Mitosis and Aneuploidy in the Vegetative Hyphae of Macrophomina Phaseoli

Giemsa and aceto‐orcein staining and an improved squash technique were used to study nuclear behavior in the vegetative hyphae of Macrophomina phaseoli. Stages in nuclear division were similar to those previously recorded in the developing pyenospores except that no spindle was revealed. Mitotic irregularities were common. The commonest chromosome number was six, but higher counts suggested a continual reassortment of chromosomes, with haploid, diploid, aneuploid and possibly polyploid nuclei occurring in the same mycelium. The nature of the division and the occurrence and possible role of aneuploidy in both saprophytic and plant pathogenic fungi are discussed.