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Toxins 2018, 10(4), 159; https://doi.org/10.3390/toxins10040159

Rice Phyllosphere Bacillus Species and Their Secreted Metabolites Suppress Aspergillus flavus Growth and Aflatoxin Production In Vitro and in Maize Seeds

Department of Plant Pathology and Crop Physiology, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA
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Received: 19 March 2018 / Revised: 9 April 2018 / Accepted: 11 April 2018 / Published: 16 April 2018
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Abstract

The emergence of super-toxigenic strains by recombination is a risk from an intensive use of intraspecific aflatoxin (AF) biocontrol agents (BCAs). Periodical alternation with interspecific-BCAs will be safer since they preclude recombination. We are developing an AF-biocontrol system using rice-associated Bacilli reported previously (RABs). More than 50% of RABs inhibited the growth of multiple A. flavus strains, with RAB4R being the most inhibitory and RAB1 among the least. The fungistatic activity of RAB4R is associated with the lysis of A. flavus hyphal tips. In field trails with the top five fungistatic RABs, RAB4R consistently inhibited AF contamination of maize by Tox4, a highly toxigenic A. flavus strain from Louisiana corn fields. RAB1 did not suppress A. flavus growth, but strongly inhibited AF production. Total and HPLC-fractionated lipopeptides (LPs) isolated from culture filtrates of RAB1 and RAB4R also inhibited AF accumulation. LPs were stable in vitro with little loss of activity even after autoclaving, indicating their potential field efficacy as a tank-mix application. A. flavus colonization and AF were suppressed in RAB1- or RAB4R-coated maize seeds. Since RAB4R provided both fungistatic and strong anti-mycotoxigenic activities in the laboratory and field, it can be a potent alternative to atoxigenic A. flavus strains. On the other hand, RAB1 may serve as an environmentally safe helper BCA with atoxigenic A. flavus strains, due its lack of strong fungistatic and hemolytic activities. View Full-Text
Keywords: aflatoxin; interspecific biocontrol; rice-associated bacilli (RABs); seed aflatoxin contamination; field trials; tip lysis; lipopeptides; fungistasis; anti-aflatoxigenic activity; hemolytic activity aflatoxin; interspecific biocontrol; rice-associated bacilli (RABs); seed aflatoxin contamination; field trials; tip lysis; lipopeptides; fungistasis; anti-aflatoxigenic activity; hemolytic activity
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Chalivendra, S.; DeRobertis, C.; Reyes Pineda, J.; Ham, J.H.; Damann, K. Rice Phyllosphere Bacillus Species and Their Secreted Metabolites Suppress Aspergillus flavus Growth and Aflatoxin Production In Vitro and in Maize Seeds. Toxins 2018, 10, 159.

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