Effect of wetting duration,and of other environmental factors,on the development ofStemphylium botryosum f. sp.lycopersici in tomatoes

In experiments on artificial inoculation of tomato leaves byStemphylium botryosum f. sp.lycopersici, infection was found to be relatively insensitive to temperature between 15° and the 25°C optimum. Wetting duration had a greater effect on infection than either temperature or spore load, and also influenced the extent of the effect of the two latter factors. The optimum temperature for leaf colonization was found to be 25°C; it was more sharply defined under constant temperature than when alternating with a night temperature of 10°C. At 39°C, colonization was inhibited only by exposure longer than 12 h. The results are used to explain the seasonal pattern of the blight in Israel.