Impact of water activity and temperature on growth and alternariol and alternariol monomethyl ether production of Alternaria alternata isolated from soybean

Abstract

The objective of this study was to determine the effect of water activity (aw; 0.995, 0.98, 0.96, 0.94, 0.92, and 0.90), temperature (5, 18, 25, and 30°C), incubation time (7 to 35 days), and their interactions on mycelial growth and alternariol (AOH) and alternariol monomethyl ether (AME) production. Two Alternaria alternata strains isolated from soybeans in Argentina were grown on 2% soybean extract agar. Maximum growth rates were obtained at the highest aw (0.995) and 25°C, with growth decreasing as the water availability of the medium was reduced. Maximum amount of AOH was produced at 0.98 aw and 25°C for both strains. Maximum AME production was obtained for both strains at 30°C but different aw values, 0.92 and 0.94, for the strains RC 21 and RC 39, respectively. The concentrations of both toxins varied considerably depending on the aw and temperature interactions assayed. The two metabolites were produced from 5 to 30°:C and at a w values of 0.92 to 0.995. Although at 5 and 18°C little mycotoxin was produced at aw lower than 0.94. Two-dimensional profiles of aw by temperature interactions were developed from these data to identify areas where conditions indicate a significant risk from AOH and AME accumulation on soybeans. All the conditions of aw and temperature that resulted in maximum production of both toxins are those found during soybean development in the field. Thus, field conditions are likely to be conducive to optimum A. alternara growth and toxin production.