Nuclear Division in the Developing Pycnospores of Macrophomina Phaseoli

Nuclear behavior was studied in Giemsa‐stained pycnidial material of Macrophomina phaseoli . The young pycnospore was at first uninucleate but repeated nuclear division occurred as it enlarged, and the mature spore was always multinucleate. The developing spore, therefore, provided a favorable site for observing mitosis. Noteworthy features were: (1) a metaphase characterized by a loss in stainability of the nucleolus and by the appearance of centrioles, spindle fibers and countable chromosomes; (2) a short early anaphase; (3) a long late anaphase with a broad band of interzonal fibers separating the daughter nuclei; (4) the occurrence of irregularities such as aneuploidy, chromosome bridge formation and chromosome lagging. The basic chromosome number was six. Following a study of Giemsa‐stained cellophane cultures of the fungus it was concluded that the method of nuclear division in the vegetative hyphae is similar to that observed in the developing spores. Some comparisons are made with observations on nuclear division in the vegetative hyphae of other fungi.