SYSTEMIC ACQUIRED-RESISTANCE IN ARABIDOPSIS-THALIANA INDUCED BY A PREDISPOSING INFECTION WITH A PATHOGENIC ISOLATE OF FUSARIUM-OXYSPORUM

Fusarium oxysporum was isolated from lesions on a naturally infected A rabidopsis 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 syste mic 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 acqu ired resistance was associated with the accumulation of transcripts fo r pathogenesis-related proteins. Histologically, a range of phenotypes was observed, from a phenocopy hypersensitive response to a trailing necrosis which ultimately contains any Peronospora hyphal growth.