Interspecific Hybridization between Aspergillus nidulans and Aspergillus rugulosus by Fusion of Somatic Protoplasts

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Abstract
Interspecific heterokaryons were produced between auxotrophic mutants of A. nidulans and A. rugulosus by polyethylene glycol induced fusion of somatic protoplasts. The heterokaryons grew very slowly producing colonies of irregular shape and, on complete medium, the parental strains were readily segregated. During long-term cultivation on minimal medium many of the heterokaryons gave rise to vigorously growing sectors characterized by the secretion of a brown pigment and by their stability when subcultured on complete medium. Protoplasts isolated from the heterokaryons gave rise to the same new colony type when regenerated on minimal medium, and to the new colony type plus the parental types on complete medium. The new colony type was assumed to be an interspecific hybrid and showed normal vegetative morphology, regular colony shape and size but produced new conidia. Conidia formed early in the development of the hybrid gave rise to hybrid colonies. Various sizes of conidia were observed; the largest were uninucleate and the smallest were enucleate. Comparisons of conidial size, numbers of nuclei in cells and DNA content per nucleus for hybrid and parental strains indicated that the hybrid was diploid. Conidia from older cultures of the hybrid were heterogeneous with hybrid, parental and recombinant colony types developing on germination. Cultivation of the hybrid in the presence of benomyl gave segregation of parental and recombinatant sectors.

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