Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School



Stock cultures of a pure strain of C. ulmi were obtained from the Plant Science Department at South Dakota State University. The inoculum was maintained on Potato Dextrose Agar (PDA) in petri dishes. On this medium, the fungus produced a grayish white rather sparse and appressed mycelium. Conidia were produced in heads on branched conidiophores. Quite often some sectoring was observed on PDA. Cultures producing coremia, obtained on 2% American elm shavings (on dry weight basis) plus bacteriological agar (8 g/1), were also used as an inoculum source. As is shown, this medium produced coremia and very little vegetative mycelium. The zonate character of the growth of the fungus on every concentrated elm-water extract is in response to alternate light and dark periods. Aseptic methods were essential in this research. All inoculating was done in a White Roomette, of which the inside surfaces were washed down with 70% ethyl alcohol. Instruments were flamed with a bunsen burner periodically during inoculations. Media and petri dishes were autoclaved for 20 minutes at 15 psi. All cultures were grown under laboratory light conditions at 25°c for 14 days. Roster, Holden and Martin (1969), McMullen (1969) and Hubbes and Pomerleau (1969) hypothesized that C. ulmi produced coremia only if grown in contact with American elm tissue and that a coremia inducing factor (CIF) was present. To test this hypothesis further, in diameter, were placed in petri dishes containing PDA and the inoculum was placed directly on the disk. Wood disks of apple, plum, walnut, silver maple and green ash were also cultured in the same manner. Wood shavings were obtained from logs of American elm (20-J6 cm in diameter) with a jointer-planer. The shavings were then blended into still finer particles with a Waring blender. Several methods were devised to test the possibility of extracting a "CIF" from American elm which contributes in some way to the production of coremia.

Library of Congress Subject Headings

Dutch elm disease

Ceratocystis ulmi

South Dakota State University Theses



Number of Pages



South Dakota State University