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Aflatoxin production and environmental oxidative stress in Aspergillus flavus: Implications for host resistance
J. C. FOUNTAIN (1), L. Yang (1), P. Khera (2), R. C. Kemerait (1), R. D. Lee (1), B. T. Scully (3), R. K. Varshney (2), B. Guo (4). (1) University of Georgia, Tifton, GA, U.S.A.; (2) International Crop Research Institute for the Semi Arid Tropics, Hyderabad, India; (3) USDA-ARS, Fort Pierce, FL, U.S.A.; (4) USDA-ARS, Tifton, GA, U.S.A.

Aflatoxin is of major concern in global food security. Host resistance to aflatoxin is negatively influenced by environmental stress. Given that reactive oxygen species (ROS) accumulate in host tissues during abiotic stress, and exacerbate aflatoxin production in <i>Aspergillus spp</i>. <i>in vitro</i>, it has been hypothesized that ROS may serve as signals between <i>A. flavus </i>and its hosts. In order to determine the potential functions of aflatoxin production in oxidative responses, we compared the responses of five toxigenic and five atoxigenic isolates of <i>A. flavus</i> and <i>A. parasiticus</i> to H<sub>2</sub>O<sub>2</sub> induced oxidative stress over a gradient ranging from 0 – 50mM in toxin-conducive and non-conducive media. There was variability among isolates with regard to their degree of oxidative stress tolerance with toxigenic isolates generally exhibiting greater levels of tolerance with highly virulent toxigenic isolates (A9, AF13, and Tox4) and well performing atoxigenic biocontrol isolates (AF36, Aflaguard, and K49) surviving the greatest levels of stress within their respective groups. To explain the functional differences between these isolates, we also performed transcriptomic and biochemical analyses examining the oxidative responses of the isolates with respect to their ability to produce aflatoxin. In application, identifying the causes of variation in oxidative stress tolerance among atoxigenic isolates may allow for prediction of their performance as biocontrols in field applications.

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