Submitted to: Canadian Journal of Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/21/2004
Publication Date: 12/14/2004
Citation: Abbas, H.K., Zablotowicz, R.M., Locke, M.A. 2004. Spatial variability of aspergillus flavus soil populations under different crops and corn grain colonization and aflatoxins. Canadian Journal of Botany.82:1768-1775. Interpretive Summary: Aflatoxin contamination is a limiting factor for Mississippi Delta corn production. Thus, understanding the relation between cropping practices and populations of Aspergillus flavus in soil is needed for strategies to manage aflatoxin. We studied seasonal changes in Aspergillus soil populations of a single grower's field under different cropping systems (cotton, corn, and wheat) under no-tillage management using geostatistics. This study showed that A. flavus populations were dynamic and were greater following corn compared to following cotton or during a winter wheat crop. Aflatoxin-producing Aspergillus were more frequently isolated from corn kernels compared to soil, and subsequently aflatoxin-producing isolates were most numerous in soil after corn was grown. This is useful information for farmers in that crop rotations are beneficial in reducing aflatoxin-producing A. flavus in soil.
Technical Abstract: Aflatoxin contamination in corn caused by Aspergillus flavus is a serious contraint for economical corn production in the Mississippi Delta. The ecology of A. flavus was evaluated in a three-year study assessing the spatial variability of soil populations of A. flavus in a Mississippi Delta field during different crops. A 1.07-ha section of the field was laid out in 126, 9.2 m2 plots, and soil was sampled after planting in May 2000, March 2001, and April 2002. A. flavus populations were determined by plating on selective media, and A. flavus colonization was assessed in corn during 2000. Aspergillus flavus populations in soil were 251 cfu per gram soil in 2000 following cotton, 457 cfu per gram following wheat in 2002 and highest (794 cfu per gram) following the corn crop in 2001. A moderate degree of spatial structure of A. flavus populations was observed in the 2001 and 2002 samples described by a spherical and exponential model, respectively, but populations in 2000 exhibited little spatial structure. Colonization of corn kernels by A. flavus in 2000 ranged from 0 to 100% (mean 15% colonized kernels), and aflatoxin levels were from 0 to 1590 ppb (mean = 57 ppb). Aflatoxin levels were randomly distributed in the field and not correlated with A. flavus colonization. Aflatoxin production was found in 43 to 59% of A. flavus soil isolates with the highest incidence in soil populations following corn in 2001. However, 84% of A. flavus isolated from corn kernels produced aflatoxin. Results indicate that within a single field there is a wide range of A. flavus soil populations. Also, A. flavus colonization of corn and aflatoxin levels vary widely across the field.