Interactions between Fusarium verticillioides and Fusarium graminearum in maize ears and consequences for fungal development and mycotoxin accumulation

Fungal interactions of Fusarium verticillioides and F.graminearum in maize ears and the impact on fungal development and toxin accumulation were investigated in a 2-year field study at two locations in France. Maize ears were inoculated either with a spore mixture of F.graminearum and F.verticillioides or using a sequential inoculation procedure consisting of a first inoculation with F.graminearum followed by a second with F.verticillioides 1 week later. Toxin and fungal biomass were assessed on mature kernels, using HPLC and quantitative PCR. Correlation between the levels of DNA and toxin was high concerning F.graminearum DNA and deoxynivalenol (R-2 = 0.73) and moderate for F.verticillioides DNA and fumonisin (R-2 = 0.44). Fusarium graminearum DNA either decreased in mixed inoculations or was not influenced by subsequent inoculations with F. verticillioides, compared to single inoculations. In contrast, F.verticillioides DNA either significantly increased or was not affected in mixed and sequential inoculations. In two of the replicates, it can be assumed that natural contamination by F.verticillioides was favoured by previous contamination with F.graminearum. Overall, the results suggest that F.verticillioides has competitive advantages over the F.graminearum strains. Additionally, the data provide, for the first time, key evidence that previous contamination by F.graminearum in maize ears can facilitate subsequent infections by F.verticillioides.