Light and electron microscopy of teliospores and teliospore germination in the rust fungus Coleosporium ipomoeae

Abstract

A combination of light, scanning, and transmission electron microscopy was used to examine teliospores and teliospore germination in the rust fungus Coleosporium ipomoeae (Schw.) Burrill, a parasite of the wild morning glory Ipomoea coccinea L. Telia developed on abaxial surfaces of infected leaves and appeared as orange, waxy crusts usually associated with uredinia. Mature teliospores were cylindrical to slightly clavate in shape and thin-walled. The presence of chitin in the spore wall was demonstrated using wheat germ agglutinin gold labeling. Teliospores were surrounded by an electron-dense extracellular material. Each spore possessed a large prominent nucleus containing synaptonemal complexes indicative of prophase I meiotic nuclei. Following hydration, the nucleus of each spore completed meiosis and the spore was divided into four uninucleate compartments by the formation of three transverse septa. Each compartment gave rise to a germ tube into which the nucleus and cytoplasm migrated. Germ tubes developed into long slender sterigmata that grew through the extracellular material within the telium to become exposed on the leaf surface. A basidiospore then developed at the tip of each sterigma. Once the nucleus moved from the sterigma into the spore, a septum formed to delimit the spore from the tip of the sterigma.Key words: fungal spores, transmission and scanning electron microscopy, high pressure freezing.