Systemic resistance induced by benzothiadiazole in pear inoculated with the agent of fire blight (Erwinia amylovora)

The benzothiadiazole derivative acibenzolar-S-methyl (BTH; Bion, Syngenta), a well known chemical inducer of systemic acquired resistance (SAR), was tested for its ability to protect pear (Pyrus communis cv. Abate Fetel) from fire blight following inoculation with Erwinia amylovora. Two-year-old pear plants sprayed with BTH 10 days before inoculation were partially protected from fire blight, both in terms of incidence (-33%) and severity (-37%). The effect of BTH proved to be systemic. However, a significant portion (28%) of BTH-treated plants showing little or no symptoms 6 months after inoculation still harboured viable E. amylovora cells, as judged by PCR-based detection. Salicylic acid, known to be physiologically implicated in the onset of SAR, gave similar protection as BTH when sprayed 24 h before inoculation. In several plants species systemic acquired resistance has been shown to correlate with the induced expression of a defined set of genes coding for pathogenesis-related (PR) proteins. However, the expression of a member of the PR-1 family in pear plants treated with BTH and salicylic acid and subsequently inoculated with E. amylovora was found to be constitutive and unaffected by treatments. These results therefore suggest that molecules other than PR-1 may be important in the BTH-induced systemic resistance of pear against E. amylovora. (C) 2004 Elsevier B.V All rights reserved.