To develop synthetic varieties, not only the estimation of General Combining Ability (GCA) for forage production is required but also the stability of GCA for parental genotypes is necessary. Little is known about genetic analysis and selection for high production, combining ability, and stability in grasses. In this study, half-sib families derived from the polycross of 25 smooth bromegrass genotypes were evaluated under 10 environments (combination of five years and two moisture environments,

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... including non-stressed and drought stress conditions). Considerable variation for genetic and Genotype×Environment (G×E) interaction was found among half-sib families. Low broad sense heritability (27%) was found for forage yield indicating that selection based on an index may be more useful for improvement of this trait in recurrent selection programs. On the other hand, since the interactions of genetic by environment are significant, selection of superior genotypes for development of synthetic varieties should be done based on multi-environments trails.