Nuclear behavior during basidiospore germination in Cronartium quercuum f. sp. fusiforme

Nuclear behavior during basidiospore germination in Cronartiunz quercuum f. sp. fusiforme was examined on glass slides and host seedlings using 4, 6-diamidino-2-phenylindole staining. Mononucleate basidiospores of Cronartium quercuum f. sp. fusiforme normally were produced following meiosis in the teliospore. However, a subsequent mitotic division often occurred within each basidiospore resulting in a short-lived binucleate condition. Within 1 h after spores were released from the basidium, one of the two nuclei in most basidiospores began to degenerate. Ninety-five percent of basidiospores directly cast from telia onto seedlings of Pinus taeda germinated directly forming thin germ tubes. More than 93% of germ tubes were mononucleate. On glass slides, however, 79% of basidiospores germinated indirectly, forming a secondary basidiospore. During indirect germination, degeneration of the second nucleus occurred quickly without exception. No differences in nuclear behavior were found between direct and indirect germination on host plants or on glass slides. However, nuclear movement from basidiospores into germ tubes was faster on the pine seedlings than on glass slides.