Reproductive biology and evidence for water dispersal of teliospores in Chrysomyxa weirii, a microcyclic spruce needle rust

Chrysomyxa weirii (Uredinales) is the only autoecious, microcyclic species of Chrysomyxa occurring in North America. The telia form on second-year nee dles of spruce, causing premature needle loss. The morphology of the telia was studied in herbarium specimens from diverse locations, and the teliospo re germination, nuclear condition, and reproductive biology of fresh collec tions were studied on microscope slides and on artificially and naturally i nfected host tissue using light and scanning electron microscopy. Basidiosp ore production was infrequent in mature sori, but teliospores dispersed rea dily in water and germinated to produce a two-celled basidium and two basid iospores. The two cells of the basidium could also separate to form two spo relike cells that could produce germ tubes, or the teliospore produced a lo ng hyphalike promycelium. The type of germination was influenced by tempera ture. The ready dispersal of teliospores in water and their presence on the surface of current-year needles confirms that they function as diaspores. The distribution pattern of this rust and the elongated, smooth, thin-walle d spores that are held rigidly together until wet suggest a water-dispersal mechanism. A cytological study showed that the vegetative hyphae are mostl y monokaryotic. Dikaryotization and karyogamy occur in the cells at the bas e of the telium and result in teliospores with one large nucleus. During ge rmination, the teliospore nucleus migrates into the basidium, where it divi des once before a septum forms. A second nuclear division occurs in each ce ll during basidiospore formation. Both nuclei move into the basidiospore, a nd subsequently divide one or more times. The two-celled basidium, the frag menting basidium. and other unusual forms of germination, and teliospore di spersal have not been previously reported in the genus Chrysomyxa.