Histology of Cochliobolus sativus infection in subcrown internodes of wheat and barley

Abstract

Histological study of the infection process of Cochliobolus sativus in subcrown internodes of postseedling plants failed to disclose differences in wheat and barley cultivars that differed markedly in resistance to common root rot in the field. Appressoria and infection cushions were formed on the host surface before penetration. The dome-shaped infection cushions consisted of short-celled hyphae surrounded by long-celled running hyphae. Penetration occurred by fine infection pegs produced from appressoria or the short-celled hyphae in the infection cushions. A lignituber occurred beneath each penetration site. The fungus penetrated wheat or barley subcrown internodes via various epidermal cells, including hair cells, stomatal guard cells, and the rectangular cells. Infection proceeded from the epidermis to the cortex and endodermis, resulting in breakdown of these tissues. Sometimes the stele also was invaded and vascular tissues were occluded. Three morphologically different hyphae, namely fine aseptate infection hyphae, long-celled running hyphae, and coarse, short-celled hyphae, were observed. Dark-stained objects, directly or indirectly associated with the fungus, frequently were found in infected tissues.