The Buller Phenomenon

Heterokaryotic basidiomycete mycelia can deliver one nucleus to unmated homokaryons in its vicinity. This ability has been called the 'Buller phenomenon' (Quintanilha, 1937). Potentially, the Buller phenomenon might lead to complicated networks of mating in a resource. In some basidiomycete species, although successfully mated, homokaryotic sectors can arise within a heterokaryotic mycelium. If such sectors come in contact with another heterokaryon, a remating may occur in line with the Buller phenomenon. Such reassortment of nuclei in somatic incompatibility interaction zones has been recorded in laboratory crossings (Hansen et al., 1993a), and recently also in dense populations under field conditions (Johannesson and Stenlid, 2004). Minute mycelia would normally be out-competed but have the potential of growing away from competitors in the relatively sheltered environment inside wood fibres. An interesting aspect of this is that a nucleus, by combining with a large number of mates, can find optimal combinations for its genetic outfit. Selection can then in essence act on the individual nucleus instead on the heterokaryon level.

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