Hyphal and Mycelial Responses Associated with Genetic Exchange Within and Between Species of the Basidiomycete Genus Stereum

Abstract

Living hyphae of Stereum hirstutum behavaved similarly prior to fusion on a cellophane membrane whether they were genetically the same or different. Fusions were generally initiated within 5-10 h of mycelial interdigitation. A period (10-35 min) of interfacial expansion usually preceded opening of the fusion pore, but in certain combinations involving an Australian homokaryon, MP16-15, refractile sheaths developed around hyphal penetration pegs. Between somatically incompatible heterokaryons, the cytoplasm in fusion compartments and some adjacent compartments progressively lysed and was replaced by refractile globules and wall deposits. Self fusions other than clamp connections results little or unidirectional nuclear movement via the fusion pore followed by cycles of nuclear aggregation, division and septation. This sequence also followed fusion between mating-compatible pairs and ‘bow-tie’-forming pairs of sibling homokaryons for 2-3 h and 18-28 h respectively. before the onset of central or eccentric septal erosion and nuclear migration Following magration, numerous intercalary septa were formed and there was no repair of eroded septa. An extended non-septate phase occurred within the Australian homokaryon, MP 16-15, in which rapid (10 μm s-1), pulsed, unidirectional, longrange protoplasmic streaming occurred. Certain combinations of homokaryons of different taxonomic species of Stereum, or of different breeding strategy or geographical origin, gave rise to unilaterally extensive degenerative reactions in plate culture accompanied by production of free crystals of (+)-torreyol. Sequential septal nuclear migration and protoplasmic lysis were all observed in the partner which become degenerate. Constitutive septal erosion, nuclear migration and intercalary septal synthess were observed in sectors of appressed mycelium in certain homokaryons after long-term.