans that did not receive glyphosate, reported Pat Donald, MU plant pathologist, and Robert Kremer, an MU soil scientist and USDA Agricultural Research Service microbiologist. In research plots at MU Delta Research Center in Portageville, Mo., and at MU Bradford Farm near Columbia, the scientists detected major colonization by several distinct types of the fungus in the glyphosate-treated fields. "Although soil Fusarium populations varied among locations, glyphosate significantly increased numbers at each location." "There is a natural ebb and flow, but with Roundup Ready beans treated with Roundup, there was always a spike in the levels of the fungi studied," Kremer said.
Fusarium fungi are almost always found in soybean fields, but at elevated levels some can become pathogenic on susceptible plants and lead to lost yields through such diseases as sudden death syndrome and other root rots, Donald said. Kremer said studies of ecological impact from transgenic plants should include an analysis of effects on the microbial makeup of the soil. "Right now, that's an ecological assessment that hasn't received much attention. The tests are often limited to small soil insects and earthworms. We think it's been an oversight." "All of the ecological assessment is aboveground," Donald said, adding that such assessments should measure plants' and products' impact on the soil system, "especially if they're going to potentially increase pathogens." Initially, the researchers believed the increased Fusarium through glyphosate application could provide a biological control for soybean cyst nematode as well as suppressing weed growth. "We thought it might be a double whammy," Donald said. "It didn't work out that way." She and Kremer emphasized that soybean yields in their experiments were not affected by application of glyphosate as opposed to conventional herbicide treatments. However, "potential yield impacts in subsequent seasons due to high soil Fusarium populations, resulting from continued use of glyphosate, needs further investigation." Kremer said the study shows the fungi "build up over the growing season. We need to look at it more and see whether there's a buildup of the organism from year to year."
He noted that more than half of Missouri soybeans are Roundup Ready. "When you think about it, you have to wonder what's happening in the soil."
Donald said soil microorganisms such as fungi and nematodes have both detrimental and beneficial associations with crops and the environment. "We need to have all the information that we can." An abstract of the study can be found at the American Society of Agronomy website: http://www.asa-cssa-sssa.org/cgi-bin/abstract_database_search.cgi?objective=Kremer
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