An Aspergillus flavus mutant producing stipitate sclerotia and synnemata

The ability to produce stipitate sclerotia by a mutant culture NRRL 29254 d erived from Aspergillus flavus NRRL 3357 that produces sessile sclerotia is reported for the first time. The mutant produced stipitate sclerotia on Cz apek agar (CZA) and synnemata formed on Murashige-Skoog agar (MSA) and on o atmeal agar. Temperature, light, and pH influenced stipitate and sessile sc lerotium formation. Sclerotial yield was greatly affected by the type and c oncentration of carbon and nitrogen sources but not significantly by the C: N ratio. Stipitate sclerotia were abundant when the carbon source in CZA wa s replaced with dextrose, fructose, melibiose or xylose whereas MSA amended with fructose, mannitol or sorbitol produced numerous erect synnematous st ructures instead of stipitate sclerotia. Glycine-, asparagine-, or threonin e-amended CZA supported abundant production of stipitate sclerotia comparab le to those obtained when the nitrogen sources were NaNO3 and KN0(3), while CZA amended with lysine, serine, proline or hydroxyproline produced mostly synnemata. The wild type and the mutant were very similar in morphology, c ultural and physiological characteristics, and DNA fingerprints, but the wi ld type produced only sessile sclerotia and no synnemata. The production of stipitate sclerotia by the mutant substantiates previous suggestions for a n evolutionary link between A. flavus and Stilbothamnium togoense, a tropic al fungus that produces stipitate and sessile sclerotia. Weak bands were de tected 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.