Submitted to: Soil Biology and Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/30/2010
Publication Date: 10/1/2010
Citation: Jaime-Garcia, R., Cotty, P.J. 2010. Crop rotation and soil temperature influence the community structure of Aspergillus flavus in soil. Soil Biology and Biochemistry. 42:1842-1847. Interpretive Summary: Aflatoxins, toxic and carcinogenic secondary metabolites produced by certain fungi, frequently contaminate several crops, including cottonseed, corn and sorghum. Fungi vary widely in aflatoxin-producing ability. However, it is unclear how crop rotation influences the average aflatoxin-producing potential of resident fungi. The effect of crop rotation on the temporal variation in communities of aflatoxin-producing fungi associated with soils in South Texas was studied from spring 2001 through spring 2003. Results indicate aflatoxin producing fungi vary significantly among seasons, with warm seasons having both higher incidences of total fungi and of high aflatoxin producers. Previous crop influences both the quantity fungus and its toxigenicity. Corn favors higher soil populations and cotton and sorghum favor highly toxic fungi. The results suggest crop rotations can be manipulated to reduce incidences of the highly toxigenic fungi and thus the vulnerability of crops to aflatoxin contamination.
Technical Abstract: Aspergillus flavus, the most important cause of aflatoxin contamination has two major morphotypes commonly named S and L strains. Strain S isolates, on average, produce more aflatoxins than the strain L isolates. The S strain has been implicated as the primary causal agent of several contamination events in both North America and Africa. Strain S incidence and A. flavus propagules were quantified periodically in 11 agricultural fields in South Texas from spring 2001 through spring 2003. Both A. flavus populations and S strain incidence varied significantly among seasons, with warm seasons having higher average quantities of A. flavus (718 CFU/g) and higher incidences of the S strain (32.3%) than cold seasons (403 CFU/g and 16.9% incidence). Previous crop influenced both the quantity of A. flavus and S strains incidence. Corn favors higher soil populations of A. flavus (1,628 CFU/g) compared to cotton (374 CFU/g) and sorghum (237 CFU/g). In the agroecosystem of South Texas, both cotton (23.7%) and sorghum (23.5%) favored greater S strain incidence compared to corn (14.0%). Soil surface temperature greatly influenced fungal communities with propagule density decreasing when daily average soil temperature was either below 18°C or above 30°C, and percent of A. flavus belonging to the S strain increasing as soil temperature increases. The results suggest it may be possible to manipulate crop rotations in order to reduce aflatoxin severity and that periods of increased temperature drive selection of the highly toxigenic S strain in already warm climates.