Water Relations of Aspergillus flavus and Closely Related Species

The water relations of three isolates representative of each of the closely related species Aspergillus flavus , A. nomius , A. oryzae and A. parasiticus were examined at three temperatures, 25°C, 30°C and 37°C. Media were prepared over a wide range of water activity (a_w) from 0.996 to 0.75, controlled by a mixture of glucose and fructose. Water relations of A. flavus , A. oryzae and A. parasiticus were very similar. The minimum a_w for germination and growth of each of these three species was 0.82 at 25°C, 0.81 at 30°C and 0.80 at 37°C. A. nomius was slightly less xerophilic, with minimum a_w values for germination and growth of 0.83 at 25 and 30°C, and 0.81 at 37°C. Reported differences in water relations between A. flavus and A. parasiticus were not substantiated. The "domestication" of A. oryzae has not affected its water relations.