Location: Pest Management and Biocontrol ResearchTitle: Founder events influence structures of Aspergillus flavus populations
|ORTEGA-BELTRAN, ALEJANDRO - International Institute For Tropical Agriculture|
Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2020
Publication Date: 6/9/2020
Citation: Ortega-Beltran, A., Callicott, K.A., Cotty, P.J. 2020. Founder events influence structures of Aspergillus flavus populations. Environmental Microbiology. https://doi.org/10.1111/1462-2920.15122.
Interpretive Summary: Aspergillus flavus is a fungus that can contaminate food with aflatoxins, which are highly toxic, cancer causing chemicals. The dynamics of A. flavus populations are of interest due to normal variation in aflatoxin production found among groups (as defined by two isolates’ fusion in laboratory tests) within the species. YV150, a particular group that dominated the corn fields for Sonora, Mexico in 2006, was found to consist of a single genetic type in those fields despite a great deal of genetic diversity found in other years and other areas when YV150 was not the most frequent group in those fields. A geographic analysis of YV150 showed that there were two distinct subgroups in Mexico and the US differentiated by their mating type, but that despite overlapping geographically, these two subgroups of YV150 had no genetic exchange. This suggests that despite readily asexually fusing in the laboratory, the two mating types within this group engaged in neither asexual nor sexual reproduction in the wild.
Technical Abstract: In warm regions, agricultural fields are occupied by complex Aspergillus flavus communities composed of isolates in many vegetative compatibility groups (VCGs) with varying abilities to produce highly toxic, carcinogenic aflatoxins. Aflatoxin contamination is reduced with biocontrol products that enable atoxigenic isolates from atoxigenic VCGs to dominate the population. Shifts in VCG frequencies similar to those caused by the introduction of biocontrol isolates were detected in Sonora, Mexico,where biocontrol is not currently practiced. The shifts were attributed to founder events. Although VCGs reproduce clonally, significant diversity exists within VCGs. Simple sequence repeat (SSR) fingerprinting revealed that increased frequencies of VCG YV150 involved a single haplotype. This is consistent with a founder event. Additionally, great diversity was detected among 82 YV150 isolates collected over 20 years across Mexico and the US. Thirty-six YV150 haplotypes were separated into two populations by Structure and SplitsTree analyses. Sixty-five percent of isolates had MAT1-1 and belonged to one population. The remaining had MAT1-2 and belonged to the second population. SSR alleles varied within populations, but recombination between populations was not detected despite co-occurrence at some locations. Results suggest that YV150 isolates with opposite mating-type have either strongly restrained or lost sexual reproduction among themselves.