Systemic Acquired Resistance in Arbidopsis thaliana Induced by a Predisposing Infection with a Pathogenic Isolate of Fusarium oxysporum . Brigitte Mauch Mani. Institute for Plant Biology, Zollikerstr. 107, CH-8008 Zurich, Switzerland. Alan J. Slusarenko. Institute for Plant Biology, Zollikerstr. 107, CH-8008 Zurich, Switzerland. MPMI 7:378-383. Accepted 22 February 1994. Copyright 1994 The American Phytopathological Society.

Fusarium oxysporum was isolated from lesions on a naturally infected Arabidopsis plant, and pathotypic variation in host response was found in different ecotypes. In some ecotypes limited necrotic lesions were produced on inoculated leaves, whereas in susceptible ecotypes a systemic infection leading to plant death was observed. Infection of lower rosette leaves in an ecotype showing a limited lesion response induced resistance in the other rosette leaves to a subsequent challenge with a virulent race of Peronospora parasitica. Induction of systemic acquired resistance was associated with the accumulation of transcripts for pathogenesis-related proteins. Histologically, a range of pheno-types was observed, from a phenocopy hypersensitive response to a trailing necrosis which ultimately contains any Peronospora hyphal growth.