EFFECTS OF TEMPERATURE AND WETNESS DURATION ON SPORULATION OF BOTRYTIS-CINEREA ON STRAWBERRY LEAF RESIDUES

Disks cut from dead strawberry leaves (autoclaved or air-dried) were i noculated with a conidial suspension of Botrytis cinprea (10(6) conidi a per mi) and incubated at various temperatures (T) ranging from 5 to 30 degrees C. Sporulation (conidia per cm(2)) on leaf disks was determ ined after exposure to wetness durations (W) of 3 to 11 days. Optimum temperature for sporulation was between 17 and 18 degrees C at all wet ness durations. Sporulation levels of 10(5) to 10(7) conidia per cm(2) were observed between 15 and 22 degrees C, after 7 days of continuous wetness. As temperature increased or decreased from the optimum, spor ulation decreased for the same wetness durations. Very little sporulat ion was observed at 25 degrees C and no sporulation was observed at 30 degrees C. Logarithmic polynomial models best described the effect of T and Won sporulation of B. cinerea on dead strawberry leaf tissue. C oefficients of determination for data from all repetitions of the expe riments were at least 0.81. The latent period of B. cinerea on dead le af tissue was longest at the lowest temperature (5 to 7 days at 5 degr ees C) and decreased to <3 days as temperature increased to the optimu m (15 to 22 degrees C). Interrupted wet and dry periods of 5, 12, and 24 h directly affected sporulation. Total hours of wetness and the dur ation of individual wet periods had the greatest effect on the amount of inoculum produced at 20 degrees C.