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Title: The vegetative compatibility group to which the US biocontrol agent Aspergillus flavus AF36 belongs is also endemic to Mexico

Author
item ORTEGA-BELTRAN, ALEJANDRO - University Of California
item GRUBISHA, LISA - University Of Wisconsin
item Callicott, Kenneth
item Cotty, Peter

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2016
Publication Date: 4/12/2016
Citation: Ortega-Beltran, A., Grubisha, L.C., Callicott, K.A., Cotty, P.J. 2016. The vegetative compatibility group to which the US biocontrol agent Aspergillus flavus AF36 belongs is also endemic to Mexico. Journal of Applied Microbiology. 120(4):986-998.

Interpretive Summary: Aflatoxin is a carcinogenic fungal metabolite produced by members of Aspergillus section Flavi. Aflatoxin contamination of maize, peanuts, and tree crops results in tremendous economic loss and human disease and even death. The most effective way to reduce aflatoxin contamination of crops is through competitive exclusion of aflatoxin-producing producers with genotypes of Aspergillus flavus that do not produce aflatoxins. These genotypes are called atoxigenic. One atoxigenic A. flavus registered with EPA for aflatoxin-prevention is AF36. AF36 is native to Arizona and Texas, states that boarder Mexico. Mexico has need of aflatoxin management and the current study was undertaken to determine the extent to which AF36 occurs in Mexico in an effort to facilitate approval of AF36 for use in that country. Among 3,581 isolates of A. flavus collected in four states of Mexico (Nayarit, Sinaloa, Sonora, and Tamaulipas), 59 (1.6%) belong to the genetic group of AF36. All 59 AF36 isolates had both the MAT1-2 idiomorph at the mating-type locus and the SNP in the polyketide synthase gene, aflC (=pksA), that confers atoxigenicity to AF36. Natural occurrence of AF36 across Mexico should facilitate the path to AF36 becoming the first pesticide registered for pre-harvest aflatoxin mitigation in Mexico. Use of AF36 in Mexico should allow for economic and health benefits to the population.

Technical Abstract: Aflatoxins are naturally occurring and carcinogenic mycotoxins produced by several members of Aspergillus section Flavi. These potent toxins frequently contaminate maize in warm production areas. Maize provides over half the caloric intake for the majority of the population of Mexico. However, most maize produced within Mexico is at risk of aflatoxin contamination. Atoxigenic strains of A. flavus are used commercially in the USA to reduce aflatoxin contamination in maize, cottonseed, peanut, fig, and pistachio. Atoxigenic strain applications alter the fungal community structure so that aflatoxin-producers are less common and this results in lower aflatoxin concentrations in crops. The first atoxigenic strain registered with USEPA as a biopesticide active ingredient was Aspergillus flavus AF36 which is currently used on cotton, corn, pistachios and fig. AF36 belongs to the vegetative compatibility group (VCG) YV36 and vegetative compatibility analyses (VCA) based on nitrate nonutilizing mutants are used to track AF36 after application. In the current study VCA were used to search for YV36 in Mexico. Among 3,581 isolates of A. flavus collected in four states of Mexico (Nayarit, Sinaloa, Sonora, and Tamaulipas), 59 (1.6%) were assigned to VCG YV36. All 59 YV36 isolates had both the MAT1-2 idiomorph at the mating-type locus and the SNP in the polyketide synthase gene, aflC (=pksA), that confers atoxigenicity to both AF36 and all other isolates in VCG YV36. In addition, three YV36 isolates endemic to Mexico had a 739 bp deletion in aflC indicating continuing degeneration of the aflatoxin biosynthesis gene cluster. 23 microsatellite loci exhibited both low levels of genetic diversity among YV36 isolates and linkage disequilibrium. The results suggest that YV36 isolates in Mexico and the US belong to a single population. Here we report that an USEPA registered biocontrol agent effective at preventing aflatoxin contamination is endemic to Mexico. There is interest in harmonization among NAFTA nations. Endemic biocontrol agents are adapted to the agroecosystem and pose no environmental risk from introduction. Natural occurrence of YV36 across Mexico should facilitate the path to AF36 becoming the first pesticide registered for pre-harvest aflatoxin mitigation in Mexico. Use of AF36 in Mexico should allow for economic and health benefits to the population.