Effects of Powdery Mildew of Grape on Carbon Assimilation Mechanisms of Potted `Chardonnay' Grapevines

Potted grapevines ( Vitis vinifera L. `Chardonnay') were inoculated with conidial suspensions of the grapevine pathogen causing powdery mildew of grape (GPM) ( Uncinula necator (Schw.) Burr.). Leaves of inoculated and noninoculated vines were studied for the effects of varying light ( PAR ) and CO 2 concentrations on factors affecting carbon assimilation. GPM reduced carboxylation efficiency ( k ), net CO 2 assimilation rate ( A ), stomatal conductance ( g s ), and internal CO 2 concentration (C i ) under ambient CO 2 , A max at >900 ppm CO 2 , stomatal limitations to A (l g ), and photochemical efficiency (Φ) on diseased leaves, while having no effect on the CO 2 compensation point (Γ) or the light compensation point (cp). GPM had no significant effect on chlorophyll fluorescence (F v /F m ).