Tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] is an important cool-season perennial forage crop. During hot and dry summers it may die and require reseeding/replanting. Summer dormancy can greatly enhance persistence of tall fescue. However, environmental and genetic factors influencing summer dormancy in tall fescue are largely unknown. The objectives of this project are to identify the environmental factor(s) responsible for inducing dormancy, construct population(s) segregating for dormancy traits, and identify quantitative trait loci (QTL) associated with the traits of interest.  Genotypes with divergent characteristics were selected from natural populations. Summer active and dormant genotypes were grown in growth chambers under contrasting levels of temperature, daylength, moisture and vernalization. Summer dormancy was visible in dormant genotype compared to the active genotype as measured by number of tillers (8.6 vs. 15.8), fresh weight (6.0 vs. 16.0g) and dry weight (3.1 vs. 8.8g) under long day-low temperature-well water-vernalized conditions. The contrasting genotypes were used to construct a biparental mapping population of >200 progenies. The population was evaluated in growth chamber under the condition induced dormancy and observed segregation for the dormancy related traits. The population was also evaluated in multiple field experiments at Ardmore, Oklahoma. Transgressive segregation was observed for dormancy related traits. The population was genotyped with SSR, STS, and DArT markers and genetic map has been constructed. Segregation distortion in the markers originated from the summer dormant parent was very high. Identification of QTLs and genomic regions responsible for the expression of the traits are in progress.