Field displacement of aflatoxigenic Aspergillus flavus strains through repeated biological control applications

Authors: Weaver, Mark; Abbas, Hamed

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2019
Publication Date: 8/6/2019
Citation: Weaver, M.A., Abbas, H.K. 0209. Field displacement of aflatoxigenic Aspergillus flavus strains through repeated biological control applications. Frontiers in Microbiology. 10:1788.

Interpretive Summary: Aflatoxin contamination of corn is an important economic and health concern. The best prevention of aflatoxin contamination is the application of biocontrol strains of the fungus Aspergillus flavus. Three biocontrol strains (Afla-Guard, AF36 and K49) were tested over a four-year period in a 3.2 ha (8 acre), commercial, dryland corn field in the Mississippi Delta to monitor the post-release establishment, spread and persistence of these products. In the two months after the first application the soil population of A. flavus shifted from about 50% aflatoxigenic to less than 10% aflatoxigenic. By the end of the four year study the population was less than 20% aflatoxigenic across the entire field, including plots that have never received biocontrol products. This study supports the efficacy of the biocontrol approach to manage the A. flavus population and shows that much of the value of this biological control occurs with the first application.

Technical Abstract: Aflatoxin contamination of corn is best prevented by field applications of non-aflatoxigenic strains of Aspergillus flavus. The basis of this biological control may involve multiple factors, but competitive displacement of aflatoxigenic strains by the biocontrol strains is a likely mechanism. Three biocontrol strains (NRRL 21882, 18543 and 30797) were tested over a four-year period in a 3.2 ha, commercial, dryland corn field in the Mississippi Delta to monitor the post-release establishment, spread and persistence of these products. In the two months after the initial biocontrol application to select plots the percentage of aflatoxigenic A. flavus strains was reduced from 48% of the population to 9% of the population. The frequency of aflatoxigenic A. flavus strains was also significantly reduced in the rest of field. After four years, even plots that had never received a biocontrol treatment and were separated by at least 20 meters from the nearest biocontrol treatment had less than 20% aflatoxigenic isolates. This significant halo effect might be attributed to movement of soil through tillage operations, but the population shift could be detected in the untreated plots within two months of the initial applications, at a time when there was no tillage. The A. flavus population that colonized the grain was also monitored and was less than 15% toxigenic in the fourth year in all treatments. Over all treatments and years, less than 2 ppb aflatoxin was detected, which could be the result of the favorable growing conditions and proactive management of plant health or a consequence of the field-wide shift of the A. flavus population to non-aflatoxigenic strains. This study supports the efficacy of the biocontrol approach to manage the A. flavus population and shows that much of the value of this biological control occurs with the first application.