[Bioproduction of sterigmatocystine by Aspergillus versicolor (Vuill.) tiraboschi in dry fodder].

Lucerne and ray-grass, sterilized or not, were equilibrated at relative humidity (E.R.H.) 84, 88, 93 p. 100, and contaminated by spores of a highly toxinogenic A. Versicolor strain and maintained in these E.R.H. during 6 months. A peculiar technique for extraction and purification was necessary; the quantification limit for sterigmatocystin was 100 ppb; measurements had been done monthly in 3 replicates. Solvent water was estimated from water sorption isotherms: Toxin yield progressively increases, then lowers and, at last, becomes stable between 1200 and 2000 p.p.b.; The maximal yield is all the higher and the different evolution stages are all the shorter as E.R.H. is higher. The substrate nature influence is different according to E.R.H.; The toxin yields are about twice lower in unsterilized forages. The main parameter for fungal development and toxinogenesis, in low E.R.H. conditions, appears to be the solvent water concentration. Taking into consideration the weak yields of sterigmatocystin obtained in these conditions with a highly toxinogenic strain, the hazard of sterigmatocystin as a natural contaminant in these forages is low, in spite of the high frequency of this fungal species.