Effects of Timing of Powdery Mildew Infection on Carbon Assimilation and Subsequent Seasonal Growth of Potted Chardonnay Grapevines

Abstract

Potted Chardonnay (Vitis vinifera L.) grapevines were inoculated with conidial suspensions of Uncinula necator (Schw.) Burr., the causal agent of powdery mildew of grape, just prior to bloom (early), just after the estimated 5-mm berry stage (late), or they were not inoculated but were treated with myclobutanil fungicide to maintain foliage free of the disease (control). The effects of the timing of initial infection on net carbon assimilation (A), carbon partitioning, stomatal conductance (g_s), internal CO₂ concentration (C_i), and transpiration (E) were studied over two seasons. Early vines had reduced A relative to late and control vines until the estimated preveraison period, when late vines also showed reduced A. Early vines had reduced fresh and dry weights compared to other treatments. Leaves on both early and late vines senesced earlier than those on control vines. During the following growing season, shoot lengths and fresh and dry weights were negatively correlated with the length of the disease development period in the previous growing season.