Physiological responses of Vitis vinifera cv. “Chardonnay” to infection by the Pierce's disease bacterium

Abstract

Physiological changes associated with water stress and senescence were compared between leaves of healthy grapevines ( Vitis vinifera cv. “Chardonnay”) and grapevines infected with the Pierce's disease (PD) bacterium. Vegetative growth of diseased vines was less than that of nearby healthy vines under natural vineyard conditions. Although stomatal resistance of diseased leaves with marginal necrosis was similar to that of healthy leaves during early morning, the stomatal resistance of diseased leaves increased greatly later in the day while that of healthy leaves remained relatively constant. The diurnal patterns of transpiration and photosynthesis demonstrated that these processes were inhibited by PD. The reduced photosynthesis of diseased leaves was at least partly due to inhibition of nonstomatal-related aspects of CO 2 fixation. Compared to healthy leaves, diseased leaves had higher concentrations of abscisic acid, glucose, fructose, Ca 2+ and Mg 2+ , but a lower concentration of K + . Sucrose accumulated in green tissue of a diseased leaf, but the concentration of sucrose and starch were lower in diseased chlorotic tissue than in diseased green or healthy leaf tissue. Chlorophyll reduction in diseased leaves was also associated with increases in electrolyte leakage, lipid peroxidation and superoxide anion. Based on these physiological changes and the similarity of PD to other “non flaccid” vascular diseases, it is proposed that the symptoms of PD are the result of relatively mild but prolonged water stress which accelerates leaf senescence.