VEGETATIVE INCOMPATIBILITY AND THE MATING-TYPE LOCUS IN THE CELLULAR SLIME MOLD DICTYOSTELIUM DISCOIDEUM

Gillian E. Robson ¹ and Keith L. Williams ¹

¹ Genetics Department, Research School of Biological Sciences, The Australian National University, P. O. Box 475, Canberra City, A.C.T., 2601, Australia

The genetic basis of vegetative incompatibility in the cellular slime mold, Dictyostelium discoideum, is elucidated. Vegetatively compatible haploid strains from parasexual diploids at a frequency of between 10^-6 and 10^-5, whereas "escaped" diploids are formed between vegetatively incompatible strains at a frequency of 10^-8. There is probably only a single vegetative incompatibility site, which appears to be located at, or closely linked to, the mating-type locus. The nature of the vegetative incompatibility is deduced from parasexual diploid formation between wild isolates and tester strains of each mating type, examination of the frequency of formation of "escaped" diploids formed between vegetatively incompatible strains, and examination of the mating type and vegetative incompatibility of haploid segregants obtained from "escaped" diploids.