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Diversity among S morphology fungi in Aspergillus section Flavi from North America

Pummi Singh: University of Arizona

<div>Aflatoxins are hepatocarcinogens that contaminate a wide range of crops in warm regions, and are produced by several species in <em>Aspergillus </em>section <em>Flavi. </em>Several phylogenetically distinct members of section <em>Flavi </em>have S morphology (small sclerotia) and produce high levels of aflatoxins (B or B and G). Fungi with S morphology have been implicated as causal agents of contamination in both the United States (US) and Africa. Several S morphology taxa remain unnamed. One of these, the Lethal Aflatoxicosis Fungus (LAF),<sub> </sub>has been associated with over 100 deaths from aflatoxicosis in Kenya. Genetic diversity of S morphology fungi in North America (NA) is poorly understood. The current study characterized fungi with S morphology (n=504) collected from 2002 to 2015 from soil and maize, collected from across the US and Mexico. Phylogenetic analyses of partial gene sequence for aflatoxin pathway transcription factor (<em>aflR</em>, 1.8 kb) resolved fungal isolates into four distinct clades. <em>Aspergillus flavus </em>S strain was predominant among S morphology fungi from NA (96%) followed by <em>A. texensis </em>(2.2%), LAF<sub> </sub>(0.6%) and a novel clade of B aflatoxin producers sister to <em>A. flavus </em>(1.2%). The S strain of <em>A. flavus</em> was found to be highly diverse at 17 microsatellite loci with 292 haplotypes from 484 isolates and 5 to 27 alleles per locus. Occurrence of distinct species and haplotypes of aflatoxin-producing fungi provide a new perspective on the etiology of aflatoxin contamination in NA.</div>

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