Studies on the Morphology and Cytology of Thielavia Basicola Zopf

SUMMARY

1.	Thielavia basicola is widespread in the soil. The species is composed of forms or strains. The production and size of perithecia are dependent on the form isolated and the substrate on which it grows. Ascospores found in tobacco roots are not as large on the average as those produced in culture.
2.	Isolates of Thielavia basicola were obtained from tobacco roots. Perithecia were produced in pure culture, sectioned and stained with crystal violet. Very young to mature asci were seen. Crozier formation occurred. The large fusion nucleus in each ascus contained a large nucleolus approximately twice the diameter of the nucleoli seen in the ascogenous hyphae. Three divisions occurred in the ascus. At prophase I the longest chromosome was not over 2 μ long. At the third division the chromosomes were 0.5 μ or less in length.
3.	Four isolates of Thielavia from different sources were grown and compared in culture. Indications are that all four isolates should be included in the species Thielavia basicola Zopf.