الفهرس 
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Abstract
Tomato is grown in most parts of the world from the tropics to within a few
degrees of the Arctic circle (Rick, 1976). It is adapted to a wide range of climates.
tomato plants require night temperature of 14 to 20°C and day temperature of 25-30°C.
When night or day temperature were either higher or lower than this range fruit setting
was reduced or completely terminated (Moore and Thomas, 1952; Schaible, 1962 and
Metwally et al., 1988). Therefore, temperature greater than 34/20°C (day/night) or a
period of four hours at 40°C will cause blossom DROP in most cultivars. The minimum
(night) and maximum (day) temperatures in Egypt are frequently getting higher than 20°C
and 30°C, respectively, during late summer season i.e. June, July and August (Metwally
et al. , 1988 and 1990). Hence, production is always limited and price is high during
October. This is due to the unfavorable temperature prevailing during flowering in the
preceding months which seriously reduce fruit set. This happens during June, July and
August when night and day temperatures become unfavorably high for fruit set. Therefore
the heat-tolerant cultivars, capable of setting fruits during this particular period. are
however urgently needed.