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

Abstract

Chrysomyxa weirii (Uredinales) is the only autoecious, microcyclic species of Chrysomyxa occurring in North America. The telia form on second-year needles of spruce, causing premature needle loss. The morphology of the telia was studied in herbarium specimens from diverse locations, and the teliospore germination, nuclear condition, and reproductive biology of fresh collections were studied on microscope slides and on artificially and naturally infected host tissue using light and scanning electron microscopy. Basidiospore production was infrequent in mature sori, but teliospores dispersed readily in water and germinated to produce a two-celled basidium and two basidiospores. The two cells of the basidium could also separate to form two sporelike cells that could produce germ tubes, or the teliospore produced a long hyphalike promycelium. The type of germination was influenced by temperature. 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-walled spores that are held rigidly together until wet suggest a water-dispersal mechanism. A cytological study showed that the vegetative hyphae are mostly monokaryotic. Dikaryotization and karyogamy occur in the cells at the base of the telium and result in teliospores with one large nucleus. During germination, the teliospore nucleus migrates into the basidium, where it divides once before a septum forms. A second nuclear division occurs in each cell during basidiospore formation. Both nuclei move into the basidiospore, and subsequently divide one or more times. The two-celled basidium, the fragmenting basidium and other unusual forms of germination, and teliospore dispersal have not been previously reported in the genus Chrysomyxa.

Key Words:

• basidium
• cytology
• microcyclic rust
• Picea
• splash dispersal
• Uredinales