To evaluate and select for drought tolerance in sunflower hybrids and their parents, this research was conducted under two experiments in stress and non-stress conditions in the form of line x tester design at Seed & Plant Research Improvment Institue, Karaj, Iran in 2002. Either of the expriments were consisted of 36 treatments including 3 lines with cytoplasmic male strilities, 8 restorers along with their 24 hybrids and one open-pollinated variety (Armaviruski). The expremental design was a simple lattice one with two replications. Plots in non-water stress condition were irrigated on the basis of 60mm class A evaporation pan and the plots in stress experiment were irrigated on the basis of 180mm class A evaporation pan. The stress was exerted at 6-8 leaf stage. Analysis of variance for measured traits, namely yield, number of normal seeds in head, seed thousand weight and head diameter in the two environmental conditions showed significant differences among genotypes in all traits. To study the combining ability, line x tester analysis was used using procedures developed by Kempthorne (1937) and Singh & Choudari (1976). On the basis of line or tester, significant variances for traits such as number of normal seeds in head and seed thousand weight, addative variance was found singificant. Also on the basis of line x tester significant variances for trait of seed thousand weight in non-stress condition; non-addative (dominance) variance was found significant. GCA/SCA variance ratio revealed that non-addative genetic variance was more important in the expression of latter trait as compared to additive variance. Lines x testers contribution for all traits was greater in either of the two experiments.
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