Water activity, temperature, and pH effects on growth of Fusarium moniliforme and Fusarium proliferatum isolates from maize

The effects of water activity (a(W), 0.994-0.90 = 0.4-14.0 (-)MPa water potential), temperature (4-45 degrees C), and pH (3.6, 5.5, 7.0), and their interactions on growth of isolates of Fusarium moniliforme and Fusarium proliferatum were determined in vitro on a maize extract agar medium. Growth of two isolates of F. moniliforme and four isolates of F. proliferatum were significantly influenced by water activity regardless of solute type used (NaCl, glycerol, or glucose). However, at steady-state a(W) levels, growth was optimum at 0.994-0.98 a(W) and reduced significantly at 0.92 a(W). Further detailed studies with one isolate of F. moniliforme (25N) and two isolates of F. proliferatum (73N, 131N) showed that growth occurred over the range of 0.994-0.90 a(W) in the temperature range 20-35 degrees C with slight differences between species. Growth did occur at 4 degrees C and 0.994-0.96 a(W), but no growth was recorded at 40 and 45 degrees C regardless of a(W). Profiles of a(W) x temperature relations for growth of these two species were constructed from these data for the first time. Optimum pH and temperature for growth was 5.5 and 25 degrees C for both isolates of F. proliferatum, and pH 7.0 and 30 degrees C for the isolate of F. moniliforme. However, for the latter isolate at < 0.98 a(W), optimum pH and temperature for growth changed. The effects of pH, temperature, and a(W) for single, two-way and three-way interactions were all found to be statistically significant for these three isolates. The ecological significance of this information for understanding these important fumonisin-producing fungi is discussed.