The data from in vitro and in vivo trials showed that grape clusters were susceptible to infection by Coniella diplodiella for a long period; effective disease control therefore requires interventions from early berry development.

Abstract

White rot, caused by the fungus Coniella diplodiella, is an important but poorly studied disease that mainly affects grapevine clusters. White rot control typically involves the repeated application of fungicides, which may be unjustified in some cases given that the key period of berry susceptibility to infection remains unclear and controversial. In this study, germination of C. diplodiella conidia and mycelium growth were investigated on water agar (conidial germination only) and artificial media similar to berry juice at five growth stages from pea-sized to berries ripe for harvest. On water agar, conidia germinated from 10°C to 35°C (with an optimum of 20–30°C) with >2 h of moisture incubation. Both conidial germination and mycelial growth were higher on agar similar to berry juice at véraison to berry softening than at other stages, with the lowest values detected for the ripe berries. The berries were also artificially inoculated with conidia at the different growth stages, showing that grape clusters were susceptible to infection for a long period, albeit with varying degrees of susceptibility at different stages. This implies that effective disease control requires interventions from early berry development, whenever weather conditions are conducive to infection. Further development of a predictive model accounting for weather conditions and berry susceptibility dynamics would facilitate the dynamic estimation of the disease risk during the grapevine-growing season and contribute to a risk-based application of fungicides for white rot control.