Comparison of growth and aflatoxin B production profiles of Aspergillus flavus strains on conventional and isogenic GM-maize-based nutritional matrices.

Maize grown in both North and South America are now predominantly genetically modified (GM) cultivars with some resistance to herbicide, pesticide, or both. There is little information on the relative colonisation and aflatoxin B (AFB) production with maize meal-based nutritional matrices based on kernels of non-GM maize and isogenic GM-ones by strains of Aspergillus flavus. The objectives were to examine the effect of interacting conditions of temperature (25-35 °C) and water availability (0.99-0.90 water activity, a) on (a) mycelial growth, (b) AFB production and (c) develop contour maps of optimum and marginal conditions of these parameters for four strains of A. flavus on three different non-GM and isogenic GM-maize based nutritional media. The growth of the four strains of A. flavus (three aflatoxigenic; one non-aflatoxigenic) was relatively similar in relation to the temperature × a conditions examined on both non-GM and GM-based matrices. Optimum growth overall was at 30-35 °C and 0.99 a for all four strains. Under water stress (0.90 a) growth was optimum at 35 °C. Statistically: non-GM, GM cultivars, temperature and a all significantly affected growth rates. For AFB production, all single and interacting factors were statistically significant except for non-GM × GM cultivar. In conclusion, colonisation of GM- and non-GM nutritional sources was similar for the different A. flavus strains examined. The contour maps will be very useful for understanding the ecological niches for both toxigenic and non-toxigenic strains in the context of the competitive exclusion of those producing aflatoxins.