Acibenzolar-S-methyl-Induced Systemic Resistance against Anthracnose and Powdery Mildew Diseases on Cucumber Plants without Accumulation of Phytoalexins


National Institute for Agro-Environmental Sciences, Tsukuba, Ibaraki, Japan


In a study to elucidate the possible involvement of phytoalexins in acibenzolar-S-methyl (ASM)-induced systemic resistance in cucumber plants (Cucumis sativus L.), the phenolic compounds were extracted from ASM-treated and inoculated plants and compared with those from Milsana®-treated plants previously reported to accumulate phytoalexins in cucumber. The glycoside-linked phenolic compounds from cucumber leaves were tested for their antifungal activity to the growth of pathogens which were most effective against the cucumber anthracnose fungus Colletotrichum orbiculare, followed by the scab fungus Cladosporium cucumerinum but ineffective against the Corynespora leaf spot fungus Corynespora cassiicola. Nevertheless, the accumulations of active compounds appeared to increase with the growth stages of cucumber plants irrespective of ASM treatment. In ASM-pretreated cucumber plants either inoculated with anthracnose or the powdery mildew fungus, there was no increase in phytoalexin-like phenolics.