Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2000
Publication Date: N/A
Interpretive Summary: An unusual mutant of an important fungus is reported for the first time. The mutant culture produces a seed-like structure called sclerotia on a stem or stipe, whereas the wild or common type produces sclerotia without the stem. The production of this stem does not in itself have economic importance, but the presence of this characteristic shows a link of this fungus with an ancient or primitive fungus found in the tropics. This information is important to people who classify this group of fungi and to those who study relationships between species of fungi. Temperature, light, pH, the type of sugar, the nitrogen source, and to some extent the proportion of sugar and nitrogen in the media, were shown to affect the production of these seed-like structures.
Technical Abstract: The ability to produce stipitate sclerotia by a mutant culture (NRRL 29254) derived from Aspergillus flavus NRRL 3357 is reported for the first time. Stipitate sclerotia were observed on Czapek agar (CZA) and synnema-like conidiomata formed on Murashige-Skoog agar (MSA) and on oatmeal agar. Temperature, light, and pH influenced sclerotium formation. Stipitate sclerotia were abundant when the carbon source in CZA was replaced with dextrose, fructose, melibiose, or xylose whereas MSA amended with fructose, mannitol, or sorbitol produced numerous erect synnema-like structures instead of stipitate sclerotia. Glycine-, asparagine-, or proline-amended CZA supported abundant production of stipitate sclerotia, comparable to those obtained when the nitrogen sources were NaNO3 and KN03. Cultures grown on CZA amended with lysine, serine, or threonine produced synnema- like conidioma. Sclerotial yield was greatly affected by the type and concentration of carbon and nitrogen sources but not significantly by the C:N ratio. The production of stipitate sclerotia by this mutant substantiates previous suggestions for an evolutionary link between A. flavus and Stilbothamnium togoense, a tropical fungus that produces stipitate and sessile sclerotia. Weak bands were detected when the genomic DNA of S. togoense was fingerprinted using the DNA probe pAF28 derived from A. flavus, suggesting some degree of DNA homology between these two fungi.