Defence reactions ofHordeum chilenseaccessions to three formae speciales of cereal powdery mildew fungi

Abstract

The histology of resistance to infection by Blumeria graminis DC Speer f.sp. hordei, Blumeria graminis f.sp. tritici, and Blumeria graminis f.sp. avenae was studied in 15 accession lines of Hordeum chilense. All were highly resistant to all formae speciales. There were small differences in spore germination rates and the morphological normality of germlings formed on the different lines. Relatively large differences between accessions were detected in terms of penetration resistance and the frequency with which attacked epidermal cells died. Greater penetration resistance was expressed by epidermal cells of the seventh-formed leaves than by earlier leaves, indicating that penetration resistance is a component of adult plant resistance in H. chilense. Epidermal cells overlying vascular tissues (long epidermal cells) were more resistant to penetration than cells adjacent or close to stomatal complexes. In a limited examination involving two accession lines, epidermal cells on the abaxial leaf surface of one line were more penetration resistant than those on the adaxial surface; the other line was highly resistant on both surfaces. However, in the few cases where long cells and abaxial cells were penetrated, the frequency of associated cell death was lower than in short cells or on the adaxial leaf surface. This is consistent with the macroscopic observation that the few colonies formed on H. chilense were often close to the mid-rib and more frequent on the abaxial leaf surface. The data support the view that H. chilense offers a valuable source of powdery mildew resistance for cultivated cereals.Key words: Blumeria graminis, Erysiphe graminis, powdery mildew, disease resistance, histology, Hordeum chilense.