2013 Annual Report
1a.Objectives (from AD-416):
1. Advance biocontrol technologies through strain selection, formulation, and adaptation to agronomic practices. Influences of agronomic practices on long-term effects of atoxigenic strain treatments will be determined. Improved criteria for selection of atoxigenic strains and strain mixtures will be sought and a collection of atoxigenics of potential value in target regions developed. Inexpensive substrates and formulations for atoxigenic product will be evaluated. Atoxigenic strain technology will be further adapted to aflatoxin management in commercial maize and tree crops.
2. Characterize adaptive differences among Vegetative Compatibility Groups (VCGs) and strains of Aspergillus flavus including adaptation to host, environment, and ecosystem. Adaptations of A. flavus to life-strategy, host, and environment will be characterized and variability within and between VCGs assessed. It will be determined if cotton and maize differentially influence the composition of A. flavus communities and if VCG composition is location dependent.
3. Use advanced molecular tools to characterize genetic basis for adaptive divergence among aflatoxin-producing and closely related fungi and to develop SNP databases and practical methods for monitoring temporal shifts in compositions of A. flavus communities. Quantitative Pyrosequencing assays will be developed that distinguish specific fungi or groups of fungi in field and laboratory samples. Relationships among morphotypes and vegetative compatibility groups will be clarified while molecular methods for identification are developed. Genome-wide comparisons will be used to identify both adaptive features and paths to adaptation among VCGs successful on different hosts.
4. Identify agronomic, environmental, and ecological factors (e.g. hosts) that favor development of highly toxic fungal community structures and practices that favor selection and retention of atoxigenics. Factors that favor dominance and dispersal of the S strain of A. flavus and that result in loss of A. flavus with reduced aflatoxin-producing potential will be determined in areas with severe levels of contamination attributable to the S strain. This will be done by examining relationships between climatic, biological, ecological, and geographical factors and the spatial and temporal distribution of Aspergillus section Flavi.
1b.Approach (from AD-416):
Develop improved formulations and production techniques to address problems in
commercial practice of biological control and to increase efficacy against aflatoxin producing fungi. Through field tests and retrospective analyses characterize influences of agronomic practices on biological control and use recommendations. Apply geostatistical and epidemiological tools to development of a model to predict aflatoxin contamination after crop maturation. Collect representative A. flavus from crops in Texas and Arizona and characterize strain specialization, adaptive traits, and optimal atoxigenic strains for distinct cropping systems. Develop both a SNP database for differentiating distinct A. flavus strains and a molecular technique for quantifying strain incidence in environmental samples. Select elite biocontrol strains based on improved knowledge of A. flavus adaptations and responses to relevant environments and ecological niches. Formerly 5344-42000-016-00D (11/05).
Related to MSA 6435-42000-020-00D. Formerly 5344-42000-019-00D (2/06).
In order to support the action plan of National Program 108 entitled Food Safety, tools for limiting aflatoxins in crops continued to be developed. This contributes to National Program 108 Component 1: Food Contaminants. Determination of the fate of the biocontrol agents during rotations out of treated target crops was continued for a second year in order to quantify the longevity of beneficial influences during commercial agronomic practices and to identify agronomic practices with positive influences on biocontrol. Rotations into and out of cotton in 12 commercial fields after treatment with the biocontrol Aspergillus (A.) flavus AF36 were associated with declines in soil population density of A. flavus after winter crops. Persistence of beneficial influences of applications varied among regions but was significant for at least 2 years. The 16 genetic groups of atoxigenic biocontrol strains from South Texas selected previously were narrowed to 8 atoxigenic strains for field evaluation of biocontrol efficacy in Texas. In collaboration with Agricultrual Research Service’s partner, the International Institute of Tropical Agriculture, atoxigenic strains native to several African nations were also selected. These included the Feed the Future countries of Zambia, Senegal, and Tanzania. Sorghum continued to prove to be a highly cost-effective and beneficial material for biocontrol formulations and a low cost, reduced energy, process for producing atoxigenic strain biocontrol products continued to be developed and scaled up. In Nigeria, construction of a facility where a large-scale version of the process will be demonstrated is underway. Plant hosts were found to differentially influence competition among A. flavus isolates and cotton and corn were found to cause different changes in fungal community structures providing clues as to important criteria for selecting future biological control strains. Populations of A. flavus associated with maize production in several regions continued to be sampled and characterized. Microsatellite typing (based on stretches of deoxyribonucleic acid within a genome that tends to vary among individuals) continued to be applied to characterizing A. flavus communities from diverse locations and to understand movement of A. flavus among regions.Influences of geographic features on variation in fungal communities across landscapes continued to be investigated. Overall progress on the project over the past year continued to provide improved bases to understanding A. flavus communities and for improving management of aflatoxin contamination with atoxigenic strains of A. flavus.
Crop nutrients influence competitiveness of aflatoxin biocontrol agents. Aflatoxins are potent cancer causing toxins that frequently contaminate several important crops reducing crop value and causing detrimental influences of human and domestic animal health. Prevention of aflatoxin contamination of crops through competitive exclusion with atoxigenic strains of Aspergillus flavus has become the preferred treatment for preventing aflatoxin contamination in corn, cotton, pistachios, and peanuts. A team of scientists working in the Agricultrual Research Service laboratory at the University of Arizona in Tucson evaluated the influence of nutrients in the environment on abilities of specific genetic groups of Aspergillus flavus to compete both during growth through a substrate and during reproduction. Different responses of Aspergillus flavus isolates to nutrient variability suggest genotypes are adapted to different nutrient environments that have the potential to influence Aspergillus flavus population structure and the epidemiology and biocontrol of aflatoxin contamination.
Mehl, H.L., Cotty, P.J. 2013. Intraspecific competition during infection by Aspergillus flavus is influenced by plant host species. Plant Pathology. 2013:1365-3059.
Mehl, H.L., Jaime, R., Callicott, K.A., Probst, C., Garber, N.P., Ortega-Beltran, A., Grubisha, L.C., Cotty, P.J. 2012. Aspergillus flavus diversity on crops and in the environment can be exploited to reduce aflatoxin exposure and improve health. Annals of the New York Academy of Sciences. 1273:7-17.
Mehl, H.L., Cotty, P.J. 2013. Nutrient environment influences competition among Aspergillus flavus genotypes. Applied and Environmental Microbiology. 79:1473-1480.
Mauro, A., Battilani, P., Giorni, P., Pietri, A., Callicott, K.A., Cotty, P.J. 2013. Structure analysis of an Aspergillus flavus kernels population in North Italy. First analysis of an Aspergillus flavus kernels population based on vegetative compatibility groups in Northern Italy. International Journal of Food Microbiology. 162(1):1-7.
Jaime, R., McKamey, J., Cotty, P.J. 2013. Leaf content, seed moisture and module storage time of seed cotton influence cotton fiber quality and aflatoxin contamination of cottonseed in South Texas. Journal of Cotton Science. 17:60-68.