Location: Office of The Director2011 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).
3. Progress Report
This project was started May 1, 2011 and replaced project 5344-42000-019-00D, “ECOLOGICAL BASIS FOR AFLATOXIN REDUCTION THROUGH CROP MANAGEMENT AND BIOLOGICAL CONTROL.” Trials of the atoxigenic strain AF36 in commercial maize and pistachio fields continued since initiation of this project. Environmental Protection Agency (EPA) accepted reports on the first two years of commercial trials on Maize as sufficient to meet requirement for a full registration of AF36 on maize. A report on Pistachio trials is in the process of submission. Work on improved, low cost formulations of atoxigenic strains continued during the first three months of the project in collaboration with the Arizona Cotton Research and Protection Council and the International Institute of Tropical Agriculture (IITA) and atoxigenic strains were selected for initial field trials in Texas and Burkina Faso. Trials of atoxigenics in Kenya, Senegal, and Nigeria were continued. Analyses to determine the fungal genetic groups differentially associated with maize and cotton production were continued during the first three months of the project. Laboratory assays to dissect adaptive differences among genetic groups of A. flavus on living hosts were put into development and efforts were continued to expand our DNA sequence database in order to support use of DNA in strain comparison tests. In collaboration with commercial elevators distributed across the aflatoxin prone regions of South Texas, the incidences of strains, species, and genetic groups of aflatoxin producing fungi on the corn crop continued to be determined in order to develop a dataset of information related to location that can be subjected to geography referenced statistical analyses.
Mehl, H.L., Cotty, P.J. 2011. Sequence of host contact influences the outcome of competition among Aspergillus flavus isolates during host tissue invasion. Applied and Environmental Microbiology. 77(5):1691-1697.