Effect of Temperature, Water Activity and Carbon Dioxide on Fungal Growth and Mycotoxin Production of Acclimatised Isolates of Fusarium verticillioides and F. graminearum

Abstract

Climate change is primarily manifested by elevated temperature and carbon dioxide (CO₂) levels and is projected to provide suitable cultivation grounds for pests and pathogens in the otherwise unsuitable regions. The impacts of climate change have been predicted in many parts of the world, which could threaten global food safety and food security. The aim of the present work was therefore to examine the interacting effects of water activity (a_w) (0.92, 0.95, 0.98 a_w), CO₂ (400, 800, 1200 ppm) and temperature (30, 35 °C and 30, 33 °C for Fusarium verticillioides and F. graminearum, respectively) on fungal growth and mycotoxin production of acclimatised isolates of F. verticillioides and F. graminearum isolated from maize. To determine fungal growth, the colony diameters were measured on days 1, 3, 5, and 7. The mycotoxins produced were quantified using a quadrupole-time-of-flight mass spectrometer (QTOF-MS) combined with ultra-high-performance liquid chromatography (UHPLC) system. For F. verticillioides, the optimum conditions for growth of fumonisin B₁ (FB₁), and fumonisin B₂ (FB₂) were 30 °C + 0.98 a_w + 400 ppm CO₂. These conditions were also optimum for F. graminearum growth, and zearalenone (ZEA) and deoxynivalenol (DON) production. Since 30 °C and 400 ppm CO₂ were the baseline treatments, it was hence concluded that the elevated temperature and CO₂ levels tested did not seem to significantly impact fungal growth and mycotoxin production of acclimatised Fusarium isolates. To the best of our knowledge thus far, the present work described for the first time the effects of simulated climate change conditions on fungal growth and mycotoxin production of acclimatised isolates of F. verticillioides and F. graminearum.

Keywords: CO2; F. graminearum; F. verticillioides; aw; climate change; mycotoxins; temperature.

Figure 1

The effect of carbon dioxide (400, 800, 1200 ppm), a_w (0.92, 0.95, 0.98 a_w), and temperature (30, 35 °C) levels on diametric growth rate (mm/d) of an acclimatised strain of F. verticillioides cultivated on milled-maize agar for seven days. Data are means of triplicates (n = 3) with bars indicating standard (SE). Different letters indicate significant difference (p < 0.05) by Tukey’s honestly significant difference (Tukey’s HSD) test.

Figure 2

The effect of carbon dioxide (400, 800, 1200 ppm), a_w (0.92, 0.95, 0.98 a_w), and temperature (30, 33 °C) levels on diametric growth rate (mm/d) of an acclimatised strain of F. graminearum cultivated on milled-maize agar for seven days. Data are means of triplicates (n = 3) with bars indicating standard (SE). Different letters indicate significant difference (p < 0.05) by Tukey’s honestly significant difference (Tukey’s HSD) test.

Figure 3

The effect of carbon dioxide (400, 800, 1200 ppm) and a_w (0.92, 0.95, 0.98 a_w) on fumonisin (FB₁, FB₂) production (µg/kg) by an acclimatised strain of F. verticillioides cultivated on milled-maize agar for 21 days at 30 °C. FB₁ and FB₂ were not detected at 33 °C. Data are means of triplicates (n = 3) with bars indicating standard (SE). Different letters (small letters for FB₁, capital letters for FB₂) indicate significant difference (p < 0.05) by Tukey’s honestly significant difference (Tukey’s HSD) test; nd = not detected.

Figure 4

The effect of carbon dioxide (400, 800, 1200 ppm) and a_w (0.92, 0.95, 0.98 a_w) on mycotoxin (deoxynivalenol and zearalenone) production (µg/kg) by acclimatised strain of F. graminearum cultivated on milled-maize agar for 21 days at 30 °C. DON and ZEA were not detected at 35 °C. Data are means of triplicates (n = 3) with bars indicating standard (SE). Different letters (small letters for DON, capital letters for ZEA) indicate significant difference (p < 0.05) by Tukey’s honestly significant difference (Tukey’s HSD); nd = not detected.