Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/15/2005
Publication Date: 1/15/2006
Citation: Jaime-Garcia, R., Cotty, P.J. 2006. Spatial relationships of soil texture and crop rotation to Aspergillus flavus community structure in South Texas. Phytopathology. 96:599-607. Interpretive Summary: Many crops, including cottonseed, corn, and sorghum are contaminated with aflatoxins, dangerous toxic chemicals produced by fungi members of Aspergillus section Flavi. Cotton, corn, and sorghum are common in South Texas crop rotations. A. flavus can grow and survive on crop residues and reside in the soil for long terms. Determining the community structure of aflatoxin-producing fungi in soils is necessary in order to establish area-wide control measures of aflatoxin contamination. The most common aflatoxin-producing species, A. flavus, can be divided into two strains. The S strain produces high levels of aflatoxins, while the L strain produces on average less aflatoxin. We studied the structure of A. flavus communities associated with soils of South Texas during 2001 through 2003. Results indicate that geographic variation in S strain incidence influences the distribution of aflatoxin contamination in South Texas. Communities of A. flavus differ by region with a higher incidence of the S strain from the Central Coastal Bend to Central Upper Coast. Total population of A. flavus differs among seasons, but not among regions. Crop rotation influence A. flavus community structure with cotton favoring the incidence of the S strain and corn favoring total population of A. flavus. This research benefits researchers and growers.
Technical Abstract: Aspergillus flavus, the causal agent of aflatoxin contamination of cottonseed is a natural inhabitant of soils. A. flavus can be divided into two strains, S and L, with S strain isolates producing greater quantities of aflatoxins than L strain isolates. Aflatoxin contamination can be severe in several crops in South Texas. The structure of A. flavus communities residing in soils of South Texas was determined by analyzing 326 soil samples from 152 fields located from the Rio Grande Valley in the south to Fort Bend County in the north from 2001 through 2003. Analysis of variance indicated significant differences in the incidence of A. flavus isolates belonging to the S strain (Percent S) among regions. The Coastal Bend (30.7%) and Upper Coast (25.5%) regions had significantly higher percent S incidences than the Rio Grande Valley (4.8%). No significant differences in Percent S among years were detected. Colony forming units per gram of soil (CFU/g) were not significantly different among regions. Correlation analysis between percent S and soil texture variables shows a positive correlation between percent S and clay and a negative correlation between percent S and sand. Fields cropped the previous year with cotton had a higher percent S, while fields cropped with corn had a higher quantity of CFU/g. Maps of S strain patterns show that the S strain constitutes over 30% of the overall A. flavus community in the area extending from the Central Coastal Bend to the Central Upper Coast regions. The West Rio Grande Valley had the lowest S strain incidence (under 10%). Geographic variation in S strain incidence influences the distribution of aflatoxin contamination in South Texas.