Soil Populations of Aspergillus Species from Section Flavi along a Transect through Peanut-Growing Regions of the United States

Abstract

Soil populations of Aspergillus species from section Flavi, several of which produce aflatoxins and cyclopiazonic acid, were examined from 166 cultivated fields along a transect extending from eastern New Mexico through Georgia to eastern Virginia. Peanut fields were sampled from four major peanut-growing regions (western Texas, central Texas, Georgia/Alabama, and Virginia/North Carolina); corn, cotton, and soybean fields also were examined from other regions along the transect where peanuts are not commonly cultivated. Soil densities of combined Aspergillus species from section Flavi were characterized by large variation among fields, with a greater frequency of fields with high densities extending from east-central Texas to south-central Georgia. Aspergillus flavus was the dominant species across most of the transect; the S strain of this species, characterized by production of numerous small sclerotia <400 μm diameter, was present primarily in the cotton-growing regions of east-central Texas and Louisiana. The highest incidences of A. parasiticus (as percentages of section Flavi) were observed from south-central Alabama to eastern Virginia. Vegetative compatibility group 1 of A. parasiticus was widely distributed in peanut fields along the transect. Aspergillus tamarii and A. caelatus also occurred along most of the transect but generally at low incidences; A. nomius was detected in only five fields from Louisiana and Mississippi. Peanut fields had significantly higher densities and incidences of A. parasiticus (P < 0.0001) than fields planted in other crops. Among the peanut-growing regions, Georgia/Alabama had the highest and western Texas had the lowest soil densities of species from section Flam. Significant positive correlations (P < 0.05) in soil density between individual Aspergillus species from section Flavi and filamentous fungi as well as between pairs of species suggest that populations were influenced by similar environmental factors. Variability in the density of A. flavus and A. parasiticus in soil may result from regional differences in the frequency of drought and in soil temperature and the influence of these factors on the susceptibility of peanut seeds to fungal invasion.