Production of fumonisins by Aspergillus species in Australian vineyards

Fumonisins are a group of carcinogenic compounds primarily produced by some Fusarium species. Recently, fumonisins were reported from Aspergillus isolates associated with vineyards overseas. Thirty-six Aspergillus isolates collected from seven vineyards in New South Wales and a vineyard in South Australia were identified using species-specific PCR primers and assessed for fumonisins in laboratory media. The effect of water activity (aw) (0.92, 0.95 and 0.98) and temperature (20°C, 25°C, 30°C and 35°C) on growth rate and the production of fumonisins was studied for three Aspergillus isolates in synthetic grape juice medium (SGJM). Liquid chromatography-tandem mass spectrometry was used to determine fumonisins in all the experimental samples. Six Aspergillus isolates produced fumonisins (FB2 & FB4), vis. three A. welwitschiae and three A. niger isolates. These isolates produced between 0.7 to 25 mg/kg and 0.4 to 13.5 mg/kg of fumonisins in Czapek Yeast Extract Agar with 5% NaCl and SGJM, respectively. For both species, maximum growth occurred at aw 0.98 and 35°C. The optimum temperature for fumonisin production was 20 - 25°C and little was produced above 25°C. Fumonisin production was greatest at aw 0.98 and less was produced at aw 0.95. This is the first report of fumonisin producing Aspergillus isolates and A. welwitschiae in Australian vineyards. These data may be useful in evaluating the risk of fumonisin occurrence in Australian grapes and grape-products and the development of predictive models of fungal growth and fumonisin contamination of grapes.