Nuclear Behavior of Phellinus arctostaphyli, P. igniarius, and P. tremulae

The number and distribution of nuclei in basidiospores, hyphae of germinating basidiospores, homokaryons (single-basidiospore isolates), heterokaryons (isolates from the context of basidiocarps), and basidiocarp tissues were examined microscopically. Three nuclear stains were used: Giemsa, hematoxylin, and DAPI (4′,6-diamidino-2-phenylindole). The nuclear behavior of the three fungal species was similar. Basidiospores were produced with one nucleus but often became binucleate prior to germination. One nucleus usually remained in the basidiospore after germination and germ tube elongation. Both homokaryons and heterokaryons had a variable number of unpaired nuclei, often spaced equidistantly between undamped septa. The dikaryophase was delayed until basidiocarp formation; paired nuclei were found in young basidia and subhymcnial mycelia. Basidia with one, two, or four nuclei were observed prior to spore formation. Four uninucleate basidiospores formed on each basidium. Homokaryotic and heterokaryotic isolates could not be distinguished by nuclear condition or colony morphology, although heterokaryons grew significantly (P = 0.05) faster.