Ultrastructure of Secondary Spore Formation in the Rust Gymnosporangium Juniperi-Virginianae

ABSTRACT

Basidiospores of G. juniperi-virginianae discharged onto water tended to form secondary spores rather than germ tubes and appressoria. Repetitive germination to form secondary spores was not simply a variation of germ tube development, but rather a distinctly different process. Within 45 minutes after landing on water, one of the two nuclei of a basidiospore undergoing repetitive germination disintegrated. The sterigma that developed from the basidiospore was approximately three times the diameter of a germ tube and lacked the copious extracellular matrix associated with germ tubes and appressoria. Virtually all the contents of the basidiospore eventually entered the sterigma and secondary spore that developed at its tip. After the surviving nucleus entered the secondary spore it underwent a mitotic division. Mature secondary spores were binucleate and morphologically identical to the parent basidiospores.

Key Words:

• Gymnosporangium juniperi-virginianae
• basidiospores
• secondary spores
• ultrastructure
• freeze substitution