ABSTRACT

Examples of fungal variability abound: many phytopathological isolates from the wild display marked phenotypic and genotypic variability (Kistler and Miao 1992). Hansen (1938) described what he called “the dual phenomenon” in which conidial fungi segregate aconidial sectors; industrial yeasts are highly polymorphic for both chromosome number and length, as well as for copy number of genes encoding industrially relevant enzymes. The black Aspergillus species, A. ellipticus, persistently throws off variants initially regarded as a different species (Al Musallam 1980 and personal communication). Some fungi, e.g., Candida albicans (see Chapter 37 on “Candidiasis”) and Penicillium marneffei (Borneman et al. 2000), are dimorphic, i.e., they can switch between yeast-like and hyphal forms. Dimorphism is of particular interest since it is associated with pathogenicity, nevertheless, the mechanism behind the switch is still little understood, although probably governed by changes in gene expression rather than genome instability. Candida also displays colony morphotype switching, in some instances associated with chromosomal polymorphism (Gow 1995).