Comparison of temperature and moisture requirements for sporulation of Aspergillus flavus sclerotia on natural and artificial substrates

A key step in the infection cycle by Aspergillus flavus in maize is sporulation of sclerotia present in soil or in crop debris. However, little information is available on this critical and important phase. This study included experiments on artificial (Czapek Dox Agar (CZ)) and natural (maize stalks) substrates under different conditions of temperature (T; from 5 to 45 °C) and water activity (aw; from 0.50 to 0.99) levels to quantify sporulation from sclerotia. The mean numbers of spores were higher on defined nutritional medium in vitro on CZ agar than on maize stalks (4.5 × 106 spores/sclerotium versus 4.2 × 104 spores/sclerotium) with production initiated after 6 and 24 h, respectively. Surprisingly, the optimal temperature was found at 30–35 °C for CZ agar (9.23 × 106 spores/sclerotium) and to be 20–25 °C for maize stalks (6.26 × 104 spores/sclerotium). Water stress imposition only reduced sporulation at ≤0.90 aw. With more available water no significant differences were found between 0.90 and 0.99 aw. This type of data is critical in the development of a mechanistic model to predict the infection cycle of A. flavus in maize in relation to meteorological conditions.

► Role of ecological conditions on Aspergillus flavus sporulation was studied.
► For the first time data on A. flavus sporulation were fitted as sporulation rates.
► Mathematical equations able to describe A. flavus sporulation were elaborated.
► This study mathematically describe a crucial step of A. flavus infection cycle.
► These equations will be used in a predictive model for aflatoxin B1 in maize.