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<ul> <LI>Determine the population biology or spectrum of diversity of Aspergillus flavus in the Louisiana corn agro-ecosystem. <LI>Determine the specificity profiles for intra-specific aflatoxin inhibition, i.e., which atoxigenic isolates are capable of inhibiting which toxigenic isolates by the touch inhibition mechanism. <LI>Determine the efficacy of selected atoxigenic isolates to inhibit aflatoxin contamination when deployed in field trials. Investigate the mechanism of touch inhibition of aflatoxin biosynthesis. <LI>Investigate the potential of Aspergillus flavus to infect roots of corn and become systemic, thereby gaining access to the developing corn kernels.
Non-Technical Summary: Aflatoxin contamination of corn is a chronic problem in the Gulf south and an economic concern to Louisiana growers. Biological control can help ameliorate this problem. Our previous work has helped elucidate the probable mechanism of biological control which is touch inhibition of aflatoxin synthesis. Further understanding of this mechanism and the specificitiy involved can lead to better approaches to deploying atoxigenic inoculum in a form which is maximally effective. <P> Approach: Fungal isolates from soil and kernels will be grown on rice and extracts checked for aflatoxins and cyclopiazonic acid by HPLC and TLC, respectively. VCG's will determined by the nit mutant method as well as attempts to develop PCR amplified microsatellite loci fingerprint patterns specific to VCG's. dsRNA's will be purified from a cellulose column and characterized on PAGE. VCG profiles from soil/saprophytic and kernels/parasitic will be compared to discern if there is specificity. Specificity profiles of intra-specific aflatoxin inhibition among paired toxigenic and atoxigenic isolates will be developed by growing conidial suspensions in Eppendorf tubes for 5 days prior to aflatoxin analysis. Patterns of inhibition will be compared among all possible combinations. Broad spectrum inhibitory isolates will be deployed in corn field trials, and challenged with toxigenic isolates to determine efficacy in minimizing aflatoxin contamination. Mechanism of touch inhibition will be investigated by comparing inhibitory and non-inhibitory atoxigenic isolates and also by comparing toxigenic isolates which are and are not inhibited by a particular non-toxigenic isolate. Ability to root infect corn will be done in the growth chamber with selected isolates. Systemic spread and ability to reach developing kernels will also be addressed by homogenizing corn tissues and selective plating. Toxin content will also be determined.