Identification of Quantitative Trait Loci for Four Physiological Traits in an Advanced Backcross Population of Wheat Under Drought Stress

Advanced backcross quantitative trait locus analysis was used to identify QTLs for chlorophyll content, flag leaf senescence, cell membrane stability and the abscisic acid content traits under water- stressed conditions in BC₂F₂ wheat families. The parents and 75 BC₂F₂ families were evaluated phenotypically for drought tolerance using two irrigation treatments [0.25 and 0.75 m³ (H₂O) m^-2 (soil)]. The polymorphism among parental genotypes and 75 BC₂F₂ families were tested using 40, 98 and 400 different TRAP, SRAP and SSR primer combinations, respectively. The results revealed that 39 QTLs for physiological traits were identified. Thirteen QTLs were significantly associated with chlorophyll content and distributed on six chromosomes. Thirteen QTLs significantly influenced flag leaf senescence and mapped on chromosomes 1A, 4A, 1B, 2B, 3B, 6B, 3D and 7D. Nine QTLs for cell membrane stability were detected and each of them explained from 6 to 33% of phenotypic variance. Fourteen QTLs were detected for abscisic acid content, explaining from 9 to 27% of the phenotypic variance. All of the QTLs for the four physiological traits had a positive additive effect except for flag leaf senescence which had negative additive effects. The results showed also that the regression analysis for the relationship between the TRAP, SRAP and SSR markers and the phenotypes of BC₂F₂ families for the four physiological traits was highly significant. Therefore, the TRAP, SRAP and SSR markers linked to the QTL for the drought tolerance can be further used in breeding for drought tolerance in wheat.