HEREDITARY VARIATION AND GENETIC RECOMBINATION IN KOJI-MOLDS (ASPERGILLUS ORYZAE AND ASP. SOJAE)

IV. CYTOLOGICAL STUDIES

Abstract

1.The causes of the difference in variability among strains of Koji-molds have been studied cytologically by examination of conidial size, number of nuclei in conidia and nuclear migration.
2. The constant strains of Koji-molds have conidia with comparatively uniform sizes (4-6μ). The inconstant strains, on the other hand, produce conidia in a variety of sizes including some with extraordinarily large diameters (6-10μ or more).
3. Feulgen-positive spherical structures are found at all growth stages in strains of Koji-molds. Mitotic-like pictures are frequently observed in germ-tubes, hyphal tips, or spore-producing tubes.
4. The conidia of the constant strains have been found to contain 1-4 nuclei; the majority contained two nuclei. The conidia of the inconstant strains, however, are multinucleate (8-20 or more). It is recognized that there is a close relationship between conidial size and the number of nuclei.
5. In the constant strains, one nucleus moves into conidium from apex of the sterigma at the beginning of the conidium formation, and is divided at once into 2-4 through what is probably mitotic division. In the inconstant strains, more than two nuclei migrate from sterigma into the newly formed conidium. The conidia become further multinucleate (8-20 or more) as a result of prompt independent nuclear divisions.
6. As concerns the migration of the nucleus from the vesicle into the sterigma, the authors have recognized that in the constant strains only one nucleus migrates into the sterigma, while in the inconstant strains at least 2-4 migrate simultaneously.
7. From the facts shown above it might be assumed that the variability of the inconstant strains of Koji-molds depends chiefly upon the multinucleate character of the conidia.