Abstract
Climate change will increase the co-occurrence of Fusarium verticillioides and Aspergillus flavus, along with their mycotoxins, in European maize. In this study, the expression profiles of two pathogenesis-related (PR) genes and four mycotoxin biosynthetic genes, FUM1 and FUM13, fumonisin pathway, and aflR and aflD, aflatoxin pathway, as well as mycotoxin production, were examined in kernels and in artificial medium after a single inoculation with F. verticillioides or A. flavus or with the two fungi in combination. Different temperature regimes (20, 25 and 30 °C) over a time-course of 21 days were also considered. In maize kernels, PR genes showed the strongest induction at 25 °C in the earlier days post inoculation (dpi)with both fungi inoculated singularly. A similar behaviour was maintained with fungi co-occurrence, but with enhanced defence response at 9 dpi under 20 °C. Regarding FUM genes, in the kernels inoculated with F. verticillioides the maximal transcript levels occurred at 6 dpi at 25 °C. At this temperature regime, expression values decreased with the co-occurrence of A. flavus, where the highest gene induction was detected at 20 °C. Similar results were observed in fungi grown in vitro, whilst A. flavus presence determined lower levels of expression along the entire time-course. As concerns afl genes, considering both A. flavus alone and in combination, the most elevated transcript accumulation occurred at 30 °C during all time-course both in infected kernels and in fungi grown in vitro. Regarding mycotoxin production, no significant differences were found among temperatures for kernel contamination, whereas in vitro the highest production was registered at 25 °C for aflatoxin B1 and at 20 °C for fumonisins in the case of single inoculation. In fungal co-occurrence, both mycotoxins resulted reduced at all the temperatures considered compared to the amount produced with single inoculation.
Highlights
Introduction conditions of the Creative CommonsClimate change (CC), with increasing temperature and CO2, different rain distribution and extreme events, impacts significantly on fungal populations, including mycotoxinproducing fungi
Key Contribution: This study provides additional information towards a better understanding of the interplay between maize and its main mycotoxigenic fungi (F. verticillioides and A. flavus) and the influence of fungal co-occurrence on maize and fungal transcriptional profiles as well as mycotoxin production
Similar expression profiles were reported for both PR5 and PRm3 genes considering the three variables examined in this study
Summary
Introduction conditions of the Creative CommonsClimate change (CC), with increasing temperature and CO2 , different rain distribution and extreme events, impacts significantly on fungal populations, including mycotoxinproducing fungi. The prevalent mycotoxin in maize is variable, between years and growing areas, but the co-occurrence of different toxins is progressively highlighted [10,11,12,13,14], even in small size territories [15]. In this variable scenario, the attention is focused on Aspergillus flavus and Fusarium verticillioides, the key actors in maize kernels infection, aflatoxin (AF) and fumonisin (FB). These fungi can grow at a wide range of temperature and water activity (aw ), the ideal growth condition for A. flavus is 30 ◦ C [18], whereas
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