title: Effects of Hydrogen Peroxide on Different Toxigenic and Atoxigenic Isolates of Aspergillus flavus.
abstract: Drought stress in the field has been shown to exacerbate aflatoxin contamination of maize and peanut. Drought and heat stress also produce reactive oxygen species (ROS) in plant tissues. Given the potential correlation between ROS and exacerbated aflatoxin production under drought and heat stress, the objectives of this study were to examine the effects of hydrogen peroxide (H2O2)-induced oxidative stress on the growth of different toxigenic (+) and atoxigenic (-) isolates of Aspergillus flavus and to test whether aflatoxin production affects the H2O2 concentrations that the isolates could survive. Ten isolates were tested: NRRL3357 (+), A9 (+), AF13 (+), Tox4 (+), A1 (-), K49 (-), K54A (-), AF36 (-), and Aflaguard (-); and one A. parasiticus isolate, NRRL2999 (+). These isolates were cultured under a H2O2 gradient ranging from 0 to 50 mM in two different media, aflatoxin-conducive yeast extract-sucrose (YES) and non-conducive yeast extract-peptone (YEP). Fungal growth was inhibited at a high H2O2 concentration, but specific isolates grew well at different H2O2 concentrations. Generally the toxigenic isolates tolerated higher concentrations than did atoxigenic isolates. Increasing H2O2 concentrations in the media resulted in elevated aflatoxin production in toxigenic isolates. In YEP media, the higher concentration of peptone (15%) partially inactivated the H2O2 in the media. In the 1% peptone media, YEP did not affect the H2O2 concentrations that the isolates could survive in comparison with YES media, without aflatoxin production. It is interesting to note that the commercial biocontrol isolates, AF36 (-), and Aflaguard (-), survived at higher levels of stress than other atoxigenic isolates, suggesting that this testing method could potentially be of use in the selection of biocontrol isolates. Further studies will be needed to investigate the mechanisms behind the variability among isolates with regard to their degree of oxidative stress tolerance and the role of aflatoxin production.
authors.affiliation: Department of Plant Pathology, University of Georgia, Tifton, GA 31793, USA. jfount1@uga.edu.|USDA-ARS, Crop Protection and Management Research Unit, Tifton, GA 31793, USA. jfount1@uga.edu.
authors.forename: Jake C
authors.initials: JC
authors.lastname: Fountain
authors.affiliation: USDA-ARS, U.S. Horticultural Research Laboratory, Fort Pierce, FL 34945, USA. brian.scully@ars.usda.gov.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Scully
authors.affiliation: Department of Plant Pathology and Crop Physiology, Louisiana State University, Baton Rouge, LA 70803, USA. zchen@agcenter.lsu.edu.
authors.forename: Zhi-Yuan
authors.initials: ZY
authors.lastname: Chen
authors.affiliation: USDA-ARS, Toxicology and Mycotoxin Research Unit, Athens, GA 30605, USA. scott.gold@ars.usda.gov.
authors.forename: Scott E
authors.initials: SE
authors.lastname: Gold
authors.affiliation: USDA-ARS, Toxicology and Mycotoxin Research Unit, Athens, GA 30605, USA. anthony.glenn@ars.usda.gov.
authors.forename: Anthony E
authors.initials: AE
authors.lastname: Glenn
authors.affiliation: USDA-ARS, Biological Control of Pests Research Unit, Stoneville, MS 38776, USA. hamed.abbas@ars.usda.gov.
authors.forename: Hamed K
authors.initials: HK
authors.lastname: Abbas
authors.affiliation: Department of Crop and Soil Sciences, University of Georgia, Tifton, GA 31793, USA. deweylee@uga.edu.
authors.forename: R Dewey
authors.initials: RD
authors.lastname: Lee
authors.affiliation: Department of Plant Pathology, University of Georgia, Tifton, GA 31793, USA. kemerait@uga.edu.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Kemerait
authors.affiliation: USDA-ARS, Crop Protection and Management Research Unit, Tifton, GA 31793, USA. baozhu.guo@ars.usda.gov.
authors.forename: Baozhu
authors.initials: B
authors.lastname: Guo
mesh_terms: D000348:Aflatoxins / Q000096:biosynthesis*; D001231:Aspergillus flavus / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D016877:Oxidants / Q000494:pharmacology*; D018384:Oxidative Stress
chemical_list: D000348:Aflatoxins; D016877:Oxidants; D006861:Hydrogen Peroxide
keywords: aflatoxin; biological controls; drought; oxidative stress; peptone; reactive oxygen species