Dissection of Resistance Pathways in Barley to Powdery Mildew Attack

Abstract

Erysiphe graminis f sp hordei is an obligate biotrophic fungus that exclusively attacks epidermal leaf tissue of its host, barley. In a compatible interaction, the following fungal structures differentiate successively within the first 24 hr after contact of a spore with the wax layer of a barley leaf [1]: the primary germ tube, the appressorial germ tube, and the haustorium, which invaginates the epidermal plasma membrane after penetration of the cell wall. Formation of aerial mycelium and sporulation represent late differentiation events between 4-7 days post inoculation. In many incompatible interactions the development of the fungus usually is abrogated either before or during haustorium differentiation. In these cases, incompatibility can be envisaged as a single-cell event mediated by the host epidermal cell attacked first. Two putative resistance responses are easily detected in the attacked host cell: a subcellularly restricted, highly localized cell wall apposition (cwa) at attempted penetration sites (which is often termed papilla) and/or the activation of a cell death response (indicated by whole-cell autofluorescence which is often termed hypersensitive response (HR);[2]).