Population ecology of Aspergillus flavus associated with Mississippi Delta soils

Understanding the source of Aspergillus flavus is required to manage aflatoxin contamination of maize (Zea mays L.). Studies assessed A. flavus propagules, Fusarium spp., and total fungi associated with Mississippi Delta soils. Soils from 12 and 15 sites were collected in 2000 and 2001, respectively. The propagule density of A. flavus ranged from log(10) 2.0 to 4.3 colony-forming units (cfu) g(-1) soil, while total fusaria ranged from log(10) 3.0 to 5.4 cfu g(-1) soil. The highest populations of A. flavus were associated with soils containing higher organic matter, especially in sites under a no-tillage management. The frequency of aflatoxin production in isolates ranged from 13 to 81% depending on soil. In 2001, there was a highly significant correlation between A. flavus and the history of maize cultivation. Soil fertility factors such as organic matter content, nitrate and extractable phosphorus correlated with the density of Aspergillus, Fusarium spp., and total fungi. The relationship between soil parameters and Aspergillus populations may be useful in predicting the contribution of soil microflora to aflatoxin contamination.