Segregation of genetic markers in the two-spored secondarily homothallic basidiomycete Coprinus bilanatus

Secondarily homothallic basidiomycetes, of which the cultivated mushroom Agaricus bisporus is an example, produce both self-fertile and non self-fertile spores. The random migration of nuclei from the basidia to give binucleate spores provides the simplest explanation for the regulation of breeding behaviour in this group of fungi. To test the predictions of the random migration hypothesis, the segregation of mating-type, auxotrophy and antimetabolite resistance has been determined in the secondarily homothallic ink-cap fungus, Coprinus bilanatus. In 41 of a total of 56 spore progenies tested, the segregation ratios conformed to the predictions of the random migration hypothesis. Poor fits to the predicted ratios were, in many instances, associated with an adenine auxotrophy. On the basis of the data reported, random migration can be regarded as the primary control of secondary homothallism.