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Poster: Biology & Disease Mgmt: Postharvest Pathology & Mycotoxins


Factors influencing Aspergillus flavus community structures in fields treated with the atoxigenic biocontrol A. flavus AF36
R. JAIME (1), P. Cotty (2) (1) University of Arizona, U.S.A.; (2) USDA-ARS, University of Arizona, U.S.A.

Aflatoxins, toxic and carcinogenic metabolites produced by several fungi in Aspergillus section Flavi, are perennial contaminants of cottonseed in Arizona and impact crop value. Atoxigenic strains of A. flavus have been used to displace aflatoxin producers and manage aflatoxins in cottonseed in Arizona for over two decades. Previous work indicated applications benefit both treated and subsequent crops and that atoxigenic strains in treated soils decrease over time to reach equilibrium with the native A. flavus community. Crop rotation has been implicated as a factor influencing atoxigenic strain retention. The present study sought to determine factors influencing both retention of the biocontrol AF36 and reestablishment of the S strain. Weather, soil type and geography were all found to influence the community structure of A. flavus with hot temperatures, heavy soils, and low elevations favoring the S strain. Regression analyses indicated significant differences among regions in rate of change of the populations of both AF36 and the S strain as a function of time after application. Populations of A. flavus in soils are highest immediately after harvest. Steep declines occur during the few months following harvest. Both the S strain and AF36 followed similar patterns, fitting an exponential decay model. However, quantities of S strain propagules decline slower than AF36, suggesting the S strain may be adapted to resist soil factors that reduce A. flavus viability.