The nature of the resistance of oat leaves to infection by Pyrenophora teres

Abstract

Although conidia of Pyrenophora teres germinated and formed appressoria on oat leaves, penetration and intracellular development of the fungus in the epidermal cells was restricted. At most sites of attempted penetration, a papilla formed on the inner surface of the epidermal cell wall, adjacent to the appressorium, and appeared to prevent the infection hypha entering the cell. When penetration occurred an intracellular vesicle was formed. In some cases this vesicle became encapsulated so that further growth was restricted, but otherwise the vesicle produced intracellular hyphae. Epidermal cells in which intracellular hyphae developed died and the cell walls of the infected cell and of the hyphae became modified. Fluorescence under u.v. light and staining with Nile blue sulphate indicated that the papillae, encapsulation material and modified cell walls of hyphae and of infected cells contained similar material. Lignin could not be detected but there appeared to be a phenolic component. Similar materials accumulated around wound-lesions inoculated with P. teres conidia and in leaves treated with a methanolic extract of P. teres mycelium. The methanolic extract was toxic to leaf tissue and it is suggested that the accumulation of the materials may be elicited by a fungal metabolite.