Effects of temperature and wetness duration on the sporulation rate of Phomopsis viticola on infected grape canes
D. J. ANCO (1), L. V. Madden (1), M. A. Ellis (1)
(1) Ohio State University, OARDC, Wooster, OH, U.S.A.
Phytopathology 101:S221

In 2008, research was initiated to examine effects of temperature (T) and wetness duration (WD) on the sporulation rate of Phomopsis viticola on infected grape canes and to determine effects of interrupted wetness duration (IWD) on sporulation (S). To determine effects of T and WD on S, a split-plot design was used, with T (5, 12, 15, 18, 20, 22, 25, 28, and 35°C) as the whole-plot and WD (11, 23, 35, 47, and 71 h) as the sub-plot. Linear and nonlinear models were fit to the data. Goodness of fit was based on residuals, (pseudo-)R², -2 log likelihood, parameter effects nonlinearity, correlation of parameter estimates, and other statistics. Lower and upper limits of S were found to be 5 and 35ºC, respectively. Optimum S was near 22ºC, and S increased with increasing WD. Of the examined models, Analytis’ Beta model fit the data best. To determine effects of wetness interruption, a split-plot was used, with T (12, 15, and 20°C) as the whole-plot and IWD (0, 2, 4, 8, 12, and 24 h) as the sub-plot. Generally, S declined with increasing IWD. An IWD of 12 h or more typically resulted in significantly less S 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; preliminary results show that the developed model can predict the temporal trend in spore density in the vineyard fairly well, although absolute magnitude of sporulation cannot be predicted.

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