Abstract
Current biological control methods to prevent pre-harvest aflatoxin contamination of corn, cottonseed, and ground and tree nuts involve field inoculation of non-aflatoxigenic Aspergillus flavus. To date, the efficacy of this approach requires annual reapplication of the biocontrol agent. The reason for this requirement is uncertain. To track the dispersal and test the longevity of these strains, we prepared fluorescent biocontrol strains by incorporating into them the gene expressing the enhanced green fluorescent protein (eGFP). We first investigated the effects of eGFP transformation on the ability of the fluorescent fungus to compete with its non-fluorescent homolog, and then with other heterologous non-aflatoxigenic strains as well as with aflatoxigenic isolates. Our findings indicate that, in these studies, detection of fluorescence was variable, with some fluorescent strains exhibiting enhanced growth and sporulation post-transformation. In our tests, not all transformed strains proved to be good candidates for tracking because their fluorescence was reduced over the course of our study. Most of the transformed strains retained fluorescence and showed robust colony growth in an artificial competitor environment; therefore, they should be suited for further trial under more natural settings. Our ultimate objective is to determine if out-crossing between biocontrol strains and native field populations is occurring in a natural setting.
Highlights
Species from Aspergillus section Flavi have the potential to contaminate agricultural commodities with carcinogenic mycotoxins such as aflatoxins
Based on this study we find that introduction of a fluorescent marker into most of these biocontrol strains does not impair their abilities to self-compete or to compete with aflatoxin-producing strains
The goal of this study was to determine if introducing enhanced green fluorescent protein (eGFP) into a biocontrol strain of A. flavus would affect its competitive ability
Summary
Species from Aspergillus section Flavi have the potential to contaminate agricultural commodities with carcinogenic mycotoxins such as aflatoxins. Field trials have shown that proper application of spores from these fungi greatly reduces the incidence of aflatoxin contamination in corn [4], cottonseed [5], and peanuts [6], and is being considered for use against contamination of tree nuts. The ability of these strains to reduce aflatoxin contamination has been postulated to be due to displacement of the aflatoxin-producing populations in the soil [5]. All of these A. flavus strains produce large sclerotia (L-strain), and contain the Mat mating type idiomorph
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