Hereditary variation and genetic recombination in Koji-molds (Aspergillus oryzae and Asp. sojae). I. Natural variation.

Natural variation in monospore lines of Koji-molds (Asp. oryzae and Asp. sojae), isolated from commercial Koji material or soil and from laboratory stock cultures, has been observed. We can divide the 58 strains of Koji-molds investigated into two groups; one group consists of inconstant strains which are very liable to produce natural variants, and the other consists of strains which remain constant through successive single spore culture. The inconstant strains develop colonies bearing various proportions of conidia and aerial mycelium (X-type). They generally form large conidia (Asp. oryzae var. magnasporus) but sometimes medium sized conidia (Asp. oryzae s. str.), which produce large conidia occasionally. The colonies of the constant strains show abundant conidial formation and smooth surfaces (C-type). The conidia are mostly small (Asp. oryzae var. microsporus) but sometimes medium in size (Asp. oryzae s. str.). The colony types of the variants are as follows: C (Conidial type, whole colony covered with conidia), M (mycelial type), R (restricted in growth rate), St (sterile type, little sporulation on all media tested), Nit (requiring reduced nitrate, very faint growth on Czapek's agar), and LS (semi lethal, growth cease immediately after germination). Pedigree cultures of the 8 inconstant strains have been made, but no definite segregation ratios for each variant type have been recognized through successive generations. The LS and N types commonly occur spontaneously from the M-type.