Identification of AtoxigenicAspergillus flavusIsolates to Reduce Aflatoxin Contamination of Maize in Kenya

Abstract

Aspergillus flavus has two morphotypes, the S strain and the L strain, that differ in aflatoxin-producing ability and other characteristics. Fungal communities on maize dominated by the S strain of A. flavus have repeatedly been associated with acute aflatoxin poisonings in Kenya, where management tools to reduce aflatoxin levels in maize are needed urgently. A. flavus isolates (n = 290) originating from maize produced in Kenya and belonging to the L strain morphotype were tested for aflatoxin-producing potential. A total of 96 atoxigenic isolates was identified from four provinces sampled. The 96 atoxigenic isolates were placed into 53 vegetative compatibility groups (VCGs) through complementation of nitrate non-utilizing mutants. Isolates from each of 11 VCGs were obtained from more than one maize sample, isolates from 10 of the VCGs were detected in multiple districts, and isolates of four VCGs were found in multiple provinces. Atoxigenic isolates were tested for potential to reduce aflatoxin concentrations in viable maize kernels that were co-inoculated with highly toxigenic S strain isolates. The 12 most effective isolates reduced aflatoxin levels by >80%. Reductions in aflatoxin levels caused by the most effective Kenyan isolates were comparable with those achieved with a United States isolate (NRRL-21882) used commercially for aflatoxin management. This study identified atoxigenic isolates of A. flavus with potential value for biological control within highly toxic Aspergillus communities associated with maize production in Kenya. These atoxigenic isolates have potential value in mitigating aflatoxin outbreaks in Kenya, and should be evaluated under field conditions.

Changes in Fungal Population and Aflatoxin Levels and Assessment of Major Aflatoxin Types in Stored Peanuts (Arachis hypogaea Linnaeus)

“…Aspergillus flavus S-strain produces high levels of B-aflatoxins (Garber & Cotty, 1997), with some S-strains producing both B-and G-aflatoxins (Barros et al, 2006;Cardwell & Cotty, 2002). Aspergillus flavus L-strain typically produces less B-aflatoxins or no aflatoxins at all (Barros et al, 2006;Garber & Cotty, 1997;Probst et al, 2011), while isolates of A. parasiticus can produce both B-and G-type aflatoxins (Ehrlich et al, 2004). Ability of A. flavus S-strain and A. parasiticus to produce both B-and G-type aflatoxins could possibly explain why AFG2 was detected in the highest incidence (89%).…”

“…It is worth noting that 9% of the assayed isolates did not produce any of the four aflatoxin types. This is significant because application of atoxigenic A. flavus L-strains has successfully reduced aflatoxin contamination of peanuts and maize through competitive exclusion of aflatoxin producers mainly the S strains (Probst et al, 2011).…”

“…Based on morphological, genetic and physiological criteria, A. flavus, the main aflatoxin producing species, can be divided into two morphotypes, the S and L strains (Cotty, 1994). The S-strain produces high levels of B-aflatoxins with some strains producing both B-and G-aflatoxins (Barros, Torres, Rodriguez, & Chulze, 2006;Cardwell & Cotty, 2002), while the L-strain produces less B-aflatoxins (Barros et al, 2006;Probst, Bandyopadhyay, Price, & Cotty, 2011). Aspergillus parasiticus and A. nomius produce both B-and G-aflatoxins (Cardwell & Cotty, 2002).…”

Genetic Analysis of the Aspergillus flavus Vegetative Compatibility Group to Which a Biological Control Agent That Limits Aflatoxin Contamination in U.S. Crops Belongs

“…A single VCG may consist of few to many A. flavus strains. Strains of the Aspergillus flavus VCGs vary widely in their aflatoxin-producing potential, with many producing no aflatoxins (15)(16)(17). Competitive exclusion of aflatoxin-producing strains by indigenous A. flavus strains that do not produce aflatoxin is a biological control strategy that substantially reduces crop aflatoxin levels and has been highly successful in commercial agriculture for over a decade (18,19).…”

Safe food and feed through an integrated toolbox for mycotoxin management: the MyToolBox approach

“…drought resistance, early mature plant cultivars) in field conditions that are likely to reduce aflatoxin contamination; and (2) applying atoxigenic Aspergillus strains that are out-competing toxigenic Aspergillus strains, which is a novel and proven technology developed in the USA and Africa (Atehnkeng et al, 2008;Bandyopadhyay et al, in press;Brown et al, 1991;Probst et al, 2011), adapted to Europe in collaboration with the international experts from those continents.…”