Chemical control of fungal growth and ochratoxin A production by Aspergillus isolated from Moroccan grapes

The aim of this study was to evaluate the effect of three fungicides azoxystrobin (Ortiva), hexaconazole (Hexa) and pyrimethanil (Pyrus) for their ability to inhibit the radial growth and ochratoxin A (OTA) production by five ochratoxigenic strains of Aspergillus carbonarius and A. niger previously iso-lated from Moroccan grapes. Our results showed that, the addition of the fungicides to the Czapek Yeast Autolysate agar culture medium reduced the growth of the ochratoxigenic strains. Pyrimethanil caused total inhibition of spore germination and growth of the five strains, for all dose tested. Where-as hexaconazole totally inhibited the growth of 4 strains and gave growth for the MUCL 49227 strain (2.67 mm/day) at sublethal concentration. The reduction in radial growth was less marked for azoxystrobin, with growth rate varying between 0 and 6.37 mm/day depending on the strain and the azoxystrobin concentration. Analysis of variance showed that the effect of single factors (fungicides, concentration and strain) and their interactions on growth and OTA production were highly significant (P=0.000).These findings suggest that the use of tested fungicides have to potential for reduction in production of OTA.

Influence of pH and Incubation Time on Ochratoxin A Production by Aspergillus carbonarius in Culture Media

The effect of pH (2 to 10) and temperature (15 and 30°C) on growth and production of ochratoxin A (OTA) of six strains of Aspergillus carbonarius was studied in two culture media: Czapek yeast autolysate agar and yeast extract sucrose agar. Isolates were selected by their different source and different reported ability to produce OTA. Regardless of the initial pH or the temperature tested, Czapek yeast autolysate agar has been shown to be the best culture medium for OTA production by A. carbonarius. In this medium, OTA was produced from pH 2 to 10 at the two incubation temperatures tested. The results obtained show the ability of A. carbonarius to not only grow but also produce OTA over a wide pH range at high or low temperatures. This may help explain why this species is considered the main OTA source in some substrata.