Variation of F-2 toxin production on different substrates.

The F-2 producing capacity of one Fusarium graminearum strain (strain No. 13) and of three hyphal tip transverse lines (a b and c) isolated from the original strain and of a mixture of these lines (a b and c) was studied in two successive years on different substrates: oats, barley, wheat, grain mixture and wheat bran. In the first year the original strain produced high amounts of F-2 but was heterogenous in toxin production. The F-2 producing capacity of one of the hyphal tip transverse lines (a) was high and that of two lines (b and c) and of the mixture of the three lines (a+b+c) was poor. In the following year the F-2 producing capacity of the fungal cultures had changed: the F-2 producing capacity of the original strain (No. 13) was greatly reduced, that of one hyphal tip transverse line (b) remained poor and that of two hyphal tip transverse lines (a and c) and of the mixture of the lines clearly increased. The F-2 production was changed in all the substrates and in about the same proportion. In general oats was the best substrate for F-2 production. The possible causes of the changed F-2 production are discussed. The estrogenic effect of F-2 produced in different substrates was studied by using as criteria the uterine weight, vaginal opening and liquid content in the uterus of immature female rats. The effect was in direct proportion to the amount of F-2 ingested by the rats. The substrate was without any influence on the physiological effect of F-2, and in this respect our results deviate from some earlier findings.