Aflatoxin in maize, a multifaceted answer of Aspergillus flavus governed by weather, host-plant and competitor fungi

Aspergillus section Flavi is able to produce aflatoxins (AFs) in vitro down to 0.85 a(w) with a potential maximum occurring between 0.95 and 0.99 a(w), while in the field AFs increased significantly with kernel humidity below 0.95 a(w). In order to clarify this apparent discrepancy, a 3-year field trial with artificial inoculation of maize ears with Aspergillus flavus strains was organised. The co-occurrence of Aspergillus section Flavi and Gibberella fujikuroi species complex (Gfsc) was observed. The incidence of A. flavus was significantly influenced by the year and negatively related to Gfsc incidence. In 2012, when the highest temperature and the lowest rain were registered, aflatoxin B1 (AFB(1)) content was the highest and a(w) < 0.95 in kernels was measured early throughout the growing season. In 2013 and 2014, the temperature was lower and rain more abundant, and a(w) decreased below 0.95 only close to harvest and AFB(1) contamination was limited. The possibility of describing/predicting reasonably well a(w) dynamic based on temperature, (degree day) was confirmed. With a(w) > 0.95, a positive correlation between AFB(1) production rate and a(w) was found, but a negative correlation resulted with a(w) < 0.95. Other factors than a(w) play a role, but a(w) = 0.95 should be considered as an indicator of suitable conditions for rapid aflatoxin accumulation. (C) 2016 Elsevier Ltd. All rights reserved.