Swedish University of Agricultural Sciences, Svalöv, Sweden

Background and objectives
Bipolaris sorokiniana is a worldwide pathogen of many cereals, including barley. In contrast to many other pathogens it can infect all parts of the plant. The diseases caused by the fungus are common root rot, leaf spot disease, seedling blight, head blight and black point of grain. In Scandinavia, B. sorokiniana, together with Drechslera teres, causes serious leaf infections in spring barley. Systemic acquired resistance (SAR) is an inducible plant defence response resulting from an earlier infection with a necrotrophic pathogen. It is distinct from other inducible resistance mechanisms such as phytoalexin biosynthesis and the hypersensitive response. SAR can provide relatively long-lasting protection against subsequent attacks by a range of pathogens, including fungi, bacteria and viruses. SAR has mainly been studied in dicotyledons. Accumulation of pathogenesis-related (PR) proteins correlates with the establishment of SAR. These proteins are induced in pathological or related situations and have been demonstrated to possess direct antimicrobial activity.

Results and conclusions
We have studied SAR using B. sorokiniana and barley as a model system. Barley roots were inoculated and the leaves were later analysed for PR proteins. The accumulation of PR proteins was analysed with isoelectric focusing (IEF) and quantified by ELISA. Northern blot hybridizations confirmed that the PR proteins were indeed synthesized in the leaves and not transported from the root. Visual differences in resistance of the leaves to a second infection by B. sorokiniana were investigated.