Influence of the Interactions among Ecological Variables in the Characterization of Zearalenone Producing Isolates of Fusarium spp.

Summary To carry out the physiological characterization of Fusarium graminearum and F. culmorun isolates with regard to its zearalenone producing ability, an in-depth experiment with a full factorial design was conducted. The effects and mutual interactions of temperature, moisture, substrate and isolate on the production of the toxin were studied. The study was done with twelve isolates of Fusarium (7 of F. graminearum and 5 of F. culmorum ). The analysis of variance shows that there is a complex interaction of all of these factors, which can influence the relative concentrations of the mycotoxin produced, and hence, the correct physiological characterization of the strain. All the tested cultures were susceptible to invasion by Fusarium . The moisture content of grains (water activity values 0.960, 0.970 and 0.980) did not constitute a limiting factor for fungal growth or ZEA production, but incubation temperature (15 °C, 20 °C, 28 °C, and 32 °C) affected the rate of zearalenone synthesis. Very low or undetectable ZEA production was observed at 32 °C. All tested isolates showed a characteristic behavior concerning the optimum temperature for ZEA production, which was usually 20 °C maintained during the whole incubation period. This finding, which does not agree with other reports obtained with strains from different origins, suggests that there are genetic differences that would explain the particular physiological behavior of each isolate related to the optimal production conditions for ZEA. The existence of significant differences regarding the susceptibility of the assayed cereal grains (wheat, corn and rice) used for ZEA production by the different Fusarium species ( F. graminearum and F. culmorum ) is described for the first time in this paper.