Cytology and genetics of a dikaryotic strain of Lentinus edodes carrying two haplolethal factors

Basidiospore progeny of a dikaryotic strain (TMI-655) of Lentinus edodes showed abnormalities in germination and subsequent hyphal growth. In the basidia, meiosis and sporulation completed normally, and mature, uninucleate basidiospores were formed. On agar medium, about half of the basidiospores either failed to germinate or ceased to grow at early stages of germination (mostly before septation) and then degenerated. Among these, irregularly swollen spores showing an apparent sign of wall autolysis were commonly observed. The other half of the basidiospores succeeded in germination and developed into multicellular germlings, but only half of them (i.e., approximately one-quarter of the initial population) survived and formed colonies. Those germlings that failed to form colonies were characterized by spherical swellings, abnormal branching, and eventual death of the component cells. These results indicated the presence of two recessive haplophasic lethal factors that segregated independently and were operative at different developmental stages. Genetic analysis showed that both of the lethal factors were carried by one of the component nuclei of TMI-655 and were transmitted through dikaryotic–monokaryotic matings, and that one of the lethal factors was linked to the A incompatibility factor. Key words: cytology, genetics, basidiospore germination, haplolethal factor, Lentinus edodes.