Induction of Disease Resistance in Cucumber by Acibenzolar-S-methyl and Expression of Resistance-related Genes.

Abstract

Systemic acquired resistance (SAR) is an inducible defense mechanism that plays a central role in plant disease resistance and can be induced by different compounds. In this study, acibenzolar-S-methyl (benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester) was shown to induce acquired resistance in cucumber. The signal(s), which induced resistance against scab (pathogen: Cladosporium cucumerinum), was systemically transferred as early as 4 to 6 hr after treatment with acibenzolar-S-methyl. Expression of resistance-related genes, i.e., genes of acidic peroxidase, acidic class III chitinase and acidic beta-1, 3-glucanase, was also induced by the treatment. Although systemic expression of peroxidase and chitinase genes was induced not only in the first leaves treated with acibenzolar-S-methyl but also in the untreated upper leaves, the induction of beta-1,3-glucanase gene was not systemically enhanced in cucumber plants within 24 hr of the treatment. Since resistance against C. cucumerinum was already induced by 24 hr after acibenzolar-S-methyl treatment, beta-1,3-glucanase might not participate in the protection against attack by the pathogen at an early stage in the SAR induced by this compound. Thus, acibenzolar-S-methyl seems to activate the SAR signal transduction pathway in cucumber plants. Subsequently, this compound rapidly induces the expression of SAR genes and disease resistance in the plants.