Effect of environmental factors on in vitro and in situ interactions between atoxigenic and toxigenic A. flavus strains and control of aflatoxin contamination of maize

Abstract

The potential of three atoxigenic strains from different geographical origins in Africa were examined for in vitro and in situ competitiveness against two toxigenic strains of Aspergillus flavus and subsequent inhibition of aflatoxin B₁ (AFB₁) production under different environmental conditions. Temperature, water activity (a _w) and substrate influenced the types of interaction between the three AFL⁻ and two AFL⁺ strains. The competitiveness and AFB₁ reduction ability of the three atoxigenic strains when interacting with the two toxigenic strains were evaluated by inoculation of 100, 25:75, 50:50, 75:25 and 100% ratios of mixed spore suspensions in vitro on malt extract and milled maize agars over 28 days and in situ on stored maize grain for 14 days, respectively at 0.99, 0.96 and 0.90 a _w. For all the treatments, the effect of a _w and inoculum ratio and their interaction was highly significant. Toxin inhibition was >80% in vitro at both 0.99 and 0.96 a _w. In situ AFB₁ reduction was influenced by the toxigenic strain assayed, a _w and the inoculum ratio. Where control was achieved, it was more variable at 0.96 a _w, while with more stringent water stress conditions (0.90 a _w) the percentage inhibition was up to 77.2%. The study shows the importance of including environmental factors in screening and identifying effective atoxigenic strains for control of AFs (aflatoxins).

Keywords:

• atoxigenic A. flavus
• index of dominance
• AFB₁ inhibition

Acknowledgement

Sejakhosi Mohale is grateful to the UK Department for International Development (DFID) through its Commonwealth Scholarship for the financial support.