ARS | Publication request: Nonaflatoxigenic Aspergillus flavus TX9-8 Competitively Prevents Aflatoxin Production by A. flavus Isolates of Large and Small Sclerotial Morphotypes

Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Proceedings/Symposium
Publication Acceptance Date: October 10, 2006
Publication Date: March 1, 2007
Citation: Chang, P., Hua, S.T. 2007. Nonaflatoxigenic Aspergillus flavus TX9-8 competitively prevents aflatoxin production by A. flavus isolates of large and small sclerotial morphotypes. In: Proceedings of the 19th Annual Multi-Crop Aflatoxin Elimination Workshop, October 16-20, 2006, Fort Worth, Texas. p. 84.

Technical Abstract: Toxigenic Aspergillus flavus is the main etiological agent for aflatoxin contamination of crops. Using nonaflatoxigenic A. flavus isolates to competitively exclude toxigenic A. flavus isolates in agricultural fields has become an adopted approach to reduce aflatoxin contamination. We determined the phylogeny of toxigenic L- and S-strain sclerotial isolates and nonaflatoxigenic L-strain isolates of A. flavus. The genetic criterion included single nucleotide polymorphisms in the omtA gene and deletions in and distal to the norB-cypA intergenic region. Phenotypical traits, such as aflatoxin production and sclerotial size, also were weighted in the analysis. A. flavus isolates are genetically diverse and were categorized into different groups. From screening subgroups of L-strain nonaflatoxigenic A. flavus, we identified an isolate, TX9-8, which competed well with three A. flavus isolates producing low, intermediate and high levels of aflatoxins, respectively. TX9-8, like A. flavus AF36, has a defective polyketide synthase gene (pksA), which is necessary for aflatoxin production. Coinoculating TX9-8 at the same time with L-strain A. flavus isolates at a ratio of 1:1 or 1:10 (TX9-8:toxigenic) prevented aflatoxin accumulation. The intervention of TX9-8 on S-strain A. flavus isolates varied and depended on isolate and ratio of coinoculation. At a ratio of 1:1, TX9-8 prevented aflatoxin accumulation by A. flavus CA28 and decreased aflatoxin accumulation 10-fold by A. flavus CA43. No decrease in aflatoxin accumulation was apparent when TX9-8 was inoculated 24 hours after toxigenic L- or S-strain A. flavus isolates started growing. The competitive effect likely is due to TX9-8 outgrowing toxigenic A. flavus isolates.