Interspecific protoplast-fusants between Aspergillus oryzae (yellow-spored, met^-) and Aspergillus sojae (white-spored, bio^-) were haploidized by benomyl. Throughout the haploidization trials, seventy-six white- or yellow-spored segregants were isolated from 9 stable green-spored fusants. All of the seventy-two color-segregants derived from 7 phenotypically A. oryzae-type fusants did show the A. sojae type alkaline proteinase. Gel-electrophoretic phenotypes of both alkaline and acid proteinases appeared to share a common behavior in fusion and haploidization, although pectin-lyase and the morphology of conidial walls behaved independently from each other in these processes. Productivities of some hydrolyzing enzymes in koji culture, especially peptidase, were found to be improved by interspecific fusion and subsequent haploidization. Productivities of kojic acid and aspergillic acid were found to be amendable through these process.

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