Comparison of local and systemic induction of acquired disease resistance in cucumber plants treated with benzothiadiazoles or salicylic acid

The accumulation of chitinase and its involvement in systemic acquired dise ase resistance was analyzed using acibenzolar-S-methyl and salicylic acid ( SA), Resistance against scab (pathogen: Cladosporium cucumerinum) and the a ccumulation of chitinase were rapidly induced in cucumber plants after trea tment with acibenzolar-S-methyl. In contrast, SA protected the plants from C. cucumerinum and the accumulation of chitinase was induced only on the tr eated leaves. The accumulation of chitinase in response to inoculation with the pathogen was induced more rapidly in cucumber plants previously treate d with acibenzolar-S-methyl than in plants pretreated with SA or water. Thu s, it appears that a prospective signal(s), that induces systemic resistanc e, can be transferred from leaves treated with acibenzolar-S-methyl to the untreated upper and lower leaves where systemic resistance is elicited. In contrast, exogenously applied SA is not likely to function as a mobile, sys temic resistance-inducing signal, because SA only induces localized acquire d resistance.