Genetic analysis of root and physiological traits of tall fescue in association with drought stress conditions

Genetic analysis of root and physiological traits and selection of genotypes with higher drought tolerance through these traits is generally limited in tall fescue. In this study, some parental genotypes of tall fescue first were assessed for field drought tolerance in 2014-2015 and then the polycross seeds were harvested to provide half-sib families. Sixteen half-sib families along with their corresponding parental genotypes were assessed in a pot experiment for root and physiological characteristics under three irrigation levels (control, mild and intense) in 2016. The results showed that drought stress decreased dry forage yield (DFY), relative water content and total chlorophyll and increased carotenoid and proline in both parental genotypes and half-sib families. Intense drought stress decreased most of the root traits at 0-30 cm soil depth while at 30-60 cm depth length, area, volume and dry weight of roots were increased. A broad range of general combining ability (GCA) was observed for DFY (21M and 9E), root (21M, 12L and 20L) and physiological characteristics (12L and 9E) at three irrigation levels. Moderate to high estimates of narrow sense heritability (0.40-0.72) as well as genetic variation for root and physiological traits, indicated that phenotypic selection can be successful to attain genetic progress. Indirect selection to improve DFY was more effective through selection for root and some physiological traits. Significant associations of root and some physiological traits with drought tolerance demonstrated that these traits could be used as appropriate selection criteria to elevate forage yield and identify superior genotypes for arid and semi-arid regions.