Comparative study of water and temperature relations of growth and T-2/HT-2 toxin production by strains of Fusarium sporotrichioides and Fusarium langsethiae

This study has compared the effect of water activity (a(w), 0.995-0.93) and two temperatures (15, 25 degrees C) on the growth and HT-2 and T-2 toxin production by three strains of Fusarium sporotrichioides and Fusarium langsethiae in an oat-based medium. There were very little intra-strain differences for each of the species in relation to growth at 0.995-0.93 a(w) and 15 and 25 degrees C. Inter-species comparisons showed that at 0.995 and 0.98 a(w) growth was similar at both temperatures. However, under water stress at 0.95 and 0.93 a(w) E sporotrichioides strains were more tolerant than those of F. langsethiae. Statistical analyse; showed that a(w) and temperature were significant factors for both species, while strain differences were not (P=0.05). In contrast, the patterns of production of T-2 and HT-2 toxins were very different from that for growth. For F sporotrichioides, a generally higher amount of toxin was produced at 15 than at 25 degrees C, with a maximum produced at 0.995 a(w), while the production decreased with water stress. Interestingly, maximum production of T-2+HT-2 toxin was achieved by E langsethiae at 0.98 a(w) and 25 degrees C, with very little produced at 0.93 a(w). Statistically, a(w) was the most significant (P=0.05) factor for the mean of the three strains of both species with a significant inter-species difference in terms of toxin production. This was confirmed by the changes in the ratio of HT-2:T-2 toxin in relation to the a(w) x temperature conditions studied. These results are discussed in the context of the effect of environment on the relative importance of these two species in contaminating oats with these toxins.