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 (CZ agar) 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 was higher on defined nutritional medium in vitro on CZ agar than on maize stalks (4.5 x 106 versus 4.2 x 104) with production initiated after 6 and 24 hours, respectively. Surprisingly, optimal temperature was found at 30-35°C for CZ agar (9.23 x 106 spores/sclerotium) and at 20-25°C for maize stalks (6.26 x 104 spores/sclerotium). Water stress imposition only reduced sporulation at ≤ 0.90 aw. With more available water no significant differences were found between 0.90-0.99 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.