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

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.