Temperature and water activity effects on growth and temporal deoxynivalenol production by two Argentinean strains of Fusarium graminearum on irradiated wheat grain

The objective of this study was to determine the effects of water activity (aW; 0.900–0.995), temperature (5, 15, 25 and 30 °C), time of incubation (7–49 days) and their interactions on mycelial growth and deoxynivalenol (DON) production on irradiated wheat grain by two strains of Fusarium graminearum isolated from wheat ears in Argentina. Optimal aW levels for growth were in the range 0.950–0.995 with a temperature optima of 25 °C. Maximum growth rates were obtained at the highest aW (0.995) and 25 °C for both strains. No growth was observed at 5 °C regardless of the aW levels assayed. Both strains were able to growth at the lowest aW assayed (0.900), although the temperature ranges allowing growth at this minimal aW was 15–25 °C. DON was produced the most rapidly (7 days) when incubated at 25 °C and 0.995 aW. All other conditions required 7–14 days before DON was produced on grain. Maximum amounts of DON for both strains were produced at the highest aW treatment (0.995) after 6 weeks at 30 °C. The range of DON concentrations varied considerably (5 to 140,000 ng g− 1) depending on aW and temperature interaction treatments. Production of DON occurred over a narrower range of aW (0.995–0.95) than that for growth (0.995–0.90). DON was more rapidly produced at 25 °C but the maximum amount produced was at 30 °C. Two-dimensional profiles of aW × temperature were developed from these data to identify areas where conditions indicate a significant risk from DON accumulation.