Optimal conditions for conidial germination and infection of European pear leaves by Diplocarpon mespili

The epidemiology of Entomosporium leaf spot (ELS) affecting European pear is poorly understood, which limits the development of an effective management strategy. In vitro assays were conducted to study the effect of temperature levels (5, 10, 15, 20, 25, and 30 °C) on Diplocarpon mespili conidial germination evaluated at different incubation times (0, 2, 4, 6, 8, 12, 24, and 48 h). Inoculation experiments were conducted to assess the effect of leaf wetness duration (0, 6, 12, 24, and 48 h) under constant temperature (20 °C) on ELS disease severity on leaves of cultivar ‘Rocha’. The temperature × time interaction significantly affected conidial germination in both experiments and a response surface model was fitted to percent conidial germination data. The optimal temperature for conidial germination was estimated at 20 °C. The incubation period was estimated at 4 days for all leaf wetness durations, excepting the ‘zero’ duration for which no infection occurred. A minimum of 6 h of leaf wetness duration was required for D. mespili infection. Severity reached maximum values after 24 h of leaf wetness duration. A linear regression model described ELS severity increase over time in the absence of reinfection conditions and a monomolecular model described the increase of disease severity influenced by leaf wetness duration in both experiments.