Temperature-Dependent Sporulation of the Fungus Coniella diplodiella, the Causal Agent of Grape White Rot.

Abstract

White rot, caused by the fungus Coniella diplodiella, can severely reduce grapevine yields worldwide. Currently, white rot control mainly relies on fungicides applied on a calendar basis or following hailstorms that favor disease outbreaks; however, the control achieved with this strategy is often inconsistent or otherwise unsatisfactory. Realizing more rational control requires an improved understanding of white rot epidemiology. To this end, we conducted experiments with grapevine berries of two Vitis vinifera cultivars (either injured or not before artificial inoculation with a conidial suspension of C. diplodiella) to determine the effect of temperature on the length of latency (i.e., the time between infection and onset of mature pycnidia on berries) and the production of pycnidia and conidia. Sporulation occurred between 10 and 35°C, with the optimum detected at 20°C. The latency period (LP) was shorter at 25 to 35°C than at lower temperatures; the shortest LP was 120 h at 30°C on injured berries. Affected berries produced abundant conidia at 15 to 30°C (the optimum was 20°C) for more than 2 months following inoculation. Mathematical equations were developed that fit the data, with strong associations with temperature for the LP (R2 = 0.831) and for the production dynamics of secondary conidia (R2 = 0.918). These equations may contribute to the development of a risk algorithm to predict infection periods, which can inform risk-based disease control strategies rather than calendar-based disease control strategies.