Ultrastructure of Teliospore Ontogeny in Tilletia indica

Abstract

Teliospores of Tilletia indica, the Karnal bunt fungus of wheat, arose from a fixed hymenium lining all surfaces of a cavity formed by separation of the inner and outer layers of the pericarp of the grain. Scanning and transmission electron microscopy showed that the spore originated as a swelling cut off at the tip of a sporogenous hypha by a septum. The wall of the parent sporogenous cell formed the primary wall of the spore initial. Centripetal deposition of secondary wall material against the primary wall produced: 1) a thin, uniform outer layer that fused with the primary wall to form a sheath; 2) an electron opaque exospore ornamented with spines; 3) a uniform, granular endospore; and 4) a thin partition layer of sinuous lamellae separating the exospore and endospore. The complex exospore was composed of a series of concentric fibrous bands divided into two layers. In the outer ornamented layer localized deposits of dense amorphous material cemented the fibrous bands into conical spines separated by interspinal areas of loosely arranged bands. Inside of the ornamented layer the deposits of amorphous material formed a continuous dense basal layer that merged with the broad bases of the spines. The apiculus sometimes present on mature spores represented the shriveled subapical cell of the sporogenous hypha.