Water and temperature relations and microconidial germination of Fusarium moniliforme and Fusarium proliferatum from maize

The effects of water activity (aw, 0.994–0.85 = 0.4–21.0 (−)MPa water potential), temperature (5–42 °C), and their interactions on microconidial germination of three isolates each of Fusarium moniliforme and Fusarium proliferatum were determined in vitro on a maize meal extract medium. Temporal germination rates of microconidia of isolates of both species were significantly influenced by both aw and temperature. Germination was very rapid at >0.94 aw with an almost linear increase with time. Germination rates of microconidia of F. moniliforme were slower than those of F. proliferatum isolates at marginal aw levels and 5–25 °C, while at higher temperature (30–37 °C), the former germinated more rapidly than the latter. The aw minima for germination of isolates of both species was 0.88, with none occurring at 0.85 aw over a 40-day incubation period. At 37 °C, isolates of F. moniliforme had slightly lower aw minima than those of F. proliferatum. The narrowest range of aw for germination was at 5 °C, and none occurred at 42 °C. The effect of aw × temperature interactions on the lag phases (h) prior to germination and the germination rates (h−1) were estimated using the Gompertz model and the Zwietering equation. This showed that lag phases were shorter at 25–30 °C and 0.994–0.98 aw, and were increased to 10–500 h at marginal temperatures (5–10 °C) for F. proliferatum and longer for F. moniliforme. At marginal aw levels (0.92–0.90), lag times were increased to >250 h. Germination rates (h−1) were different for the two species. Microconidia of F. moniliforme germinated optimally at 25–37 °C and 0.96–0.98 aw, but this changed to 30 °C at 0.90–0.94 aw, while germination of microconidia of F. proliferatum remained optimum at 30 °C, regardless of aw. There were statistically significant (P < 0.01) effects of aw, temperature, isolate, and two- and three-way interactions for F. proliferatum, but there were no intraisolate effects for F. moniliforme. The ecological significance of these data for understanding colonization patterns of these important fumonisin-producing fungi are discussed.Key words: water activity, temperature, germination, fumonisin producing, Fusarium spp.