Analysis of heterokaryon incompatibility between heterokaryon-compatibility (h-c) groups R and GL provides evidence that at least eight het loci control somatic incompatibility in Aspergillus nidulans.

Protoplast fusion was used to hybridize strains 99-6 (h-cR) and 7-141 (h-cGL) in the Birmingham collection of Aspergillus nidulans. A sparsely conidiating, brown-pigmented diploid strain (MA7) was isolated. Inocula from MA7 were haploidized on medium containing Benlate and a haploid progeny sample collected. Heterokaryon compatibility testing of selected progeny strains assayed each linkage group in turn and established that h-cR and h-cGL were hetero-allelic for heterokaryon incompatibility (het) loci located on linkage groups III and V. Two selected MA7 progeny strains were sexually crossed to an h-cGL strain. Compatibility classification of the progenies of these crosses indicated that three het genes were located on linkage group III and two on linkage group V. Combination of these results with previous work using h-c groups A, B and Q in comparison with h-cGL indicates that a minimum number of eight and a maximum number of 18 het loci, spread over five linkage groups, are necessary to explain the compatibility relationships among these five h-c groups.