INVESTIGATION OF THE HET GENES THAT CONTROL HETEROKARYON INCOMPATIBILITY BETWEEN MEMBERS OF HETEROKARYON-COMPATIBILITY (H-C) GROUP-A AND GROUP-G1 OF ASPERGILLUS-NIDULANS

A chromosome assay method was used to determine the heterokaryon compatibility relationships between strains belonging to heterokaryon-compatibility (h-c) groups A and G1 of Aspergillus nidulans. A hybrid strain (RD15) was isolated following protoplast fusion of strains 65-5 (h-cA) and 7-141 (h-cG1). The morphology of RD15 was severely abnormal compared to diploid strains of A. nidulans produced from heterokaryon-compatible haploid parents. Inocula of RD15 were induced to haploidize on medium containing Benlate and a parasexual progeny sample of 291 haploid segregants was obtained. The progeny strains were genotyped for standard markers. Allelic ratios and pairwise marker segregations were determined. Pairs of progeny strains that carried different alleles for the standard markers of each linkage group in turn were tested for compatibility. Strain pairs that possessed different alleles for the markers on linkage groups II, III, V, VI and VII were incompatible indicating the presence of heterokaryon-incompatible (het) genes on these linkage groups. Backcrosses to an h-cG1 strain showed that two het genes were located on linkage group III and confirmed a total of six het gene differences between the h-cA and h-cG1 strains.