Location: Peanut Research
Title: Effect of sexual recombination on population diversity in aflatoxin production by Aspergillus flavus Authors
Submitted to: American Phytopathogical Society Southern Division
Publication Type: Abstract Only
Publication Acceptance Date: January 26, 2013
Publication Date: February 8, 2013
Citation: Olarte, R.A., Horn, B.W., Dorner, J.W., Monacell, J.T., Singh, E.A., Carbone, I. 2013. Effect of sexual recombination on population diversity in aflatoxin production by Aspergillus flavus. American Phytopathogical Society Southern Division Annual Meeting. Feb. 8-10, 2013. Baton Rouge, LA. Interpretive Summary: none required
Technical Abstract: Aspergillus flavus is the major producer of carcinogenic aflatoxins (AFs) in crops worldwide. Recent efforts to reduce AF concentrations in crops have focused on the use of two non-aflatoxigenic A. flavus strains, AF36 and NRRL 21882 (Afla-Guard), as biological control agents. These products are applied at high densities to agricultural fields, where they competitively exclude native aflatoxigenic strains and thereby reduce AF contamination. Natural populations of A. flavus show tremendous variation in AF production, some of which can be attributed to environmental conditions, differential regulation of the AF biosynthetic pathway, and deletions or loss-of-function mutations in the AF gene cluster. Understanding the evolutionary processes that generate genetic diversity in A. flavus may also explain quantitative differences in aflatoxigenicity. Several population studies using multilocus genealogical approaches provide indirect evidence of recombination in the genome and specifically in the AF gene cluster. More recently A. flavus has been shown to be functionally heterothallic and capable of sexual reproduction in laboratory crosses. In the present study, we characterize the progeny from nine A. flavus crosses using toxin phenotype assays, DNA sequence-based markers and array comparative genome hybridization. We show high AF heritability linked to genetic variation in the AF gene cluster, as well as recombination through the independent assortment of chromosomes and through crossing over within the AF cluster that coincides with inferred recombination blocks and hotspots in natural populations. Moreover, the vertical transmission of cryptic alleles indicates that while an A. flavus deletion strain is predominantly homokaryotic, it may harbor AF cluster genes at a low copy number. Results from experimental matings indicate that sexual recombination is driving genetic and functional hyperdiversity in A. flavus. The results of this study have significant implications for managing AF contamination of crops and for improving biocontrol strategies using non-aflatoxigenic strains of A. flavus.