Title: Modeling the Colonization of Maize by Toxigenic and Non-toxigenic Aspergillus flavus Strains: Implications for Biological Control Authors
Submitted to: World Mycotoxin Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 18, 2008
Publication Date: August 3, 2008
Citation: Abbas, H.K., Zablotowicz, R.M., Bruns, H.A. 2008. Modeling the Colonization of Maize by Toxigenic and Non-toxigenic Aspergillus flavus Strains: Implications for Biological Control. World Mycotoxin Journal. 1:333-340. Interpretive Summary: Aflatoxin, caused by the mold Aspergillus flavus, is a continuing problem challenging corn production in the Mid South area of the United States. Biological control using strains of this mold that do not produce toxin to compete against natural toxin producing molds is an attractive and scientifically sound approach. This manuscript describes the use of a artificial inoculation technique and a growth model to characterize colonization and toxin accumulation in corn. This method provides a relatively easy way to study the efficacy of a biological control strain and the dynamics of toxin accumulation. This work can be used to determine when the biological control mold needs to be applied.
Technical Abstract: This study assessed field colonization of maize by Aspergillus flavus strains as biological control agents to reduce aflatoxin contamination. Maize (corn, Zea mays L.) ears were inoculated with A. flavus using a pin-bar technique in 2004 and 2005. Non-aflatoxigenic strains K49 & CT3 and toxigenic F3W4 were compared against a carrier control (0.2% aqueous Tween 20). Ten ears were sampled over 12 to 20 days, visually assessed, and curves fit to a three compartment Gompertz equation or other best appropriate regressions. Aflatoxin was determined by HPLC and cyclopionic acid (CPA) by LC/MS. Strain K49 demonstrated superior colonization to strain CT3. The Gompertz model characterized colonization for most inoculated treatments. Aflatoxin accumulation in maize inoculated with F3W4 was about 35,000 ng/g in 2004 and 2005, with kinetics of aflatoxin accumulation in 2005 well described by the Gompertz equation. Less than 200 ng/g was observed in maize inoculated with strains CT3 & K49 and accumulation was described by a linear or logistic model. Maize inoculated with strains CT3 and F3W4 accumulated a maximum of 220 and 169 'g/g CPA, respectively, compared to 22 and 0.2 'g/g in the control and K49 inoculated, respectively. This technique can be used to elucidate colonization potential of non-toxigenic A. flavus in maize in relation to biological control of aflatoxin. The greatest reduction of aflatoxin and CPA in maize inoculated with strain K49 indicates its superiority to CT3 as a biological control agent. The dynamics of maize colonization by A. flavus strains and subsequent mycotoxin accumulation generated by using the pin-bar technique has implications for characterizing the competence of biocontrol strains for reducing aflatoxin contamination.