The objective of the present investigation was to identify desired parents and
cross combinations show high yielding ability under heat stress conditions in Egypt as
well as to gather information on genetic behavior of some traits associated with yield
and its components under heat stress conditions.                 .        Nine parents diallel crosses, involving Egyptian and exotic tomato germplasm were done. Then the parents and their 36 F1'S were evaluated during the late summer
season 2002. The results revealed that both general and specific combining abilities were
highly significant for all studied traits. Therefore, both additive and non-additive gene
actions were important in the expression of these traits. The magnitudes of additive
genetic variances were larger than those of the non-additive variances for number of
branches I plant, total yield and TSS%. However for other traits, the dominance gene
effects play the major role in the inheritance of these traits. Heterosis over mid-parents or better parents was present in most of crosses for
these traits. Edkaway, CLN 1355 and CLN 2026D, were good combiners for
vegetative traits. The parental lines CLN 1355, Tolalakheen and EM9 were
considered good combiners for fruit set percentage. Talalakheen, CLN 1355, CLN
2025C and EM9, were good combiners for early and total yield. FM9, Castle Rock and
LHT 24 were good combiners for average fruit weight. FLa 7156 was the best
combiner for fruit firmness, TSS% and ascorbic acid content. In addition both broad and narrow-sense heritabilities values were high for all
studied traits, indicating that all traits were highly heritable. Out of the present study, there were some desirable genotypes appeared high
yielding ability and quality traits under heat stress conditions in late summer in Kafr EI-
Shiekh, Egypt, these genotypes were FM9 as cultivar and the hybrid Castle Rock x
FM9.