SPLS Seminar: Growth and competition between biocontrol and aflatoxin-producing genotypes of Aspergillus flavus in soil

Abstract: Aspergillus flavus is a saprotrophic soil fungus and opportunistic pathogen of oilseed crops. During crop colonization, A. flavus can produce highly potent carcinogens called aflatoxins, resulting in economic losses. A. flavus resides in soil on crop debris, and sporulates and disperses onto the crop during the growing season. One effective method of reducing aflatoxin contamination is the application of non-aflatoxigenic A. flavus genotypes as biocontrol (BC) agents that competitively exclude aflatoxin-producing A. flavus (AF) in field soil and on crops. Survival, growth, and competition between BCs and AFs in the soil impact persistence of applied BCs over multiple growing seasons.  

The objective of this study was to quantify the effects of biotic and abiotic soil factors on growth and competition between biocontrol and aflatoxigenic isolates of A. flavus. A series of experiments were conducted to evaluate the impact of crop debris type (maize/cotton), crop debris placement (on top of/mixed into soil), and temperature on growth, sporulation capacity, and competition between AF and BC genotypes over time. Though A. flavus growth and sporulation varied among soils and crop debris types, trends were similar among treatments with total A. flavus biomass in soil increasing over time but the capacity for crop debris to support sporulation decreasing over time. The BC genotype comprised a greater proportion of the total A. flavus biomass when crop debris was buried when compared to on the soil surface, while the opposite was true for the AF genotype, suggesting that soil microbes and/or soil physical properties may modulate interactions between AF and BC genotypes.  

Future directions involve evaluating differences among soil microbial communities and physical properties of different soils in relation to BC persistence in the field. Characterization of factors that favor growth and sporulation of BCs in soil will help to predict long-term persistence of BCs and enhance mitigation of aflatoxin contamination.