1.4.10
ISOLATION OF AN ANTIFUNGAL COMPOUND FROM CUCUMBER TREATED WITH THE DISEASE RESISTANCE INDUCER ACIBENZOLAR-S-METHYL

T HORIO, Y NARUSAKA and H ISHII

National Institute of Agro-Environmental Sciences, Tsukuba, Ibaraki 305-8604, Japan

Background and objectives
The benzothiadiazole compound acibenzolar-S-methyl (benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl) is used for the control of wheat powdery mildew as a plant activator [1]. Although this compound has no antifungal activity, it has control effects against scab and anthracnose on cucumber (Ishii H et al., unpublished data). The objectives of this study were to isolate an antifungal compound found in cucumber plants treated with acibenzolar-S-methyl and to establish its chemical structure.

Results and conclusions
Methanol extracts of cucumber plants were separated into an ethyl acetate-soluble fraction and a water-soluble one. Individual fractions were tested for their antifungal activity against Cladosporium cucumerinum conidia directly on TLC plates. An antifungal compound was found in the ethyl acetate fraction of cucumber plants sampled 7 days after treatment with acibenzolar-S-methyl, but little of the compound was contained in the fraction from control plants. The compound was observed even from the sample collected 2 days after treatment. Since the compound was also found in plants inoculated with conidial suspensions of C. cucumerinum without the chemical treatment, it was certain that this antifungal compound was derived not from acibenzolar-S-methyl but from the plant itself. After separation by silica gel column chromatography and preparative TLC, a compound possessing antifungal activity was isolated. By instrumental analysis of FI-MS and NMR, this compound was identified as benzyl hydroperoxide. The chemical structure was confirmed by comparison with a synthesized authentic sample.

References
1. Ruess W, Mueller K, Knauf-Beiter G et al., 1996. Proceedings Brighton Crop Protection Conference: Pests and Diseases, pp. 53-60.