HEAT-INDUCED RESISTANCE IN BARLEY TO THE POWDERY MILDEW FUNGUS ERYSIPHE-GRAMINIS F-SP HORDEI

A hear-treatment (30-60 s at 50 degrees C) of young barley seedlings of the highly susceptible cultivar Golden Promise reduced subsequent infection by the powdery mildew fungus Erysiphe graminis f.sp. hordei. Shorter heat-treatments (30 or 40 s) caused transient protection, whereas protection after longer heat-treatments (50 or 60 s) was more persistent. On heat-treated leaves, the fungus was mainly stopped at the stage of first appressorial penetration, in the absence of papilla formation or hypersensitive cell death. Heat-treated leaves produced fewer protoplasts on treatment with cellulase and pectinase than controls thus indicating effects on cell-walls. Protection did not correlate with enhanced accumulation of extracellular, pathogenesis-related (PR) proteins, compared to the susceptible interaction on control leaves. Two-dimensional analysis of in vitro translation products revealed a pattern of accumulating transcripts 14 h after heat-treatment, that was different from the pattern induced during a 4 h heat-shock period at 38 degrees C, with partial overlap. A new mechanism of acquired resistance is proposed that is independent of papilla Formation, hypersensitive cell death or accumulation of extracellular PR proteins but may be based on cell-wall modification and the induction of new host genes. (C) 1995 Academic Press Limited.