CYTOLOGY OF HELMINTHOSPORIUM TURCICUM AND ITS ASCIGEROUS STAGE,TRICHOMETASPHAERIA TURCICA

Knox- Davies , P. S., and J. G. Dickson . (U. Wisconsin, Madison.) Cytology of Helmintho sporium turcicum and its ascigerous stage, Trichometasphaeria turcica . Amer. Jour. Bot. 47(5) : 328—339. Illus. 1960.–The cells of the vegetative hyphae were generally multinucleate. Interphase nuclei resembled those of higher organisms, with a matrix of thread-like chromatin material surrounding a spherical nucleolus. “Beaked” nuclei frequently associated with anastomosing hyphae were interpreted as migrating nuclei. Nuclear division in the vegetative hyphae was rapid. Various division stages were distinguished but it was difficult to make accurate chromosome counts. The nucleoli were discarded at prophase or prometaphase and were reorganized in daughter nuclei at telophase. An outstanding feature of nuclear division was that all the nuclei in a cell divided simultaneously. Conidiophores and conidia were occasionally joined by wide cytoplasmic connections. They were multinucleate throughout their development. Mechanisms therefore exist for the perpetuation of heterokaryons through the conidium. Ascus development was studied in a hybrid between a dark and an albino isolate. Crozier formation was typical and nuclear fusion occurred in the young ascus. Four nuclear divisions were completed in the ascus before there was evidence of ascospore delimitation. Further nuclear division took place in the ascospores whose cells were multinucleate. The occurrence of less than 8 ascospores in an ascus appeared to follow degeneration of nuclei rather than the incorporation of a number of division-Ill nuclei in a single ascopore. Chromosome counts and irregularities in the appearance and behavior of nuclei and chromosomes in the asci indicate that aneuploidy occurs in Trichometasphaeria turcica. It is suggested that aneuploidy is a common phenomenon in the conidial stage of the fungus H. turcicum, and possibly also in other imperfect fungi.