Influence of water activity and anti-fungal compounds on development and competiveness of F. verticillioides

A study was undertaken to investigate the role of water activity (aw) and fungicides on the competitiveness of two Fusarium verticillioides strains against other spoilage fungi commonly present in maize (F. proliferatum, Aspergillus niger, A. flavus, A. ochraceus and Penicillium verrucosum). Fungal strains were inoculated on artificial media containing maize flour. The effect of three aw levels (0.99, 0.98 and 0.95) and 3 fungicides (Tebuconazole, Procloraz and Prothioconazole) on fungal interactions, the Index of Dominance (ID) of isolates and fumonisin B1+B2 (FBs) production were determined. The two strains of F. verticillioides showed similar behaviour in conditions where water was freely available (0.99 aw); at 0.98 and 0.95 aw both F. verticilliodes strains had the lowest total ID scores (8-6 and 10-12, respectively). They showed the same ability to compete against other fungi having the highest ID scores against P. verrucosum and A. ochraceus and the lowest against A. niger and A. flavus. Interestingly, 0.95 aw was the most conducive condition for fumonisin production with significant differences respect to 0.98 and 0.99 aw. In co-inoculation experiment, only FBs production obtained with P. verrucosum resulted significantly higher from those obtained in the presence of the other fungi. The use of fungicides reduced both F. verticilliodes strains Index of Dominancy (ID). In particular, a significant reduction in F. verticilloides strain growth was observed when combining water stress x fungicide treatments. This information could be useful for a better understanding of the colonisation patterns of F. verticillioides in relation to other mycobiota and to both environmental and chemical stresses, also in future climate change scenarios.