Abstract
Heat stress is one of the most important abiotic factor limiting productivity of tomato in Saudi Arabia. Therefore, the aim of this study was to identify the best parental combinations having high yield and quality under heat stress condition through studying heterosis and combining ability for some plant characters and fruit yield of tomato. Twelve F-1 hybrids were produced by crossing between four heat tolerant lines (CLN2123, CLN2400A, CLN2400B and CLN2498E) with three cultivars as testers (Castle Rock, Peto86, and Super strain B) using line x tester mating design. During the summer season of 2019, crosses and their parents were evaluated in a field experiment in randomized complete block design with three replications. Significant variation among the genotypes was noticed for all traits except chlorophyll content and this indicating sufficient variability existed among the genotypes. Both positive and negative heterotic values were detected, indicating the potential of hybrid combinations for traits improvement in breeding programs. Combining ability analysis indicated that both additive and non-additive actions were important for the inheritance of most studied traits. Generally, results indicated that hybrid vigor exploitation could be harnessed to produce high yielding and heat tolerant tomato hybrid under heat stress condition.