The NRRL 3112 strain of Aspergillus awamori showed spontaneous segregation and sector formation tentatively attributed to a chromosomal instability. Spontaneous segregants showing stable pro1 (proline) requirement were easily isolated and stable pro+ strains were not isolated at all. Derivatives showing lower frequency of pro1 conidia produced significantly more glucoamylase than the parental strain. © 1988 Kluwer Academic Publishers.1010737740