Effects of oak powdery mildew (Erysiphe alphitoides [Griffon and Maubl.] U. Braun and S. Takam.) on photosynthesis of pedunculate oak (Quercus robur L.)

The aim of the present study was to evaluate the effect of one of the most important foliar diseases, powdery mildew, on the leaf physiological traits of Quercus robur L. using chlorophyll a fluorescence parameters in combination with parameters of leaf gas exchange. For this purpose, greenhouse semi-controlled experiment was conducted with 25 one-year-old seedlings kept in optimal conditions, and the same number of seedlings infected with the mentioned pathogen. Measurements were carried out when the coverage of epiphytic micelia visually reached more than 75% of the surface of leaves in the infected seedlings. The results of gas exchange measurement showed that Erysiphe alphitoides (Griffon and Maubl.) U. Braun and S. Takam caused a significant reduction of net photosynthesis (A) and a significant increase in substomatal CO2 concentration (Ci). Furthermore, considering the fast kinetics of chlorophyll a fluorescence, all of the observes parameters were significantly affected by oak powdery mildew. On the other hand, pulse amplitude modulated fluorescence parameters were mildly affected, with only minimal (Fo?) and maximal (Fm?) fluorescence of dark adopted leaves showing significant difference. This study presented the possibility of usage and the effectiveness of chlorophyll a fluorescence parameters in detection the severe stress conditions, on the example of leaves infected with oak powdery mildew over 75%. Some additional studies should be conducted in the future to determine the possibility of usage and the effectiveness of the observed fluorescence parameters of fast kinetics in detection of mild and early stress.