One of the properties of systemically acquired resistance in plants is their concomitance with the biochemical changes including enhancement of activities of defense-related enzymes. The leaf extract of Reynoutria sachalinensis (F. Schmidt) Nakai is known to be an effective compound for the control of a few plant diseases particularly powdery mildew of cucurbits (caused by fungal pathogen Podosphaera fusca), by inducing host defense responses. In the present investigation, the effects of this extract on some defense responses of cucumber plants were studied via in vivo tests. Changes of defense responses in the extract treated-cucumber plants, with or without pathogen inoculation, were studied and compared with those of non-treated control plants. Results indicated that specific activity of peroxidase increased significantly in treated tissues. Enhancement of enzyme activity showed the same patterns in both the pathogen inoculated- and non-inoculated-plants thus the pathogen attack did not affect the enzyme activity. Specific activity of phenylalanine ammonia-lyase in the non-inoculated extract treated-plants showed a transient fast increase during 24 hours after the treatment, whereas in the inoculated ones, it showed a permanent slow increase probably due to the interaction between extract treatment and pathogen attack. Phenolic content of extract treated-plant tissues, despite small fluctuations, did not show any definite pattern of changes.

Keywords: Cucumber, Powdery mildew, Podosphaera fusca, Phenolic content, Peroxidase, Phenylalanine ammonia-lyase.

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