Date of Award


Degree Type


University or Center

Atlanta University (AU)

Degree Name




First Advisor

Dr. John E. Mayfield


Verticillium dahliae, an asexual fungus that produces unicellular conidia as its primary mode of reproduction, forms thick-walled melanized microsclerotia cells (MS) which serve as survival structures. These large globose budding structures are characteristic of older hyphal regions. In order to observe changes at the cellular level during MS development hypha 1 tips were placed into polygalacturonic acid medium (PGAM) which induces synchronous development of microsclerotia. Samples were taken from the medium at 24 h intervals up to five days and prepared for phase contrast and electron microscopic observations. Elongation at hyphal tips and rapid conidiation was followed by a brief period of germination of the conidia which was observed at about 48 h. On the third day (72 h) of incubation the germinating conidia were observed making their conversion into recognizable microsclerotia. Mature microsclerotia were observed four or five days (96 or 120 h) after inoculation. The cellular changes that accompanied the conversion of conidia to mature MS structures were the increase in lipid bodies and the occurrence of altered mitochondria such as the absence of cristae in portions of the mitochondria and a decrease in elctron density of the matrix. There were also nuclear changes such as folding of the nuclear membrane, membrane discontinuity and the inclusion of vesicles within th enuclear membrane. By using3,3'diaminobenzidine, cytochrome oxidase activity was demonstrated only in mitochondrial regions with intact cristae. It is suggested that a period of conidation and conidialenlargement preceds the formation of MS in PGAM. The subsequent changes in organellur structure and arrangement can be correlated with Ms metabolic activites.

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