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Title: Frequent shifts in aspergillus flavus populations associated with maize production in Sonora, Mexico

Author
item ORTEGA-BELTRAN, ALEJANDRO - International Institute Of Tropical Agriculture (IITA)
item Cotty, Peter

Submitted to: American Phytopathology Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2017
Publication Date: 1/22/2018
Citation: Ortega-Beltran, A., Cotty, P.J. 2018. Frequent shifts in aspergillus flavus populations associated with maize production in Sonora, Mexico. American Phytopathological Society. 108(3):412-420. https://doi.org/10.1094/PHYTO-08-17-0281-R.
DOI: https://doi.org/10.1094/PHYTO-08-17-0281-R

Interpretive Summary: Aflatoxin contamination of maize is a serious health and economic problem throughout warm production regions. Maize is cultivated throughout Mexico on one third of cultivable land and makes up a majority of caloric daily intake for Mexico’s population. Biological control with natural atoxigenic strains of A. flavus is the most effective aflatoxin management tool. It is based on a natural reshaping of A. flavus populations. In order to gain a better understanding of how A. flavus populations change over time during maize production in a warm region, populations of A. flavus associated with maize were monitored over a three year period in Sonora Mexico. The results indicate that compositions of A. flavus populations frequently shift across seasons apparently driven by founder effects. The study suggests biological control of aflatoxins using atoxigenic strains of A. flavus may be optimized by timing applications to trigger founder events that allow rapid establishment of A. flavus isolates that do not produce aflatoxins.

Technical Abstract: Aspergillus flavus frequently contaminates maize, a critical staple of billions, with aflatoxins. Diversity among A. flavus L morphotype populations associated with maize in Sonora, Mexico was assessed and a total of 869 isolates from 83 fields were placed into 136 vegetative compatibility groups (VCGs) using nitrate-nonutilizing mutants. VCG diversity indices did not differ in four agroecosystems (AES) but diversity significantly differed among years. Frequencies of certain VCGs changed manyfold over single years in both multiple fields and multiple AES. Certain VCGs were highly frequenct (>1%) in 2006, but frequencies declined repeatedly in each of the two subsequent years. Other VCGs that had low frequencies in 2006 increased in 2007 and subsequently declined. None of the VCGs were consistently associated with any AES. Only 9% of VCGs were detected all three years while 66% were detected in only one year. Shifts in population composition may be explained by combinations of cycling of population magnitude, founder effects, high fecundity, and rapid dispersal over relatively large distances. Results suggest that the most realistic measurements of both genetic diversity and the importance of frequent A. flavus VCGs are obtained by sampling multiple locations in multiple years. Single season sampling in many locations should not be substituted for sampling over multiple years.