Aflatoxin Formation in Preharvest Maize Ears Coinoculated with Aspergillus Flavus and Aspergillus Niger

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Abstract
Aspergillus flavus and Aspergillus niger commonly co-occur in preharvest maize and one report suggests that this association promotes a greater incidence of aflatoxin. Other studies have shown that Aspergillus niger can prevent, or substantially reduce, aflatoxin formation by Aspergillus flavus in autoclaved maize kernels, and this led us to examine the effect of A. niger on aflatoxin formation by A. flavus in preharvest maize where the bulk of aflatoxin accumulation occurs. Samples of kernels simultaneously wound-inoculated with equivalent numbers of A. flavus and A. niger conidia showed substantial aflatoxin contamination (mean = 9900 ppb) even though significantly more (P =.04) aflatoxin was produced in kernels wound-inoculated only with A. flavus (mean = 36,700). These same wounded kernels had a mean sample pH of 5.45 ± 0.44, well above substrate acidity levels (<pH 3.4) reported to prevent aflatoxin formation in autoclaved maize meal.