2011 Annual Report
1a.Objectives (from AD-416)
Optimize agronomic systems and environmental practices, including fertilization and rotation that minimize inoculum potential of Aspergillus flavus and other mycotoxin-producing fungi while maximizing corn yield and profits in the Mid-south USA. Gain an understanding of the role of crop management practices on the ecology of Aspergillus flavus and aflatoxin contamination in order to optimize the application of competitive exclusion products. Develop economical biologically-based strategies, including antagonists from soil fungi and bacteria, microbial competitors and antagonists, and natural compounds from biological sources, to minimize mycotoxins and their respective fungi in corn, and continue ecological studies on Aspergillus populations under various management strategies, e.g., rotations, tillage, and cover crops, and herbicide-resistant crops. Evaluate insect-resistant and susceptible maize lines for insect damage and aflatoxin and fumonisin contamination. Evaluate corn accession for aflatoxin resistance. Develop isolines with stable resistance and susceptibility. Cooperate with industry in using molecular markers to develop resistent inbreds/hybrids.
1b.Approach (from AD-416)
Evaluate potassium fertility as a means to decrease mycotoxins. Evlaluate corn maturity as a management practice to avoid heat and/or drought stress and mycotoxins. Evaluate double-cropped corn for mycotoxin contamination. Evaluate corn-soybean rotation to reduce fungal inoculum. Characterize population dynamics of Aspergillus propagules in soil, air, insects and corn at various ontogeny in BT and conventional corn. Compare efficacy of non-toxigenic A. flavus strains as biocontrol agents. Optimize surfactant concentration and formulation for improvement of efficacy of non-toxigenic strains. Determine efficacy of Pichia anomala to control aflatoxin and fumonisin. Identify and characterize bacteria from corn field soils as biocontrol agents of Aspergillus and Fusarium. Isolate and identify factors in corn-earn-worm-resistant corn silks for control of insects and mycotoxins. Cooperate with breeders to develop isolines and inbreds/hybrids.
Substantial results were realized over the 5 years of this project.
Contamination of corn by Aflatoxins is a problem in corn in the mid south especially in the Mississippi Delta. Reduction of contamination will produce a safer feed/food supply readily acceptable on the world market. Developoment of strain K49 has shown superiority in reducing contamination when co-inoculated with a toxigenic isolate of Aspergillus (A.) flavus. A patent, U.S. 7,361,499 B1, was issued April 22, 2008, and licensed in 2010 to Syngenta. This allows industry to test the use of non-toxigenic strains to develop a commercial product to control aflatoxin contamination in corn.
Three years of field studies show effects of planting date on mycotoxins in Bt- corn hybrids in Arkansas. Bt- and non-Bt corn hybrids in mid-April showed a reduction in mycotoxin levels compared to mid-May plantings. Bt-corn hybrids showed more resistance to mycotoxin than non-Bt corn hybrids. These data show the value of Bt-corn hybrids in the avoidance of mycotoxins.
A quantitative pin – bar inoculation technique was developed for use in field studies and the Gompertz model was used to characterize dynamic and optimum colonization of non-toxigenic A. flavus as biological control strains. Use of this technique found non-toxigenic strain K49 to be a superior biocontrol agent for aflatoxin contamination in harvested corn, and that formulation did not reduce colonization potential. This research has led to collaborations with scientists in Lithuania, Nigeria and Italy and is being used in their research.
A 4-year field experiment was initiated to determine the effects of eight different corn and soybean rotation schemes on aflatoxin and fumonisin contamination levels in crops on colonization of the grain by A. flavus. A. flavus isolates were associated more with corn compared to soybean and significantly higher levels of fumonisin contamination were found in corn as compared to soybean. The experiment did not undergo a full sequence of rotation treatments; so it is impossible to completely assess the impact of rotation on mycotoxin contamination.
ARS collaborative research resulted in discovery of a water dispersible granule formulation of A. flavus strain K49. This material is suitable for spray application to the reproductive tissue of corn and is more effective in controlling aflatoxin than wheat based soil applications of strain K49.
Research showed bacteria living inside plants (endophytes) can reduce mycotoxin contamination in corn.
Collaborations with researchers at University of Bologna, Italy, ARS, and Mississippi State University have confirmed that A. flavus is biologically active in soil. Five aflatoxin biosynthesis genes were detected.