GRAPEVINE LEAF TRANSPIRATION RESPONSES TO DOWNY AND POWDERY MILDEW INFECTIONS

The effects of pathogen fungi on water relationships of grapevine (Vitis vinifera) were investigated in a field experiment made in Mondeggi farm, Florence (Italy). The effects of downy mildew (Plasmopara viticola) and powdery mildew (Uncinula necatrix) were studied by means of measurements of gas exchange both under field and controlled conditions (to avoid the effects of temporary stresses). On leaves infected by mildews, transpiration was found to be altered and related to the area of the lesions. In the healthy portion of diseased leaves transpiration was always lower than in healthy leaves, confirming that the pathogen can affect the leaf physiology also outside the visible symptoms.