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A Bacillus-based biocontrol system for the mitigation of Aspergillus ear rot and aflatoxin contamination
Subbaiah Chalivendra: Louisiana State UniversityAgCenter; Jorge Reyes-Pineda: Louisiana State UniversityAgCenter; Catherine DeRobertis: Louisiana State UniversityAgCenter; Kenneth Damann: Louisiana State University AgCenter
<div>The intraspecific aflatoxin (AF) biocontrol requires a physical contact of the biocontrol strain with the toxigenic strain within the first 24 h. This necessitates a continuous deployment of atoxigenic strains every season and may risk the emergence of super toxigenic strains. Biocontrol systems that do not need the presence of another living organism or preclude recombination when physically present will be better alternatives to intraspecific ones. We are developing a biocontrol system using <i>Bacillus</i> isolates commensalistic on the surface of rice leaves. Of the 28 isolates tested on 3 different <i>A. flavus</i> lines, >50% showed a zone of inhibition, with the isolate 4R being the most fungistatic. The top 5 isolates were field tested for their suppression of AF in corn and 4R proved to be the most effective. Since a zone of <i>A. flavus</i> growth inhibition around the <i>Bacillus</i> isolates obviates the need for physical contact and implies the involvement of diffusible antifungal compounds, we tested all isolates on <i>A. flavus</i> growth and AF production. Results showed that the AF-suppressive action is independent of the fungistatic activity and many isolates inhibited AF without affecting <i>A. flavus</i> growth. Further, we extracted lipopeptides (LPs) from culture filtrates of isolates 1 and 4R and demonstrated their AF-suppressive activity by infusing them into the medium. Currently, we are purifying the LPs by preparative HPLC and testing them on <i>A. flavus</i> growth and AF synthesis. This approach may prove to be effective on a range of preharvest and postharvest fungal diseases, while avoiding the risk of developing super-toxigenic strains.</div>

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