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Abstract
SummaryIn 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 United States. 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.
Highlights
In warm agricultural areas, fungi belonging to Aspergillus section Flavi frequently infect and contaminate maize with aflatoxins (Cotty et al, 1994; Probst et al, 2010)
The objectives of the present work were (i) to assess genetic diversity within 82 isolates of vegetative compatibility groups (VCGs) YV150 from Mexico and the United States collected over 20 years using 24 microsatellite markers for A. flavus previously shown to be useful for quantifying variability within a VCG (Grubisha and Cotty, 2010, 2015; Ortega-Beltran et al, 2016) and (ii) to determine if members of this VCG from spatially and temporally distinct populations possess clonal or recombinant population structures
Each of the 82 VCG YV150 isolates (Table 1; Fig. 1) produced a single amplicon (Ramirez-Prado et al, 2008), either a PCR product 395 bp in length associated with MAT1-1 or a PCR product 273 bp in length associated with MAT1-2 (Table 2)
Summary
Fungi belonging to Aspergillus section Flavi frequently infect and contaminate maize with aflatoxins (Cotty et al, 1994; Probst et al, 2010). In nations where regulations are either poorly enforced or non-existent, humans and domestic animals are continuously exposed to aflatoxins (Gong et al, 2008; Shephard, 2008; Hoffmann et al, 2018; Voth-Gaeddert et al, 2018). This results in losses in human health and livestock productivity that have a proportionately greater economic impact than that seen in the developed world (Udomkun et al, 2017; Nishimwe et al, 2019)
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