This study was carried out during three successive summer seasons of
2002, 2003 and 2004 at Kaha Vegetable Research Station, Kalubia, Egypt. Seven
tomato (Lycopersicon esculentum Mill.) cultivars were evaluated for heat tolerance
and the ability of set fruits under field high- temperature conditions. The cultivars Cal
Ace, Castle rock and Mobile were classified as heat-sensitive cultivars, while cultivars
Peto 86, Chico III, Super Strain Band Tallalakhin were classified as heat-tolerant
cultivars based on their pollen viability, fruit-setting ability, and yielding under high
temperatures. High temperature reduces pollen viability, fruit set percentage and increased
stigma elongation, stigma coloration and unmarketable fruits, i.e. cracks, blossom-end
rot and small mature fruits. Pollen viability percentage ranged from 41.43% to 50.2 %
and 36.97 to 48.65 for heat-sensitive cultivars and 55.10% to 64.32% and 51.53 to
65.28% for heat-tolerant genotypes during 2002 and 2003 seasons respectively. Fruit
set percentage at high temperatures ranged from 31.25% to 38.22 % and 37.30% to
40.00% in the heat-sensitive and from 48.47% to 79.00% and 53.42% to 82.92% in
the heat-tolerant genotypes, respectively during the successive summer seasons. Pollen viability and fruit set percentage, total yield and average fruit weight
behaved as a quantitative characters and both environment and genetics were
involved in the inheritance of this characters. Inheritance of pollen viability (%) under
high temperature was governed by absence of dominance or partial dominance
toward the lower percentage of pollen viability. While, partial dominance toward the
high fruit set (%), over"dominance of the high total yield and partial dominance toward
the heavy fruit weight were responsible for the inheritance of percentage of fruit set,
total yield and average fruit weight under high temperature respectively. Additive
effect appeared to be important in the inheritance of the previous characters. Narrow-sense heritability was high for total yield and average fruit weight
under the heat stress of summer in Egypt. Herltabillty and genetic advance values
showed that effective selection might be made for percentage of fruit set, total yield
and average fruit weight. Pronounced positive heterosis was observed for fruit set
percentage, total yield and average fruit weight, while negative heterosis was
observed for pollen viability percentage.