2013 Annual Report
1a.Objectives (from AD-416):
In order to support efforts to improve aflatoxin management methodologies, assess the extent to which agronomic practices, including winter cropping, differentially affect long-term influences of atoxigenic strain treatments. Evaluate inexpensive substrates and formulation for atoxigenic product development. Identify agronomic, environmental, and ecological factors (i.e. hosts, etc.) that favor development of highly toxic fungal community structures and practices that favor selection and retention of atoxigenics.
1b.Approach (from AD-416):
In collaboration with USDA-ARS and commercial farmers, The University of Arizona will perform field and laboratory studies to assess influences of real world agronomic practices on the aflatoxin producing potential of fungal communities and on the long-term effectiveness of biological control agents directed at limiting aflatoxin contamination. Advanced statistical methods such as geostatistics and multiple regression analysis will be applied to population data to identify influences of potential interests. The opinion of farmers and agricultural groups will be sought to identify potential practices that may be modified to improve aflatoxin management.
Research activities for the current project are carried out in Agricultural Research Service (ARS) laboratories on the campus of the University of Arizona, Tucson, AZ, and on commercial agricultural fields. Aflatoxins, toxic and carcinogenic metabolites produced by Aspergillus (A.) flavus, frequently contaminate crops. Competitive displacement by atoxigenic A. flavus is the only proven method to reliably reduce aflatoxins in crops. The atoxigenic strain AF36 is typically applied on colonized, steam sterilized wheat grain. The traditional process of producing this formulation is slow, expensive and requires considerable capital. To meet increased demand, lower cost manufacturing was developed. The updated process provides the opportunity to produce biocontrol product at greatly reduced cost allowing for economic access of the product by more farmers and, as a result, greater reductions in incidences of the highly carcinogenic aflatoxins throughout the environment. The updated process also utilizes far less energy than the original process and far less capital investment is required. Facilities utilizing the original process have a much lower throughput than facilities utilizing the updated process. The only original process facility currently in existence cannot make enough product to meet demand. Field performance of the two formulations of AF36 biocontrol product were evaluated in commercial fields in two regions, four commercial fields per region. Large plots (114 rows by 400 m long) were used to reduce cross over effects between plots. From each sample the percentage of both the highly toxigenic strain S and the atoxigenic strain AF36 was determined and the total number of A. flavus cfu (colony forming units) was obtained. The effect of the treatments on displacement of aflatoxin producing isolates and aflatoxin content in cottonseed was obtained by determining both the highly toxigenic strain S and the atoxigenic AF36. Results indicate sorghum product made with the updated process performs as good as or better than the currently registered wheat based product in displacement of aflatoxin-producing fungi and in prevention of aflatoxin contamination. Significantly more spores per gram were produced by the new product 10 days after application. Differences are due to more sorghum grains persisting in the field. The sorghum product had better persistence and sporulation in the field with double the number of both total and sporulating grain products compared to wheat. Displacement results indicate a significantly higher percentage of the strain S in soils after harvest in the controls compared to treated plots. Percentage of A. flavus AF36 was similar in both sorghum and wheat plots, with a slightly higher percentage in sorghum. In the crop there was a higher percentage of the strain S in the control than treated plots. Treated plots with both sorghum and wheat had significantly higher percentage of A. flavus AF36 in the crop compared to the control. Aflatoxin was lower in the treated plots than the controls, with the new process sorghum slightly, but not significantly, lower that inoculated wheat in both areas. The new sorghum product should be useful for expanded commercial application of aflatoxin biocontrol.