Variability of root traits in sesame genotypes under different irrigation regimes

Abstract Water and nutrient absorption is closely associated with the root system structure and root characteristics. This study was designed to evaluate root characteristics of six sesame (Sesamum indicum L.) genotypes grown under full and deficit irrigation regimes in two-year rhizotube experiments. The results revealed that deficit irrigation regime resulted in higher root depth and root to shoot ratio, but the lower root length compared with that in the full irrigation regime. In addition, all the genotypes respond to deficit irrigation by increasing root depth. Although root depth increased in response to deficit irrigation, Sudan-94 genotype showed the maximum increase (44%), followed by USA-ns-96 genotype (35%). Similarly, root to shoot ratio increased due to deficit irrigation and Oltan and USA-ns-96 genotypes showed the maximum increase. Under deficit irrigation regime, root biomass decreased with increasing soil depth in Naz, Dashtestan-2, Darab-1, Oltan and USA-ns-96 genotypes; however, root biomass increased in Sudan-94 with increasing soil depth until a reduction was found at a depth of 0.6–0.9 m. The maximum values for dry root weight (10.89 g) and root length (25,875 mm) were related to USA-ns-96, but Sudan-94 showed the maximum root depth (114 cm) and root to shoot ratio (0.36) compared with other genotypes. Sudan-94 genotype was the only genotype in which all root traits increased due to deficit irrigation, suggesting that Sudan-94 genotype may be associated with increased tolerance to drought stress and can be considered as a desirable genotype in breeding programs.