In vitro effect of pyrimethanil on the fungal growth of ochratoxigenic and non-ochratoxigenic species of Aspergillus tubingensis and Aspergil-lus foetidus isolated from Moroccan grapes

Abstract

The contamination of Moroccan grapes by ochratoxin A is mainly due to the contamination of grapes by some species of Aspergillus section Nigri with prevalence of A. niger aggregate. Pyrimethanil, systemic fungicide of the anilinopyrimidine family, is commonly used in vineyard to control grey mould caused by the fungus Botrytis cinerea. In the current study, the effica-cy of this chemical compound for controlling growth of eight strains of A. tubingensis and A. foetidus (4 ochratoxigenic and 4 non-ochratoxigenic strains) isolated from Moroccan grapes was examined at 25°C on CYA medi-um. The results of molecular identification showed that similarity of all iso-lates studied compared with various sequences of references strains of A. tubingensis and A. foetidus from GenBank ranged from 100 to 99%, differing then by one to 4 positions. OTA produced by ochratoxigenic strains varied from 0.02 to 0.13 μg/g of CYA. Pyrimethanil effectively reduced the growth rate of A. tubingensis and A. foetidus. In general, there was a decrease of the RGR and an increase of lag phase as the fungicide dose increased regardless of strain. The EC50 concentrations ranged from 0.00013 to 2.89 mg/L (average = 1.15 mg/L) and EC90 varied from 26.75 to 502.81 mg/L. Statistical analysis revealed that fungicide concentrations, strains and their two inter-actions had significant effects on radial growth rate (p-values = 0.000). At concentration above 0.5xRD, growth of all strains was inhibited. Low doses of pyrimethanil (0.01xRD and 0.02xRD) reduced significantly the mycelia growth but the ochratoxigenic isolates were favoured.