A closed system of cytoplasmic variation in Aspergillus glaucus

A strain of the homothallic ascomycete Aspergillus glaucus was isolated from nature and found to produce sectors continually during subculturing (figure 25, plate 18). Sectors (here called the ' A ’ type) on certain media differ quantitatively from the original parent mycelium (the ‘ B ’ type) in at least five characters, the most easily observable being greatly enhanced conidium formation. When propagated asexually and sexually the ‘ A ’ and ‘ B ’ types behave in an unexpected manner (figure 24, observation, also Subak Sharpe 1956 a,b ). When subculturing from ‘ A ’ type is done with inocula of large overall cytoplasmic volume, that is, when colonies are started from hyphal tips, mycelium blocks or masses of either ascospores or conidia, then only ‘A ’ type colonies are formed.But when new cultures initiate from small cytoplasmic volumes, i.e. when conidial suspensions or ascospores from single perithecia are dilution plated, then some spores germinate to give ‘ A ’ colonies and the others ' B ' colonies. The relative proportions can vary greatly and depend on the parent colony’s medium, the age of the spores and other factors. Ascospore segregations from single perithecia actually frequently mimic 1:1 single nuclear gene segregation. (Ascospores of this strain are haploid and uninucleate in origin, conidia are binucleate in origin.)