Field efficacy of a mixture of atoxigenic Aspergillus flavus Link:Fr vegetative compatibility groups in preventing aflatoxin contamination in maize (Zea mays L.)

Competitive exclusion of aflatoxin producers by endemic atoxigenic strains of Aspergillus flavus is a proven tool for aflatoxin management being adapted for use in Africa. Field efficacy of an experimental formulation consisting of four native atoxigenic strains (La3303, La3304, La3279 and Ka16127) was evaluated on maize in 2007 and 2008 in four agroecological zones in Nigeria. The four atoxigenic strains were individually formulated on sterile sorghum grain and subsequently mixed in equal proportions. The blended product was applied on soil (40 kg/ha), 2–3 weeks before flowering. Grains from treated and untreated fields were analyzed for aflatoxins at harvest and after storage. Proportions of the A. flavus population composed of each of the four applied strains in soil before treatment and in harvested grains were determined using vegetative compatibility analyses. Application of the strain mixture resulted in reduced aflatoxin content and significantly (P < 0.05) increased the combined frequencies of the vegetative compatibility groups (VCGs) of the applied strains recovered from the soil and grain. Aflatoxin reductions of 67–95% were associated with a 74–80% combined incidence of the VCGs of the four atoxigenic strains on the treated crops. The applied atoxigenic strains remained with the crop into storage and reduced postharvest increases in contamination. The results suggest that the evaluated multi-strain formulated product has potential to contribute to reduced aflatoxin contamination in Nigeria. This is the first report of a field evaluation of an endemic strain mixture effective at reducing aflatoxin contamination during crop development.