Maize–fusarium interactions: Tunisian insights into mycotoxin ecology

Maize is a worldwide crop yet can be associated with mycotoxigenic fungi, much investigated in humid tropical and cooler, wet temperate regions. However, in hot, arid/semi-arid regions data on their occurrence are poor. In this paper, we focused on interactions between maize and Fusarium fungal species in Tunisia, which has a Mediterranean climate, with hot, dry summers and milder, damper winters. Maize kernels, stalks, and roots were sampled from 19 agricultural fields and 56, 72, and 88 % of samples, respectively, yielded Fusarium isolates. Based on molecular identifications, these were mainly F. verticillioides (67 %), and other species of Fusarium fujikuroi species complex and members of Fusarium incarnatum-equiseti-, oxysporum-, burgessii-, solani- and concolor species complexes. In addition, five isolates were identified as Clonostachys rosea. Fusarium verticilloides and Fusarium proliferatum, that produce fumonisins, suspected carcinogenic compounds, were isolated from all kinds of samples, whereas the other species were isolated only from root and stems. Fumonisin B₁ was higher in kernels than in silage, while deoxynivalenol, potent protein synthesis inhibiting compound, was detected (at low levels) in grains and silage. A subset of selected strains, representative of all species identified, was also used to evaluate their ability to produce mycotoxins. Fusarium verticillioides, Fusarium proliferatum and Fusarium nygamai produced high levels of fumonisin B₁ in vitro, as well as beauvericin and enniatins. These findings confirm that, even in hot arid regions, which generally do not favour fungal growth, mycotoxin-producing fungi can be reason of concern for human and animal health.