Compatibility and stability of diploids in Coprinus lagopus

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Abstract
Artificially selected diploids of Coprinus lagopus when mated in compatible combinations, either together or with haploids, produce dikaryotic mycelia which are typical of normal haploid-haploid dikaryons. In a diploid-haploid dikaryon, the diploid nucleus is not as stable as when alone in a monokaryon but it can persist through repeated sub-culturing into a fruiting body and eventually through meiosis into the basidiospores. In a diploid–diploid dikaryon either one or the other nucleus becomes haploid so that fruiting bodies with two diploid nuclei are never formed. This fact constitutes a restriction on diploidy in nature and a useful method of reducing diploids to the haploid state.Matings that might be considered to be incompatible at the B mating gene show a significant difference which is related to the number of B alleles common to the mating colonies. Matings with one B allele in common, e.g. B3B6+B2B3 produce fully compatible and normal dikaryons. Matings with two B alleles in common, e.g. B3B6+B3B6 have, at first while the diploid nuclei still persist, the appearance of an incompatible common B haploid heterokaryon. This indicates that the B incompatibility system is based not on a complementary action between different B alleles but on an oppositional action between the same alleles neutralizing the B gene product which is necessary for dikaryon formation.