Some Oxidative Responses in Rhododendron Leaves Infected with Pythium and Phomopsis

The aim of the present study was to evaluate peculiarities of plant defence responses in the detached leaves of evergreen rhododendron 'Spriditis' (R. catawbiense Michx. hybrid) infected with different microorganisms: pathogenic oomycete Pythium or endophytic fungus Phomopsis. Some parameters, characterizing oxidative stress reactions of plants, such as total phenolic content, guaiacol and ascorbate peroxidase activities, were determined. The first necrotic lesions on the leaves infected with Pythium were noticed on the fourth day after treatment, but in the case with Phomopsis small necrotic spots were observed only after three weeks. The activity of guaiacol peroxidase increased significantly in the leaves infected with Phomopsis and reached their maximum on the third day. In the case with Pythium, there were not observed any significant changes in the activity of guaiacol peroxidase during the whole experiment. In regard to the ascorbate peroxidase activity, no significant differences were detected among all experimental treatments and control. Under the influence of Pythium or Phomopsis the total phenolic content in the leaves started to slightly increase only on the 7th day and reached their maximum only on the 14th day of the experiment.