Effects of Temperature and Wetness Duration on the Sporulation of Phomopsis viticola on Infected Grape Canes
In 2008, research was initiated to examine effects of temperature and wetness duration on the sporulation of Phomopsis viticola on infected grape canes and to determine effects of interrupted wetness duration on sporulation. To determine effects of temperature (T) and wetness duration (WD) on sporulation, a split-plot experimental design was used, with T (5, 12, 15, 18, 20, 22, 25, 28, and 35°C) assigned to whole-plots and WD (11, 23, 35, 47, and 71 h) assigned to sub-plots. Linear and nonlinear mixed models were fitted to the data. Lower and upper limits of sporulation were found to be at 5 and 35°C, respectively. Optimum sporulation was near 22°C, and sporulation increased with increasing WD. Of the examined models, a generalized Analytis Beta model fit the data best. To determine effects of wetness interruption (IWD), a split-plot was used, with T (12, 15, and 20°C) assigned to whole-plots and IWD (0, 2, 4, 8, 12, and 24 h) assigned to sub-plots. Generally, sporulation declined with increasing IWD. An IWD of 12 h or more resulted in significantly and substantially less sporulation compared to the control (0 h IWD). Using a repeated-measures design, spore density and environmental data were measured in the vineyard during and following individual rain events; a preliminary model predicted the temporal trend in spore density within the vineyard fairly well (R2 = 0.719), although absolute magnitude of sporulation could not be predicted. Accepted for publication 27 April 2012. Published 23 July 2012.